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Proposed Rule2024-07116

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

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Published

April 17, 2024

Issuing agencies

Transportation DepartmentNational Highway Traffic Safety Administration

Abstract

This notice proposes to establish two new Federal Motor Vehicle Safety Standards (FMVSS) specifying performance requirements for all motor vehicles that use hydrogen as a fuel source. The proposed standards are based on Global Technical Regulation (GTR) No. 13. FMVSS No. 307, "Fuel system integrity of hydrogen vehicles," which would specify 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," would specify requirements for the compressed hydrogen storage system to ensure the safe storage of hydrogen onboard vehicles. The two proposed standards would reduce deaths and injuries that could occur as a result of fires due to hydrogen fuel leakages and/or explosion of the hydrogen storage system.

Full Text

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[Federal Register Volume 89, Number 75 (Wednesday, April 17, 2024)]
[Proposed Rules]
[Pages 27502-27561]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-07116]

[[Page 27501]]

Vol. 89

Wednesday,

No. 75

April 17, 2024

Part II

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; Proposed Rule

Federal Register / Vol. 89, No. 75 / Wednesday, April 17, 2024 /
Proposed Rules

[[Page 27502]]

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0006]
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: Notice of proposed rulemaking (NPRM).

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SUMMARY: This notice proposes to establish two new Federal Motor
Vehicle Safety Standards (FMVSS) specifying performance requirements
for all motor vehicles that use hydrogen as a fuel source. The proposed
standards are based on Global Technical Regulation (GTR) No. 13. FMVSS
No. 307, ``Fuel system integrity of hydrogen vehicles,'' which would
specify 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,'' would specify
requirements for the compressed hydrogen storage system to ensure the
safe storage of hydrogen onboard vehicles. The two proposed standards
would reduce deaths and injuries that could occur as a result of fires
due to hydrogen fuel leakages and/or explosion of the hydrogen storage
system.

DATES: You should submit your comments early enough to be received not
later than June 17, 2024. In compliance with the Paperwork Reduction
Act, NHTSA is also seeking comment on a revision to an existing
information collection. For additional information, see the Paperwork
Reduction Act Section under the Regulatory Notices and Analyses section
below. All comments relating to the information collection requirements
should be submitted to NHTSA and to the Office of Management and Budget
(OMB) at the address listed in the ADDRESSES section on or before June
17, 2024.
Proposed Effective Date: The date 180 days after the date of
publication of the final rule in the Federal Register.
Proposed Compliance Date: The September 1st that is two years
subsequent to the publication of the final rule.

ADDRESSES: You may submit comments to the docket number identified in
the heading of this document by any of the following methods:
<bullet> Federal eRulemaking Portal: Go to <a href="http://www.regulations.gov">http://www.regulations.gov</a>. Follow the online instructions for submitting
comments.
<bullet> Mail: Docket Management Facility: U.S. Department of
Transportation, 1200 New Jersey Avenue SE, West Building Ground Floor,
Room W12-140, Washington, DC 20590-0001.
<bullet> Hand Delivery or Courier: 1200 New Jersey Avenue SE, West
Building Ground Floor, Room W12-140, between 9 a.m. and 5 p.m. ET,
Monday through Friday, except Federal holidays.
<bullet> Fax: 202-493-2251.
Instructions: All submissions must include the agency name and
docket number. Note that all comments received will be posted without
change to <a href="http://www.regulations.gov">http://www.regulations.gov</a>, including any personal
information provided. Please see the Privacy Act discussion below. We
will consider all comments received before the close of business on the
comment closing date indicated above. To the extent possible, we will
also consider comments filed after the closing date.
Docket: For access to the docket to read background documents or
comments received, go to <a href="http://www.regulations.gov">http://www.regulations.gov</a> at any time or to
1200 New Jersey Avenue SE, West Building Ground Floor, Room W12-140,
Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday,
except Federal Holidays. Telephone: 202-366-9826.
Privacy Act: In accordance with 5 U.S.C. 553(c), DOT solicits
comments from the public to better inform its decision-making process.
DOT posts these comments, without edit, including any personal
information the commenter provides, to <a href="http://www.regulations.gov">www.regulations.gov</a>, as
described in the system of records notice (DOT/ALL-14 FDMS), which can
be reviewed at <a href="http://www.transportation.gov/privacy">www.transportation.gov/privacy</a>. In order to facilitate
comment tracking and response, we encourage commenters to provide their
name, or the name of their organization; however, submission of names
is completely optional. Whether or not commenters identify themselves,
all timely comments will be fully considered.
Confidential Business Information: If you wish to submit any
information under a claim of confidentiality, you should submit three
copies of your complete submission, including the information you claim
to be confidential business information, to the Chief Counsel, NHTSA,
at the address given under FOR FURTHER INFORMATION CONTACT. In
addition, you should submit two copies, from which you have deleted the
claimed confidential business information, to the Docket at the address
given above. When you send a comment containing information claimed to
be confidential business information, you should include a cover letter
setting forth the information specified in our confidential business
information regulation (49 CFR part 512).

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#034a626d2d4e62604a6d776a716643676c772d646c75">[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#025263776e2c416d6c6c677642666d762c656d74">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary
II. Background
A. Hydrogen Fueled Vehicles
1. Hydrogen as a Motor Fuel
2. Hydrogen Vehicle Systems
B. Global Technical Regulation (GTR) No. 13
1. Overview of the GTR Process
2. History of GTR No. 13
III. Why is NHTSA issuing this proposal?
IV. Overview of Proposed Rules
A. FMVSS No. 308, ``Compressed Hydrogen Storage System
Integrity''
1. Compressed Hydrogen Storage System
2. General Requirements for the CHSS
3. Performance Requirements for the CHSS
4. Tests for Baseline Metrics
5. Test for Performance Durability
6. Test for Expected On-Road Performance
7. Test for Service Terminating Performance in Fire
8. Tests for Performance Durability of Closure Devices
9. Labeling Requirements
B. FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles''
1. Fuel System Integrity During Normal Vehicle Operations
2. Post-Crash Fuel System Integrity
C. Lead Time
V. Rulemaking Analysis and Notices
VI. Public Participation

I. Executive Summary

Vehicle manufacturers have continued to seek out renewable and
clean alternative fuel sources 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

[[Page 27503]]

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 and compressed natural gas in FMVSS No. 304, and the fuel integrity
systems of those systems in FMVSS No. 301 and FMVSS No. 303,
respectively. No such standards currently exist in the United States
covering vehicles that operate on hydrogen. Accordingly, this document
proposes two new Federal Motor Vehicle Safety Standards (FMVSSs) to
address safety concerns relating to storage and use of hydrogen in
motor vehicles, and to align the safety regulations of hydrogen
vehicles with vehicles that operate using other fuel sources. This
proposed rule was developed in concert with efforts to harmonize
hydrogen vehicle standards with international partners through the
Global Technical Regulation (GTR) process, and if adopted, would
harmonize the FMVSSs with GTR No. 13, Hydrogen and Fuel Cell Vehicles.
This document proposes the creation of two new safety standards:
FMVSS No. 307, ``Fuel system integrity of hydrogen vehicles,'' and
FMVSS No. 308, ``Compressed hydrogen storage system integrity.'' FMVSS
No. 307 would regulate 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 would regulate the compressed hydrogen storage
system (CHSS) itself, and would primarily include performance
requirements that would 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.
NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all motor
vehicle that use compressed hydrogen gas as a fuel source to propel the
vehicle, regardless of the vehicle's gross vehicle weight rating
(GVWR). However, while FMVSS No. 307 fuel system integrity requirements
during normal vehicle operations would 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 post-crash
fuel system integrity requirements would only apply to compressed
hydrogen fueled light vehicles and to all compressed hydrogen fueled
school buses regardless of GVWR.
While the proposed safety standards are drafted in accordance with
GTR No. 13, there are differences between some proposed requirements
and test procedures and GTR No. 13. This document highlights these
differences and provides reasons for these differences in relevant
sections of the preamble, and seeks public comment.

