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Rule2024-31367

Federal Motor Vehicle Safety Standards; Fuel System Integrity of Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity; Incorporation by Reference

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Published

January 17, 2025

Effective

July 16, 2025

Issuing agencies

Transportation DepartmentNational Highway Traffic Safety Administration

Abstract

This final rule establishes two new Federal Motor Vehicle Safety Standards (FMVSS) specifying performance requirements for all motor vehicles that use hydrogen as a fuel source. The final rule is based on Global Technical Regulation (GTR) No. 13, Hydrogen and Fuel Cell Vehicles. FMVSS No. 307, "Fuel system integrity of hydrogen vehicles," specifies requirements for the integrity of the fuel system in hydrogen vehicles during normal vehicle operations and after crashes. FMVSS No. 308, "Compressed hydrogen storage system integrity," specifies requirements for the compressed hydrogen storage system to ensure the safe storage of hydrogen onboard vehicles. These two standards will reduce deaths and injuries from fires due to hydrogen fuel leakages and/or explosion of the hydrogen storage system.

Full Text

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[Federal Register Volume 90, Number 11 (Friday, January 17, 2025)]
[Rules and Regulations]
[Pages 6218-6295]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-31367]

[[Page 6217]]

Vol. 90

Friday,

No. 11

January 17, 2025

Part III

Department of Transportation

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National Highway Traffic Safety Administration

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49 CFR Part 571

Federal Motor Vehicle Safety Standards; Fuel System Integrity of
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity;
Incorporation by Reference; Final Rule

Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules
and Regulations

[[Page 6218]]

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0090]
RIN 2127-AM40

Federal Motor Vehicle Safety Standards; Fuel System Integrity of
Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity;
Incorporation by Reference

AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).

ACTION: Final rule.

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SUMMARY: This final rule establishes two new Federal Motor Vehicle
Safety Standards (FMVSS) specifying performance requirements for all
motor vehicles that use hydrogen as a fuel source. The final rule is
based on Global Technical Regulation (GTR) No. 13, Hydrogen and Fuel
Cell Vehicles. FMVSS No. 307, ``Fuel system integrity of hydrogen
vehicles,'' specifies requirements for the integrity of the fuel system
in hydrogen vehicles during normal vehicle operations and after
crashes. FMVSS No. 308, ``Compressed hydrogen storage system
integrity,'' specifies requirements for the compressed hydrogen storage
system to ensure the safe storage of hydrogen onboard vehicles. These
two standards will reduce deaths and injuries from fires due to
hydrogen fuel leakages and/or explosion of the hydrogen storage system.

DATES:
Effective date: This final rule is effective July 16, 2025.
IBR date: The incorporation by reference of certain publications
listed in the rule is approved by the Director of the Federal Register
as of July 16, 2025.
Compliance Dates: The compliance date is September 1, 2028.
Petitions for reconsideration: Petitions for reconsideration of
this final rule must be received no later than March 3, 2025.

ADDRESSES: Petitions for reconsideration of this final rule must refer
to the docket and notice number set forth above and be submitted to the
Administrator, National Highway Traffic Safety Administration, 1200 New
Jersey Avenue SE, West Building, Washington, DC 20590. All petitions
received will be posted without change to <a href="http://www.regulations.gov">http://www.regulations.gov</a>,
including any personal information provided.
Privacy Act: DOT will post any petition for reconsideration, and
any other submission, without edit, to <a href="http://www.regulations.gov">http://www.regulations.gov</a>, as
described in the system of records notice, DOT/ALL-14 FDMS, accessible
through <a href="https://www.transportation.gov/individuals/privacy/privacy-act-system-records-notices">https://www.transportation.gov/individuals/privacy/privacy-act-system-records-notices</a>. Anyone is able to search the electronic form of
all submissions to any of our dockets by the name of the individual
submitting the submission (or signing the comment, if submitted on
behalf of an association, business, labor union, etc.). You may review
DOT's complete Privacy Act Statement in the Federal Register published
on April 11, 2000 (Volume 65, Number 70; Pages 19477-78).

FOR FURTHER INFORMATION CONTACT: For technical issues, Ian MacIntire,
General Engineer, Special Vehicles & Systems Division within the
Division of Rulemaking, at (202) 493-0248 or <a href="/cdn-cgi/l/email-protection#4009212e6e0d2123092e3429322500242f346e272f36">[email&#160;protected]</a>. For
legal issues, Paul Connet, Attorney-Advisor, NHTSA Office of Chief
Counsel, at (202) 366-5547 or <a href="/cdn-cgi/l/email-protection#2a7a4b5f4604694544444f5e6a4e455e044d455c">[email&#160;protected]</a> or Evita St. Andre,
Attorney-Advisor, NHTSA Office of Chief Counsel, at (617) 494-2767 or
<a href="/cdn-cgi/l/email-protection#ace9dac5d8cd82ffd882edc2c8dec9ecc8c3d882cbc3da">[email&#160;protected]</a>. The mailing address of these officials is:
National Highway Traffic Safety Administration, 1200 New Jersey Avenue
SE, Washington, DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary
II. Background
III. Summary of Comments
IV. Response to Comments on Proposed Requirements
V. Other Changes to the Regulatory Text
VI. Rulemaking Analyses and Notices

I. Executive Summary

Vehicle manufacturers have continued to seek out renewable and
clean fuel sources as alternatives to gasoline and diesel. Compressed
hydrogen has emerged as a promising potential alternative because
hydrogen is an abundant element in the atmosphere and does not produce
tailpipe greenhouse gas emissions when used as a motor fuel. However,
hydrogen must be compressed to high pressures to be an efficient motor
fuel and is also highly flammable, similar to other motor fuels. NHTSA
has already set regulations ensuring the safe containment of other
motor vehicle fuels such as gasoline in FMVSS No. 301, ``Fuel system
integrity,'' and compressed natural gas (CNG) in FMVSS No. 304,
``Compressed natural gas fuel container integrity,'' and the fuel
integrity systems of those fuels in FMVSS No. 301 and FMVSS No. 303,
``Fuel system integrity of compressed natural gas vehicles,''
respectively. No such standards currently exist in the United States
covering vehicles that operate on hydrogen. Accordingly, this document
establishes two new FMVSS to address safety concerns relating to the
storage and use of hydrogen in motor vehicles, and to align the safety
regulations of hydrogen vehicles with those of vehicles that operate
using other fuel sources.
NHTSA published the Notice of Proposed Rulemaking (NPRM) on April
17, 2024, seeking comments on the proposed standards.\1\ This final
rule responds to and addresses the comments to the NPRM, reflecting
input from stakeholders on various concerns and recommendations. The
rule was developed in concert with efforts to harmonize hydrogen
vehicle standards with international partners through the GTR process
and harmonizes the FMVSS with GTR No. 13, Hydrogen and Fuel Cell
Vehicles.\2\
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\1\ See 89 FR 27502 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
\2\ A copy of GTR No. 13 as updated by the Phase 2 amendments is
available at: <a href="https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf">https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf</a>
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The two new FMVSS established by this document are: FMVSS No. 307,
``Fuel system integrity of hydrogen vehicles,'' and FMVSS No. 308,
``Compressed hydrogen storage system integrity.'' FMVSS No. 307
regulates the integrity of the fuel system in hydrogen vehicles during
normal vehicle operations and after crashes. To this end, it includes
performance requirements for the hydrogen fuel system to mitigate
hazards associated with hydrogen leakage and discharge from the fuel
system, as well as post-crash restrictions on hydrogen leakage,
concentration in enclosed spaces, container displacement, and fire.
FMVSS No. 308 regulates the compressed hydrogen storage system (CHSS)
itself and primarily includes performance requirements that ensure the
CHSS is unlikely to leak or burst during use, as well as requirements
intended to ensure that hydrogen is safely expelled from the container
when it is exposed to a fire. FMVSS No. 308 also specifies performance
requirements for different closure devices in the CHSS.
FMVSS No. 308 applies to all motor vehicles that use compressed
hydrogen gas as a fuel source to propel the vehicle, regardless of the
vehicle's gross

[[Page 6219]]

vehicle weight rating (GVWR), except vehicles that are only equipped
with cryo-compressed hydrogen storage systems or solid-state hydrogen
storage systems to propel the vehicle. Portions of FMVSS No. 307 also
apply to all motor vehicles that use compressed hydrogen gas as a fuel
source to propel the vehicle, regardless of the vehicle's GVWR.
However, while FMVSS No. 307's fuel system integrity requirements
during normal vehicle operations apply to both light vehicles (vehicles
with a GVWR of 4,536 kg or less) and to heavy vehicles (vehicles with a
GVWR greater than 4,536 kg), FMVSS No. 307's post-crash fuel system
integrity requirements apply only to compressed hydrogen-fueled light
vehicles and to all

II. Background

A. Overview of GTR No. 13

1. The GTR Process
The United States is a contracting party to the the Agreement
concerning the Establishing of Global Technical Regulations for Wheeled
Vehicles, Equipment and Parts which can be fitted and/or be used on
Wheeled Vehicles (``1998 Agreement''). This agreement entered into
force in 2000 and is administered by the United Nations Economic
Commission for Europe's (UN ECE's) World Forum for the Harmonization of
Vehicle Regulations (WP.29). The purpose of this agreement is to
establish Global Technical Regulations (GTRs).
At its 160th session in June 2013, UN ECE WP.29 formally adopted
the proposal to establish GTR No. 13. NHTSA chaired the development of
GTR No. 13 and voted in favor of establishing GTR No. 13. The Phase 2
updates to GTR No. 13 were adopted at the 190th Session of WP.29 on
June 21, 2023.\3\
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\3\ See <a href="https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf">https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf</a>.
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As a Contracting Party Member to the 1998 Global Agreement that
voted in favor of GTR No. 13 and the Phase 2 updates to GTR No. 13,
NHTSA is obligated to initiate the process used in the U.S. to adopt
Phase 2 GTR No. 13 as an agency regulation. This process was initiated
by the NPRM published on April 17, 2024. NHTSA is not obligated to
adopt the GTR, in whole or in part, after initiating this process.
Additionally, NHTSA may adopt a modified version of the GTR to ensure
that it meets relevant requirements. In deciding whether to adopt a GTR
as an FMVSS, NHTSA follows the requirements for NHTSA rulemaking,
including the Administrative Procedure Act, the National Traffic and
Motor Vehicle Safety Act (Vehicle Safety Act), Presidential Executive
Orders, and DOT and NHTSA policies, procedures, and regulations. Among
other things, FMVSS issued under the Vehicle Safety Act ``shall be
practicable, meet the need for motor vehicle safety, and be stated in
objective terms.''
2. GTR No. 13 and Phase 2 Updates
GTR No. 13 specifies safety-related performance requirements and
test procedures with the purpose of minimizing human harm that may
occur as a result of fire, burst, or explosion related to the hydrogen
fuel system of vehicles. The regulation consists of system performance
requirements for CHSS, CHSS closure devices, and the vehicle fuel
delivery system. GTR No. 13 does not specify the type of crash tests
for post-crash safety evaluation and instead permits Contracting
Parties to use their domestic regulated crash tests.
The Phase 2 updates of GTR No. 13 accomplished several goals,
including: broadening of the scope and application of GTR No. 13 to
cover heavy/commercial vehicles; harmonizing, clarifying, and expanding
the requirements for thermally-activated pressure relief device (TPRD)
discharge direction in case of controlled release of hydrogen;
strengthening test procedures for containers with pressures below 70
MPa, including comprehensive fire exposure tests; and extending the
requirements to 25 years to more accurately capture the expected useful
life of vehicles.

B. April 2024 NPRM

The April 2024 NPRM \4\ proposed to establish two new FMVSS for
hydrogen vehicles that are based on GTR No. 13, Phase 2. The proposed
FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles,'' is
designed to set performance requirements to ensure the integrity of the
hydrogen fuel system during normal vehicle operations and after
crashes. These requirements aimed to mitigate safety risks associated
with hydrogen fuel leakages, fires, and explosions, ensuring that
hydrogen would not pose risks to vehicle occupants or those nearby. The
standard addressed the hazards posed by the flammability of hydrogen
and its tendency to leak under high pressure, particularly in crash
scenarios.
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\4\ See 89 FR 27502 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
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FMVSS No. 307 prescribes a series of performance standards aimed at
ensuring the safety of hydrogen vehicle fuel systems during both normal
operations and post-crash scenarios. The NPRM proposed five key
performance requirements for hydrogen fueling receptacles to prevent
leakage, incorrect fueling, and contamination from dirt or water. These
included reverse flow prevention, clear labeling, positive locking,
protection against contamination, and secure placement to avoid crash-
related deformations. An over-pressure protection device requirement
was proposed to protect downstream components from excessive pressure.
The proposal also included requirements for hydrogen discharge
mechanisms, specifying that vent lines must be protected from dirt and
water and that hydrogen gas discharge must be directed safely away from
critical components like the wheels, doors, and emergency exits.
The NPRM also proposed requirements in FMVSS No. 307 to protect
against flammable conditions. These included a visual warning system
that would alert the driver if hydrogen concentrations reached
dangerous levels (above 3% in enclosed or semi-enclosed spaces), and an
automatic shut-off valve closure if hazardous hydrogen concentrations
were detected. The proposed standard further specified that hydrogen
concentrations in the exhaust system must not exceed set thresholds
during normal vehicle operation.
In post-crash scenarios, the proposal set limits on fuel leakage
and specified crash tests to ensure that the hydrogen containers
remained intact and that any post-crash hydrogen leakage remained
within manageable limits. The proposal allowed a hydrogen leak rate not
to exceed 118 normal liters per minute for a duration of 60 minutes
after impact.
The NPRM also proposed establishing FMVSS No. 308, ``Compressed
Hydrogen Storage System Integrity,'' focused on ensuring the safety and
durability of the CHSS used in hydrogen vehicles. The proposed standard
outlined performance requirements for the CHSS to prevent leaks,
bursts, and other failures during normal vehicle use and under extreme
conditions, such as exposure to fire. The proposal included tests and
performance criteria to evaluate the CHSS's resistance to various
stress factors that could occur over the vehicle's lifetime. The CHSS,
which includes components such as the hydrogen container, check valve,
shut-off valve, and TPRD, was required to meet several durability and
safety benchmarks throughout its operational lifespan.
The proposal established specific requirements for hydrogen
containers,

[[Page 6220]]

which are the primary components of the CHSS. Testing procedures for
these containers included hydraulic pressure tests to evaluate burst
thresholds, pressure cycling tests to simulate long-term use in
service, and tests applying a series of external stress factors such as
impact, chemical exposure, high and low temperatures, high pressure
hold, and over-pressure along with pressure cycling to assess the
container's durability against leak or burst during its lifetime.
The proposed FMVSS No. 308 also included an on-road performance
test for the entire CHSS to ensure the CHSS contains hydrogen without
leak or burst. This test uses on-road operating conditions including
fueling and defueling the container at different ambient conditions
with hydrogen gas at low and high temperatures, a static high-pressure
hold, and an overpressure, designed to replicate the stress factors the
system could encounter during a vehicle's operational life.
Fire exposure testing was another critical aspect in the proposed
FMVSS No. 308, evaluating whether the CHSS could prevent dangerous
hydrogen release or explosion in a vehicle fire scenario. The proposed
fire test includes a localized and engulfing stage, which were
developed based on real vehicle fire data. The NPRM also proposed
requirements for the CHSS's closure devices (check valves, shut-off
valves, and TPRDs). Additionally, the NPRM proposed labeling
requirements in FMVSS No. 308 for hydrogen containers.
Together, the two proposed standards, FMVSS No. 307 and FMVSS No.
308, aimed to align U.S. regulations with GTR No. 13 and address the
specific safety challenges posed by hydrogen as a vehicle fuel source.

C. How the Final Rule Differs From the NPRM

The final rule largely mirrors the proposed standards, with some
minor changes to the requirements and test procedures based on the
public comments and feedback received. Details of the reasoning behind
each of the changes is provided in relevant sections of the notice.
FMVSS No. 307, established by this final rule, differs from the
proposed FMVSS No. 307 in the following ways:
<bullet> Revises the definition for enclosed or semi-enclosed
spaces to be more specific and avoid ambiguity.
<bullet> Removes the requirement for an overpressure protection
device.
<bullet> Removes the requirement that the fueling receptacle
``shall not be mounted to or within the impact energy-absorbing
elements of the vehicle.''
<bullet> Removes the requirements for specific TPRD discharge
angles.
<bullet> Eliminates the option to use an electronic leak detector
in section S6.6, leaving leak detection liquid as the only applicable
test method.
<bullet> Revises the regulatory text in instances where the NPRM
stated that the vehicle is set to the ``on'' or ``run'' position (and
preventing the vehicle from idling) to instead state that the
propulsion system shall be operational.
FMVSS No. 308, established by this final rule, differs from the
proposed FMVSS No. 308 in the following ways:
<bullet> Excludes cryo-compressed and solid-state hydrogen storage
systems from the requirements in FMVSS No. 308.
<bullet> Requires manufacturers to provide the median initial burst
pressure for a container (BP<INF>O</INF>) within fifteen business days
instead of five.
<bullet> Removes the requirement to include BP<INF>O</INF> on the
container label.
<bullet> Removes the requirement for container burst pressure
variability to be within 10 percent of BP<INF>O</INF>.
<bullet> Changes the requirement that the manufacturer specify the
primary constituent of the container to specifying whether the primary
constituent of the container is glass fiber composite.
<bullet> Increases the timeframe from 5 business days to 15
business days for manufacturers to submit vehicle-specific information
for testing purposes.
<bullet> Revises the cycling rate for the baseline initial pressure
cycle test to be no more than ten cycles per minute.
<bullet> Removes the minimum time of three minutes to sustain a
visible leak before the baseline initial pressure cycle test can end
successfully due to ``leak before burst.''
<bullet> Removes the proof pressure test from both the test for
performance durability and the test for expected on-road performance.
<bullet> Permits the option to conduct the closure tests with an
inert gas such as helium instead of hydrogen gas.
For both standards, various editorial and clerical updates were
made to improve clarity and consistency throughout the document.

III. Summary of Comments

The NPRM preceding this final rule included requests for comment on
several topics. From April 17, 2024, to July 17, 2024, the agency
received 31 comments on the NPRM, four of which were requests to extend
the NPRM comment period.\5\ The comments were generally supportive of
the proposed rule, particularly regarding harmonization with
international regulations. Many commenters suggested modifications to
the proposed requirements, including details of various test
procedures. Of the 26 unique comments, the majority (21 comments) were
submitted by vehicle and component manufacturers and industry
associations. Comments were also submitted by standards testing
laboratories (1 comment), and other stakeholders (4 comments).
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\5\ In response to the comments to extend the comment period,
NHTSA extended the comment period for the NPRM by 30 days. The
original comment period for the NPRM was scheduled to end on June
17, 2024. The extended comment period ended on July 17, 2024.
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The vehicle and component manufacturers that provided comments were
Ballard Power Systems (``Ballard''), Daimler Truck North America
(``DTNA''), Ford Motor Company (``Ford''), Glickenhaus Zero and
Scuderia Cameron Glickenhaus LLC (collectively, ``Glickenhaus''),
Hexagon Agility, Inc. (``Agility''), Hyundai America Technical Center,
Inc. (``HATCI''), Hyundai Motor Group (``Hyundai''), Luxfer Gas
Cylinders, New Flyer of America (``NFA''), Nikola Corporation
(``Nikola''), Noble Gas Systems (``NGS''), Hyzon Motors Inc. (Hyzon),
H2MOF, Inc. (``H2MOF''), Quantum Fuel Systems, LLC (``Quantum''),
Verne, Inc. (``Verne''), Westport Fuel Systems Canada, Inc. (``WFS''),
and Air Products and Chemicals, Inc. (``Air Products'').
The industry associations that provided comments were the Alliance
for Automotive Innovation (``Auto Innovators''), The Vehicle Suppliers
Association (``MEMA''), the Transport Project (``TTP''), and the Truck
and Engine Manufacturers Association (``EMA''). Some manufacturers
stated support for the comments submitted by an industry association.
The testing laboratory that provided comments was TesTneT Canada,
Inc. (``TesTneT''). The other stakeholders that provided comments were
Faurecia Hydrogen Solutions (``FORVIA''), Consumer Reports, Newhouse
Technology, LLC (``Newhouse''), and an anonymous commenter.