II. Background

A. Hydrogen Fueled Vehicles

1. Hydrogen as a Motor Fuel
In the pursuit of sustainable, renewable, and clean transportation,
vehicle manufacturers have continued to expand their pursuits of
hydrogen as an alternative fuel source for automobiles. Unlike their
gasoline or diesel counterparts, hydrogen-powered vehicles (hydrogen
vehicles) do not produce carbon dioxide or other emissions.
Furthermore, in contrast with battery electric vehicles, hydrogen
vehicles do not require extended recharging from an external electrical
source. These advantages, coupled with the relative abundance of
hydrogen, make hydrogen vehicles an intriguing alternative to vehicles
already offered in the market.
Hydrogen vehicles harness the chemical energy within hydrogen using
one of two methodologies. The first technique is similar to
conventional internal combustion engines (ICE) powered by petroleum
products. Hydrogen can be burned in a combustion engine and the energy
released from this process used to move pistons that provide mechanical
power to the vehicle. The second method utilizes a component called a
fuel cell that converts the chemical energy in hydrogen into
electricity. In this energy conversion process, hydrogen stored in the
vehicle reacts with oxygen in the air to produce water and energy, in
the form of electricity, which is then used to power the vehicle's
mechanical operations. Hydrogen fuel cell vehicles (HFCVs), which are
sometimes also referred to as fuel cell electric vehicles (FCEVs), are
capable of continuous electrical generation so long as they have a
steady supply of hydrogen fuel and oxygen.
One complicating factor of using hydrogen as a mobile fuel source
is its relatively low energy density. Compared to gasoline, which has a
mass density of 803 grams per liter at 15 [deg]C, uncompressed hydrogen
is extremely light, with a mass density of just 0.09 grams per liter at
15 [deg]C, which means a vehicle operating on uncompressed hydrogen
will have a significantly shorter range than a comparable gasoline-
powered vehicle. To overcome this, hydrogen is compressed to a very
high pressure of up to 70 megaPascals (MPa) while stored on a hydrogen
vehicle.\1\ Hydrogen compressed to 70 MPa at 15 [deg]C has a volumetric
energy density of 4.8 mega Joules per liter (MJ/L), which is similar in
order of magnitude to gasoline's volumetric energy density of 32 MJ/
L.2 3
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\1\ At atmospheric pressure and ambient temperature, hydrogen is
in a gaseous state. The physical state of hydrogen can be changed
from gas to liquid through compression and cryogenic cooling, so
hydrogen can be stored in both compressed gaseous and liquid forms.
However, hydrogen typically exists in gaseous form at essentially
all normal usage and storage temperatures.
\2\ See Patrick Molloy, ``Run on Less with Hydrogen Fuel
Cells.'' RMI, Oct. 2, 2019, <a href="https://rmi.org/run-on-less-with-hydrogen-fuel-cells/">https://rmi.org/run-on-less-with-hydrogen-fuel-cells/</a>.
\3\ See Department of Energy Hydrogen and Fuel Cell Technologies
Office, ``Hydrogen Storage,'' <a href="https://www.energy.gov/eere/fuelcells/hydrogen-storage">https://www.energy.gov/eere/fuelcells/hydrogen-storage</a>.
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While compressed hydrogen is an excellent fuel source due to its
high energy density, its high storage pressure and wide limits of
flammability (i.e., concentrations at which a mixture of fuel and air
is flammable) raise safety concerns. Specifically, hydrogen is
flammable at concentrations ranging from 4 to 75 percent, by volume.\4\
By contrast, gasoline limits of flammability when mixed with air are
from 1.0 to 7.6 percent, by volume.\5\ The velocity at which a hydrogen
flame spreads at room temperature and atmospheric pressure is
approximately 200 to 300 cm/s, whereas the velocity with which gasoline
flames spread under the same conditions is approximately 40 cm/
s.6 7 These characteristics make hydrogen fuel sources more
volatile than gasoline, and while NHTSA has existing FMVSS for gasoline
vehicle fuel system integrity, no FMVSS yet apply to hydrogen storage
and fuel systems. In particular, the safe use of hydrogen vehicles lies
in preventing explosion of

[[Page 27504]]

the hydrogen container(s) and preventing leaks from the container(s)
and fuel system which could lead to fire. Given the greater
flammability of compressed hydrogen, safety standards applicable to
their fuel system integrity are not only reasonable, but necessary.
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\4\ See Hydrogen Compared with Other Fuels, <a href="https://h2tools.org/bestpractices/hydrogen-compared-other-fuels">https://h2tools.org/bestpractices/hydrogen-compared-other-fuels</a>.
\5\ Id.
\6\ See 6 Things to Remember about Hydrogen vs Natural Gas,
<a href="https://www.powereng.com/library/6-things-to-remember-about-hydrogen-vs-natural-gas">https://www.powereng.com/library/6-things-to-remember-about-hydrogen-vs-natural-gas</a>.
\7\ See Combustion fuels: density, ignition temperature and
flame speed, <a href="https://thundersaidenergy.com/downloads/combustion-fuels-density-ignition-temperature-and-flame-speed/">https://thundersaidenergy.com/downloads/combustion-fuels-density-ignition-temperature-and-flame-speed/</a>.
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Despite the promise offered by hydrogen vehicles, they are still a
diminutive fraction of the fleet. For model year 2022, there were two
light hydrogen vehicle models offered for sale in the United States,
whose sales by volume represented approximately 0.03% of the overall
light vehicle fleet. There were no medium-or heavy-duty \8\ hydrogen
vehicles offered for sale in the U.S. during the 2022 model year; \9\
however, manufacturers continue to state their intentions to explore
hydrogen across all fleets.
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\8\ Medium-duty vehicles have a gross vehicle weight rating
(GVWR) greater than 4,536 kg and less than or equal to 11,793 kg.
Heavy-duty vehicles have a GVWR greater than 11,793 kg.
\9\ Toyota has a commercial bus called the Sora that is
currently sold in Japan and Europe.
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2. Hydrogen Vehicle Systems
Hydrogen vehicles--both fuel cell and ICE--share the same basic
structure. Hydrogen enters the vehicle through the fueling receptacle,
is stored in the CHSS, and is released from the CHSS as needed to power
either the combustion engine or fuel cell where the energy stored in
hydrogen is converted into mechanical.\10\ Figure-1 below shows an
example of a hydrogen fuel cell vehicle (HFCV).\11\ A diagram of the
main elements of a vehicle fuel system is shown in Figure-2.\12\
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\10\ The chemical energy stored in the hydrogen fuel is
converted into electric energy by the fuel cell, and the resulting
electric energy is then be converted into mechanical energy by
electric drive motor(s), thereby propelling the vehicle.
\11\ Note that the vehicle depicted is a fuel cell vehicle. For
a hydrogen ICE vehicle, the fuel cell would be replaced with a
combustion engine.
\12\ Figure-2 shows the main elements of a HFCV fuel system. In
the case of a hydrogen ICE vehicle, the fuel cell system would be
replaced by the ICE, and the electric propulsion management system
would be replaced by the vehicle powertrain.
[GRAPHIC] [TIFF OMITTED] TP17AP24.000

Figure-1: Example of a HFCV Design 13
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\13\ For further information on HFCV design, see <a href="https://afdc.energy.gov/vehicles/fuel_cell.html">https://afdc.energy.gov/vehicles/fuel_cell.html</a>, and <a href="https://afdc.energy.gov/vehicles/how-do-fuel-cell-electric-cars-work">https://afdc.energy.gov/vehicles/how-do-fuel-cell-electric-cars-work</a>.
[GRAPHIC] [TIFF OMITTED] TP17AP24.001

[[Page 27505]]

Figure-2: A Schematic of a HFCV and Its Major Systems

a. CHSS
During fueling, hydrogen is supplied from the fueling station to
the vehicle through the vehicle's fueling receptacle. The hydrogen then
flows to the CHSS for storage in the hydrogen container(s). The key
functions of the CHSS are to receive compressed hydrogen through a
check valve during fueling, contain the hydrogen until needed, and
release hydrogen through an electrically activated shut-off valve to
the hydrogen delivery system for use in powering the vehicle. The check
valve prevents reverse flow in the vehicle fueling line. The shut-off
valve between the storage container and the vehicle fuel delivery
system controls the fuel flow out of the CHSS and automatically
defaults to the closed fail-safe position when unpowered. In the event
of a fire impinging on the CHSS, the TPRD provides a controlled release
of hydrogen from the CHSS before the high temperature causes a
hazardous burst of the container.
b. Hydrogen Delivery
The hydrogen delivery system transfers hydrogen from the CHSS to
the fuel cell system at the proper pressure and temperature for fuel
cells to operate. This transfer process is accomplished through a
series of flow control valves, pressure regulators, filters, piping,
and heat exchangers.
c. Fuel Cell System
The fuel cell system provides high-voltage electric power to the
drive-train and vehicle batteries and capacitors. The fuel cell stack
is the electricity-generating component of the fuel cell system.
Individual fuel cells are electrically connected in series such that
their combined voltage is between 300 and 600 Volts in direct current
(VDC). Fuel cell stacks operate at high-voltage, which means a voltage
greater than 60 VDC. The high voltage aspect of fuel cells are covered
by FMVSS No. 305, ``Electric-powered vehicles: electrolyte spillage and
electrical shock protection,'' and are not considered in this proposal.
A typical fuel cell system includes a blower to feed air to the
fuel cell system. Most of the hydrogen that is supplied to the fuel
cell system is consumed within the fuel cells, but a tiny excess of
hydrogen is required to ensure that there is no damage to the fuel cell
from a lack of hydrogen, which can cause undesired chemical reactions
that damage and degrade the fuel cell.\14\ The excess hydrogen is
either catalytically removed or vented to the atmosphere in accordance
with the requirements discussed below. A fuel cell system also includes
auxiliary components to remove heat. Most fuel cell systems are cooled
by a mixture of glycol and water. Pumps circulate the coolant between
the fuel cells and a radiator.
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\14\ A lack of hydrogen in a fuel cell, also known as hydrogen
starvation, occurs when hydrogen fuel is exhausted at the fuel cell
anode. This condition can lead to undesired chemical reactions
occurring inside the fuel cell which can quickly degrade the fuel
cell's catalyst and other components.
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d. Electric Propulsion and Power Management System
The electric power generated by the fuel cell system is supplied to
the electric propulsion power management system where it is used to
power the electric drive-train that propels the vehicle. The throttle
position is used by the drive-train controllers to determine the amount
of power to be sent to the drive wheels. Many HFCVs use batteries or
ultra-capacitors to supplement the output of the fuel cells. These
vehicles may also recapture energy during braking through regenerative
braking, which recharges the batteries or ultra-capacitors and thereby
maximizes efficiency.\15\
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\15\ The electric propulsion and power management system is
covered by FMVSS No. 305, ``Electric-powered vehicles: electrolyte
spillage and electrical shock protection,'' and is not considered in
this proposal.
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e. Hydrogen ICE Vehicles
Hydrogen ICE vehicles have an ICE instead of a fuel cell system.
The ICE engine burns hydrogen to generate mechanical energy to propel
the vehicle. These vehicles use a mechanical propulsion system instead
of an electric propulsion system.

B. Global Technical Regulation (GTR) No. 13

The proposed rule initiates the process of adopting Global
Technical Regulation (GTR) No. 13 into the FMVSS. Based on GTR No. 13,
this NPRM proposes requirements for the safe onboard storage and
utilization of hydrogen in vehicles.
1. Overview of the GTR Process
The United States became the first signatory to the 1998 United
Nations/Economic Commission for Europe (UNECE) agreement (1998
Agreement). The 1998 Agreement entered into force in 2000 and is
administered by the World Forum for Harmonization of Vehicle
Regulations working party (WP.29).\16\ The 1998 Agreement established
the development of global technical regulations (GTRs) regarding the
safety, emissions, energy efficiency and theft prevention of wheeled
vehicles, equipment and parts.
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\16\ The World Forum was initially named the Working Party on
the Construction of Vehicles, a subsidiary of the Inland Transport
Committee. It was renamed to the World Forum in 2000.
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The 1998 Agreement contains procedures for establishing GTRs either
through harmonizing existing regulations or developing new regulations.
The GTR process provides NHTSA unique opportunities to enhance vehicle
safety and improve government efficiency. It assists in developing the
best safety practices from around the world, identifying and reducing
unwarranted regulatory requirements, and leveraging scarce government
resources for research and regulation. The process facilitates our
effort to continuously improve and seek high levels of safety,
particularly by helping us develop regulations that reflect a global
consideration of current and anticipated technology and safety
problems.
Contracting Parties who vote in favor of a GTR are obligated by the
1998 Agreement to ``submit the technical Regulation to the process''
used in the country to adopt the requirement into the agency's law or
regulation.\17\ In the U.S., that process usually commences with an
NPRM or Advance NPRM (ANPRM). The 1998 Agreement does not obligate
Contracting Parties to adopt the GTR after initiating this process.\18\
The 1998 Agreement recognizes that governments have the right to
determine whether the global technical regulations established under
the Agreement are suitable for their own particular safety needs. Those
needs vary from country to country due to differences in laws and in
factors such as the traffic environment, vehicle fleet composition,
driver characteristics and seat belt usage rates.
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\17\ Article 7, 1998 Agreement, available at <a href="https://unece.org/text-1998-agreement">https://unece.org/text-1998-agreement</a>.
\18\ Id.
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2. History of GTR No. 13
NHTSA began collaborating with the international community to
develop a global technical regulation for hydrogen vehicles in the
early 2000s. In 2005, WP.29 agreed to a proposal from Germany, Japan
and the United States of America regarding how best to manage the
development process for a hydrogen vehicle GTR. Pursuant to the
proposal, the United States and Japan were designated co-chairs of an
informal

[[Page 27506]]

working group (IWG) to explore the safety aspects of hydrogen vehicles.
In June 2007, WP.29 adopted an action plan prepared by the co-
sponsors to develop a GTR for compressed gaseous and liquefied hydrogen
fuel vehicles. At the time, no hydrogen vehicles were commercially
available. To allow for the advancement of hydrogen technologies, the
co-sponsors' action plan split the GTR into two phases. Phase 1 would
focus on developing a GTR for hydrogen vehicles based on current best
practices. Phase 2 would commence subsequent to Phase 1, and supplement
it by assessing any technological advancements and explore ways to
harmonize vehicle crash tests to evaluate fuel system integrity.
The IWG evaluated existing research and design standards for the
development of a hydrogen vehicle GTR. To the extent possible, the
group avoided design specific requirements and considered requirements
and specification that were supported by research and technically
justified. The main areas of focus in Phase 1 were: performance
requirements for hydrogen storage systems, high-pressure closures,
pressure relief devices, and fuel lines; specifications on limits on
hydrogen releases during normal vehicle operations and post-crash; and
requirements for electrical isolation and protection against electric
shock during normal vehicle operations and post-crash.
The draft GTR was recommended by the IWG at the December 2012
session, and GTR No. 13 for Hydrogen and Fuel Cell Vehicles was
codified by WP.29 on June 27, 2013, after a 6-year effort, with the
United States voting in favor of the GTR. It specified 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, and/or from
electric shock caused by a fuel cell vehicle's high voltage power train
system.\19\ The regulation consists of system performance requirements
for compressed hydrogen storage systems (CHSS), CHSS closure devices,
and the vehicle fuel delivery system. In Phase 1, the IWG purposefully
did not harmonize crash tests and instead elected to have Contracting
Parties use their own methodologies.
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\19\ The electrical safety requirements in GTR No. 13 Phase 1
were incorporated into FMVSS No. 305. See 82 FR 44945.
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Phase 2 was adopted at the 190th Session of WP.29 on June 21,
2023.\20\ Phase 2 accomplished several goals, including: broadening of
the scope and application of GTR No. 13 to cover heavy-duty/commercial
vehicles; harmonizing, clarifying, and expanding the requirements for
thermal-pressure relief devices' 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. The U.S. voted in favor of
adopting Phase 2 and is proposing to adopt the changes made to GTR No.
13 by Phase 2 with this proposal.
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\20\ 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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III. Why is NHTSA issuing this proposal?

As a Contracting Party who voted in favor of GTR No. 13, the United
States is obligated under the 1998 Agreement to ``submit the technical
Regulation to the process'' used to adopt the requirement into the
agency's law or regulation as a domestic standard. Today's proposal
satisfies that obligation. In deciding whether to adopt a GTR as an
FMVSS, we follow the procedural and substantive requirements for any
other agency rulemaking, including the Administrative Procedure Act,
the National Traffic and Motor Vehicle Safety Act (Safety Act) (49
U.S.C. Chapter 301), Presidential executive orders, and DOT and NHTSA
policies, procedures, and regulations.\21\ Under 49 U.S.C. 30111(a),
FMVSSs must be practicable, meet the need for motor vehicle safety, and
be stated in objective terms.\22\ Section 30111(b) states that, when
prescribing such standards, NHTSA must, among other things, consider
all relevant, available motor vehicle safety information; consider
whether a standard is reasonable, practicable, and appropriate for the
types of motor vehicles or motor vehicle equipment for which it is
prescribed; and consider the extent to which the standard will further
the statutory purpose of reducing traffic crashes and associated deaths
and injuries.
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\21\ NHTSA's policies in implementing the 1998 Agreement are
published in 49 CFR part 553, appendix C, ``Statement of Policy:
Implementation of the United Nations/Economic Commission for Europe
(UNECE) 1998 Agreement on Global Technical Regulations--Agency
Policy Goals and Public Participation.'' NHTSA's paramount policy
goal under the 1998 Agreement is to ``[c]ontinuously improve safety
and seek high levels of safety, particularly by developing and
adopting new global technical regulations reflecting consideration
of current and anticipated technology and safety problems.''
\22\ ``Motor vehicle safety'' is defined in the Safety Act as
``the performance of a motor vehicle or motor vehicle equipment in a
way that protects the public against unreasonable risk of accidents
occurring because of the design, construction, or performance of a
motor vehicle, and against unreasonable risk of death or injury in
an accident, and includes nonoperational safety of a motor
vehicle.'' 49 U.S.C. 30102(a)(8).
---------------------------------------------------------------------------

This proposal marks a substantial step in meeting those procedural
and substantive requirements. The proposal serves as notice of our
intention to adopt the requirements of GTR No. 13 as FMVSS Nos. 307 and
308 and provides an opportunity for the public to comment on the
proposed requirements. In accordance with the APA, we seek comment on
this proposal to help inform our decision-making, and will take all
timely public comments into consideration when deciding whether (and if
so, how) to proceed with a final rule, and the appropriateness of any
potential modifications to the proposed performance standards that are
appropriately within scope of the NPRM.
NHTSA tentatively finds that the proposed standards fulfill a
clear, if not immediately present, need for motor vehicle safety. The
purpose of FMVSS No. 307, ``Fuel system integrity of hydrogen
vehicles,'' and FMVSS No. 308, ``Compressed hydrogen storage system
integrity,'' is to reduce deaths and injuries in hydrogen-powered
vehicles occurring from fires that result from leakage after motor
vehicle crashes. Hydrogen is highly flammable, with an exceptionally
wide limit of flammability in the air and a high burning velocity. If
hydrogen leaks from the fuel system, the risk of fire in or near the
vehicle is substantial and gravely impairs the safety of vehicle
occupants and others within the vicinity of the vehicle.
Although the potential safety risk from hydrogen vehicles has not
necessarily materialized, due to their current scarcity in the on-road
fleet, NHTSA made the same determination about the safety need for fuel
system and container integrity systems when it adopted FMVSS No. 301,
Fuel system integrity, with the initial FMVSSs adopted in 1968,\23\ and
in 1994 when NHTSA adopted FMVSS No. 303, Fuel system integrity of
compressed natural gas vehicles,\24\ and FMVSS No. 304, Compressed
natural gas fuel container