IV. Response to Comments on Proposed Requirements

A. Deviation From GTR No. 13

Several commenters submitted repeated comments for many sections of
the proposed FMVSS Nos. 307 and 308 asking that the agency follow GTR
No.

[[Page 6221]]

13 exactly, often without further explanation or justification. Several
commenters also stated that the agency should completely harmonize with
various industry standards.
Commenters seem to misunderstand the requirements of the 1998
Agreement and NHTSA's obligation under the Agreement. As noted earlier,
under the 1998 Agreement, NHTSA must propose a GTR on which it has
voted in the affirmative. NHTSA is committed to harmonizing to the
extent practical, but NHTSA is not required to finalize the text of a
GTR when it has justification to deviate from that text. The 1998
Agreement, by design, does not include mutual recognition \6\ because
the 1998 Agreement spans different regulatory regimes (i.e., type
approval and self-certification), and it acknowledges the domestic
rulemaking and substantive legal requirements in the United States.
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\6\ Mutual recognition occurs when two or more countries or
other institutions recognize one another's decisions or policies,
for example in the field of conformity assessment, professional
qualifications or in relation to criminal matters.
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The FMVSS are designed to be a unique set of regulations tailored
specifically for the United States' regulatory approach to vehicle
safety. FMVSS must adhere strictly to principles of objectivity and
verifiability, as these are foundational to the self-certification
process required in the U.S. automotive market. Some other standards,
like industry standards and regulations from other countries, may
include some degree of subjectivity or flexibility in their criteria
due to their broader focus and the differing regulatory frameworks
across countries.
NHTSA aimed to harmonize FMVSS Nos. 307 and 308 with GTR No. 13 and
the related industry standards to the maximum extent possible. However,
it was not always feasible or appropriate to match the regulations word
for word. FMVSS must remain objective, ensuring that every requirement
is clear, measurable, and enforceable. FMVSS must also have clear,
unambiguous test procedures with minimal discretion given to test
facilities. This requirement ensures the integrity of the self-
certification system and protects consumers and manufacturers alike.
Ignoring these fundamental requirements for FMVSS would undermine the
effectiveness of FMVSS and could potentially compromise vehicle safety
in the U.S.

B. FMVSS No. 308, ``Compressed Hydrogen Storage System Integrity''

1. FMVSS No. 308 as a Vehicle-Level Standard
Background
Consistent with GTR No. 13, NHTSA proposed that FMVSS No. 308 be a
vehicle-level standard, rather than an equipment standard. Some
performance requirements and test procedures for the CHSS in FMVSS No.
308 are specific to the vehicle design and to its gross vehicle weight
rating. NHTSA sought comment on whether FMVSS No. 308 should remain a
vehicle standard.
Comments Received
Auto Innovators expressed concern about NHTSA's proposal to
structure FMVSS No. 308 as a vehicle-level standard, arguing that the
development and quality assurance of CHSS require specialized
knowledge. Since many vehicle manufacturers source CHSS from
independent suppliers, Auto Innovators suggested that compliance
responsibility should lie with the CHSS supplier. It further stated
that it is unclear how vehicle manufacturers could practically
implement testing, given that CHSS design is more applicable to
suppliers. It also emphasized the importance of including replacement
parts in FMVSS No. 308 to maintain consistency and ensure integrity
during repairs.
DTNA supported the proposal to maintain FMVSS No. 308 as a vehicle-
level standard. It agreed that the performance requirements should
apply only to originally equipped CHSS and stated that further research
is needed before addressing replacement CHSS. It also concurred that
the CHSS performance should be evaluated based on vehicle design and
gross vehicle weight rating.
EMA recommended revising FMVSS No. 308 to apply as an equipment
standard that would also include replacement containers. It proposed
that both motor vehicles using compressed hydrogen gas and containers
designed to store it should be subject to the standard.
Glickenhaus advocated for FMVSS No. 308 to focus on tank-level
testing rather than vehicle-level certification, arguing that CHSS
components should be certified by the component manufacturer. It
pointed out that NHTSA has a precedent in other FMVSS standards for
differentiating requirements based on vehicle weight and size, and
suggested that FMVSS No. 308 could follow a similar approach. This
approach, according to Glickenhaus, would reduce costs by allowing
tanks to be certified for use across multiple vehicle platforms without
re-certification for each vehicle.
H2MOF proposed that FMVSS No. 308 remain a component standard with
applicability for hydrogen storage systems ranging from 10 MPa to 70
MPa.
Nikola stated that FMVSS No. 308 should remain a separate standard
but questioned why replacement parts should not be required to meet the
standard and suggested using separate markings to indicate which
vehicle types a particular component is suitable for.
Newhouse suggested that FMVSS No. 308 should be an equipment
standard focusing on the fuel container and directly integral
components, such as the valve and TPRD. It recommended that FMVSS No.
307 cover system issues, including the connection of fuel containers
with tubing.
FORVIA agreed with not extending FMVSS No. 308 to replacement
parts, stating it would provide replacement parts equivalent to the
original ones.
Luxfer Gas Cylinders referenced compliance with FMVSS No. 304,
where CNG fuel containers were purchased directly from manufacturers,
and questioned whether NHTSA intended to purchase hydrogen vehicles to
obtain CHSS for testing. It also asked if NHTSA plans to test both
containers and TPRDs from container manufacturers or vehicle providers.
It stated that FMVSS No. 308 would be more appropriate as a component-
level standard since it focuses on performance tests for CHSS rather
than the vehicle as a whole.
Agency Response
NHTSA is maintaining FMVSS No. 308 as a vehicle-level standard, as
proposed. Several requirements in FMVSS No. 308 are specific to the
vehicle design and to the gross vehicle weight rating of the vehicle in
which a CHSS is installed.\7\ It is not possible to fully evaluate the
performance of a CHSS without knowledge of the vehicle in which it is
installed.
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\7\ For example, as discussed below, the number of pressure
cycles to which the container is subjected during the baseline
initial pressure cycle test is dependent on the vehicle GVWR, with a
different number of cycles required for light and heavy vehicles.
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While CHSSs may be sourced from specialized equipment suppliers,
vehicle manufacturers must ensure that the CHSS installed on their
vehicles meet all applicable FMVSS requirements to certify that the
entire vehicle is compliant. Vehicle manufacturers may consider working

[[Page 6222]]

closely with CHSS suppliers regarding system design to ensure all
requirements are met for a particular vehicle.
Following the lead of GTR No. 13, FMVSS No. 308 establishes
standards intended to ensure the safety and integrity of the CHSS
throughout the lifetime of a vehicle. NHTSA recognizes that some
containers and parts may still need to be replaced due to damage
incurred through extraordinary events or due to defects, but in
general, the agency expects the demand for replacement CHSS parts to be
minimal. Given the likely low demand for replacement containers by
ordinary consumers, the limited current market penetration of hydrogen
vehicles, and the fact that any recalls will be serviced by
manufacturers, we expect the market for aftermarket products to be
negligible, and that replacement parts will be supplied predominantly
through OEMs, therefore obviating the safety need to set an equipment-
level standard. However, NHTSA will monitor the deployment of hydrogen
vehicles and how consumers are replacing parts of the fuel system and
update the standard as necessary.
While NHTSA recognizes that some manufacturers would prefer that
FMVSS No. 308 be an equipment standard, thus potentially shifting the
burden of certification onto other entities like suppliers, NHTSA
remains invested in ensuring that the end product it regulates--the
vehicle--is as safe as possible. The safety of the end product is most
important to protecting consumers and the public. Because a compliant
CHSS is essential to certifying the safety of the end product, NHTSA
maintains the vehicle-level standard. Additionally, NHTSA expects that
manufacturers will maintain proper record-keeping practices, including
detailed hardware bills of materials, to ensure traceability to
originating suppliers.
Regarding the procurement of CHSS or subcomponents for compliance
testing, NHTSA will have the option of purchasing complete vehicles or
the relevant replacement parts from the vehicle or sub-component
manufacturer. This flexibility will enable NHTSA to obtain the needed
vehicle and components to conduct compliance testing efficiently.
Additionally, final-stage vehicle manufacturers will not
necessarily be required to conduct CHSS testing themselves. Vehicle
manufacturers must take reasonable care in certifying that their
vehicles meet FMVSS No. 308, but they are not required to follow any
set testing procedure and may, if they find it reasonable, work with
CHSS suppliers to ensure compliance with FMVSS No. 308. This approach
allows vehicle manufacturers to use their discretion in determining
which party is best suited to conduct specific tests. This arrangement
is often formalized through contractual obligations, with CHSS
suppliers guaranteeing the functionality of their systems and agreeing
to supply replacement parts exclusively through the vehicle
manufacturer, ensuring consistency and regulatory compliance.
2. FMVSS No 307 and 308 as Separate Standards
Background
NHTSA sought comment on whether FMVSS Nos. 307 and 308 should be
combined into a single standard in the final rule.
Comment Received
Luxfer Gas Cylinders commented that it would be better to keep
FMVSS Nos. 307 and 308 separate. EMA also supported maintaining
separate standards, recommending that FMVSS No. 308 be applicable to
vehicles using hydrogen as a motor fuel, as well as to hydrogen
containers designed for on-board storage, similar to FMVSS No. 304 for
CNG containers. Glickenhaus agreed that FMVSS Nos. 307 and 308 should
remain distinct. H2MOF similarly stated that the two standards should
not be combined. Nikola argued that FMVSS No. 308 should remain its own
standard, pointing out that component-specific testing is common in
FMVSS regulations, citing examples such as FMVSS Nos. 106, 108, and
304. Nikola further suggested that FMVSS No. 307 should cover vehicle-
level requirements, while FMVSS No. 308 should address component-
specific requirements. Hyundai supported the separation of the
standards, stating that it is logical to distinguish between fuel
system integrity and hydrogen storage system requirements, drawing a
parallel with FMVSS Nos. 303 and 304 for CNG vehicles. FORVIA, while
generally neutral, expressed a preference for combining the standards,
suggesting that doing so could simplify future amendments and create a
more consistent alignment with GTR No. 13.
Agency Response
NHTSA is keeping FMVSS No. 307 and FMVSS No. 308 as separate
standards, as proposed. This separation will make future management of
the standards more efficient and is consistent with FMVSS No. 303,
``Fuel system integrity of compressed natural gas vehicles,'' and FMVSS
No. 304. All commenters on this matter supported requirements in
separate standards, as proposed. Regarding H2MOF's comment, NHTSA does
not believe that combining FMVSS No. 307 and 308 into a single standard
will improve consistency with GTR No. 13. Consistency relates to the
specifics of the requirements themselves, and is not based on whether
those requirements are in a single standard or in two standards.
3. Change of Design Table
Background
Some international standards include what is known as a ``change of
design table.'' This type of table is used in type-approval regulatory
systems to specify what qualification testing must be redone for a
given change in an approved system's design. GTR No. 13 does not
contain a change of design table because GTRs are neutral toward the
different national certification systems used and change of design
tables are only relevant in type-approval systems.
Comments Received
Quantum Fuel Systems, LLC commented that the proposed standard
omits the deviation table, also known as a change of design table, that
is included in Economic Commission for Europe Regulation No. 134, (UN
ECE R134).\8\ Quantum Fuel Systems, LLC stated that the only difference
between GTR No. 13 and UN ECE 134 is that UN ECE 134 also includes a
deviation table. Quantum Fuel Systems, LLC provided a copy of the
change of design table in UN ECE R134. Quantum Fuel Systems, LLC stated
it would like the change of design table to be added to the FMVSS Nos.
307 and 308 standards.
---------------------------------------------------------------------------

\8\ See Economic Commission for Europe Regulation No. 134,
Uniform provisions concerning the approval of motor vehicles and
their components with regard to the safety related performance of
hydrogen-fuelled vehicles. <a href="https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2015/R134e.pdf">https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2015/R134e.pdf</a>.
---------------------------------------------------------------------------

Agency Response
NHTSA is not including a change of design table in FMVSS Nos. 307
and 308. Change of design tables are not relevant to FMVSS because
FMVSS are self-certification standards. Manufacturers themselves are
responsible for determining if any design changes require re-
certification of the overall design or system.

[[Page 6223]]

4. Compressed Hydrogen Storage System
a. Container Definition
Background
GTR No. 13 defines a container as ``the pressure-bearing component
on the vehicle that stores the primary volume of hydrogen fuel in a
single chamber or in multiple permanently interconnected chambers.''
NHTSA proposed a similar definition with the following modifications:
<bullet> Replace ``the vehicle'' with ``a compressed hydrogen
storage system'' to clarify that the container is a subcomponent of a
CHSS, and therefore a container cannot exist on its own without the
other components of the CHSS.
<bullet> Remove the word ``primary'' because this word introduces
ambiguity regarding secondary or tertiary volumes of stored hydrogen.
<bullet> Add the word ``continuous'' to clarify that a container
does not have any valves or other obstructions that may separate its
different chambers.
Thus, NHTSA proposed that ``container means pressure-bearing
component of a compressed hydrogen storage system that stores a
continuous volume of hydrogen fuel in a single chamber or in multiple
permanently interconnected chambers.'' NHTSA sought comment on the
proposed definition for the container.
Comments Received
Commenters provided a range of opinions on NHTSA's proposed
definition of ``container'' in FMVSS No. 308. Auto Innovators suggested
that NHTSA should harmonize with the definition in GTR No. 13, stating
that it is well understood and provides sufficient clarity without
necessitating a new definition. Similarly, DTNA raised concerns that
removing the word ``primary'' could introduce ambiguity, particularly
in relation to whether plumbing and piping systems might be considered
part of the container and thus subject to the same testing requirements
as the container itself. It requested clarification that such systems
are not part of the container.
Glickenhaus and H2MOF expressed support for the proposed
definition, with Glickenhaus backing the entire proposal and H2MOF
agreeing with the characterization of a container as consisting of a
single chamber or multiple interconnected chambers. However, Agility
voiced concerns about the practicality of certain performance tests,
specifically with live lines, and requested clarification on how
multiple-chamber containers would be tested.
Several commenters, including Nikola, WFS, TesTneT, and FORVIA,
advocated for retaining the definition from GTR No. 13. WFS suggested
that if changes are necessary, only the modification to replace ``the
vehicle'' with ``a compressed hydrogen storage system'' should be
adopted, while the term ``primary'' should remain to prevent confusion
between containers and the CHSS. FORVIA also opposed adding the term
``continuous,'' noting that it could mislead interpretations of
interconnected chambers. It suggested that further clarification could
be provided through additional notes, especially regarding the
definition of ``permanently interconnected.''
HATCI supported NHTSA's proposed definitions for the container,
closure devices, shut-off valves, and container attachments, stating
agreement with the rationale provided.
Agency Response
NHTSA is maintaining the definition of container as proposed. It is
important to indicate in the definition that a container is a component
of a CHSS, rather than simply a component of a vehicle. This language
makes clear that a container cannot exist outside a CHSS. In other
words, there can be no ``independent'' containers that are not part of
a CHSS. This clarification is important because the CHSS includes the
critical safety functions of shut-off valve, check valve, and TPRD, as
discussed below. A container without these functions is unsafe and is
not permitted by the standard. All containers must exist as a component
of a CHSS, and a vehicle may not have containers that are not part of a
CHSS.
It is also important to remove the word ``primary'' from the
definition of container. Including the word ``primary'' could introduce
ambiguity about secondary or tertiary volumes of stored hydrogen, or
secondary or tertiary containers on the vehicle. All containers onboard
a vehicle that supply hydrogen to propel the vehicle need to be
regulated by the standard, and including the word primary in the
definition could imply that only the ``first'' or ``primary'' container
is covered by the regulation, while other ``secondary'' containers and
their respective CHSS are unregulated. This is not NHTSA's intent, and
therefore the word ``primary'' has been removed.
Additionally, it is important to include the word ``continuous'' in
the definition. This word is used to determine the specific volume that
constitutes a container's single or multiple permanently interconnected
chambers. The continuous volume that constitutes the container
continues until it is ``interrupted'' or ``broken'' by a shut-off
valve. Any continuous volume up to the shut-off valve is considered
part of the container. For example, if there are lines \9\ between a
cylindrical chamber and the shut off valve, then those lines are
considered part of the continuous volume that constitutes the container
with hydrogen stored at high pressure. A conformable container design
consisting of multiple small high-pressure cylinders interconnected by
high-pressure piping that are all enclosed in a casing, and that
collectively have one set of closure devices (i.e. shut-off valve,
TPRD, check valve), would be considered as one container by this
definition. Such conformable containers are in development for vehicle
application in the near future.
---------------------------------------------------------------------------

\9\ In this context, ``lines'' refers to any plumbing, piping,
and/or connections where hydrogen fuel may be present.
---------------------------------------------------------------------------

Similarly, if two conventional high-pressure containers share a
single shut-off valve through piping or lines, such lines present the
same safety risks as the container itself, due to the large quantity of
stored high-pressure hydrogen that could be uncontrollably released in
the event of a failure of those lines to contain the hydrogen.
Therefore, those lines would be required to undergo durability testing
along with the remainder of the container. However, if the lines are
attached to the cylindrical chamber with high pressure hydrogen after
the shut-off valve, then they would not be considered part of the
continuous volume that constitutes the container. These lines after the
shut-off valve do not present the same safety risk of uncontrolled
release of high-pressure hydrogen, due to the shut-off valve's ability
to close and isolate the stored hydrogen.
Including the word continuous is also important to clarify that a
container does not have any valves or other obstructions that may
separate its different chambers, in the case of a container with
multiple permanently interconnected chambers. There cannot be a shut-
off valve or other obstruction between any of the chambers of a
container that is composed of multiple permanently interconnected
chambers (such as the example provided earlier of a conformable
container). Containers composed of multiple chambers forming a
continuous volume are tested as a single unit, whereas if there are
valves or other obstructions that separate the chambers and ``break''
the continuous volume, the chambers are considered separate containers
and are evaluated