[[Page 27507]]

integrity.\25\ NHTSA faced a similar crossroads when developing FMVSS
Nos. 303 and 304. Compressed Natural Gas (CNG) vehicles represented a
very small portion of the total fleet size when NHTSA finalized the
standards. The agency decided that the safety risk posed by CNG
necessitated immediate action.\26\ Members of the public shared a
similar sentiment with the agency and urged quick action at that time
to coalesce safety practices.\27\ Today's proposal is the logical
extension of NHTSA's existing standards that cover vehicles powered by
other combustible fuel sources, except, for this NPRM, the agency has
been able to draw on and benefit from the work of the international GTR
No. 13 community in developing the proposed standards.
---------------------------------------------------------------------------

\23\ See 32 FR 2414 (February 3, 1967).
\24\ See 59 FR 19648 (April 25, 1994).
\25\ See 59 FR 49010 (September 26, 1994).
\26\ 58 FR 5323 (January 23, 1993)
\27\ See 59 FR 19648, 19657.
---------------------------------------------------------------------------

We tentatively find the proposed requirements in this NPRM to be
practicable. Both automobile and hydrogen container manufacturers
provided technical expertise to the IWG on test procedures and
determining the boundaries of practicability of requirements during the
development of GTR No. 13. Furthermore, GTR No. 13 incorporates a
number of voluntary industry standards, which are discussed throughout
this preamble, that have been demonstrated as practicable. Given the
industry input informing the GTR and that the GTR incorporates current
technical standards now used in hydrogen vehicle safety designs, NHTSA
believes that the proposed standards are practicable.
The 1998 Agreement provides flexibilities to propose alternative
technical regulations as necessary to ensure compliance with a
jurisdiction's specific legal and safety need requirements. As noted in
the forthcoming sections, NHTSA is proposing several modifications to
the requirements in GTR No. 13 to conform with the Safety Act
requirements for FMVSS, clarify the wording of the regulation, and
improve objectivity.
The agency believes that this proposed rule is timely. While
hydrogen vehicles currently represent less than half a percent of the
total sales of light vehicles and are still in the prototypical stage
for heavier vehicles, there are several trends that may point to
increased growth in the coming years. The slow adoption of hydrogen
vehicles can be attributed to both the expense associated with
developing a new powertrain and the lack of existing fueling
infrastructure.\28\ Recent Federal legislation and spending has renewed
the country's focus on incentivizing clean vehicles. The Inflation
Reduction Act (IRA) allotted billions towards the development of clean
vehicles and the infrastructure to support them. Manufacturers can
claim credits for building or retooling facilities to build hydrogen-
powered vehicles under Qualifying Advanced energy project credit or can
claim credits for each hydrogen vehicle produced pursuant to the
Advanced manufacturing production credit.\29\ Consumers who purchase
hydrogen vehicles can qualify for a $7,500 tax credit, and commercial
enterprises can claim up to $40,000 for hydrogen fuel cell
vehicles.\30\ Additionally, producers of clean hydrogen are also
eligible for tax credits on a per-gallon basis.\31\ This list of
incentives is not exhaustive, and NHTSA recognizes that the collective
efforts at both the Federal and State level to incentive clean energy
in the transportation industry are extensive and underline the
importance of establishing safety standards presently, so that they are
in place as the vehicles arrive in the marketplace.
---------------------------------------------------------------------------

\28\ See, e.g. S. Hardman, E. Shiu, R. Steinberger-Wilckens, and
T. Turrentine., Barriers to the adoption of fuel cell vehicles: A
qualitative investigation into early adopters attitudes, 95
Transportation Research Part A: Policy and Practice 166-82 (2017).
https://www.sciencedirect.com/science/article/abs/pii/
S0965856415302408#:~:text=FCVs%20have%20some%20specific%20challenges,
and%20balance%20of%20plant%20components.
\29\ See 26 U.S.C. 48C and 26 U.S.C. 45X, respectively.
\30\ See 26 U.S.C. 30D and 26 U.S.C. 45W, respectively.
\31\ 26 U.S.C. 45Z.
---------------------------------------------------------------------------

Manufacturers continue to announce new forays into hydrogen
vehicles, with some manufacturers citing the IRA as a catalyst for
further development of hydrogen-powered vehicles.\32\ Hyundai and
Toyota, the only two manufacturers with hydrogen vehicles for sale
currently in the United States, have announced plans to introduce more
consumer hydrogen vehicle lines covering additional body styles and
expand their hydrogen vehicle offerings.\33\ Other manufacturers have
announced plans to introduce their own hydrogen vehicle models,\34\ and
new entrants to the automotive market are testing prototypes and
concept vehicles.\35\ Manufacturers have also stated that they are
exploring the viability of hydrogen heavy-duty vehicles.\36\
---------------------------------------------------------------------------

\32\ See, e.g. Elizabeth Sturcken, ``Leading companies are using
IRA tax credits for clean manufacturing and technology. Are you?''
Environmental Defense Fund, June 7, 2023, <a href="https://business.edf.org/insights/leading-companies-are-using-ira-tax-credits-for-clean-manufacturing-and-technology-are-you/">https://business.edf.org/insights/leading-companies-are-using-ira-tax-credits-for-clean-manufacturing-and-technology-are-you/</a>.
\33\ See Remeredzai J. Kuhadzai, ``Toyota Hilux Hydrogen Fuel
Cell Pickup Prototype Unveiled'' <a href="https://cleantechnica.com/2023/01/11/toyota-starts-work-on-the-development-of-prototype-hydrogen-fuel-cell-toyota-hilux-pickup/">https://cleantechnica.com/2023/01/11/toyota-starts-work-on-the-development-of-prototype-hydrogen-fuel-cell-toyota-hilux-pickup/</a> (Toyota plans to release the Helix only in
Japan for the upcoming model year) and Toyota, ``PACCAR and Toyota
Expand Hydrogen Fuel Cell Truck Collaboration to Include
Commercialization.'' May 2, 2023, <a href="https://pressroom.toyota.com/paccar-and-toyota-expand-hydrogen-fuel-cell-truck-collaboration-to-include-commercialization/">https://pressroom.toyota.com/paccar-and-toyota-expand-hydrogen-fuel-cell-truck-collaboration-to-include-commercialization/</a>; see also Michelle Thompson, ``Hyundai
hires new exec to help lead hydrogen initiatives.'' Repairer Driven
News, June 29, 2023. <a href="https://www.repairerdrivennews.com/2023/06/29/hyundai-hires-new-exec-to-help-lead-hydrogen-initiatives/">https://www.repairerdrivennews.com/2023/06/29/hyundai-hires-new-exec-to-help-lead-hydrogen-initiatives/</a>.
\34\ For example, see Ken Silverstein, ``Electric Vehicles or
Hydrogen Fuel Cell Cars? The Inflation Reduction Act Will Fuel
Both.'' Forbes, Aug. 10, 2022, <a href="https://www.forbes.com/sites/kensilverstein/2022/08/10/electric-vehicles-or-hydrogen-fuel-cell-cars-the-inflation-reduction-act-will-fuel-both/?sh=2841d7634d01">https://www.forbes.com/sites/kensilverstein/2022/08/10/electric-vehicles-or-hydrogen-fuel-cell-cars-the-inflation-reduction-act-will-fuel-both/?sh=2841d7634d01</a>;
see also Joey Capparella, ``Hydrogen-Powered Honda CR-V to Be Built
in the U.S. Starting in 2024.'' Car and Driver, Nov. 30, 2022.
\35\ See, Ezra Dyer, ``Pininfarina Reveals Pura Vision SUV
Concept.'' Car and Driver, Aug. 1, 2023, <a href="https://www.caranddriver.com/news/a44690183/pininfarina-pura-vision-suv-concept-revealed/">https://www.caranddriver.com/news/a44690183/pininfarina-pura-vision-suv-concept-revealed/</a>.
\36\ See Rebecca Martineau, ``Fast Flow Future for Heavy-Duty
Hydrogen Trucks: Expanded Capabilities at NREL Demonstrate High-
Flow-Rate Hydrogen Fueling for Heavy-Duty Applications.'' National
Renewable Energy Laboratory, June 8, 2022, <a href="https://www.nrel.gov/news/program/2022/fast-flow-future-heavy-duty-hydrogen-trucks.html">https://www.nrel.gov/news/program/2022/fast-flow-future-heavy-duty-hydrogen-trucks.html</a>.
---------------------------------------------------------------------------

NHTSA faced a similar crossroads when developing FMVSS Nos. 303 and
304. Compressed Natural Gas (CNG) vehicles represented a very small
portion of the total fleet size when NHTSA finalized the standards. The
agency decided that the safety risk posed by keeping CNG at a high
pressure necessitated an immediate action.\37\ Members of the public
have shared a similar sentiment with the agency and urged quick action
to coalesce safety practices for hydrogen powered vehicles.\38\
---------------------------------------------------------------------------

\37\ 58 FR 5323.
\38\ See 59 FR 19648, 19657.
---------------------------------------------------------------------------

We believe that the proposed standards would provide regulatory
certainty for manufacturers. Given manufacturers' purported interest in
expanding their hydrogen offerings and the IRA incentives reducing the
comparative costs of hydrogen vehicles, adopting safety regulations now
would provide manufacturers clarity on how to design new vehicle lines.
Further, having hydrogen safety standards in place should assist in
alleviating the trepidation consumers have of newer technologies,
whereas a failure to adequately address safety concerns in the earliest
stages of development could have a negative impact on the deployment of
this new technology. Manufacturers have also informed

[[Page 27508]]

NHTSA that they would like to see the agency coordinate and harmonize
hydrogen standards with other nations.\39\ This proposal would
accomplish all of these tasks.
---------------------------------------------------------------------------

\39\ See, e.g. NHTSA-2004-18039-0020 at 17.
---------------------------------------------------------------------------

IV. Overview of Proposed Safety Standards

The safe use of compressed hydrogen in vehicles lies primarily in
preventing explosion of the hydrogen container(s) and preventing fuel
leaks which could lead to fire or explosion. The leakage of hydrogen
from the fuel system during normal vehicle operations and post-crash
can pose safety hazards (fire or explosion) to vehicle occupants and
the surroundings. In order to address the fire and explosion hazards
associated with hydrogen vehicles, NHTSA is proposing to set
performance requirements for the CHSS and the overall fuel system that
are generally consistent with GTR No. 13.
GTR No. 13, Section 5.1, ``Compressed hydrogen storage system,''
specifies performance-based CHSS requirements which address documented
on-road stress factors. These stress factors include those identified
in CNG vehicle containers as well as those that are unique to
containment of high-pressure hydrogen. These requirements were
developed to demonstrate the CHSS's capability to perform critical
functions throughout service, including fueling/defueling events,
parking under extreme vehicle and environmental conditions,
environmental exposures, and performance in fire without explosion.
GTR No. 13, Section 5.2, ``Vehicle fuel system,'' includes
performance requirements to prevent and mitigate hydrogen leak from the
fuel system and to warn vehicle occupants in the event of hydrogen
concentration in the vehicle above flammable limits during normal
vehicle operations and post-crash.
Similar to how NHTSA originally established CNG standards, we are
proposing to implement GTR No. 13 by establishing two new FMVSSs that
would specify minimum performance standards for vehicles that use
compressed hydrogen gas as a motor fuel.\40\ FMVSS No. 308,
``Compressed hydrogen storage system integrity,'' would set out
requirements for CHSS integrity. FMVSS No. 307, ``Fuel system integrity
of hydrogen vehicles,'' would set out in-use and post-crash
requirements for the overall fuel system, including the CHSS, hydrogen
delivery system, and fuel cell.
---------------------------------------------------------------------------

\40\ The standards proposed in this document would not apply to
vehicles that use liquified hydrogen as a motor fuel.
---------------------------------------------------------------------------

NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all
hydrogen-powered vehicles. This is a departure from Phase 1 of GTR No.
13 which only applies to hydrogen powered light vehicles. As discussed
below, the IWG of GTR No. 13 Phase 2 has expanded the applicability of
the standard to hydrogen powered heavy vehicles. With the exception of
crash tests for heavy vehicles, NHTSA finds that the technical
standards in GTR No. 13 are practicable for heavy vehicles and address
the same safety need found in light vehicles.
Note that, consistent with GTR No. 13, NHTSA is proposing that
FMVSS No. 308 be a vehicle-level standard, rather than an equipment
standard.\41\ 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 is aware this is a departure from
FMVSS No. 304 that is an equipment standard which applies to CNG
containers sold as replacement parts for CNG vehicles. At this time,
hydrogen vehicle manufacturers are strictly controlling the CHSS
installed in their vehicles and replacement parts are obtained from the
vehicle manufacturer (similar to electric vehicle batteries). NHTSA
will monitor the deployment of hydrogen vehicles and how consumers are
replacing parts of the fuel system. Since such data is lacking at this
time, NHTSA is proposing FMVSS No. 308 as a vehicle standard,
consistent with GTR No. 13. NHTSA will re-evaluate this decision based
on comments received and on field data on hydrogen vehicle deployment,
repair, and replacement parts. NHTSA seeks comment on whether FMVSS No.
308 should remain a vehicle standard, as well as whether FMVSS Nos. 307
and 308 should be combined into a single standard in the final rule.
---------------------------------------------------------------------------

\41\ This is in contrast to FMVSS No. 304, Compressed natural
gas fuel container integrity, which is an equipment standard.
---------------------------------------------------------------------------

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

FMVSS No. 308 would set out requirements for the performance of the
CHSS and its subcomponents during normal use, with a particular focus
on how the CHSS performs in a variety of incidents that a vehicle could
experience during its lifetime operations and how well the component
withstands usage.
NHTSA is proposing that FMVSS No. 308 only be a vehicle standard.
As explained in more detail below, some of the proposed requirements
are conditional on the vehicle type and characteristics. Without the
knowledge of the relevant vehicle, some of the proposed CHSS standards
cannot be tested. For these reasons, NHTSA does not intend that the
proposed standard should extend to cover replacement parts, even though
they would be considered motor vehicle equipment and still subject to
NHTSA's safety defect authority, and replacement parts when installed
may not take the vehicle out of compliance with the proposed new FMVSS
No. 308, per 49 U.S.C. 30122. NHTSA seeks comment on this approach.
1. Compressed Hydrogen Storage System
The CHSS is defined to include all closure surfaces that provide
primary containment of high-pressure hydrogen storage. The CHSS is
defined to include the hydrogen container, check valve, shut-off valve
and thermally-activated pressure relief device (TPRD), which are
discussed in the sections below. Figure-3 illustrates a typical CHSS.
[GRAPHIC] [TIFF OMITTED] TP17AP24.002

Figure-3: Typical CHSS

a. Hydrogen Container
The hydrogen container is the main component of a CHSS. The
hydrogen container stores hydrogen at extremely high pressure. On
current hydrogen vehicles, hydrogen has typically been stored at a
nominal working pressure (NWP) of 35 MPa or 70 MPa, at 15 [deg]C. NWP
means the gauge pressure that characterizes the normal operation of the
system. Typically, the container is designed for a maximum allowable
gas temperature of 85 [deg]C. If the temperature of hydrogen stored at
NWP is increased from 15 [deg]C to 85 [deg]C, then the pressure inside
the container will rise to the maximum allowable pressure of 25

[[Page 27509]]

percent above NWP.\42\ A container may consist of a single chamber or
multiple permanently interconnected chambers. This allows designers
flexibility in the overall shape of the CHSS.
---------------------------------------------------------------------------

\42\ This is based on data published in the NIST Chemistry
WebBook, Standard Reference Database Number 69, Thermophysical
Properties of Fluid Systems (isochoric properties for hydrogen),
available at <a href="https://webbook.nist.gov/chemistry/fluid/">https://webbook.nist.gov/chemistry/fluid/</a>.
---------------------------------------------------------------------------

Most containers used in hydrogen vehicles consist of two layers.
The inner liner prevents gas leakage/permeation and is usually made of
metal or thermoplastic polymer. The outer layer provides structural
integrity and is usually made of metal or thermoset resin-impregnated
fiber-reinforced composite. For instance, Type 3 containers consist of
a metal liner reinforced with resin impregnated continuous filament,
and Type 4 containers consists of a non-metallic liner with resin-
impregnated continuous filament.\43\
---------------------------------------------------------------------------

\43\ The American National Standard for Compressed Natural Gas
Fuel Vehicle Containers (2007) classifies containers into Types 1
through 4 as follows:
Type 1--Metal.
Type 2--Resin impregnated continuous filament with metal liner
with a minimum burst pressure of 125 percent of service pressure.
This container is hoop-wrapped.
Type 3--Resin impregnated continuous filament with metal liner.
This container is full-wrapped.
Type 4--Resin impregnated continuous filament with a non-
metallic liner.
---------------------------------------------------------------------------

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 is proposing 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 the
CHSS, and therefore a container cannot exist on its own without the
other components of the CHSS.
<bullet> Remove the word ``primary'' because this introduces
ambiguity regarding secondary or tertiary volumes of 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's proposed definition for ``container'' would be
``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.'' These changes are
intended to clarify the definition and provide greater regulatory
certainty as to what is considered part of the container. The changes
do not alter the substantive requirements. NHTSA seeks comment on the
proposed definition for the container.
b. Closure Devices
GTR No. 13 refers to closure devices as ``primary'' closure
devices. This creates ambiguity about potential secondary or tertiary
closure devices. As a result, NHTSA will refer simply to ``closure
devices.'' NHTSA therefore proposes 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,'' so it will be clear what components are
covered under the standard. NHTSA seeks comment on removal of the word
``primary'' and on the proposed definition for ``closure devices.''
(1) TPRD
In the event of a fire, the TPRD provides a controlled release of
hydrogen from the container before the high temperature from the fire
weakens the container and causes a hazardous burst. TPRDs are designed
to vent the entire hydrogen content of the container rapidly. These
devices are designed to not be reset or reused once they have been
activated.
(2) Check Valve
During fueling, hydrogen enters the CHSS through a check valve. The
check valve prevents back-flow of hydrogen into the fueling line or out
of the fueling receptacle.
(3) Shut-Off Valve
A shut-off valve prevents the outflow of stored hydrogen from the
container when the vehicle is not operating or when a fault is detected
that requires isolation of the CHSS. In GTR No. 13, the shut-off valve
is defined 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 proposes 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.'' NHTSA seeks comment on the proposed definition of
shut-off valve.
(4) Container Attachments
The CHSS may include container attachments, which are non-pressure
bearing parts attached to the container that provide additional support
and/or protection to the container. Container attachments may only be
removed with the use of tools for the purpose of maintenance and/or
inspection. Container attachments include devices such as bump stops to
mitigate impacts or shielding to mitigate surface damage to the
container.
In the GTR No. 13 test procedures, container attachments are
included in some tests. Importantly, in some cases, the container
attachments provide protection to the container that improves test
performance. Including container attachments for testing is discussed
in the sections below where applicable and where the container
attachments may affect test performance.
NHTSA proposes 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.'' NHTSA seeks comment on the proposed definition of
container attachments. In this definition, the word ``temporarily'' has
been removed from the GTR definition because anything that can be
removed temporarily can also be removed permanently. For clarity, NHTSA
has also shifted the order of some words relative to the definition in
GTR No. 13.
2. General Requirements for the CHSS
NHTSA is proposing that the CHSS be required to include the
functionality of a TPRD, shut-off valve, and check valve. These
functions are required for the reasons stated above. However, NHTSA is
aware of CNG vehicles that do not include check valves as part of their
CNG storage system. In such CNG vehicles, the check valves are
installed upstream between the fueling port and the CNG container, with
additional valves to contain high pressure gas. NHTSA seeks comment on
whether the check valves should be required as part of the CHSS.
The CHSS would be required to have an NWP of 70 MPa or less. This
is because working pressures above 70 MPa 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.
As a result, NHTSA proposes that all CHSS