[[Page 6224]]

separately. For example, in the case of three permanently
interconnected chambers joined together by piping before a single shut-
off valve, all three chambers and the piping together would be
considered ``the container.'' Alternatively, if each of the three
chambers had its own shut-off valve prior to the piping connections,
then each of the three chambers would be a separate container.
Finally, NHTSA does not intend to apply the definition of container
to fuel lines outside a CHSS after the shut-off valve, or to low
pressure fuel system components downstream of the shut-off valve that
may contain residual hydrogen. These lines are covered by other
requirements such as the fuel system leakage requirement in FMVSS No.
307, discussed below, which specifies that the fuel system shall not
leak, as evaluated by FMVSS No. 307 S6.6, Test for fuel system leakage.
b. Container Attachments Definition
Background
NHTSA proposed defining ``container attachments'' as ``non-pressure
bearing parts attached to the container that provide additional support
and/or protection to the container and that may be removed only with
the use of tools for the specific purpose of maintenance and/or
inspection.'' GTR No. 13 defined container attachments as ``non-
pressure bearing parts attached to the container that provide
additional support and/or protection to the container and that may be
only temporarily removed for maintenance and/or inspection only with
the use of tools.'' NHTSA's definition is similar to that in GTR No. 13
with some exceptions.
GTR No. 13 uses the phrase ``only temporarily removed for
maintenance and/or inspection'' in the definition of container
attachment. In the NPRM proposed definition, the words ``only
temporarily'' and ``for maintenance and/or inspection,'' were removed
because anything that can be removed temporarily can also be removed
permanently. Additionally, from a regulatory perspective, it is not
possible to control and monitor the purpose of removing the container
attachments and so the phrase ``for maintenance and/or inspection'' was
removed.
Comments Received
Several commenters, including Nikola, Auto Innovators, TesTneT,
NGS, and FORVIA, suggested that the definition should remain aligned
with GTR No. 13 to maintain consistency. Nikola expressed concern that
changes could lead to unintended consequences, while Auto Innovators
acknowledged NHTSA's rationale for removing the term ``temporary'' but
stated that the amendment was unnecessary and recommended harmonization
with GTR No. 13. TesTneT also noted that the proposed change was
insignificant, and NGS recommended keeping the GTR No. 13 definition
but adding a safety mark to parts critical to the system's function.
EMA proposed adding ``repair'' to the definition and emphasized the
need for consistency between FMVSS Nos. 307 and 308. It pointed out a
discrepancy in the wording of the definitions between the two standards
and suggested it be addressed. FORVIA opposed permitting permanent
removal of container attachments, stating that it could pose safety
risks, and emphasized the need for allowing only temporary removal for
repairs.
In contrast, H2MOF and HATCI supported NHTSA's proposed definition,
with H2MOF agreeing directly and HATCI expressing support for the
definitions of container attachments as well as other related
components.
Agency Response
NHTSA is maintaining the definition of container attachments as
proposed. The agency does not anticipate unintended consequences from
removing the word ``temporary'' from the definition. By removing the
word ``temporary,'' NHTSA is avoiding having to determine whether an
attachment was designed to be removed permanently or temporarily. As
stated in the NPRM, anything that can be removed temporarily can also
be removed permanently, so a distinction between temporary removal and
permanent removal is not meaningful.
It is also not necessary to add the word ``repair'' to the
definition or keep the phrase ``for maintenance and/or inspection,''
because any attachments that can be removed for maintenance,
inspection, or repair can also be removed for other reasons and FMVSS
No. 308 cannot enforce the purpose of removing the attachments.
In response to the comment from EMA regarding discrepancy in the
definition of container attachment in FMVSS Nos. 307 and 308, NHTSA
acknowledges that the omission of ``and/'' from the definition in FMVSS
No. 307 was a clerical omission and the definition has been corrected
in this final rule.
c. Closure Devices Definition
Background
GTR No. 13 refers to closure devices as ``primary'' closure
devices. This language creates ambiguity about potential secondary or
tertiary closure devices. As a result, NHTSA proposed to define the
term ``closure devices'' as ``the check valve(s), shut-off valve(s) and
thermally-activated pressure relief device(s) that control the flow of
hydrogen into and/or out of a CHSS'' and does not use the word
``primary.''
Comments Received
Commenters provided mixed feedback on NHTSA's proposal to remove
the word ``primary'' from the definition of closure devices. HATCI
supported NHTSA's proposed definitions and agreed with the rationale
provided. On the other hand, Auto Innovators opposed the removal,
stating that ``primary'' is necessary to distinguish between primary,
secondary, and tertiary closure devices, which may be outside the
regulation's scope. It recommended harmonizing with GTR No. 13, which
it argued provides sufficient clarity by defining primary closure
devices as those directly attached to the chamber or manifold.
Glickenhaus also disagreed with the proposed change, noting that its
design approach includes redundant safety measures for critical
components. It questioned whether secondary shut-off valves would be
considered part of the CHSS if the term ``primary'' was removed.
H2MOF commented that ``primary'' should remain, as additional
devices like pressure-activated pressure relief devices may be required
in some cases. It also suggested adding a clarification that CHSS test
units do not need closure devices, as most tests are performed
hydraulically. Nikola agreed that the definition should retain
``primary'' to differentiate between main shut-off valves and secondary
valves like manual isolation valves, which are outside the document's
scope.
DTNA noted its concern for removal of the word ``primary'' from the
definition of ``closure devices.'' It stated that ``volumes of hydrogen
that are located between other valves, often along the piping, could be
considered part of the CHSS.'' WFS similarly recommended keeping the
word ``primary,'' as its removal would create more ambiguity regarding
the distinction between the CHSS and the broader fuel system. TesTneT
and FORVIA also opposed the change, with FORVIA asserting that the
differentiation between primary and

[[Page 6225]]

secondary closure devices is essential, as GTR No. 13 only covers
primary devices. It stated that removing ``primary'' would create
uncertainty about whether secondary closures are included.
Agency Response
NHTSA is keeping the proposed definition of closure devices.
NHTSA's intention is to subject all TPRDs, check-valves, and shut-off
valves that directly control flow of hydrogen into and/or out of the
CHSS to the requirements of FMVSS No. 308 S5.1.5. Therefore, there is
no need to identify closure devices as ``primary.'' Whether a closure
device directly controls the flow into and/or out of the CHSS will be
dispositive. Redundant, back-up, or downstream devices are not intended
to be subject to the requirements of FMVSS No. 308 S.5.1.5.
There will be no confusion about ``other'' closure devices because
the proposed definition specifically identifies only ``the check
valve(s), shut-off valve(s) and thermally-activated pressure relief
device(s) that control the flow of hydrogen into and/or out of a
CHSS,'' and the CHSS is defined as ``a system that stores compressed
hydrogen fuel for a hydrogen-fueled vehicle, composed of a container,
container attachments (if any), and all closure devices required to
isolate the stored hydrogen from the remainder of the fuel system and
the environment.'' Any other device types, as well as any devices that
do not directly control flow into and/or out of a CHSS, are not closure
devices under this definition, or are not part of the CHSS and
therefore are not subject to the requirements of FMVSS No. 308 S5.1.5.
For example, a valve that is not providing the CHSS with one or all of
its required functions of check valve, shut-off valve, and TPRD is not
considered a closure device and would not be tested under the standard.
Similarly, a valve located ``downstream'' from the CHSS shut-off valve
is not considered a closure device since it would not be controlling
flow into or out of the CHSS. Likewise, a ``manual isolation valve'' is
not a shut-off valve because it is not automatically activated, and so
would not be considered a closure device per the final rule.
d. Shut-Off Valve Definition
Background
GTR No. 13 defines a shut-off valve as ``a valve between the
container and the vehicle fuel system that must default to the `closed'
position when not connected to a power source.'' NHTSA proposed adding
the words ``electrically activated'' to the definition, so that a shut-
off valve would be ``an electrically activated valve between the
container and the vehicle fuel system that must default to the `closed'
position when not connected to a power source.''
Comments Received
Commenters expressed a strong preference for maintaining alignment
with the definition of a shut-off valve as outlined in GTR No. 13.
Nikola commented that the existing GTR No. 13 definition should be
retained, arguing that other activation methods, such as pneumatic, are
possible and that the proposed change to ``electrically activated''
would be overly prescriptive. Auto Innovators recommended harmonizing
the definitions of shut-off valves in FMVSS Nos. 307 and 308 with the
definition in GTR No. 13, noting that the definitions in these FMVSS
standards are currently inconsistent. Similarly, DTNA requested the
removal of ``electrically activated'' from the definition, suggesting
that the term is not design-neutral and could limit future innovations.
DTNA further proposed using the term ``automatically activated'' as a
more inclusive option. EMA supported consistency with GTR No. 13 and
recommended that NHTSA harmonize the definition of shut-off valves
across FMVSS Nos. 307 and 308, offering an alternative definition that
would omit ``electrically activated.''
Several commenters, including H2MOF and TesTneT, opposed adding
``electrically activated,'' with H2MOF stating that shut-off valves can
also be pneumatically activated. WFS suggested that while leaving the
definition as written in GTR No. 13 would suffice, there would be no
harm in adding ``electrically activated'' if NHTSA felt it improved
clarity. NGS and FORVIA also raised concerns about restricting future
innovations, such as pneumatic systems, if the definition were limited
to electrically activated valves. Both commenters advocated for
retaining the GTR No. 13 wording to avoid stifling potential
advancements in valve technology.
Agency Response
NHTSA agrees with the commenters and has removed the words
``electrically activated,'' consistent with the definition in GTR No.
13. This change avoids the possibility of being design restrictive by
specifying ``electrically activated.'' NHTSA notes, however, that the
definition indicates that the valve must default to the ``closed''
position when not connected to a power source, which directly implies
the valve must utilize electrical actuation of some kind.
NHTSA made an editorial modification to the definition of ``shut-
off valve'' by replacing the words ``when not connected to a power
source'' with ``unpowered.'' This was an editorial change for
conciseness. However, NHTSA omitted this update from the definition for
shut-off valve in FMVSS No. 307, and only applied it in FMVSS No. 308.
In the final rule, both definitions have been revised to reflect this
update.
e. CHSS Definition
Background
NHTSA proposed a definition of the CHSS that matches the definition
in GTR No. 13, with the exception of the removal of the word
``primary'' before ``closure devices,'' as discussed above.
Comments Received
Luxfer Gas Cylinders commented that the proposed definition of CHSS
is appropriate but noted that most of the hydraulic performance tests
in FMVSS No. 308 cannot be conducted with the check valve, shut-off
valve, and TPRD attached to the container. NFA suggested that NHTSA
should consider including Figure-3, the Typical CHSS diagram from the
NPRM, in the standard to help clarify the definition.
Agency Response
NHTSA is maintaining the definition of CHSS as proposed. The
regulatory text clearly specifies where the CHSS or its subcomponents,
such as the container, must meet the various requirements. For example,
FMVSS No. 308 S5.1.2 specifies that the test for performance durability
is conducted only with the container, and in some cases, container
attachments. As Luxfer Gas Cylinders points out, it is not possible to
conduct hydraulic tests with the closure devices attached to the
container.
NHTSA is not including a figure in the definition because the
definition is already clear, and the referenced figure only shows a
generic CHSS that may not be representative of all CHSS types that meet
the definition.
f. Cryo-Compressed Hydrogen Systems
Background
Cryo-compressed hydrogen (CcH2) storage systems store compressed
hydrogen gas at very low temperatures and high pressures. NHTSA
proposed that FMVSS No. 307 and 308 would apply to ``each motor vehicle
that uses compressed hydrogen gas as a fuel source.''

[[Page 6226]]

Comments Received
Verne, Inc. commented that many of the performance requirements in
GTR No. 13 and FMVSS Nos. 307 and 308 are relevant for ensuring the
safety of some aspects of cryo-compressed hydrogen storage systems.
These aspects include crash safety, fire resistance, external vehicle
hazards, and performance durability. However, Verne stated that these
regulations do not adequately address the specific design, components,
and service conditions of CcH2 systems. It further noted that CcH2
technology, which operates at a nominal working pressure (NWP) of 35
MPa and temperatures below -200 [deg]C, is not sufficiently covered by
existing global or local regulations, codes, and standards.
Verne requested clarification from NHTSA on whether CcH2 storage
systems and hydrogen-powered vehicles using such systems fall under the
scope of FMVSS Nos. 307 and 308 as a type of CHSS. Verne also stated
that while CcH2 is not explicitly out of scope in GTR No. 13, there is
a note in GTR No. 13 Part I Section C.3 that could suggest it should
not be included. It emphasized that CcH2 systems meet the definition of
CHSS, including key components like a container, TPRD, shut-off valve,
and check valve.
Verne listed several ways in which CcH2 systems differ from
conventional gaseous CHSS, such as the inclusion of additional devices
like multiple pressure relief devices, insulation, and an all-metal
vacuum jacket. It also highlighted that due to the pressure dynamics
after fueling, the target and maximum fueling pressure should be set
lower than 43.75 MPa, suggesting a target of 35 MPa and operational
relief at 40 MPa. Furthermore, Verne noted that CcH2 systems are
designed to operate at temperatures far below the typical range for
gaseous hydrogen systems, with expected operational temperatures
between -253 [deg]C and +85 [deg]C.
Verne requested an exemption from FMVSS No. 308 S5.1.3, Test for
expected on-road performance, for CcH2 systems, stating that test
primarily assesses the performance of non-metallic liners in Type 4
containers and non-metallic sealing interfaces. Verne stated that since
CcH2 systems rely on metal-to-metal sealing designs to perform at
cryogenic temperatures, they do not face the same vulnerabilities as
systems using non-metallics. Verne also stated that the temperature
conditions in the on-road performance test do not accurately reflect
the normal or extreme operational conditions of CcH2 systems. It stated
that the current requirements would make the test impossible to execute
due to the lower setpoints of the PRDs in CcH2 systems. Finally, Verne
stated that the test for on-road performance, as currently written, is
costly and provides little safety assurance for CcH2 systems,
recommending that it be revised to better suit the technology.
Agency Response
Verne, Inc. has highlighted significant differences between CcH2
and conventional CHSS,\10\ including very low operational temperatures,
the use of metal-to-metal sealing at cryogenic temperatures, and the
presence of PRDs in the storage system. CcH2 systems operate under
significantly different conditions than conventional CHSS, including
lower temperatures and altered pressure dynamics. These technological
distinctions would pose challenges for applying FMVSS No. 308 to CcH2
systems given that the current testing protocols do not adequately
address these differences.\11\
---------------------------------------------------------------------------

\10\ By ``conventional CHSS,'' we mean a CHSS that stores
hydrogen in gaseous form at high pressures, typically 35 to 70 MPa
\11\ There are varied CcH2 system designs under development and
there are no standardized testing protocols that address safety
issues unique to each of these CcH2 systems. CcH2 storage system
manufacturers conduct Failure Modes Effects Analysis (FMEA) to
identify potential failure modes, analyze the causes of these
failures, and assess their potential effects on the system's safety
and functionality, including hydrogen leaks, pressure surges,
thermal issues, and component malfunctions. The manufacturers take
steps to ensure their CcH2 system designs prevent occurrence of
these failures and mitigate the safety effects of any failure mode.
---------------------------------------------------------------------------

GTR No. 13, on which FMSS No. 308 is based, was developed to
consider conventional CHSS and does not yet provide sufficient guidance
for CcH2 systems. GTR No. 13 acknowledges the potential inclusion of
additional storage technologies, such as cryo-compressed systems, in
future revisions of the GTR and as the development of these systems
progresses. However, it is likely that more research and safety
standard development will be required to address the technological
distinctions between CcH2 systems and conventional CHSS before GTR No.
13 can be expanded to include these systems.
As such, applying the specific performance requirements of FMVSS
No. 308 to vehicles utilizing CcH2 systems is not feasible. Therefore,
NHTSA will not apply the requirements of FMVSS No. 308 to vehicles
using CcH2 storage systems at this time. However, while CcH2 systems
are unique hydrogen storage systems and distinct from conventional
CHSSs, most of the vehicle fuel delivery system (piping, pressure
regulators, filters, flow control valves, and heat exchangers) and the
fuel cell system used to power and propel a vehicle with CcH2 storage
systems are similar to those in hydrogen powered vehicles with
conventional CHSSs. Additionally, the safety aspects associated with
the hydrogen fuel delivery system and the fuel cell system in vehicles
with CcH2 storage systems would be similar to that in vehicles with
conventional CHSSs. Therefore, NHTSA will still require that vehicles
utilizing CcH2, like all vehicles that use hydrogen fuel, meet the
vehicle safety requirements outlined in FMVSS No. 307. These include
provisions for in-use fuel system integrity and post-crash fuel system
integrity, ensuring that vehicles using CcH2 technology maintain
overall vehicle safety. Additionally, while NHTSA is exempting CcH2
systems from the requirements of FMVSS No. 308 at this time, NHTSA will
continue to monitor developments in cryogenic storage technologies and
associated safety standards to inform future regulatory actions.
g. Solid State Hydrogen Systems
Background
Solid-state hydrogen storage systems use advanced materials
designed for the storage of hydrogen within solid structures. These
materials are composed of porous frameworks onto which hydrogen can
adsorb. These frameworks feature expansive internal surface areas that
allow the capture and storage of hydrogen molecules within porous
networks. These systems can store hydrogen at high densities due to
their structural versatility and their ability to reversibly absorb and
release hydrogen.
Comments Received
H2MOF commented that its solid-state hydrogen storage systems use
adsorbent materials to store hydrogen safely and efficiently. H2MOF
stated this method helps reduce costs associated with hydrogen storage,
transportation, and use by avoiding the expenses of gas compression and
cryogenic liquefaction. H2MOF stated its system involves hydrogen
adsorption materials housed within a metallic pressure vessel, which
typically operates at 5 MPa, and is enclosed in an insulated outer
shell. H2MOF requested that low-pressure solid-state storage solutions
operating below 10 MPa be exempted from the requirements of the NPRM,
which H2MOF stated are designed for non-metallic high-pressure

[[Page 6227]]

vessels functioning at 35 MPa and 70 MPa.
Agency Response
Similar to the case of CcH2 systems discussed in the previous
section, H2MOF has highlighted significant differences between its low-
pressure solid-state storage systems and conventional CHSS. These
distinctions include the use of adsorbent materials within metallic
pressure vessels, lower operational pressures, and the avoidance of
high-pressure compression fueling typically seen in traditional CHSS.
As with CcH2 systems, these technological differences present
challenges for applying the proposed FMVSS No. 308, which was developed
for conventional high-pressure gaseous CHSS and does not consider the
unique characteristics of solid-state hydrogen storage systems. As with
CcH2 systems, NHTSA recognizes the need for more research and standards
development to address the specific safety characteristics of solid-
state hydrogen storage systems.
Therefore, NHTSA has determined that it is not feasible to apply
the performance requirements of FMVSS No. 308 to vehicles using solid-
state hydrogen storage systems. However, similar to vehicles with CcH2
storage systems and for the same reasoning, vehicles that use solid-
state hydrogen storage technology must still comply with the overall
vehicle safety requirements specified in FMVSS No. 307, including in-
use fuel system integrity and post-crash fuel system integrity.\12\
While NHTSA is exempting solid-state hydrogen storage systems from the
requirements of FMVSS No. 308 at this time, NHTSA will continue to
monitor advancements in solid-state hydrogen storage technology and
consider future regulatory updates as these systems and associated
safety standards further develop.
---------------------------------------------------------------------------

\12\ The vehicle fuel delivery system and the fuel cell system
in vehicles using solid-state hydrogen storage systems are similar
to hydrogen powered vehicles with conventional CHSSs.
---------------------------------------------------------------------------