[[Page 27510]]

must have an NWP less than or equal to 70 MPa. NHTSA seeks comment on
this requirement, and specifically asks commenters to identify any
technologies that can safely store hydrogen at pressures above 70 MPa.
GTR No. 13 provided contracting parties with the discretion to
require that the closure devices be mounted directly on or within each
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, the definition of a
container is sufficiently broad that it includes such lines as part of
the container. These lines will be considered part of the permanently
interconnected chambers storing the continuous volume of hydrogen.
Thus, any lines connecting to closure devices are themselves part of
the container and will be included in the extensive container
performance testing discussed below. If a container (which includes any
lines connecting to closure devices) can successfully complete the
performance testing in FMVSS No. 308, then the risk of failure of the
lines has been addressed. Therefore, NHTSA tentatively concludes that
it is not necessary to specify that closure devices be mounted directly
on or within each container. NHTSA is also concerned that such a
specification would be design restrictive. NHTSA is aware of CNG fuel
systems where the closure devices are neither on nor within each
container, and there have been no reported safety issues with such
systems. Therefore, NHTSA is not proposing to include a requirement for
closure devices to be on or within each container, and would instead
leave the location of closure devices to manufacturer discretion. NHTSA
seeks comment on requiring closure devices to be mounted directly on or
within each container.
3. Performance Requirements for the CHSS
The CHSS would be required to meet specific performance
requirements when subjected to the performance tests listed below. The
performance tests and the respective performance requirements are
discussed in detail in subsequent sections:

<bullet> Tests for baseline metrics
<bullet> Test for performance durability
<bullet> Test for expected on-road performance
<bullet> Test for service terminating performance in fire
<bullet> Tests for performance durability of closure devices

Several of these tests utilize 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 to establish the expected initial burst
pressure of the container. It is NHTSA's understanding that
BP<INF>O</INF>, associated with median or midpoint burst pressure for a
batch of containers, can vary between batches of containers. Therefore,
in order to facilitate compliance testing, NHTSA is proposing that
manufacturers specify the BP<INF>O</INF> associated with each container
on the required container label (discussed below). NHTSA seeks comment
on this labeling requirement, noting that it is not required by GTR No.
13.
4. Tests for Baseline Metrics
The container must be able to withstand high pressurization, as
well as pressure cycling, which is a repeated pressurization and
depressurization. Both of these stress factors occur during the service
life of the vehicle as its fuel system is repeatedly depleted and
refilled. Consistent with GTR No. 13, the proposed tests for baseline
metrics would include two tests for the container: the baseline initial
burst pressure test to evaluate resistance to burst at high pressure,
and the baseline initial pressure cycle test to ensure the container is
designed to leak before burst \44\ and to evaluate its ability to
withstand pressure cycling without burst and without leakage within its
service life.
---------------------------------------------------------------------------

\44\ Leak before burst design of high pressure containers is a
common safety feature to ensure a leak will develop before a
catastrophic burst will occur. A leak is a less severe failure mode
compared to a catastrophic burst of the high pressure container.
---------------------------------------------------------------------------

During the initial burst pressure test, the container must
demonstrate that as the pressure is increased inside the container, the
point of failure is above a minimum pressure level, discussed below. In
other words, the container must demonstrate a minimum burst pressure.
Burst pressure is defined as the highest pressure reached inside a
container during a burst test which results in structural failure of
the container and resultant fluid loss through the container, not
including gaskets or seals. Burst pressure is determined by the
baseline initial burst pressure test discussed below.
During the baseline initial pressure cycle test, the container must
withstand pressure cycling that simulates repeated fueling and
defueling by increasing the pressure inside the container to a high
pressure level, then depressurizing it to low pressure, and repeating
that process for a set number of cycles. The container must neither
leak nor burst during an initial set of pressure cycles, and must not
burst during a set number of pressure cycles beyond the initial set.
These requirements are evaluated by the baseline pressure cycle life
test discussed below.
The physical forces on the load-bearing components of a container
are the same regardless of whether the pressure is being applied with
hydraulic fluid, hydrogen gas, or any other medium. Therefore, for
practicability and safety purposes both tests would be conducted using
hydraulic fluid to exert pressure inside the container.\45\ Hydraulic
fluids, such as water or water with additives, are advantageous for
these tests because they reduce the explosion risk associated with
pneumatic pressurization. The explosion risk from pneumatic
pressurization is high because compression of gas stores pressure-
volume energy (PV energy), whereas during hydraulic pressurization with
an incompressible fluid, PV energy is negligible. In addition, the
incompressible nature of hydraulic fluids means that pressure cycles
can be accomplished much faster than pneumatic pressurization cycles.
This is important given the high number of cycles required for the
baseline pressure cycle test. The use of hydrogen gas pneumatic
pressure cycling does introduce stress factors beyond basic
pressurization/depressurization, as discussed later, and these are
addressed separately in the test for expected on-road performance.
Given that hydraulic pressure cycling provides these benefits without
compromising the safety or stringency of the proposed standards,
hydraulic pressure cycling is used for these tests.
---------------------------------------------------------------------------

\45\ This is consistent with GTR No. 13.
---------------------------------------------------------------------------

a. Baseline Initial Burst Pressure
The baseline initial burst pressure test verifies that the initial
burst pressure of a container is both above a minimum specified
pressure level and 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> is 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 seeks comment on the safety need
for specifying a limit on burst pressure variability in a batch and
whether the 10 percent limit is appropriate; if commenters believe
another limit is

[[Page 27511]]

appropriate, they are asked to provide supporting data.
The minimum burst pressure, BP<INF>min</INF>, in GTR No. 13 Phase 1
was set at 225 percent of NWP for carbon fiber composite containers,
and 350 percent NWP for glass fiber composite containers. The value for
carbon fiber composite containers was chosen to be a conservative
starting point based on experience from CNG vehicles. GTR No. 13 Phase
1 made clear that the burst pressure requirement would be reviewed in
Phase 2. The IWG of GTR No. 13 Phase 2 did review data on variability
in initial burst pressure and end-of-life burst pressure (i.e., burst
pressure after the test for performance durability, discussed in a
later section), and determined that variation in burst pressure is
actually low and that a minimum initial burst pressure of 200 percent
NWP was appropriate for carbon fiber composite containers.\46\ The GTR
No. 13 Phase 2 IWG assessment also noted that manufacturers generally
design containers to have burst pressures well above the required
minimum burst pressure, to ensure that a container can meet the
performance requirements of the test for performance durability. These
findings suggest it is possible to lower the minimum burst pressure
requirement to 200 percent of NWP without reducing safety, because
manufacturers will generally be outperforming this requirement anyway.
---------------------------------------------------------------------------

\46\ A study was conducted by the Japanese Automobile Research
Institute which evaluated the variability of containers' initial
burst pressure, as well as the variability in end-of-life burst
pressure. The study concluded that variability among the containers
was low, and therefore a minimum initial burst pressure of 200
percent NWP was acceptable and most consistent with the end-of-life
burst pressure requirement.
See GTR No. 13 Phase 2 file GTR13-3-03: <a href="https://wiki.unece.org/download/attachments/58525915/GTR13-3-03%20Initial%20burst%20pressure%20requirement%20_3rd%20GTR13%20IWG_June2018.pdf?api=v2">https://wiki.unece.org/download/attachments/58525915/GTR13-3-03%20Initial%20burst%20pressure%20requirement%20_3rd%20GTR13%20IWG_June2018.pdf?api=v2</a>.
---------------------------------------------------------------------------

Furthermore, a 200 percent minimum initial burst pressure can be
supported when coupled with the following requirements from the
proposed test for performance durability (which are discussed in the
following section): \47\
---------------------------------------------------------------------------

\47\ The tests conducted by the Japanese Automobile Research
Institute showed that containers with burst pressure which met the
BP<INF>O</INF> <plus-minus>10 percent requirement and subjected to
the durability sequential tests, were able to withstand the end-of-
life 180 percent NWP for four minutes and have an end-of-life burst
pressure within -20 percent of BP<INF>O</INF>, even if the minimum
initial burst pressure is reduced to 200 percent NWP.
---------------------------------------------------------------------------