5. General Requirements for the CHSS
a. Maximum CHSS Working Pressure of 70 MPa
Background
Consistent with GTR No. 13, NHTSA proposed requiring that CHSS have
a NWP of 70 MPa or less. This is because working pressures above 70 MPa
for motor vehicle applications are currently considered impractical and
may pose a safety risk given current known technologies. The energy
density of hydrogen does not increase significantly when pressurized
above 70 MPa, so there is no significant improvement in hydrogen
storage efficiency at pressures above 70 MPa. Pressures above 70 MPa,
however, may present a greater safety hazard. NHTSA sought comment on
this requirement, and specifically asked commenters to identify any
technologies that can safely store hydrogen at pressures above 70 MPa.
Comments Received
Nikola stated that CHSS are identified by NWP and maximum filling
pressure, with pressures above 70 MPa offering diminishing returns.
Nikola also commented that current industry does not have containers
that operate above this threshold. Auto Innovators generally agreed
with NHTSA's rationale but requested a plan for adapting to future
technological developments. It recommended aligning with GTR No. 13,
which sets 70 MPa as the highest NWP, and expressed that it would be
inappropriate to specify anything higher. Luxfer Gas Cylinders
commented that 70 MPa is the appropriate limit due to the absence of
filling infrastructure for pressures above this level.
Glickenhaus raised concerns about unintended consequences from
limiting the NWP of CHSS to 70 MPa. It pointed out that limiting
pressures could hinder future research, comparing this to past
limitations when 35 MPa was the industry standard. Glickenhaus
commented that today's 70 MPa containers were made possible by
technological advances, and a similar restriction in the past might
have hindered progress. It also stated that high temperature conditions
could reduce the effectiveness of refueling at a fueling station with
70 MPa containers, leading to slower refills and greater energy
consumption due to the thermodynamics relating pressure, volume,
temperature, and amount of gas.
H2MOF supported the proposal to limit NWP to 70 MPa and requested
that FMVSS Nos. 307 and 308 apply to containers ranging from 10 MPa to
70 MPa NWP. WFS agreed with NHTSA's proposal, noting that it aligns
with GTR No. 13 and the practical limit for on-board storage. While
hydrogen can be safely stored above 70 MPa at fueling stations, it
commented that 70 MPa is the practical upper limit for on-board
storage.
TesTneT referenced the GTR No. 13 requirement that all new
compressed hydrogen storage systems produced for on-road vehicle
service have an NWP of 70 MPa or less. TesTneT also noted that there is
no increased risk with higher storage pressures, and stated that
greater container wall thickness at higher pressures provides more
resistance to damage and fire effects. TesTneT noted that the safety
issues at pressures higher than 70 MPa involves the ability to seal
connections within valves and regulators. It mentioned that it
currently use 95 MPa and 100 MPa containers for storing hydrogen at a
fueling station. FORVIA agreed with the proposal and commented that
introducing additional pressure levels would not benefit
interoperability between vehicles and fueling stations, further
supporting the 70 MPa limit.
Agency Response
NHTSA is adopting its proposal to limit the NWP of CHSS to 70 MPa
or less. Most commenters agreed with the proposal, noting that NWP
above 70 MPa offer diminishing returns and that current fueling
infrastructure is not compatible with CHSS with NWP greater than 70
MPa. NHTSA has determined that limiting the NWP of CHSS to 70 MPa or
less is critical due to safety concerns at higher pressures.
TesTneT noted that it uses 95 MPa and 100 MPa NWP containers to
store hydrogen at a fueling station and that the thicker walls of these
containers make them inherently safer against damage and fire. NHTSA
notes that TesTneT's example of containers with NWP greater than 70 MPa
are stationary storage containers. While containers with thicker walls
are more resistant to damage and fire, they are significantly heavier
and likely not practical for use in hydrogen vehicles.
The requirements in this final rule do not fully address the safety
risks associated with storage pressures above 70 MPa. Higher pressures
present a greater risk of severe leaks and/or rupture, and the
consequences of such failures at increased pressures are more severe
due to the larger quantity of energy that could be released. TPRD
releases may also be unsafe due to the quantity of hydrogen that must
be released at pressures above 70 MPa. Additionally, the test for
performance durability of containers in this final rule may not be
sufficient to address stress rupture risk for containers with NWP
greater than 70 MPa. NHTSA is concerned that a container with NWP
greater than 70 MPa may comply with the performance durability
requirements and yet have a significant risk of catastrophic stress
rupture. As a result, additional safety considerations are necessary
for pressures exceeding 70 MPa, and the safety of such systems is not
yet known.

[[Page 6228]]

Therefore, consistent with GTR No. 13, NHTSA is maintaining the
requirement that all CHSS must have an NWP of 70 MPa or less.\13\
---------------------------------------------------------------------------

\13\ Storing hydrogen above 70 MPa is also impractical given
current technology. As pressure increases beyond 70 MPa, hydrogen
becomes increasingly difficult to compress. This difficulty leads to
diminishing returns in terms of hydrogen storage density, where only
a small increase in stored hydrogen results from a
disproportionately higher input of compression energy. Storing
hydrogen at higher pressures also requires containers with thicker
walls to manage the increased stress from extreme pressurization.
These thicker containers add considerable weight, which is
impractical for vehicle use where minimizing weight is critical.
---------------------------------------------------------------------------

Glickenhaus stated that limiting the NWP of CHSS to 70 MPa could
have unintended consequences by hindering technological advances in
hydrogen storage. While Auto Innovators generally agreed with the
proposal to limit NWP of CHSS to 70 MPa, it requested a plan for
adopting future technological developments. NHTSA agrees with the
commenters that technological advances are likely to continue in this
space and the agency will monitor such advancement and continue
research work on CHSS and hydrogen fuel system integrity. NHTSA
coordinates closely with the U.S. Department of Energy (USDOE) and the
Pipeline and Hazardous Materials Safety Administration (PHMSA) on
research, technical advancements, and standards development for
hydrogen vehicles, and plans to update the standards in the future, as
needed. Additionally, for vehicles using CHSS with NWP greater than 70
MPa, NHTSA has provisions for exemptions for alternative fuel vehicles
that vehicle manufacturers may use.\14\
---------------------------------------------------------------------------

\14\ See Part 555--Temporary Exemption from Motor Vehicle Safety
and Bumper Standards, <a href="https://www.ecfr.gov/current/title-49/part-555">https://www.ecfr.gov/current/title-49/part-555</a>.
---------------------------------------------------------------------------

Glickenhaus commented that fueling stations with 70 MPa tanks would
take longer and more energy to refuel hydrogen powered vehicle tanks in
extremely hot weather. NHTSA notes that the NPRM and final rule apply
to hydrogen storage systems in vehicles used for vehicle propulsion and
not the tanks used in fueling stations. Generally, the tanks in fueling
stations are at about 100 MPa (similar to those noted by TesTneT). This
final rule does not apply to hydrogen tanks in fueling stations.
Limiting CHSS NWP to 70 MPa does not mean 70 MPa is the maximum
pressure that can occur inside a CHSS. Under hot conditions or during
fueling, a fully fueled CHSS may experience pressures of 125 percent
NWP (87.5 MPa for a 70 MPa CHSS). Limiting CHSS NWP to 70 MPa does not
limit the maximum allowable working pressure of the container to 70
MPa, nor does it limit manufacturers' ability to design containers that
can withstand severe over-pressurization events as tested in subsequent
tests.
Finally, H2MOF requested that low-pressure solid-state storage
systems typically operating at pressure below 10 MPa be exempted from
the requirements of the NPRM, which H2MOF stated are designed for non-
metallic high-pressure vessels functioning at 35 MPa and 70 MPa. NHTSA
notes that it is not limiting applicability of the standard to vehicles
with CHSS pressures above 10 MPa. Instead, NHTSA is excluding low-
pressure sold-state hydrogen storage systems from FMVSS No. 308
requirements, as explained earlier in this notice.
b. Mounting Closure Devices On or Within Each Container
Background
GTR No. 13 provided contracting parties with the discretion to
require that the closure devices be mounted directly on or within each
hydrogen fuel container. The relevant safety concern is that the high-
pressure lines required to connect remotely located closure devices
with the container could be susceptible to damage or leak. However, as
discussed above, the definition of a container is sufficiently broad
that it includes lines that are part of the continuous volume of stored
hydrogen (as determined by the location of the shut-off valve or any
other obstruction that ``breaks'' or ``interrupts'' the container's
continuous volume). Thus, any lines that form part of the container's
continuous volume are themselves part of the container and will be
included in the container performance testing discussed below. If a
container (which includes any lines that are part of the container's
continuous volume) can successfully complete the performance testing in
FMVSS No. 308, then the risk of failure of the lines has been
addressed. As a result, NHTSA tentatively concluded that it is not
necessary to specify that closure devices be mounted directly on or
within each container. NHTSA sought comment on requiring closure
devices to be mounted directly on or within each container.
Comments Received
Commenters generally supported NHTSA's proposal not to require
closure devices to be mounted directly on or within each container,
with most agreeing that this approach provides necessary flexibility
for system design. Auto Innovators noted that discussions within the
GTR No. 13 Phase 2 Informal Working Group suggested mounting the
closure device directly on a chamber for single-chamber systems or on
one of the chambers for multi-chamber systems, but also highlighted the
benefits of allowing manufacturers discretion, particularly for non-
traditional designs like conformable tanks. H2MOF, HATCI, and WFS also
supported leaving the location of closure devices to manufacturer
discretion, stating that this flexibility enhances design options. WFS
and TesTneT pointed out that allowing remote TPRDs, which have been
safely used in the CNG industry, could enhance system safety in fire
protection. However, Nikola disagreed with NHTSA's approach, stating
that ``CNG is not the same as hydrogen'' and that allowing this could
lead to unintended issues. Luxfer Gas Cylinders and NGS agreed with
NHTSA's proposal, with NGS emphasizing the importance of not limiting
manufacturers' ability to design systems tailored to their specific
applications.
Agency Response
NHTSA will not require closure devices to be mounted on or within
each container. As discussed above, the definition of ``container'' in
the final rule is sufficiently broad to include any lines that may form
part of the container's continuous volume of pressurized hydrogen up to
the closure device.\15\ Therefore, these lines must be included in the
applicable performance testing as part of the container itself. If a
container, including all portions of the container's continuous volume,
can successfully complete the performance testing in FMVSS No. 308,
then the risk of failure of the lines has been sufficiently addressed.
---------------------------------------------------------------------------

\15\ In this context, ``lines'' refers to any pluming, piping,
and/or connections where hydrogen fuel may be present.
---------------------------------------------------------------------------

c. Requiring Check Valve Functionality as Part of the CHSS
Background
During fueling, hydrogen enters the CHSS after passing through a
check valve. The check valve prevents back-flow of hydrogen into the
fueling supply line or even out of the fueling receptacle to the
atmosphere. NHTSA proposed that the CHSS be required to include the
functionality of a check valve. However, NHTSA is aware of CNG vehicles
that do not include check valves as part of their CNG storage system.
NHTSA sought comment on whether the check valves should be required as
part of the CHSS.

[[Page 6229]]

Comments Received
Commenters expressed mixed opinions on whether check valves should
be required as part of the CHSS. Some, including Nikola, EMA, HATCI,
and FORVIA, supported requiring check valves, citing the higher
pressure of hydrogen and the role of check valves in ensuring safety,
especially for multi-container systems. FORVIA stated that not
including a check valve would leave the fueling line vulnerable to
hydrogen leakage.
Others, such as Agility, Glickenhaus, H2MOF, and TesTneT, opposed
making check valves a mandatory component of the CHSS. Agility stated
that system-level protections are appropriate and requested
clarification whether a single check valve near the fuel receptacle is
adequate. Glickenhaus argued that a remotely located check valve could
offer advantages. H2MOF pointed to the safety record of millions of CNG
vehicles without check valves in its storage systems and suggested the
requirement would be too design restrictive. TesTneT noted that check
valve functionality could be integrated into other components, making a
separate check valve unnecessary.
WFS commented that the key issue is not having a dedicated check
valve but ensuring ``check valve functionality,'' which could be
incorporated into other system components, as outlined in GTR No. 13.
Agency Response
Consistent with GTR No. 13, NHTSA is requiring that the CHSS
include a check valve or the function of a check-valve. A check valve
means ``a valve that prevents reverse flow.'' Therefore, each CHSS must
have hydrogen flow control functionality equivalent to a valve that
prevents reverse flow. This requirement is not design restrictive
because manufacturers have the option to design systems that provide
the required functionality without the need for a traditional check
valve. For example, the functions of check valve and shut-off valve may
be combined into a single device, or multiple containers may share a
single check valve. Additionally, it may be possible for a vehicle to
use a single check valve located at the fueling receptacle to provide
check valve functionality to multiple CHSS. In such a design, each CHSS
onboard the vehicle would derive the function of check valve from the
single check valve located at the fueling receptacle.
6. Specification of BP<INF>O</INF> on the Container Label
Background
Several of the performance tests in FMVSS No. 308 use a
manufacturer-supplied value known as BP<INF>O</INF>. A container's
BP<INF>O</INF> is a design parameter specified by the manufacturer that
represents the median burst pressure for a batch of containers. To
facilitate compliance testing, NHTSA proposed that manufacturers
specify the BP<INF>O</INF> associated with each container on the
container label.
Comments Received
Several commenters addressed the proposal to include the
manufacturer-specified median burst pressure (BP<INF>O</INF>) on
container labels. Nikola stated that BP<INF>O</INF> is not useful to
and could confuse end users, suggesting that if BP<INF>O</INF> is not
available for compliance testing, NHTSA should assume a value of 2.25
times NWP. Luxfer Gas Cylinders argued that requiring BP<INF>O</INF> on
labels is unnecessary, as the burst pressure is a quality control
measure, and the median burst pressure of a batch is irrelevant to
manufacturers or end users. Auto Innovators disagreed with the
assertion that BP<INF>O</INF> varies significantly between batches,
stated that BP<INF>O</INF> is based on manufacturer testing, and
recommended consistency with GTR No. 13. Auto Innovators opposed
including BP<INF>O</INF> on labels, citing potential confusion for end
users and lack of safety benefits, and noted that BP<INF>O</INF> can be
provided to NHTSA during testing without needing to be on the label.
EMA echoed concerns about potential customer confusion and recommended
alignment with GTR No. 13, suggesting that BP<INF>O</INF> could be
provided by the manufacturer upon request.
Glickenhaus supported a labeling requirement for burst pressure but
raised concerns that NHTSA's proposed definition of BP<INF>O</INF>
could restrict manufacturers' ability to maintain higher safety
margins. It proposed an alternative definition of BP<INF>O</INF> based
on the minimum burst pressure from the design and manufacturing process
to allow for increased safety margins. H2MOF and HATCI both stated the
requirement was impractical and unnecessary, with HATCI stressing that
BP<INF>O</INF> is primarily a design parameter and market strategy
issue, often considered confidential. Agility and TesTneT also opposed
the requirement, with Agility calling it impracticable and TesTneT
suggesting that compliance testing should focus on meeting minimum
standards rather than a manufacturer-specified value.
Other commenters, including NGS and Newhouse, requested aligning
with GTR No. 13, with Newhouse noting that BP<INF>O</INF> information
can be found through part numbers if needed. FORVIA expressed strong
opposition to including BP<INF>O</INF> on labels, citing concerns over
confidentiality and potential misinterpretation by consumers and
requested alignment with GTR No. 13. Several commenters, including Auto
Innovators and Luxfer Gas Cylinders, reiterated concerns that labeling
BP<INF>O</INF> would create confusion and add unnecessary burdens
without any clear safety benefit, recommending harmonization with GTR
No. 13 instead.
Agency Response
After consideration of the comments, NHTSA will not require
BP<INF>O</INF> to be listed on the container label. NHTSA agrees this
requirement could cause confusion for consumers regarding slight
differences in BP<INF>O</INF> that may exist between vehicles. Such
differences will have no impact on safety or performance. NHTSA also
acknowledges that listing BP<INF>O</INF> on the container label could
create confusion about the highest rated pressure for a given vehicle.
Since BP<INF>O</INF> will typically be a multiple of NWP, but have the
same pressure units, it could be dangerous for a user to mistake
BP<INF>O</INF> for NWP.
Nevertheless, NHTSA still needs to know the value of BP<INF>O</INF>
to conduct compliance testing on a given vehicle. Instead of requiring
BP<INF>O</INF> on the container label, NHTSA will obtain BP<INF>O</INF>
directly from the vehicle manufacturer. The method for obtaining
BP<INF>O</INF> from the manufacturer will match that for obtaining the
primary constituent of the container, discussed below.
Some comments appear to reflect a misunderstanding of the role of
BP<INF>O</INF> within the proposed regulation. The BP<INF>O</INF> is a
manufacturer-specified parameter that represents the median burst
pressure for a batch of containers. Manufacturers are free to
incorporate additional safety factors into their designs if they wish.
The use of BP<INF>O</INF> in the requirements does not restrict this
ability. As discussed in the NPRM, the use of BP<INF>O</INF> during the
residual strength burst test ensures that containers at the end of
their service life would still be safe even if they were to remain in
service.\16\ Specifically, the burst pressure after testing must be at
least 80% of the container's BP<INF>O</INF>. This

[[Page 6230]]

requirement controls the degradation rate of the container over time,
preventing a high degradation rate that could lead to dangerous bursts
if the container were to remains in use beyond its intended life. This
standard is comparable to safety standards for other vehicle components
like seatbelt webbing.
---------------------------------------------------------------------------

\16\ See 89 FR 27518 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
---------------------------------------------------------------------------

Additionally, the concerns raised about the ambiguity of the
BP<INF>O</INF> definition are misplaced, as the regulation does not
provide a prescriptive definition but rather relies on the
manufacturer's expertise in determining BP<INF>O</INF>. There is no
requirement to calculate a mean burst pressure by bursting every tank
in a batch. Manufacturers may use standard industry practices based on
their design, materials, manufacturing processes, and testing to
determine BP<INF>O</INF>.
7. Tests for Baseline Metrics
a. Required Number of Containers Tested
Background
GTR No. 13 requires three new containers to be tested during the
baseline initial burst test and the baseline pressure cycle test. As
NHTSA explained in the proposal, this requirement originates from the
type-approval certification process commonly found in other nations and
that NHTSA did not believe that three new containers needed to be
tested under the U.S. self-certification system where NHTSA buys and
tests vehicles and equipment at the point of sale. Therefore, NHTSA
proposed basing the results of testing of any container for the
baseline initial pressure cycle test. NHTSA sought comment on this
decision.
Comments Received
FORVIA and TesTneT agreed with the proposal, stating that only one
container needs to be pressure cycled to demonstrate compliance with
the cycle life requirements. TesTneT likened this approach to batch
testing, where only one container is required to be tested, rather than
three.
DTNA expressed concern that testing only one container for baseline
metrics might not provide sufficient information on the burst behavior
of all containers in vehicles equipped with multiple containers. DTNA
acknowledged that NHTSA purchases vehicles and equipment from the
public market to monitor FMVSS compliance, but proposed that for
vehicles with multiple containers, at least two should be subjected to
the baseline initial pressure cycle test.
Luxfer Gas Cylinders commented that testing any one container is
reasonable, noting that all cylinders must pass the minimum required
cycle tests and that testing three containers does not represent a
significant statistical sample.
Nikola disagreed with the proposal, suggesting that NHTSA obtain
containers directly from tank manufacturers, similar to how testing is
conducted under FMVSS No. 304 compliance.
H2MOF supported NHTSA's proposal to test one container for the
baseline initial pressure cycle test and recommended allowing a retest
if there is an assignable cause of any non-compliance.
Agency Response
NHTSA is maintaining its decision that it is not required to test
three containers for the baseline initial burst test, as specified by
GTR No. 13. Under the U.S. self-certification system, NHTSA purchases
vehicles and equipment for testing randomly at the point of sale, and
the selected container must meet all applicable safety requirements.
This approach ensures that manufacturers are incentivized to ensure all
vehicles consistently comply with safety standards, knowing that any
one of their containers could be tested. Removing the requirement to
test three containers, the test burden is potentially reduced without
compromising safety, and allowing NHTSA to potentially test more
containers with the same operating budget. Manufacturers must still
ensure that each vehicle meets the standard.
Additionally, concerns about variability among containers are
addressed through the random selection process, which provides an
effective representation of real-world conditions. While some
commenters raised concerns about vehicles with multiple containers,
NHTSA has the flexibility to conduct repeat tests, as well as
additional tests on any of the various container types if needed. This
allows NHTSA to respond to specific cases where there may be a safety
concern without mandating the testing of three containers in every
instance, which maintains an efficient means of ensuring safety.
b. Baseline Initial Burst Pressure Test
(1) Need for the Baseline Initial Burst Test
Background
Consistent with GTR No. 13, NHTSA proposed the baseline initial
burst pressure test in addition to the test for performance durability,
which includes a 1000 hour high-temperature (85 [deg]C) static pressure
test designed to evaluate the container's resistance to stress rupture,
in combination with other lifetime stress factors. Given that the high-
temperature static pressure test evaluates stress rupture risk, and the
test for performance durability represents an overall worst-case
lifetime of multiple stress factors, NHTSA sought comment on whether
the baseline initial burst pressure test even needs to be included in
the standard's requirements.
Comments Received
Nikola commented that the baseline initial burst pressure test is
necessary to ensure that the container meets its initial strength
integrity requirements, which can then be compared to the final burst
pressure. Agility expressed concern that the high-temperature static
pressure test does not sufficiently evaluate reliability against stress
rupture, stating that testing one million cylinders would be required
to demonstrate the same reliability. EMA recommended that the baseline
initial burst pressure test is unnecessary, proposing the removal of
S5.1.1.1 from the standard. H2MOF stated that the residual burst
pressure after the performance durability test is a better indicator of
design fitness than an initial burst pressure test. Auto Innovators
suggested aligning with GTR No. 13, which uses the initial baseline
burst pressure for comparison with residual values.
TesTneT clarified that the high-temperature static pressure test,
originally called the ``accelerated stress rupture test,'' was
developed to assess combined effects on the container but not the
individual stress rupture characteristics of fiber strands. TesTneT
stated that the baseline initial burst pressure test is necessary for
container design and manufacturing control. Newhouse commented that
both tests should be conducted, as they assess different factors.
FORVIA recommended including the baseline initial burst pressure test
for harmonization with GTR No. 13, while also questioning whether NHTSA
must perform all tests during field surveillance or if it has
discretion in test selection. Auto Innovators reiterated its support
for harmonizing with GTR No. 13.
Agency Response
NHTSA is maintaining the proposed baseline initial burst pressure
test. Several commenters provided sufficient explanation of why the
baseline initial pressure test is different from the test for
performance durability. On the other

[[Page 6231]]

hand, the commenters proposing the removal of the baseline initial
burst pressure test did not provide sufficient justification why the
baseline initial burst pressure test is not needed. The initial burst
pressure test evaluates the container's start-of-life integrity,
whereas the test for performance durability examines different aspects
of material performance and stresses, such as resistance to physical
damage, chemical exposure, and extreme environmental temperatures, and
the container's subsequent end-of-life integrity. Therefore, both
testing requirements should be included in the standard, as proposed.
NHTSA notes, however, that the results of the baseline initial burst
pressure test are not referenced in subsequent tests as a comparison or
``baseline.'' Instead, subsequent tests reference the BP<INF>O</INF>
value discussed above. Regarding field surveillance, NHTSA may conduct
any of the tests in the FMVSS as part of field surveillance.
(2) Burst Pressure Within <plus-minus>10 Percent of BP<INF>O</INF>
Background
As proposed, the baseline initial burst pressure test would have
verified that the initial burst pressure is within 10 percent of the
manufacturer specified BP<INF>O</INF>. The requirement that the
container tested must have a burst pressure within <plus-minus>10
percent of BP<INF>O</INF> was based on the need to control variability
in container production. If a manufacturing process produces containers
with highly variable initial burst pressures, there is a possibility of
a container with a dangerously low burst pressure. NHTSA sought comment
on the safety need for specifying a limit on burst pressure variability
in a batch and whether the 10 percent limit is appropriate. Commenters
were asked to provide supporting data if they believed another limit
was appropriate.
Comments Received
Commenters provided mixed opinions regarding the proposal for a
<plus-minus>10 percent limit on burst pressure variability, with some
supporting the limit and others suggesting it is unnecessary or
impractical. Nikola commented that the <plus-minus>10 percent limit is
achievable and accepted by manufacturers. Agility stated that limiting
maximum burst pressure does not necessarily improve safety and
suggested that variability in carbon fiber strength would take up most
of the proposed limit, making it impractical. Agility also recommended
omitting the requirement, stating that the existing minimum burst
requirement already addresses safety concerns. HATCI and Auto
Innovators both noted that burst pressure variability could be managed
through a manufacturer's quality management system, with Auto
Innovators supporting alignment with GTR No. 13 and affirming the
appropriateness of the <plus-minus>10 percent limit. Luxfer Gas
Cylinders stated that specifying a limit is unnecessary, as
manufacturers already ensure no cylinder bursts below the minimum
level, typically by setting burst pressures significantly higher than
required. TesTneT also supported the <plus-minus>10 percent limit,
noting that burst testing in accordance with GTR No. 13 had not
revealed any issues with the limit.
In contrast, Quantum suggested that the 10 percent requirement is
unrealistic due to the influence of factors such as carbon fiber
performance, recommending a more lenient limit of 20 percent. NGS and
H2MOF commented that managing batch variation should be left to the
manufacturer as long as the minimum burst pressure is met. Newhouse
questioned the practicality of the <plus-minus>10 percent limit, noting
that variability is inherent in the production process and that meeting
the minimum burst pressure is a more meaningful safety measure. MEMA
and FORVIA both supported maintaining alignment with GTR No. 13, with
FORVIA emphasizing that the 10 percent variability allowance accounts
for reasonable manufacturing differences while maintaining safety
margins. FORVIA also discouraged adding new batch-related requirements,
suggesting that automotive production often relies on other control
methods, such as sampling in continuous production.
Agency Response
NHTSA is removing the requirement that the burst pressure of the
container be within 10 percent of the BP<INF>O</INF>. FMVSS are
designed to set minimum safety performance standards for vehicles,
rather than control variability in manufacturing processes. This
approach ensures that every vehicle meets a baseline level of safety,
regardless of specific manufacturing methods or variability in
production. The responsibility for managing variability and ensuring
consistent quality within manufacturing processes falls to the
manufacturers themselves. They must ensure that their production
processes consistently produce vehicles that meet or exceed the FMVSS
requirements.
When NHTSA tests a vehicle component to ensure it meets the FMVSS,
the component is expected to meet or exceed the specified performance
criteria every time it is tested, regardless of variability in the
manufacturing process. NHTSA's approach to testing typically involves
randomly selecting a single test article for evaluation. If this single
component fails to meet the standard, it indicates that the entire
batch, or potentially the entire production process, may be flawed.
Per the requirements of the Safety Act, manufacturers are required
to ensure that every unit produced meets the FMVSS requirements. This
requirement compels manufacturers to control the variability within
their production processes. If a manufacturer allows too much
variability, there is a risk that the vehicle may not meet the
standards, which could result in non-compliance. The prospect of non-
compliance drives manufacturers to maintain high levels of consistency
and quality control, ensuring that every component or vehicle produced
is likely to pass NHTSA's testing, no matter which one is chosen for
evaluation. This method of testing essentially requires control of
variability indirectly, as manufacturers must ensure that all of their
products, not just a select few, comply with FMVSS requirements.
(3) BP<INF>min</INF> of 200% NWP
Background
For the reasons discussed in the NPRM, NHTSA believes that the
minimum burst pressure, BP<INF>min</INF>, of 200 percent NWP, as set
forth in GTR No. 13 Phase 2, meets the need for safety.\17\ The
proposed BP<INF>min</INF> of 200 percent NWP facilitates hydrogen
vehicle development without unnecessary overdesign of components. NHTSA
sought comment on the proposed BP<INF>min</INF> of 200 percent NWP
instead of the 225 percent NWP specified in GTR No. 13 Phase 1.
---------------------------------------------------------------------------

\17\ See 89 FR 27511 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>. This section's discussion applies to containers
that do not contain glass fiber composite as a primary constituent.
Containers with glass fiber composite as a primary constituent are
discussed in the following section.
---------------------------------------------------------------------------

Comments Received
Several commenters supported NHTSA's proposal to set the
BP<INF>min</INF> at 200 percent of NWP as aligned with GTR No. 13 Phase
2. Luxfer Gas Cylinders commented that the 200 percent of NWP for
BP<INF>min</INF> is ``acceptable.'' Auto Innovators expressed support
for both the harmonization with GTR No. 13 and the

[[Page 6232]]

BP<INF>min</INF> of 200 percent, noting that it reflects the consensus
of the Informal Working Group from GTR No. 13 Phase 2. Nikola also
agreed with the proposed 200 percent BP<INF>min</INF>.
Agility commented that while 200 percent NWP may be adequate for
high-strength carbon fiber, it may not be sufficient for other
materials or thin-walled cylinders. Agility suggested requiring 225
percent for NWP values of 35 MPa or lower, as permitted by GTR No. 13.
HATCI expressed support for both the proposed BP<INF>min</INF> and the
harmonization with GTR No. 13.
Glickenhaus disagreed with reducing the burst pressure for carbon
fiber containers from 225 percent to 200 percent NWP, stating that the
proposed 200 percent is too low and could create safety risks,
particularly when considering variability in actual burst pressures.
Glickenhaus provided an example involving a theoretical container with
an NWP of 100 bar. Based on the example where a container with a
baseline initial burst pressure of 200 percent NWP had an end-of-life
burst pressure of only 160 percent NWP, it recommended retaining a 225
percent BP<INF>min</INF>.
H2MOF supported the proposal, stating that a BP<INF>min</INF> of
200 percent would avoid unnecessary overdesign. TesTneT also supported
the 200 percent NWP BP<INF>min</INF>, stating it is safe as proposed.
NGS agreed with the 200 percent BP<INF>min</INF> for carbon fiber but
requested that other fibers be allowed if sufficient data proves their
durability.
Newhouse commented that 200 percent NWP should be adequate for
carbon fiber reinforced containers, but it suggested establishing a
minimum NWP of 350 bar for this standard. For containers with lower
NWP, Newhouse recommended retaining a BP<INF>min</INF> of 225 percent
due to concerns about reduced damage tolerance and safety. Newhouse
further noted that stress rupture is not adequately addressed by
specifying a burst ratio and recommended using stress ratios to ensure
safety for different container types, especially Type 2 and Type 3
containers.
FORVIA expressed agreement with the 200 percent BP<INF>min</INF>,
stating that GTR No. 13 Phase 2 has demonstrated that this value is
sufficient based on performance data.
Agency Response
NHTSA is maintaining the proposed BP<INF>min</INF> of 200 percent
NWP for containers that do not contain glass-fiber as the primary
constituent. The counterexample given by a commenter in which a
container with a BP<INF>O</INF> of 200 percent NWP underwent the test
for performance durability and finished with an end-of-life burst
pressure of 160 percent NWP is not valid. The residual pressure test at
the end of the test for performance durability requires a four-minute
hold period at 180 percent of NWP. Therefore, a container with an end-
of-life burst pressure of 160 percent would fail to meet the
performance requirements of the standard and thereby be prohibited from
entering service. There is no option to meet some but not all the
requirements of the test for performance durability.
NHTSA is not currently considering requirements related to strain
gauges to further address stress rupture, nor is it considering
prohibitions on metal liners as that would likely be design
restrictive. Regarding the concerns about the durability of thin-walled
containers, the durability of all containers is rigorously evaluated
with the test for performance durability. The baseline initial burst
pressure test is not intended to address container durability
throughout its lifetime.
Regarding allowing the use of other fiber types, NHTSA is not
restricting designs to any particular fiber type nor excluding any
particular fiber type. Manufacturers are free to design products using
any material they choose. The requirements are designed to apply to
containers regardless of material type. The only material-specific
consideration for containers is for those containers that have glass
fiber composite as a primary constituent, as discussed in the next
section.
Lastly, burst ratios such as BP<INF>min</INF> are a well-
established safety metrics that ensure containers' structural
integrity, even if differences exist between burst ratio and stress
ratio for some container types. The proposed requirement for
BP<INF>min</INF> of at least 200 percent NWP along with the 1,000 hour
high temperature pressure hold test in the sequential test for
performance durability are in accordance with the requirements in GTR
No. 13 Phase 2 and likely sufficient to mitigate the risks associated
with stress rupture in most containers. Further research would be
needed to fully understand the relationship between burst ratios,
stress ratios, and risk of stress rupture. For now, this final rule
adopts the proposed requirement for an initial baseline burst pressure
of at least 200 percent NWP.
(4) Primary Constituent
Background
NHTSA sought comment on how NHTSA could determine if a container
has glass fiber as a primary constituent and on appropriate criteria to
determine the primary constituent of a container.
In the case of containers constructed of both glass and carbon
fibers, NHTSA proposed to apply the requirements according to the
primary constituent of the container as specified by the manufacturer.
NHTSA proposed that the manufacturer shall specify upon request, in
writing, and within five business days, the primary constituent of the
container. NHTSA proposed that if the manufacturer fails to specify
upon request, in writing, and within five business days, the primary
constituent of a container, the burst pressure of the container must
not be less than 350 percent of NWP.
Comments Received
Luxfer Gas Cylinders commented that a higher minimum burst pressure
is typically required for containers with glass-fiber composites and
suggested that NHTSA request information from manufacturers regarding
the container's composite overwrap and stress analysis to assess the
load share of glass fiber in hybrid designs. Nikola had no objections
to the 350 percent NWP requirement and stated that NHTSA could either
ask the manufacturer for details or cut a container to determine its
composition. Agility expressed concern over the definition of ``primary
constituent'' and suggested that other materials might also be
inappropriate at 200 percent NWP burst. It recommended that
manufacturers be asked to provide the load share of glass fiber, which
could then be used to adjust the minimum burst pressure.
HATCI supported confirming the primary constituent with
manufacturers but opposed the proposed five-day response time,
recommending that NHTSA use its existing information request authority
without specifying a timeline in the regulation. Luxfer Gas Cylinders
added that the five-day period was too short, suggesting a revision to
at least 14 business days due to potential delays in identifying the
appropriate contact at the container manufacturer. EMA requested a ten-
day response period and recommended that the required burst pressure be
based on the material specified by the manufacturer rather than
defaulting to 350 percent NWP. Glickenhaus suggested that the primary
container composition be included in labeling requirements to ensure
transparency throughout the container's lifecycle, eliminating the need
for inquiries to manufacturers. It also proposed that container
manufacturers be required to register with NHTSA, similar to other
safety-critical component

[[Page 6233]]

manufacturers, and submit relevant data such as burst pressures and NWP
ratings.
TesTneT downplayed concerns about glass-fiber-reinforced containers
in hydrogen service, noting that such designs are rare and impractical
for hydrogen applications. It also pointed out the lack of a test
method for determining the primary constituent, suggesting that asking
the manufacturer is the only feasible approach. NGS supported the
requirement for manufacturers to provide primary constituent details
but argued that the response time should be extended to 30 days.
Newhouse highlighted the complexity of determining the primary
constituent in hybrid designs, noting that analysis is required to
assess load-sharing between fibers, and simply specifying a burst ratio
does not ensure safety. Newhouse provided an alternative approach which
provides specific guidelines for hybrid constructions based on fiber
load sharing.
MEMA questioned the implementation and enforcement of the response
time requirements, suggesting that the information could be provided as
part of the self-certification process without the need for a specified
deadline. FORVIA disagreed with changing requirements based on
potential delays in mailing and proposed that NHTSA conduct field
surveillance testing. If a burst test raises suspicions of glass fiber
being a primary constituent, further investigation could be conducted.
Auto Innovators expressed support for harmonization with GTR No. 13 and
agreed with the 350 percent NWP burst pressure requirement for glass-
fiber-reinforced containers. H2MOF also supported the higher burst
pressure requirement, citing its success in CNG containers over the
past two decades. It suggested that the test agency could verify the
container's composition after conducting a burst test.
Agency Response
NHTSA is maintaining the requirement that container with glass
fiber composite as a primary constituent shall have a BP<INF>min</INF>
of 350 percent of NWP. However, commenters did not provide a specific
method for determining the primary constituent of a container. Since
NHTSA has no way of determining the load sharing properties of a
container's individual fibers, nor a way to determine whether that load
sharing is fundamental to the strength of the container, whether or not
glass fiber composite is the container's primary constituent must be
determined by and specified by the manufacturer.
NHTSA will not require the primary constituent to be listed on the
label. Similar to BP<INF>O</INF>, listing the primary constituent on
the container label could potentially confuse consumers. Additionally,
NHTSA does not need to know the specifics of the container's primary
constituent other than whether the primary constituent is glass fiber
composite. Therefore, NHTSA will require that the manufacturer specify
upon request, and in writing, whether the primary constituent of the
container is glass fiber composite or not. Based on the comments,
however, the timeline for responding to the request has been increased
to 15 business days instead of five business days.\18\ NHTSA is
removing the option that if the manufacturer fails to respond to the
request, then the container minimum burst pressure must not be less
than 350 percent of NWP. This option is not appropriate for containers
other than those with glass fiber composite as a primary constituent,
and therefore, the only option is for the manufacturer to specify
whether the container's primary constituent is glass fiber composite.
FMVSS No. 308 S5.1.1.1 has been updated to reflect this change.
S6.2.2.2(e), which contained a similar five business day response
timeline, has also been updated to 15 business days.
---------------------------------------------------------------------------

\18\ The increase from five days to 15 days is intended to give
manufacturers additional time to respond to NHTSA's request.
---------------------------------------------------------------------------

Furthermore, NHTSA will not obtain a copy of the stress analysis
for the container to determine the load sharing from glass fiber in a
mixed fiber overwrap. The stress analysis for the container is outside
the scope of the proposed regulation. NHTSA will simply obtain the
primary constituent from the manufacturer, and then conduct the tests
as specified depending on whether the container includes glass fiber
composite as a primary constituent.
(5) Pressurization Rates Above 0.35 MPa/sec
Background
GTR No. 13 states that if the pressurization rate exceeds 0.35 MPa/
s at pressures higher than 150 percent NWP, then either the container
must be placed in series between the pressure source and the pressure
measurement device, or the time at the pressure above a target burst
pressure must exceed 5 seconds. The first option of placing the
container in series between the pressure source and the pressure sensor
ensures that the container will experience the pressure before the
sensor, so there is no chance that the pressure sensor could read a
pressure level that is not being experienced by the container. However,
NHTSA did not propose the second option that the time at the pressure
above the target burst pressure exceeds 5 seconds because it is unclear
and difficult to enforce. It is not clear what pressure the ``target
burst pressure'' is referring to since during the test, pressure will
be increasing continuously.
Comments Received
Nikola stated that it do not want any changes to the procedure
outlined in GTR No. 13. Luxfer Gas Cylinders commented that while the
procedure is effective for cycle tests, it may not be feasible for
burst testing due to the risk of damaging the pressure measurement
device when placed after the container. It suggested either placing the
container in series between the pressure source and the measurement
device or including a five-second hold at the minimum burst pressure to
ensure the container experiences the correct pressure. TesTneT agreed
with NHTSA's approach of situating the container between the pressure
source and the sensor but noted that this setup is not always practical
or necessary. It mentioned that it has performed many burst tests with
the sensor positioned before the container and have not encountered any
issues, as the slow pressurization rate effectively eliminates pressure
drop concerns. It also stated that holding the pressure for five
seconds at the target burst pressure is clear and enforceable.
Glickenhaus supported NHTSA's decision not to adopt the second
option from GTR No. 13, agreeing that the sensor should be placed in
series between the pressure source and the container to maintain clear
and objective testing. H2MOF recommended including the second method,
noting that various industry standards specify a five-second hold at
the target burst pressure. Newhouse commented that the five-second hold
allows time for the pressure to equalize inside the container, ensuring
accurate readings in cases where flow restrictions may be present.
FORVIA stated that the ``target burst pressure'' should be understood
as the minimum burst pressure. It suggested keeping the pressurization
rate below 0.35 MPa/s at pressures exceeding 150 percent NWP or placing
the container in series between the pressure source and the sensor,
maintaining the wording of GTR No. 13.
Auto Innovators stated that is not practical for all designs to
have