<bullet> The container must withstand 180 percent NWP for 4 minutes
at the end of the test for performance durability.
<bullet> The minimum burst pressure after the completion of the
test for performance durability cannot be lower than 80 percent of
BP<INF>O</INF>.
In light of the variability in the minimum burst pressure and the
need to meet the above two requirements at the end of the test for
performance durability, NHTSA expects that manufacturers will
ultimately design the container with an initial burst pressure well
above 200 percent NWP.
Accordingly, NHTSA believes that proposing BP<INF>min</INF> to 200
percent NWP, as set forth in GTR No. 13 Phase 2, meets the need for
safety. Proposing the BP<INF>min</INF> to 200 percent NWP facilitates
hydrogen vehicle development without unnecessary overdesign of
components. NHTSA seeks 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.
In the case of containers having glass-fiber as a primary
constituent, consistent with GTR No. 13 Phase 2, NHTSA is proposing a
higher BP<INF>min</INF> of 350 percent of NWP because these containers
are highly susceptible to stress rupture as compared to carbon fiber
containers. Stress rupture is a failure mode that relates to the
intrinsic failure probability of the individual fibers that overwrap
the container for support. This failure mode can occur when the fibers
are held under stress for long periods of time (such as in a
continuously pressurized container).\48\ The higher BP<INF>min</INF> of
350 percent of NWP provides protection from the risk of stress rupture
in containers having glass-fiber composite as a primary constituent.
NHTSA seeks comment on this proposed requirement and how NHTSA can
determine if a container has glass-fiber as a primary constituent.
NHTSA seeks comment on appropriate criteria to determine the primary
constituent in this context.
---------------------------------------------------------------------------

\48\ SAE Paper 2009-01-0012. Rationale for Performance-based
Validation Testing of Compressed Hydrogen Storage by Christine S.
Sloane, available at <a href="https://www.sae.org/publications/technical-papers/content/2009-01-0012/">https://www.sae.org/publications/technical-papers/content/2009-01-0012/</a>.
---------------------------------------------------------------------------

In the case of containers constructed of both glass and carbon
fibers, NHTSA proposes to apply the requirements according to the
primary constituent of the container as specified by the manufacturer.
NHTSA proposes that the manufacturer shall specify upon request, in
writing, and within five business days, the primary constituent of the
container. NHTSA proposes that the burst pressure of the container, for
which the manufacturer fails to specify upon request, in writing, and
within five business days, the primary constituent of the container,
must not be less than 350 percent of NWP. NHTSA seeks comment on this
proposed requirement.
The test for performance durability, described below, includes a
1000 hour high-temperature (85 [deg]C) static pressure test, which is
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 is focused directly on evaluating
stress rupture risk, and the test for performance durability represents
an overall worst-case lifetime of stress factors, regardless of fiber
type, NHTSA seeks comment on whether the baseline initial burst
pressure test even needs to be included in the standard's requirements.
GTR No. 13 specifies that the baseline initial burst pressure test
(as well as the initial pressure cycle test described below) be
conducted at ambient temperatures between 5 [deg]C and 35 [deg]C. The
IWG of GTR No. 13 determined that container burst strength is not
affected by using this range of ambient temperature between 5 [deg]C
and 35 [deg]C.\49\ This temperature range reduces test costs (thus
improving the practicability of the proposed requirements) by enabling
outdoor testing without special temperature controls. Extreme
temperatures are addressed in later tests.
---------------------------------------------------------------------------

\49\ See GTR No. 13, Part I, paragraph 81(d)(v).
---------------------------------------------------------------------------

GTR No. 13 requires that the rate of pressurization be less than or
equal to 1.4 MPa/s for pressures higher than 150 percent of the nominal
working pressure. If the pressurization rate exceeds 0.35 MPa/s at
pressures higher than 150 percent NWP, GTR No. 13 also requires that
either the container is placed in series between the pressure source
and the pressure measurement device, or that the time at the pressure
above a target burst pressure exceeds 5 seconds. These requirements are
designed to ensure that a pressure sensor will measure the pressure
inside the container accurately. The pressurization rate limit ensures
the pressure sensor will have enough time to read the pressure level as
it rises. 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 is concerned that the second option that the
time at the pressure above the target burst pressure exceeds 5 seconds
is unclear and difficult to enforce. For example, it is not clear what
pressure

[[Page 27512]]

the ``target burst pressure'' is referring to since the pressure may be
increasing continuously. Therefore, this option is not being proposed
as an alternative and the container will simply be placed in series
between the pressure source and the pressure measurement device. NHTSA
seeks comment on this decision.
b. Service Life and Number of Cycles for the Baseline Initial Pressure
Cycle Test for Containers on Light and Heavy Vehicles
As discussed above, hydrogen is highly flammable, and therefore,
hydrogen containers must not leak during their service life. While
hydrogen leakage is a serious safety concern, leaking hydrogen will
likely dissipate quickly into the atmosphere given its density, and may
or may not ignite/explode, whereas, a hydrogen container burst involves
an explosion by definition and is therefore a far worse, catastrophic
failure mode that must be prevented under all circumstances regardless
of service life. As a result, hydrogen containers are designed to leak
before bursting beyond their service lives. This ``leak before burst''
safety feature is also followed for other high-pressure vehicle fuel
containers such as vehicle CNG fuel containers. Systems are typically
designed such that the occurrence of leakage should result in vehicle
shut down and subsequent repair or removal of the container from
service, thereby preventing a burst of the container from occurring.
The baseline pressure cycle test requirement is designed to provide
an initial check for resistance to leak or burst due to pressure
cycling during service, and a check that the container does in fact
leak before burst after the container service life has been exceeded.
Accordingly, the baseline initial pressure cycle test requires the
container to (i) not leak or burst for a specified number of pressure
cycles that are meant to represent maximum container service life, and
(ii) leak before burst for a specified number of pressure cycles beyond
the maximum service life. In the case of (i), the IWG of GTR No. 13
Phase 1 gave contracting parties the option of selecting either 5,500,
7,500, or 11,000 cycles as the expected maximum service life
containers. In the case of (ii), the GTR explains that a greater number
of pressure cycles (22,000) that far exceeds service life of containers
is used to ensure that a container should leak before bursting during
the expected service life.
GTR No. 13 provides several examples of the maximum number of
empty-to-full fueling cycles for vehicles under extreme service. These
examples are described below and summarized in Table-1.
<bullet> Sierra Research Report No. SR2004-09-04 for the California
Air Resource Board (2004) reported on vehicle lifetime distance
traveled by scrapped California vehicles, which all showed lifetime
distances traveled below 350,000 miles. Based on these figures and 200-
300 miles driven per full fueling, the maximum number of lifetime
empty-to-full fuelings can be estimated as 1,200-1,800.
<bullet> Transport Canada reported that required emissions testing
in British Columbia, Canada, in 2009 showed the five most extreme usage
vehicles had odometer readings in the 500,000-600,000 miles range.
Using the reported model year for each of these vehicles, this
corresponds to less than 300 full fuelings per year, or less than one
full fueling per day. Based on these figures and 200-300 miles driven
per full fueling, the maximum number of empty-to-full fuelings can be
estimated as 1,650-3,100.
<bullet> The New York City (NYC) taxicab fact book reports extreme
usage of 200 miles in a shift and a maximum service life of five
years.\50\ Less than 10 percent of vehicles remain in service as long
as five years. The average mileage per year is 72,000 for vehicles
operating two shifts per day and seven days per week. There is no
record of any vehicle remaining in high usage through-out the full 5-
year service life. However, if a vehicle were projected to have fueled
as often as 1.5-2 times per day and to have remained in service for the
maximum 5-year NYC taxi service life, the maximum number of fuelings
during the taxi service life would be 2,750-3,600.
---------------------------------------------------------------------------

\50\ New York City taxicab fact book, Schaller Consulting
(2006), <a href="http://www.schallerconsult.com/taxi/taxifb.pdf">http://www.schallerconsult.com/taxi/taxifb.pdf</a>.
---------------------------------------------------------------------------

<bullet> Transport Canada reported a survey of taxis operating in
Toronto and Ottawa that showed common high usage of 20 hours per day,
seven days per week with daily driving distances of 335-450 miles.
Vehicle odometer readings were not reported. In the extreme worst-case,
it might be projected that if a vehicle could remain at this high level
of usage for seven years (the maximum reported taxi service life); then
a maximum extreme driving distance of 870,000-1,200,000 miles is
projected. Based on 200-300 miles driven per full fueling, the
projected full-usage 15-year number of full fuelings could be 2,900-
6,000.