[[Page 6234]]

containers placed in series between pressure source and pressure
measurement device. It requested an alternative method be provided. It
also stated that the pressure pulsations are small to moderate compared
to the absolute pressure level.
Agency Response
Consistent with GTR No. 13, NHTSA proposed that ``If the rate
exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP,
then the container is placed in series between the pressure source and
the pressure measurement device.'' GTR No. 13 also provides the
alternative option that ``the time at the pressure above a target burst
pressure exceeds five seconds.'' As discussed in the NPRM, NHTSA did
not select this latter option because it is unclear.\19\ A five-second
hold period may be feasible for manufacturers that are ``targeting'' a
particular burst pressure. In such a case, manufacturers can simply
pressurize the container to the ``target'' pressure and hold for five
seconds. NHTSA, however, will need to determine an unknown burst
pressure for the container. Since there is no ``target'' burst pressure
stated in the test procedure, the pressure inside the container is
increased continuously until the container bursts. It is not possible
to hold for five seconds at each and every pressure level that occurs
during a burst test. The commenters did not provide any explanation
regarding how, with continuously increasing pressure, any single
specific pressure could be considered to have been held for five
seconds. Instead, NHTSA has selected to use only the option to put the
container in series between the pressure source and the measurement
device. This way the container can be pressurized continuously until it
bursts, and the container's burst pressure can be determined without
prior knowledge of a target burst pressure.
---------------------------------------------------------------------------

\19\ See 89 FR 27511 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
---------------------------------------------------------------------------

Additionally, a configuration where the container is placed in
series between the pressure source and the pressure measurement device
can be achieved regardless of container design and does not necessitate
alternative methods for different container designs. For example, a
pressurization setup that includes a T-fitting, through which the
container connects to both the pressure source and to a line leading to
the pressure measurement device, in which the line leading to the
pressure measurement device is equal in length to or longer than the
connection from the container to the T-fitting, would meet the
requirement for the container to be placed in series between the
pressure source and the pressure measurement device. This configuration
ensures that the container experiences all pressure increases as or
before the sensor records them, accurately reflecting the container's
pressurization level. Furthermore, the maximum allowable pressurization
rate of 1.4 MPa/s for pressures exceeding 150 NWP provides adequate
time for the pressure measurement device to capture accurate pressure
readings during pressurization without premature or unrepresentative
measurements.
c. Number of Cycles for the Baseline Initial Pressure Cycle Test for
Containers on Light and Heavy Vehicles
Background
NHTSA proposed 7,500 as the number of cycles in the baseline
initial pressure cycle test for which the container does not leak nor
burst for light vehicles. To ensure the container leaks before bursting
after reaching the maximum service life, the container is pressure
cycled beyond the 7,500 cycles (representing maximum service life)
until either a container leak occurs without burst or the container
does not leak nor burst for up to a maximum of 22,000 hydraulic
pressure cycles. In accordance with GTR No. 13 Phase 2, NHTSA proposed
that heavy vehicle containers to neither leak nor burst for 11,000
hydraulic pressure cycles, and also to leak without burst (or neither
leak nor burst) beyond the 11,000 hydraulic pressure cycles up to a
maximum of 22,000 pressure cycles. As discussed in the NPRM, these
number of cycles are based on a service life for light and heavy
vehicles of 25 years.\20\ This service life, number of hydraulic
pressure cycles representing the maximum service life for which the
container is required to not leak nor burst, and the number of pressure
cycles beyond that representing maximum service life of the container
for which the container is required to leak without burst or not leak
nor burst at all are summarized in Table 1 for light and heavy
vehicles.
---------------------------------------------------------------------------

\20\ See 89 FR 27513 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.

Table 1--Service Life and Number of Cycles in the Baseline Hydraulic Pressure Cycle Test for Light and Heavy
Vehicles
----------------------------------------------------------------------------------------------------------------
Number of cycles
representing maximum Numbe of cycles for
Service life service life for which the container
Vehicle type (years) which the container leaks without burst,
does not leak nor or does not leak nor
burst burst
----------------------------------------------------------------------------------------------------------------
Light.............................................. 25 7,500 7,501-22,000
Heavy.............................................. 25 11,000 11,001-22,000
----------------------------------------------------------------------------------------------------------------

NHTSA sought comment on the proposed number of cycles in Table 1.
NHTSA also sought any additional data available related to vehicle
life, lifetime miles travelled, and number of lifetime fuel cycles.
Comments Received
Several commenters provided feedback on the proposed number of
pressure cycles in Table 1 of the NPRM. Nikola expressed agreement with
the approach outlined, while Luxfer Gas Cylinders also stated that the
cycle values were appropriate. Auto Innovators supported the approach
and suggested that it would be more straightforward to define the
number of cycles beyond the maximum service life as double the number
of cycles for which the container does not leak nor burst. It stated
that specifying 15,000 cycles for light vehicles and 22,000 cycles for
heavy vehicles would be sufficient.
H2MOF, however, recommended a significantly lower cycle count,
suggesting that 1,500 cycles as recommended by the USDOE would be more
appropriate. It calculated that at

[[Page 6235]]

300 miles per fill, this would result in 450,000 miles of service.
TesTneT commented that while light vehicles may experience fewer fill
cycles than heavy vehicles, factors such as partial fill cycles should
be considered. It stated that the industry is not particularly
concerned with fatigue cracking, as no fuel cylinder in CNG or hydrogen
service has experienced this issue. Additionally, it noted that there
is little cost or weight savings in reducing the cycle numbers and
suggested aligning with GTR No. 13 cycle numbers.
FORVIA commented that the proposed numbers were conservative but
reasonable. It indicated that these cycle numbers would cover all
vehicle service life expectations and that containers could handle
these cycles without issue. Therefore, it supported keeping the table
as it is.
Agency Response
NHTSA is maintaining the number of cycles of the baseline initial
pressure cycle test as proposed in the NPRM and listed in Table-1
above. NHTSA is not lowering the number of cycles for which the light
vehicle container leaks without burst, or does not leak nor burst, to
15,000. Because the potential harm from a potential burst would be
catastrophic, the number 22,000 was selected to both exceed extreme on-
road vehicle lifetime range and promote global harmonization with GTR
No. 13, as requested by commenters, and therefore there is no need to
lower this number of cycles. As discussed in the NPRM, 22,000 cycles
simulate over 6 million miles of driving, which is well beyond extreme
vehicle lifetimes. The use of 22,000 cycles ensures that containers
leak before bursting in all extreme cases.\21\
---------------------------------------------------------------------------

\21\ See 89 FR 27512 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
---------------------------------------------------------------------------

The comment regarding a 1,500-cycle recommendation from USDOE
appears to be referring to technical performance targets for CHSS
published by USDOE.\22\ However, performance targets are not the same
as safety standards. Performance targets are goals for how a system
performs under optimal conditions, whereas safety standards are
designed to protect users by minimizing risks and preventing harm in
hazardous or sub-optimal conditions. Therefore, NHTSA is not lowering
the number of cycles for the baseline initial pressure cycle test to
1,500.
---------------------------------------------------------------------------

\22\ See <a href="https://www.energy.gov/eere/fuelcells/doe-technical-targets-onboard-hydrogen-storage-light-duty-vehicles">https://www.energy.gov/eere/fuelcells/doe-technical-targets-onboard-hydrogen-storage-light-duty-vehicles</a>.
---------------------------------------------------------------------------

d. Details of the Baseline Initial Cycle Test for Containers on Light
and Heavy Vehicles
(1) Leak Before Burst and Sustaining a Visible Leak for 3 Minutes
Background
A burst may be preceded by an instantaneous moment of leakage,
especially if observed in slow motion. Therefore, NHTSA proposed a
minimum time of 3 minutes to sustain a visible leak before the test can
end successfully due to ``leak before burst.'' NHTSA sought comment on
this additional requirement.
Comments Received
Luxfer Gas Cylinders commented that NHTSA's proposed wording
regarding the number of hydraulic pressure cycles is unclear. It noted
that the phrasing ``neither leak nor burst'' contradicts itself by
allowing leakage after 11,000 cycles but also stating neither leakage
nor bursting should occur. It suggested the wording should be revised
to state: ``The cylinder shall be allowed to leak, but not burst,
beyond the 11,000 cycles up to a maximum of 22,000 pressure cycles.''
Luxfer also expressed concerns about the 3-minute sustained leak
requirement, stating that most pressure equipment is designed to shut
off when detecting pressure loss, making it difficult to hold a leak
under pressure for three minutes. It proposed alternative wording to
state that containers should fail by leakage but not rupture.
H2MOF raised concerns about the proposed 3-minute hold requirement
for a visible leak, stating that if the pressure vessel leaks, the pump
may not be able to maintain pressure, potentially causing the test to
abort.
Nikola disagreed with NHTSA's proposal, commenting that leak-
before-burst is not currently a requirement and that the term implies
the container should leak and never burst at the end of its life.
FORVIA also disagreed with the 3-minute sustained leak requirement
and recommended keeping the test procedure harmonized with GTR No. 13.
It questioned the justification for the 3-minute requirement and noted
that the behavior described, where a burst is preceded by leakage, is
extremely improbable. It suggested that pressure should be allowed to
drop below a certain level instead of imposing a time-based
requirement, as this behavior is unknown in its experience.
TesTneT commented that the 3-minute sustained leak requirement
changes the test from a leak-before-burst test to a stress rupture
test. Based on its 35 years of experience performing leak-before-burst
testing, it stated it has never encountered an issue distinguishing
between a leak and a burst. TesTneT also referred to NHTSA's mention of
observing leaks in slow motion and suggested that it is unnecessary to
observe the location of failure during testing. It recommended
maintaining the current wording in GTR No. 13 without any changes.
Agency Response
The requirements regarding the number of cycles for which a
container shall not leak nor burst, and thereafter shall not burst are
clarified in the proposed FMVSS No. 308 S5.1.1.2. The proposed S5.1.1.2
clearly specifies the number of cycles for which a container shall not
leak nor burst and thereafter the number of cycles for which the
container shall not burst. The number of cycles specified is dependent
on the GVWR of the vehicle under test.
Based on the comments, however, NHTSA is removing the statement
about sustaining a visible leak for three minutes before the test can
end successfully due to ``leak before burst.'' Instead, the final rule
simply states that if a leak occurs while conducting the test as
specified in S5.1.1.2(a)(2) or S5.1.1.2(b)(2), the test is stopped and
not considered a failure. Test labs will not observe the baseline
initial pressure cycling test in slow motion and therefore it will be
clear to the test lab whether the test has resulted in leakage or in a
burst.
NHTSA also made a clerical correction to S6.2.2.2(e) to remove the
word ``container,'' such that S6.2.2.2(e) reads ``The manufacturer may
specify a hydraulic cycling profile within the specifications of
S6.2.2.2(c).''
(2) Effect of the Cycling Profile
Background
NHTSA proposed a maximum hydraulic pressure cycle rate of five to
ten cycles/minute for the baseline initial pressure cycle test. This
rate was selected to allow for efficient compliance testing. Actual
fueling cycles for hydrogen vehicles occur more slowly. Therefore, the
container manufacturer may specify a hydraulic pressure cycle profile
that will prevent premature failure of the container due to test
conditions outside of the container design envelope. NHTSA sought
comment on cycling profiles and whether the pressure cycling profile

[[Page 6236]]

will significantly affect the test result. NHTSA sought comment on more
specifics of what manufacturers should be allowed to specify regarding
an appropriate pressure cycling profile for testing their system.
Comments Received
Luxfer Gas Cylinders stated that the maximum cycle rate of 10
cycles per minute specified in GTR No. 13 is rarely approached in
testing, noting that Luxfer uses 4 cycles per minute for larger
containers. Auto Innovators commented that cycle rates and profiles do
affect container performance, and manufacturers should be allowed to
specify these parameters, as unrealistic testing conditions could lead
to failures not representative of actual service. It suggested that
NHTSA consider aligning with GTR No. 13 Phase 2, which specifies a
maximum of 10 cycles per minute. It also stated that the pressure
cycling profile has not been seen to significantly affect test results
and that manufacturers generally cycle as quickly as is safe and
practical.
H2MOF agreed with NHTSA that the cycling profile can impact test
results depending on materials and design margins, emphasizing the
importance of the number of cycles and pressure limits. It supported
allowing manufacturers to specify pressurization and depressurization
rates, as well as hold times.
TesTneT, drawing on over 35 years of experience, disagreed with the
idea that cycling profiles affect test results, stating that no
evidence supports this concern and criticizing the Powertech report
referenced by NHTSA. It also noted that GTR No. 13 allows manufacturers
to specify any cycle profile as long as it stays within the 10 cycles
per minute limit.
Nikola commented that the defueling or unloading phase of the
pressure cycle can impact container life, supporting the idea that
manufacturers should be allowed to specify an appropriate profile.
HATCI recommended that NHTSA fully harmonize with the GTR No. 13 Phase
2 requirement where the container is cycled less than or equal to 10
cycles per minute.
Agency Response
NHTSA is maintaining the maximum hydraulic pressure cycle rate of
10 cycles/minute for the baseline initial pressure cycle test,
consistent with GTR No. 13. However, NHTSA will remove the lower
cycling limit of 5 cycles per minute. As a result, the cycling rate may
be any rate up to 10 cycles per minute. This change will accommodate
larger containers which may take longer to cycle.
While some commenters stated that the cycling profile is
inconsequential, others stated the profile can have an effect for some
container designs. NHTSA acknowledges that the cycling profile may
affect the test result for some containers. As a result, NHTSA will
maintain the specification that manufacturers may specify a pressure
cycling profile for testing their system. The manufacturer's
specifications will need to be within the above cycling rate range and
the other conditions specified in FMVSS No. 308 S6.2.2.2(c). At NHTSA's
option, NHTSA will cycle the container within 10 percent of the
manufacturer's specified cycling profile.
8. Test for Performance Durability
Background
The test for performance durability addresses impact (drop during
installation and/or road wear), static high pressure from long-term
parking, over-pressurization from fueling and fueling station
malfunction and environmental exposures (chemicals and temperature/
humidity). These stresses are compounded in a series is because a
container may experience all of these stresses during its service life,
and the safety need for a hydrogen system remains an issue for the
vehicle's entire service life.
Comments Received
Luxfer Gas Cylinders commented that the verification tests for
performance durability, on-road performance, and service-terminating
performance in fire can be expensive, with costs exceeding $500,000,
and potentially reaching $1,000,000 for larger containers. It asked
whether NHTSA was aware of the high cost associated with conducting the
proposed test program.
Quantum stated that completing the entire hydraulic and pneumatic
test sequences with the on-tank-valves (OTV) installed would
significantly increase the time required for testing. It explained that
the small orifice size of OTVs restricts hydrogen or hydraulic fluid
flow, thus extending the duration of each test sequence. Additionally,
Quantum noted that other components of the CHSS, such as the TPRD,
check valve, and shut-off valve, are tested separately from the
container for cycle life. Since these valves are designed for gas use
rather than continuous liquid flow, Quantum recommended removing the
requirement for the OTV to be installed during testing.
Agency Response
NHTSA is aware of the test burden of the proposed tests. FMVSS
establish minimum safety requirements and the FMVSS test procedures
establish how the agency would verify compliance. However,
manufacturers are not required to conduct the exact test in the FMVSS
to certify their vehicles. The Safety Act requires manufacturers to
certify that their vehicles meet all applicable FMVSS, and specifies
that manufacturers may not certify compliance if, in exercising
reasonable care, the manufacturer has reason to know the certificate is
false or misleading. Manufacturers may use different types of tests or
even simulations to certify their vehicles if they exercise reasonable
care in doing so. In other words, manufacturers must ensure that their
vehicles will meet the requirements of FMVSS No. 308 when NHTSA tests
the vehicles in accordance with the test procedures specified in the
standard, but manufacturers may use different test procedures and
evaluation methods to do so.
Regarding Quantum's comment regarding testing with OTVs, the NPRM
clearly specifies that only the container is subject to the
requirements of the test for performance durability. The ``container,''
as defined the regulation, does not include closure devices. On the
other hand, the test for expected on-road performance is conducted
using hydrogen gas, and with the entire CHSS. The test for expected on-
road performance therefore includes closure devices as part of the
CHSS.
a. Proof Pressure Test
Background
GTR No. 13 states that a container that has undergone a proof
pressure test in manufacture is exempt from this test. However, NHTSA
may not know whether a container has undergone the proof pressure test.
As a result, NHTSA proposed that all containers will be subjected to
the proof pressure test as part of the test for performance durability.
In the event that a proof pressure test is conducted during manufacture
and as part of the tests for performance durability, the container
would experience two proof pressure tests. NHTSA sought comment on
conducting the proof pressure test on all containers.
Comments Received
Nikola opposed NHTSA's proposal to add the proof pressure test,
stating that all onboard vehicle containers already undergo 100 percent
proof pressure tests by manufacturers. Luxfer Gas Cylinders

[[Page 6237]]

supported the decision to require all containers to undergo the proof
pressure test as part of the test for performance durability. Auto
Innovators disagreed, arguing that this would add unnecessary burden
without additional safety benefits, as proof pressure testing is
already required before service. It requested harmonization with GTR
No. 13 Phase 2, which exempts containers that have already undergone
proof testing during manufacturing.
Air Products suggested reviewing the proposed 30- to 35-second hold
time, as it is significantly shorter than the 10-minute hold period
specified in other industry standards. DTNA supported NHTSA's proposal
for consistency, stating that all containers should undergo the proof
pressure test regardless of prior testing during manufacturing. H2MOF
opposed duplicating the test, stating that the additional high-stress
cycle would negatively impact container performance during durability
testing, as containers are already factory proof tested according to
industry standards. HATCI also opposed the requirement, recommending
the adoption of GTR No. 13 Phase 2, which exempts containers that have
undergone proof pressure testing in manufacture.
TesTneT commented that proof pressure testing is conducted on all
designs during production, not merely to confirm the container's
resistance to over-pressurization, but to ensure consistency in
manufacturing through measurements of elastic and permanent expansion.
It suggested that if a design is damaged by a proof pressure test, it
would become apparent during pressure cycle testing, thus rendering
additional proof pressure testing unnecessary.
MEMA disagreed with the assumption that it is unknown whether a
container has undergone proof testing during manufacturing, stating
that some manufacturers conduct this test as part of the fabrication
process, which is required under GTR No. 13. MEMA suggested adding
language to FMVSS No. 308 allowing an exemption for containers that
have already undergone proof pressure testing.
FORVIA acknowledged concerns about dual testing but suggested that
NHTSA incorporate language from GTR No. 13 Phase 2, which allows for
exemptions for duplicative proof tests, ensuring that all containers
comply with FMVSS requirements. It further argued that if a second test
is deemed not to significantly stress the container, the first test
should also be considered adequate, as repeated pressurizations are
unlikely to make a significant difference.
Agency Response
Based on the comments received, NHTSA is removing the proof
pressure test. Commenters emphasized that 100 percent of all containers
already undergo a proof pressure test during manufacturing, as part of
standard production practices, and that requiring an additional proof
pressure test would be redundant and burdensome without offering any
additional safety benefits. Several commenters also raised concerns
that subjecting a container to multiple proof pressure tests could
introduce unnecessary stress and possibly affect the container's
performance in subsequent tests.
After considering these comments, NHTSA agrees that a second proof
pressure test would not provide additional safety benefits and could
possibly impose undue stress on the container. As a result, the proof
pressure test has been removed from the test for performance durability
and the test for expected on-road performance, discussed below.
b. Drop Test
(1) Damage That Prevents Further Testing
Background
It is possible that the container could experience damage from the
drop test that prevents continuing with the remainder of the tests for
performance durability. This damage would prevent NHTSA from completing
the evaluation of a container. To address this possibility, NHTSA
proposed that if any damage to the container following the drop test
prevents further testing of the container, the container is considered
to have failed the tests for performance durability and no further
testing is conducted.
Comments Received
HATCI commented that the inability to conduct subsequent tests
after damage from the drop test should not automatically result in a
failed test for performance durability. It suggested that additional
containers should be used for further testing in such cases. As an
example, it noted that deformation of an aluminum nozzle opening or
valve connection after a drop test could prevent further testing, but
this deformation does not necessarily indicate a lack of durability.
MEMA agreed with the single drop event specified in FMVSS No. 308
S5.1.2.2 but raised concerns about the potential for confusion
regarding the damage criteria. It suggested that NHTSA clarify the
wording to specify ``irrecoverable damage'' or ``damage that cannot be
readily repaired'' to account for conditions where minor repairs, such
as fixing damaged threads on a shut-off valve, could allow testing to
continue.
Agency Response
NHTSA is maintaining the test requirements as proposed. Damage that
prevents the continuation of testing under S6.2.3.4 must be considered
a failure of the test for performance durability because the required
test sequence cannot be completed in its entirety. NHTSA will not
repair containers that are damaged during the drop test.
(2) Including Container Attachments for the Drop Test
Background
The drop test is a test in which container attachments may improve
performance by protecting the container when it impacts the ground.
Consistent with GTR No. 13, the drop test is conducted on the container
with any associated container attachments. NHTSA sought comment on
including container attachments for the drop test.
Comments Received
EMA stated that its members lack experience with dropping
containers with attachments and are unsure of what qualifies as a
``container attachment'' for heavy vehicles, which often use multiple
hydrogen containers. EMA commented that including attachments could
make it difficult to ensure consistent impact locations during the test
and recommended aligning FMVSS No. 308 with UN ECE R134, dropping the
container without attachments unless the manufacturer opts to include
impact-mitigating attachments. It suggested requiring the manufacturer
to specify whether container attachments should be included for the
test.
H2MOF supported conducting the drop test with container
attachments, as it reflects real-life scenarios. Auto Innovators
opposed including attachments unless they are permanently fixed to the
container, arguing that removable attachments should be excluded to
maintain flexibility and focus on container robustness. It noted that
this approach aligns with GTR No. 13's intent to demonstrate container
durability before installation.
Nikola commented that attachments should be included only if they
are present during shipping; if added during vehicle assembly, they
should be excluded. Luxfer Gas Cylinders opposed dropping containers
with attachments,

[[Page 6238]]

stating that the attachments are more likely to break than the
container itself, and including them would complicate the test by
introducing additional variables. It also noted that conducting the
test with valves and PRDs attached would be impractical. TesTneT
commented that if attachments are part of the container when it leaves
production, they should remain for the drop test, as the test addresses
potential handling damage before installation. FORVIA supported
including container attachments in the drop test, referencing that
their inclusion was a key factor in the development of GTR No. 13.
Agency Response
``Container attachments'' means non-pressure bearing parts attached
to the container that provide additional support and/or protection to
the container and that may be removed only with the use of tools for
the specific purpose of maintenance or inspection. Container
attachments do not refer to the structures that physically attach the
container(s) to the vehicle. NHTSA will not rely on the manufacturer to
specify container attachment configurations as this adds unnecessary
complexity. NHTSA will simply purchase vehicles or replacement
containers at the point of sale and conduct the drop test with any
included, pre-installed container attachment that meet the definition
for container attachments. Given that manufacturers are required to
ensure that the vehicle is compliant at the time it is delivered to a
dealer or distributor, manufacturers should take reasonable care to
ensure they are not damaging or installing damaged containers into
vehicles. If a container is sold at the point of sale without pre-
installed container attachments, it will be tested as such.
(3) Center of Gravity
Background
In the case of a non-cylindrical or asymmetric container, the
horizontal and vertical axes may not be clear. The proposed rule
provided that in such cases, to conduct the drop test, the container
will be oriented using its center of gravity and the center of any of
its shut-off valve interface locations. The two points will be aligned
horizontally (i.e., perpendicular to gravity), vertically (i.e.,
parallel to gravity) or at a 45[deg] angle relative to vertical. The
center of gravity of an asymmetric container may not be easily
identifiable, so NHTSA sought comment on the appropriateness of using
the center of gravity as a reference point for this compliance test and
how to properly determine the center of gravity for a highly asymmetric
container.
Comments Received
Auto Innovators supported NHTSA's proposal to align with GTR No.
13, stating that for asymmetric containers, orientation is typically
determined when mounted in a vehicle. It added that technical
information on the center of gravity could be provided to NHTSA if
needed, noting that identifying the center of gravity, even for
asymmetric shapes, is not particularly difficult. It advocated for
maintaining the same specifications as GTR No. 13 Phase 2, which it
found to be adequate.
DTNA agreed that using the center of gravity as a reference for the
drop test was appropriate, as it ensures reproducibility in test
results. It emphasized that determining the center of gravity
accurately is critical for valid test outcomes. DTNA recommended that
manufacturers provide this data to NHTSA prior to testing, allowing the
agency to verify the information and request clarification if
necessary. It highlighted that the accuracy of this reference point is
essential, especially given the NPRM's proposal that failure of the
drop test would result in failing the entire performance durability
testing process.
H2MOF proposed that the center of gravity for a highly asymmetric
container be determined using the container's geometric CAD file.
Nikola suggested maintaining the current center of gravity definition
as outlined in GTR No. 13.
TesTneT supported using the center of gravity as a reference,
noting that it is a physical characteristic shared by all container
designs, including asymmetric ones. It added that orientation for such
containers could be determined when installed on a vehicle, and the
center of gravity could be established in consultation with the
manufacturer.
FORVIA stated that keeping the test procedure harmonized with GTR
No. 13 was appropriate. It noted that identifying the center of gravity
experimentally is not overly difficult, and it believed that fully
asymmetric containers are unlikely to be prevalent in the market.
Instead, it anticipated new rectangular designs with centers of gravity
near their geometric centers, providing a good basis for testing.
Agency Response
The center of gravity is not defined in GTR No. 13, nor is a method
provided for determine the center of gravity for an asymmetric
container. NHTSA will not have access to CAD files for the container.
Therefore, in the case of an asymmetric container, NHTSA will obtain
the center of gravity from the manufacturer, similar to how it obtains
the primary constituent and BP<INF>O</INF>. The manufacturer shall
specify, in writing, and within 15 business days, the center of gravity
of the container. In the drop test, t container will be oriented using
its center of gravity and the center of any of its shut-off valve
interface locations. These two points will be aligned horizontally
(i.e., perpendicular to gravity), vertically (i.e., parallel to
gravity) or at a 45[deg] angle relative to vertical, as specified.
c. Surface Damage Test
Background
NHTSA proposed the surface damage test based on GTR No. 13 Phase 2.
The surface damage test applies cuts and impacts to the surface of the
container. The surface damage test consists of two linear cuts and five
pendulum impacts.
Comments Received
MEMA commented on the surface damage test proposed by NHTSA,
stating that there were differences between the proposed requirements
and those in GTR No. 13. It stated that in Section 6.2.3.3(a), for non-
metallic containers, NHTSA's proposal includes two longitudinal saw
cuts, which is consistent with GTR No. 13. However, it stated that
NHTSA proposed different lengths and depths for the cuts without
explaining why the differences are necessary or how they might improve
test results.
MEMA further stated that NHTSA's proposal specifies the first cut
as being 0.75 millimeters to 1.25 millimeters deep and 200 millimeters
to 205 millimeters long, while the second cut, only required for
containers affixed to the vehicle by compressing its composite surface
(i.e., clamped), would be 1.25 millimeters to 1.75 millimeters deep and
25 millimeters to 28 millimeters long. MEMA stated that GTR No. 13
requires two cuts regardless of how the container is affixed, with the
first cut being at least 1.25 millimeters deep and 25 millimeters long
toward the valve end, and the second cut being at least 0.75
millimeters deep and 200 millimeters long toward the opposite end.
MEMA stated that its members believe that the GTR No. 13
requirements provide a better minimum threshold and requested that
NHTSA harmonize FMVSS No. 308 with GTR No. 13 on this matter. It also
expressed concern that additional surface damage test requirements, as
part of the already lengthy pressure cycling test, would

[[Page 6239]]

increase the complexity, duration, and cost of the process without
delivering more representative or improved results. MEMA proposed that
FMVSS No. 308 S6.2.3.3. be revised to align with GTR No. 13.
Agency Response
The commenter appears to be referencing the original version of GTR
No. 13. GTR No. 13 has undergone a comprehensive Phase 2 revision that
was adopted at the 190th Session of WP.29 on June 21, 2023.\23\ Phase 2
accomplished several goals, including strengthening test procedures for
containers with pressures below 70 MPa. The U.S. voted in favor of
adopting Phase 2 and the changes made to GTR No. 13 by Phase 2 are
reflected in NHTSA's proposal for FMVSS Nos. 307 and 308 and in this
final rule. GTR No. 13 Phase 2 states in section 6.2.3.3(a): ``Surface
flaw generation: A saw cut at least 0.75 mm deep and 200 mm long is
made on the surface specified above. If the container is to be affixed
to the vehicle by compressing its composite surface, then a second cut
at least 1.25 mm deep and 25 mm long is applied at the end of the
container which is opposite to the location of the first cut.''
Regarding the difference in lengths of the proposed FMVSS No. 308
S6.2.3.3(a), these differences are simply due to tolerances added to
FMVSS No. 308, as discussed below.
---------------------------------------------------------------------------

\23\ A copy of GTR No. 13 as updated by the Phase 2 amendments
is available at <a href="https://unece.org/transport/documents/2023/07/standards/un-global-technical-regulation-no-13-amendment-1">https://unece.org/transport/documents/2023/07/standards/un-global-technical-regulation-no-13-amendment-1</a>.
---------------------------------------------------------------------------

(1) Including Container Attachments
Background
The surface damage test is a test in which container attachments
may improve performance by shielding the container from the impacts.
For containers with container attachments, GTR No. 13 specifies that if
the container surface is accessible, then the test is conducted on the
container surface. Determining whether the container surface is
accessible is subjective because ``accessible'' is not defined in the
GTR and could have many potential meanings. Therefore, NHTSA did not
propose a specification involving the accessibility of the container
surface. Instead, NHTSA proposed that if the container attachments can
be removed using a process specified by the manufacturer, they will be
removed and not included for the surface damage test nor for the
remaining portions of the test for performance durability. Container
attachments that cannot be removed are included for the test. NHTSA
sought comment on including container attachments for the surface
damage test.
Comments Received
HATCI expressed agreement with NHTSA's proposal to remove container
attachments, when possible, and to exclude them from the surface damage
test. Auto Innovators recommended harmonizing with GTR No. 13,
supporting the removal of attachments if specified by the manufacturer,
and including non-removable attachments, as doing so ensures the test
is conducted on the container's pressure-bearing chamber. H2MOF agreed
that non-removable container attachments should be included in the
test.
Luxfer Gas Cylinders commented that containers can be used in
various vehicle systems with different attachments, making it
impractical to test each type of attachment. It supported testing
containers without attachments if they can be removed, adding that the
drop test and the four-minute hold at 180 percent NWP are the primary
design drivers, and it is unnecessary to include attachments in any
tests. TesTneT stated that pendulum impacts do not affect the integrity
of composite containers and were originally intended to test protective
coatings. It recommended including attachments in the test if these
attachments are designed to protect the container surface from road
conditions. FORVIA requested keeping non-removable attachments in the
surface damage test, noting that these attachments were introduced in
GTR No. 13 due to the surface damage test.
Agency Response
NHTSA is maintaining the surface damage test as proposed. If the
container attachments can be removed using a process specified by the
manufacturer, they will be removed and not included for the surface
damage test nor for the remaining portions of the test for performance
durability. Testing the container without its container attachments is
representative of a situation in which installation personnel remove
the container attachments and fail to re-install them before the
container enters service. Additionally, since the goal of a surface
damage test is to test the surface, it makes sense to remove the
container attachments that are capable of being removed. While NHTSA
has chosen to keep container attachments on for other tests (e.g. the
drop test, if the container attachment is pre-installed and meets the
definition of container attachment), the surface damage test is
different enough to warrant a deviation from that practice. Container
attachments that cannot be removed are included for the test.
If different vehicles require different configurations of container
attachments, each configuration would be subject the requirements
separately. If some of the configurations have removable container
attachments, those container attachments would be removed. If some
configurations have non-removable container attachments, those
container attachments would remain in place during the surface damage
test.
(2) Exempting All-Metal Containers
Background
GTR No. 13 exempts all-metal containers from the linear cuts.
NHTSA's proposal included this exemption, but NHTSA sought comment on
whether another objective and practicable procedure exists for
evaluating surface abrasions that could apply to all containers, such
as, for example, the application of a defined cutting force to the
container surface.
Comments Received
TesTneT commented that its experience with CNG cylinders has shown
that steel cylinders are resistant to abrasion damage of the magnitude
proposed for composite containers. It noted that developing a
performance test to simulate defect dimensions as outlined in GTR No.
13 would be complicated, involving variables such as the shape, angle,
and force of impact. Since surface abrasions do not cause failure in
thinner-walled CNG cylinders, it suggested such abrasions would not
pose a problem for hydrogen containers. Nikola and H2MOF both agreed
with the exemption for all-metal containers from the linear cuts.
Auto Innovators supported the proposed exemption for metal
containers and stated that requiring a test for a defined cutting force
would add unnecessary regulatory burden. It emphasized that container
manufacturers should provide sufficient technical information for
compliance purposes. Verne, Inc. recommended extending the exemption to
all-metal container attachments as well, noting that metal is resistant
to scratches and cuts, and flaw cut depths may exceed the wall
thickness of metal attachments.
Luxfer Gas Cylinders raised the concern that containers could
experience cuts during service, such as from poorly fitted brackets. It
suggested that metal containers with walls thin enough to be penetrated
by cuts would be unsuitable for high-pressure vehicle

[[Page 6240]]

fuel systems and recommended a more clearly defined test instead of a
blanket exemption. FORVIA requested that the test procedure remain
harmonized with GTR No. 13, noting that GTR No. 13 sets minimum
requirements. It asked for clear justification if flaws in metallic
containers are considered a concern and suggested discussing this issue
in GTR No. 13 phase 3.
Agency Response
NHTSA is maintaining the exemption from the linear cuts for all-
metal containers. The commenters did not provide sufficient information
regarding how to conduct an alternative test with a defined cutting
force applied to the metal container surface. Moreover, as stated by
the commenters, metal containers are resistant to abrasions so this
form of surface damage is not expected to be a significant safety
concern. NHTSA is not extending the exemption to all-metal container
attachments, however. Doing so would add complexity to the testing
process where some container attachments would be treated differently
from others. Furthermore, container attachments may be in place to
protect the containers from abrasions and other surface damage, so the
container attachments themselves should be able to tolerate surface
damage.
The global community also considered this issue in developing GTR
13 and found that an exemption for-all metal containers was appropriate
based on challenges with an adequate test procedure. Accordingly, both
harmonization and practical challenges favor exempting all-metal
containers from the linear cuts at this time. However, NHTSA has robust
enforcement authority to address defects that pose an unreasonable risk
to safety, including in all-metal containers. NHTSA will continue to
monitor the state of the industry and will revise the standard in a
future rulemaking as necessary.
(3) Applying Impacts on the Opposite Side vs. a Different Chamber
Background
In accordance with GTR No. 13, NHTSA specified the pendulum impacts
``on the side opposite from the saw cuts.'' For containers with
multiple permanently interconnected chambers, GTR No. 13 specifies
applying the pendulum impacts to a different chamber to that where the
saw cuts were made. However, the agency did not propose this
distinction for pendulum impact location for containers with multiple
permanently interconnected chambers because NHTSA was concerned that it
may be less stringent than when impacts are to the same chamber where
the cuts were applied. NHTSA sought comment on whether applying the
impacts to the opposite side of the same chamber that received the saw
cuts may be more stringent than applying the impacts to a separate
chamber, and whether including the specification as written in GTR No.
13 would reduce stringency for containers with multiple permanently
interconnected chambers relative to containers with a single chamber.
Comments Received
H2MOF supported the approach in GTR No. 13, stating that the
likelihood of both saw cuts and pendulum impacts affecting the same
chamber is extremely low. HATCI supported NHTSA's proposal to harmonize
with the GTR No. 13 surface damage test but recommended also adopting
the GTR No. 13 requirement to apply the pendulum impact to a different
chamber when multiple chambers are present. While acknowledging NHTSA's
concerns, HATCI recommended harmonization with GTR No. 13 Phase 2
specifications.
Auto Innovators supported adopting the GTR No. 13 requirements and
commented that applying impacts to the same chamber does not make the
test more stringent than performing the impacts on separate chambers.
TesTneT stated that pendulum impacts are designed to puncture
protective coatings or resin gel coats but do not affect the structural
integrity of the composite reinforcement. It argued that there is no
reason to deviate from GTR No. 13 since stringency is not an issue.
MEMA members also supported the procedure outlined in GTR No. 13
and did not see the need for modifications. MEMA encouraged NHTSA to
fully align with GTR No. 13 for the pendulum impact portion of the
surface damage test. FORVIA echoed the recommendation to align with GTR
No. 13 Phase 2, stating that different specifications based on chamber
type could introduce confusion in testing. It added that there is no
evidence suggesting changes in the surface cut and pendulum impact
locations would impact safety and recommended following the industry
standard until further research is conducted. FORVIA also commented
that combining surface flaws with pendulum impacts and chemical
exposure in testing is unnecessary since such damage combinations are
highly improbable during service life.
Agency Response
Based on the comments received, in the case of a container with
multiple permanently interconnected chambers, NHTSA will specify the
impacts on the surface of a different chamber. NHTSA is convinced that
applying the impacts to a different chamber is equivalently stringent
to applying the impacts on the opposite side of a single chamber. NHTSA
agrees that the pendulum impacts were not intended to be compounded in
close proximity with the surface cuts as would occur if both types of
damage were applied to a single small chamber of a multi-chamber
container. FMVSS No. 308 S6.2.3.3(b) has been updated to reflect this
change.
d. Chemical Exposure and Ambient Pressure Cycling Test
Background
The chemical exposure test is a test in which container attachments
may improve performance by shielding the container from the chemical
exposures. The proposed rule provided that container attachments will
be included in the chemical exposure test unless they were removed
prior to the surface damage test. NHTSA sought comment on including
container attachments for the chemical exposure test.
Comments Received
Auto Innovators supported harmonizing these requirements with GTR
No. 13, commenting that if attachments can be removed, they should be
removed before testing, but if they cannot be removed, they should be
included in the test. Auto Innovators added that if chemicals can reach
the surface of removable attachments, then the surface should also be
exposed to chemicals. EMA recommended modifying FMVSS No. 308, S6.2.3.4
to state that each of the five areas preconditioned by pendulum impact
should be exposed to a different solution. H2MOF agreed that container
attachments may be present during the chemical exposure test, as they
are present during regular service. TesTneT commented that any
attachments included in a vehicle installation should also be included
in the chemical exposure test, as these attachments might protect the
container surface from road conditions. FORVIA stated that non-
removable container attachments should be allowed in the chemical
exposure test, noting that the test contributed to the introduction of
container attachments in GTR No. 13.

[[Page 6241]]

Agency Response
NHTSA is maintaining the inclusion of container attachments in the
chemical exposure test unless they were removed prior to the surface
damage test, as discussed above. NHTSA is not including 'EMA's proposed
edit specifying that a different solution is applied to each
preconditioned area. There is no need to specify that a different
solution is applied to each area. This language is consistent with GTR
No. 13, which specifies that each of the five areas ``is exposed to one
of five solutions.''
e. High Temperature Static Pressure Test
Background
Consistent with GTR No. 13, the high temperature static pressure
test involves holding the container for 1000 hours at 85 [deg]C and 125
percent NWP.
Comments Received
Auto Innovators stated that it supports NHTSA's proposal to
harmonize these requirements with GTR No. 13.
Agency Response
NHTSA is maintaining the high temperature static pressure test as
proposed.
f. Extreme Temperature Pressure Cycling Test
Background
Consistent with GTR No. 13, the extreme temperature pressure
cycling test involves pressure cycling at extreme temperatures and
simulates operation (fueling and defueling) in extreme temperature
conditions. The test for performance durability uses the same number of
cycles as required by the baseline initial cycle test before leakage.
This is a total of 7,500 cycles for light vehicles or 11,000 cycles for
heavy vehicles. The extreme temperature pressure cycling test consists
of 40 percent of these total cycles, of which half (20 percent of the
total) are conducted at -40 [deg]C and the other half are conducted at
85 [deg]C.
Comments Received
Quantum Fuel Systems, LLC commented on an ambiguity in GTR No. 13
related to the number of cycles required for the extreme cold and hot
tests. It stated that clarification is needed to determine whether the
total number of cycles for the extreme temperature pressure cycling
test should be 22,000 or 11,000. Quantum also proposed edits to Table 6
of GTR No. 13 to address this ambiguity. Auto Innovators expressed
support for NHTSA's proposal to harmonize these requirements with GTR
No. 13.
Agency Response
NHTSA is maintaining the extreme temperature pressure cycling test
as proposed. The proposed requirement clearly specifies that ``the
container is pressure cycled in accordance with S6.2.3.6 for 40 percent
of the number of cycles specified in S5.1.1.2(a)(1) or S5.1.1.2(b)(1)
as applicable.'' FMVSS No. 308 S5.1.1.2(a)(1) and S5.1.1.2(b)(1)
clearly list 7,500 and 11,000 cycles, respectively. The number of
cycles used for the extreme temperature pressure cycling test is not
based on 22,000 cycles.
g. Residual Pressure Test
Background
Consistent with GTR No. 13, the residual pressure test requires
pressurizing the container to 180 percent NWP and holding this pressure
for 4 minutes.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the residual pressure test requirements with GTR No. 13. Agility
commented that the residual pressure test requirement should remain at
180 percent NWP, regardless of BP<INF>O</INF>. It added that
manufacturers would still have incentives to limit performance
degradation due to its effects on cost and repeatability.
Agency Response
NHTSA is maintaining the residual pressure test as proposed. The
requirement of 180 percent NWP with a four-minute hold period is
independent of BP<INF>O</INF>. The residual pressure test does not
address degradation rate. Degradation rate is addressed by the residual
strength burst test, discussed in the next section.
h. Residual Strength Burst Test
Background
Consistent with GTR No. 13, the residual strength burst test
involves subjecting the end-of-life container to a burst test identical
to the baseline initial burst pressure test. The burst pressure at the
end of the durability test is required to be at least 80 percent of the
BP<INF>O</INF> specified on the container label. This requirement
effectively controls the burst pressure degradation rate throughout an
extreme service life.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
these requirements with GTR No. 13. Luxfer Gas Cylinders commented on
the likelihood of a rapid rate of degradation in end-of-life burst
pressure, stating that there is a ``vanishingly small likelihood that
this would occur.'' It noted that no manufacturer would produce
containers with a BP<INF>O</INF> double the specified minimum
requirement and questioned what mechanism would cause such degradation,
suggesting that only severe damage could lead to it, in which case the
container would be removed from service.
Agency Response
NHTSA is maintaining the residual strength burst test as proposed.
As the commenter states, it is unlikely that a container would have
such high degradation as to fail to maintain at least 80 percent of
BP<INF>O</INF> at its end-of-life burst pressure. However, the residual
strength burst test is straightforward to pass for containers that do
not experience severe burst strength degradation in service. Therefore,
including this requirement does not significantly challenge container
design or create an unnecessary burden on manufacturers. Instead, it
simply prevents the possibility of a poor-performing container from
posing a serious risk to safety due to severe burst strength
degradation while in service.
9. Test for Expected On-Road Performance
Background
Consistent with GTR No. 13, NHTSA proposed the test for expected
on-road performance. The proposed test is closely consistent with the
industry standard SAE J2579_201806, ``Standard for Fuel Systems in Fuel
Cell and Other Hydrogen Vehicles.'' \24\
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\24\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles. <a href="https://www.sae.org/standards/content/j2579_201806/">https://www.sae.org/standards/content/j2579_201806/</a>.
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Comments Received
Luxfer Gas Cylinders commented that the proposed test is time-
consuming and expensive to conduct. It stated that for large 800 liter
containers, there is only one test lab that can conduct the test. It
stated that the cost of testing exceeds $500,000. It questioned if
NHTSA proposing to evaluate containers using the proposed test
procedures.
Agency Response
NHTSA is aware of the burden of the proposed test. FMVSS establish
minimum safety requirements and the FMVSS test procedures establish how
the agency would verify compliance. However, manufacturers are not

[[Page 6242]]

required to conduct the exact test in the FMVSS to certify their
vehicles. The Safety Act requires manufacturers to certify that their
vehicles meet all applicable FMVSS, and specifies that manufacturers
may not certify compliance if, in exercising reasonable care, the
manufacturer has reason to know the certificate is false or misleading.
A manufacturer may use different types of tests or even simulations to
certify its vehicles if the manufacturer exercises reasonable care in
doing so. In other words, manufacturers must ensure that their vehicles
will meet the requirements of FMVSS No. 308 when NHTSA tests the
vehicles in accordance with the test procedures specified in the
standard, but manufacturers may use different test procedures and
evaluation methods to do so. Additionally, as hydrogen vehicles become
more common, the number of test labs performing this test will likely
increase, and the costs associated with testing will likely come down
as a result.
a. Proof Pressure Test
Background
Consistent with GTR No. 13, NHTSA proposed a hydrogen-gas proof
pressure test at the start of the test for expected on-road
performance.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the proof pressure test with GTR No. 13. Agility questioned the purpose
of performing the proof test with hydrogen instead of using a hydraulic
testing method, commenting that the proposed approach seems
unnecessarily high-risk and costly.
Agency Response
For the reasons discussed above for the test for performance
durability, NHTSA is removing proof pressure testing from FMVSS No.
308. Since 100 percent of all containers already undergo the proof
pressure test during manufacture, including this test would be
redundant and unnecessary.
b. Ambient and Extreme Temperature Gas Pressure Cycling Test
Background
NHTSA proposed an ambient and extreme temperature gas pressure
cycling test that is closely consistent with GTR No. 13.
Comments Received
Auto Innovators expressed support for NHTSA's proposal to harmonize
the ambient and extreme temperature gas pressure cycling test with GTR
No. 13, stating that tests should be conducted with temperature and
pressure control devices in place, or that equivalent measures should
be used to strictly adhere to the parameters. HATCI requested that
NHTSA either harmonize with GTR No. 13 Phase 2 requirements or ensure
strict adherence to proposed pressure and temperature ranges during
testing. HATCI noted that container pressure should not exceed 100
percent state of charge (SOC) and that the minimum pressure should be 2
MPa. Based on internal testing, HATCI commented that temperatures
outside the specified operational range could lead to o-ring failures,
resulting in leakage. It added that during low-temperature pneumatic
tests, internal temperatures can drop below -40 [deg]C, sometimes
reaching -45 [deg]C, which does not reflect real environmental
conditions and is not considered in container design. HATCI also
recommended that NHTSA test CHSS within the manufacturer's design
limits or within a temperature range of -40 [deg]C to 85 [deg]C, with
manufacturers responsible for providing design temperature data upon
NHTSA's request.
Agency Response
NHTSA is maintaining the ambient and extreme temperature gas
pressure cycling test as proposed. The ambient and extreme temperature
gas pressure cycling test does not subject the container to external
temperature conditions below -30 [deg]C. Additionally, the ambient and
extreme temperature gas pressure cycling test does not consider the
internal temperature of the container; only the ambient temperature
surrounding the container is controlled, along with the fuel delivery
temperature and the initial system equilibration temperature. Neither
GTR No. 13 nor by the commenters provide a method for monitoring the
internal temperature of the container during cycling. Instead, the
container must be able to withstand the internal temperatures that
result from the pressure cycling series as specified. As discussed in
the NPRM, the pressurization rates specified in Table 5 to S6.2.4.1(c)
of FMVSS No. 308 are based on real-world refueling rates, and the
temperatures specified during the test are also based on real-world
conditions, so this test for expected on-road performance is
representative of conditions that can occur in-service.\25\ The other
differences noted by HATCI are related to test tolerances, which are
discussed below.
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\25\ See 89 FR 27520 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
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c. Extreme Temperature Static Gas Pressure Leak/Permeation Test
Background
NHTSA proposed the extreme temperature static gas pressure leak/
permeation test consistent with GTR No. 13, except for the removal of
the localize leak requirement in the proposed standard. The localized
leak limit was removed because it is not objectively enforceable due to
the subjective estimation of bubble sizes. NHTSA sought comment on not
including the localize leak requirement during the extreme temperature
static gas pressure leak/permeation test and specifically requested
that if commenters believed it should be included, that they explain
(1) how they believe it could be made more objective and (2) how
specifically it would add to the standard's ability to meet the safety
need.
Comments Received
Commenters provided diverse feedback on the proposed removal of the
localized leak requirement from the extreme temperature static gas
pressure leak/permeation test.
Nikola suggested that while the bubble requirement could be
removed, the single-point leak rate should not be eliminated, and a
mass spectrometer could be used by testing facilities instead. It also
noted that numerous hydrogen performance test facilities that can
evaluate localized leaks.
Luxfer Gas Cylinders stated that permeation rate measurements are
well-established, typically involving the CHSS in an airtight container
with surrounding gas content measured accurately. Luxfer supported the
decision to remove the localized leak requirement.
Auto Innovators agreed with the decision not to include the
localized leak test. Similarly, DTNA commented that the localized leak
test was unnecessary because the full system permeation test evaluates
the overall system. However, if a localized leak test were necessary,
DTNA suggested replacing the bubble test with a concentration-based
hydrogen leak limit of 0.5 percent, derived from standards applied to
CNG and propane vehicles.
TesTneT described its method of using a gas chromatograph or mass
spectrometer in an enclosed, temperature-controlled chamber for
accurate permeation measurement. It also use a mass spectrometer to
quantify leakage after locating potential leak sites

[[Page 6243]]

with a soapy solution. TesTneT raised concerns about hydrogen
permeation risks in enclosed spaces, pointing out that hydrogen can
leak out over time, making it difficult to accumulate in dangerous
amounts.
Newhouse commented that NHTSA's proposed permeation rate of 46 mL/
L/h at 55 [deg]C is unreasonably low and noted several issues, such as
considering worst-case scenarios and ventilation assumptions. Newhouse
suggested allowing a higher limit of 100 percent of the lower
flammability limit (LFL), or 4 percent hydrogen in air, and questioned
the use of 55 [deg]C as a peak temperature, stating that a lower
average would be more representative. Newhouse also recommended
increasing the allowable permeation rate to 184 mL/L/h at 55 [deg]C and
noted that the probability of failure remains low, even with more
conventional ventilation rates in garage spaces.
FORVIA acknowledged that different methods can accurately measure
leakage and permeation and suggested that guidance on measurement could
be provided outside the FMVSS text. It was open to considering
localized leak requirements but noted that the submersion method,
though simple, may require more accurate measurements near the limits.
It indicated that omitting this test for field surveillance would be
acceptable, as production containers typically exhibit far less
leakage. H2MOF proposed exempting all-metal containers from the static
gas leak/permeation test and suggested that procedures from industry
standards be used for guidance.
Agency Response
NHTSA is maintaining the extreme temperature static gas pressure
leak/permeation test as proposed, without the localized leak limit. The
commenters did not provide any explanation for the safety need of the
localized leak limit. Commenters did not provide any evidence that
omitting the localized leakage requirement is less stringent when there
is also an overall permeation limit applied to the CHSS as a whole.
Furthermore, commenters did not provide sufficient explanation of
how, if included, the localized leakage limit could be made more
objective. Some commenters suggested using analytical chemistry
equipment such as mass spectrometers. However, these types of
instruments are highly complex, and additional research would be needed
by NHTSA before they could be used to objectively quantify a leak. Even
if the agency determined that mass spectrometers were viable for
detecting localized leaks, the agency would still need to consider the
safety need being addressed by the requirement.
NHTSA is not changing the overall permeation rate of 46 mL/L/h
based on the comments. This permeation limit is found in GTR No. 13 and
is widely accepted by the industry as an appropriate permeation limit.
Well-developed rationale for this limit is provided in GTR No. 13 and
in the NPRM.\26\ In particular, the conservative 25 percent LFL limit
accounts for concentration non-homogeneities that may be present, and
the choice of 55 [deg]C is a worst-case temperature condition, not one
that is expected to occur commonly. Permeation is higher at higher
temperatures, so NHTSA considered this worst-case condition when
evaluating the permeation limit. This permeation limit is also applied
in the industry standard SAE J2579_201806. The commenters did not
establish sufficient rationale for NHTSA to deviate from the
established 46 mL/L/h.
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\26\ See 89 FR 27522 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
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NHTSA is not exempting CHSS with all-metal containers from the
extreme temperature static gas pressure leak/permeation test. All-metal
containers must demonstrate the same level of performance and safety as
other containers. NHTSA is not replacing the proposed test with either
of the standards recommended by H2MOF. The commenter did not establish
any justification for why doing so would improve safety, nor did it
provide any detailed information regarding the alternative standards.
d. Residual Pressure Test & Residual Strength Burst Test
Background
The residual pressure test and residual strength burst test are
conducted in the same manner and for the same reasons discussed above
for the test for performance durability.
Comments Received
Auto Innovators stated support for NHTSA's proposal to harmonize
these requirements with GTR No. 13.
Agency Response
NHTSA is maintaining the residual pressure test and residual
strength burst test as proposed.
10. Test for Service Terminating Performance in Fire
Background
NHTSA proposed a fire test based closely on the GTR No. 13 Phase 2
fire test. The updates to the fire test by the IWG of GTR No. 13 Phase
2 focused on improving the repeatability and reproducibility across
test laboratories. Two significant improvements to the fire test are
(1) the use of a pre-test checkout procedure and (2) basic burner
specifications. The pre-test checkout requires conducting a preliminary
fire exposure on a standardized steel container to verify that
specified fire temperatures can be achieved for the localized and
engulfing fire segments of the test prior to conducting the fire test
on a CHSS. During this pre-test checkout, the fuel flow is adjusted to
achieve fire temperatures within the specified limits as measured on
the surface of the pre-test steel container. The use of a pre-test
steel container instead of an actual CHSS improves the accuracy and
repeatability of the test because it avoids possible container material
degradation that could affect the temperature measurements.
Comments Received
Luxfer Gas Cylinders commented that the recent changes introduced
in GTR No. 13 regarding the fire test are ``excessive'' and do not
enhance test performance. Luxfer stated that the pre-test using a steel
container is only relevant when the steel container matches the size of
the composite container being tested. For larger containers, such as
those used in heavy vehicles, Luxfer stated that the pre-test becomes
unnecessary. Luxfer and H2MOF both suggested that NHTSA consider
adopting the Bonfire test from NGV 2 2019, ``Compressed natural gas
vehicle fuel containers.'' \27\ Additionally, Luxfer expressed concerns
about the increased costs of the new GTR No. 13 fire test. It
questioned whether NHTSA intends to apply this test to containers that
have been withdrawn from service.
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\27\ See <a href="https://webstore.ansi.org/standards/csa/csaansingv2019">https://webstore.ansi.org/standards/csa/csaansingv2019</a>.
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Agility commented that the fire source and pre-test procedures in
GTR No. 13 do not accurately represent vehicle fire scenarios,
particularly for heavy applications. It highlighted that the fire
source width is set at 500 mm regardless of the container's diameter
and that the temperature requirements focus solely on the area beneath
and directly on the container surface. Agility further pointed out the
lack of

[[Page 6244]]

requirements for measuring temperatures around the container, which is
where remotely mounted PRDs are typically located.
Agency Response
NHTSA acknowledges the comments regarding the proposed fire test
based on GTR No. 13 Phase 2 but does not find them persuasive enough to
warrant any significant changes to the proposed test procedures.
Specifically, the concern that the pre-test checkout using a steel
cylinder is only relevant if it matches the size of the composite
container is not valid. The pre-test checkout procedure is designed to
ensure the consistency of fire temperature measurements, which can be
achieved regardless of the difference in size between the pre-test
container and the actual CHSS. The objective of the pre-test checkout
is to verify the fire conditions produce the specified temperatures,
which improves the accuracy and repeatability of the test across
different laboratories.
Regarding the commenters' suggestions to adopt the fire test in NGV
2 2019, NHTSA is aware of ANSI NGV 2 2019, but the GTR No. 13 fire test
remains more representative of real-world conditions. The proposed fire
test procedure based on GTR No. 13 includes both localized and
engulfing fire stages, which are designed based on actual vehicle fire
data, as discussed in the NPRM.\28\ The proposed fire test procedure is
the most realistic fire test available that is representative of a
range of possible real-world vehicle fires. The NGV 2 fire test does
not provide the same level of comprehensiveness as the standard. The
NGV 2 fire test does not include any pre-test procedures to improve
repeatability and reproducibility, nor does it include a localized fire
exposure. The fire test procedure, on the other hand, provides a
rigorous, repeatable test that accounts for both localized and
engulfing fire conditions, addressing various fire exposure scenarios.
Due to the large volumes of hydrogen stored on hydrogen fueled
vehicles, NHTSA maintains that the proposed fire test procedure is
needed to ensure vehicles are designed with a high level of performance
in fire conditions. NHTSA further notes that the pre-test checkout
includes temperature specifications for the bottom, sides, and top of
the pre-test container.
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\28\ See 89 FR 27523 (Apr. 17, 2024), available at <a href="https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed">https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed</a>.
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Regarding the concern about increased costs, vehicle manufacturers
are already designing their vehicles to meet or exceed the requirements
of the proposed fire test based on GTR No. 13, so NHTSA does not expect
significant increased costs from implementing the proposed fire test.
Regarding applying the requirements to containers that have been
withdrawn from service, NHTSA purchases new vehicles at the point of
sale for compliance testing. NHTSA does not conduct compliance testing
on used vehicles or equipment.
a. Burner Specification
Background
To further improve test reproducibility, a burner configuration is
defined with localized and engulfing fire zones. These specifications
allow the fire test to be performed without a burner development
program. NHTSA explained in the NPRM that it believes that the use of a
standardized burner configuration is a practical way of conducting fire
testing and should reduce variability in test results through
commonality in hardware.\29\ Flexibility is provided to adjust the
length of the engulfing fire zone to match the CHSS length, up to a
maximum of 1.65 m. The width of the burner, however, is fixed at 500 mm
for all fire tests, regardless of the width or diameter of the CHSS
container to be tested, so that each CHSS is evaluated with the same
fire condition regardless of size. The length of the localized fire
zone is also fixed to 250 mm for all fire tests. NHTSA sought comment
on a specification for the burner rail tubing shape and size, which can
affect the spacing between the nozzle tips

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