Table 1--Expected Vehicle Usage Data Summary
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of lifetime empty-to-full
Data source Lifetime traveling distance (miles) Distance per full-fueling (mile) filling
--------------------------------------------------------------------------------------------------------------------------------------------------------
Sierra Research Report No. SR2004- 350,000.............................. 200-300.............................. 1,200-1,800.
09-04: California vehicles.
Transport Canada: Vehicle fleet 500,000-600,000...................... 200-300.............................. 1,650-3,100.
&Taxi.
The New York City (NYC) taxicab 360,000 (5 year life)................ N/A (Fueling frequency 1.5-2 times/ 2750-3600 (5 year life).
fact book: Taxi usage. day).
Transport Canada: Taxi usage....... 870,000-1,200,000.................... 200-300.............................. 2,900-6,000.
--------------------------------------------------------------------------------------------------------------------------------------------------------

Based on these examples, the IWG of GTR No. 13 Phase 1 set the
minimum number of pressure cycles before leak at 5,500. The maximum
number of cycles before leak was set at 11,000 cycles, which
corresponds to a vehicle that remains in service with two full fuelings
per day for 15 years (expected lifetime vehicle mileage of 2.2-3.3
million miles). The last example above shows it is possible for a high
usage taxi to experience 6,000 fueling cycles during seven years of
service. Taxi service is representative of the most demanding
circumstances a light vehicle will experience, so this example is
considered worst-case. Furthermore, such a vehicle could be
subsequently resold and experience further fuelings beyond 6,000. As a
result, the IWG of GTR No. 13 Phase 2 concluded that the

[[Page 27513]]

choice of 5,500 cycles is not sufficient for containers on light
vehicles. However, NHTSA concludes that the maximum choice of 11,000
cycles is too extreme for light vehicles. A vehicle traveling 2.2-3.3
million miles is unrealistic even for the most extreme service life for
light vehicles. Accordingly, NHTSA proposes 7,500 as the number of
cycles in the baseline initial pressure cycle test for which the
container does not leak or burst. NHTSA believes that 7,500 pressure
cycles is a reasonable representation of the maximum service life of a
container, and notes that is greater than that presented in Table 1 for
the Transport Canada taxi usage data.
As discussed above, the worst-case scenario is a container failure
by burst. To ensure the container leaks before burst beyond the maximum
service life, the container is pressure cycled beyond the 7,500 cycles
(representing maximum service life) until leak occurs without burst or
up to a maximum of 22,000 hydraulic pressure cycles. For vehicles with
nominal on-road driving range of 300 miles per full-fueling, 22,000
hydraulic pressure cycles correspond to over 6 million miles, which is
beyond extreme on-road vehicle lifetime range.
The analysis summarized above considered light vehicles with a
service life of 15 years. When conducting their analysis, the IWG of
GTR No. 13 Phase 1 had limited information available on lifetime
vehicle mileage and fuelings. In addition, hydrogen vehicles were a new
technology and there was very little field experience available to draw
upon. As a result, the IWG of GTR No. 13 Phase 1 was conservative in
setting the number of cycles for the baseline initial cycle test. In
the analysis provided above, short periods of extreme service were
extrapolated to a full 15-year service life. This is not a realistic
assumption because vehicles generally cannot last in extreme service
for a full 15 years.
To address this issue, the IWG of GTR No. 13 Phase 2 reviewed new
data on the number of vehicle miles traveled. The analysis was also
expanded to include heavy vehicles in addition to light
vehicles.51 52 The data shows that the number of cycles
presented in GTR No. 13 for light vehicles correspond more
appropriately to a 25-year service life.
---------------------------------------------------------------------------

\51\ See GTR No. 13 Phase 2 file GTR13-11-12b: The number of
cycles, <a href="https://wiki.unece.org/download/attachments/123666576/GTR13-9-07%20TF1%20OICA%20GTR13%20Baseline%20Initial%20Cycles.pdf?api=v2">https://wiki.unece.org/download/attachments/123666576/GTR13-9-07%20TF1%20OICA%20GTR13%20Baseline%20Initial%20Cycles.pdf?api=v2</a>.
\52\ See GTR No. 13 Phase 2 file GTR13-9-07: Extension of the
service life of the container to 25 years, <a href="https://wiki.unece.org/download/attachments/140706658/GTR13-11-12b%20TF1%20%20210927%20Estimation%20of%20VMT%20TF1-JAMA.pdf?api=v2">https://wiki.unece.org/download/attachments/140706658/GTR13-11-12b%20TF1%20%20210927%20Estimation%20of%20VMT%20TF1-JAMA.pdf?api=v2</a>.
---------------------------------------------------------------------------

For heavy vehicles, the new data on the number of vehicle miles
traveled that was collected in Phase 2 indicates a higher number of
cycles are required for a 25-year service life than that for light
vehicles. This is consistent with the fact that heavy vehicles
typically travel farther and remain in service longer than light
vehicles. Consequently, for heavy vehicle containers, the IWG of GTR
No. 13 Phase 2 set the number of pressure cycles representing maximum
container service life at 11,000. In accordance with GTR No. 13 Phase
2, NHTSA proposes to require 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. The proposed
service life, number of hydraulic pressure cycles representing the
maximum service life for which the container is required not to 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 is
summarized in Table-2 for light and heavy vehicles.

Table 2--Proposed Service Life and Number of Cycles in the Baseline Hydraulic Pressure Cycle Test for Light and
Heavy Vehicles
----------------------------------------------------------------------------------------------------------------
Number of cycles
representing maximum Number of cycles for
Vehicle type Service life service life for which which the container
(years) the container does not leaks without burst, or
leak nor burst does not leak nor burst
----------------------------------------------------------------------------------------------------------------
Light......................................... 25 7,500 7,501-22,000
Heavy......................................... 25 11,000 11,001-22,000
----------------------------------------------------------------------------------------------------------------

NHTSA seeks comment on the proposed number of cycles in Table-2.
NHTSA seeks any additional data available related to vehicle life,
lifetime miles travelled, and number of lifetime fuel cycles.
c. Details of the Baseline Initial Cycle Test for Containers on Light
and Heavy Vehicles
The low pressure during each cycle has been set at between 1 MPa to
2 MPa. This is selected to make the test easy to conduct. NHTSA seeks
comment whether this low-pressure range is sufficiently wide for test
lab efficiency. The high pressure of 125 percent NWP is selected
because this is the peak pressure that typically occurs during fueling.
Furthermore, this is the high pressure used in the ANSI NGV 2-2007,
Compressed Natural Gas Vehicle Fuel Containers, ambient cycling
test.\53\
---------------------------------------------------------------------------

\53\ ANSI NGV 2-2007, Compressed Natural Gas Vehicle Fuel
Containers, 16.3 Ambient Cycling Test. <a href="https://webstore.ansi.org/standards/csa/ansingv22007">https://webstore.ansi.org/standards/csa/ansingv22007</a>.
---------------------------------------------------------------------------

GTR No. 13 requires three new containers to be tested during the
baseline initial pressure cycle test. However, NHTSA does not believe
three new containers need 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 has instead decided to base the
value on the results of testing any one container for the baseline
initial pressure cycle test. NHTSA seeks comment on this decision.
---------------------------------------------------------------------------

\54\ Id.
---------------------------------------------------------------------------

GTR No. 13's maximum hydraulic pressure cycle rate of 10 cycles/
minute is based on the requirement in ANSI NGV 2-2007 for the ambient
cycling test.\54\ This pressure cycling rate is selected to allow for
efficient compliance testing. Actual fueling cycles for hydrogen
vehicles occur more slowly. For these reasons, 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. Changing the hydraulic
cycling profile does not

[[Page 27514]]

change the stringency of the test or the safety of the container.
However, the cycling profile can be important because testing NHTSA
conducted resulted in a container failure attributed to a rapid
defueling profile that was not representative of defueling rates during
normal use.55 56 NHTSA seeks comment on cycling profiles and
whether the pressure cycling profile will significantly affect the test
result. NHTSA seeks comment on more specifics of what manufacturers
should be allowed to specify regarding an appropriate pressure cycling
profile for testing their system.
---------------------------------------------------------------------------

\55\ DOT HS_812_988. Hydrogen Container Performance Testing,
<a href="https://rosap.ntl.bts.gov/view/dot/62645">https://rosap.ntl.bts.gov/view/dot/62645</a>.
\56\ Details are provided in the technical document ``Quantum
GTR Pressure Cycle Discussion.pdf'' submitted to the docket of this
NPRM.
---------------------------------------------------------------------------

A burst may be preceded by an instantaneous moment of leakage,
especially if observed in slow motion. Therefore, NHTSA proposes a
minimum time of 3 minutes to sustain a visible leak before the test can
end successfully due to ``leak before burst.'' NHTSA seeks comment on
this additional requirement.
5. Test for Performance Durability
The container must withstand stress factors beyond basic
pressurization and pressure cycling without leakage or burst. The
container must demonstrate its durability by not leaking or bursting
during a service life of pressure cycling that includes the application
of external stress factors. The container must also withstand 180
percent NWP for four minutes \57\ after the application of all the
external stress factors and have a burst pressure that is at least 80
percent of its BP<INF>O</INF> at the end of a service life that
includes external stress factors. This requirement is evaluated by the
test for performance durability. The test for performance durability
uses the same service life described above for the tests for baseline
metrics, along with external stress factors applied to the container.
---------------------------------------------------------------------------

\57\ The 180 percent NWP hold for 4 minutes is a simulation of a
fueling station pressure regulation failure that results in over
pressurization of the container. This test is conducted after all
other external stresses have been applied to the container to
simulate over-pressurization near the end-of-life of the container.
---------------------------------------------------------------------------

A container is expected to encounter six types of external stress
factors:

1. Impact (drop during installation and/or road wear)
2. Static high pressure from long-term parking
3. Over-pressurization from fueling and fueling station malfunction
4. Environmental exposures (chemicals and temperature/humidity)
5. Vehicle fire
6. Vehicle crash

The test for performance durability addresses the first four of
these external stresses. Fire is addressed in a separate section for
fire. Crash performance is addressed through crash testing in FMVSS No.
307. The test for performance durability is closely consistent with the
industry standard SAE J2579_201806, Standard for Fuel Systems in Fuel
Cell and Other Hydrogen Vehicles.\58\
---------------------------------------------------------------------------

\58\ 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>
---------------------------------------------------------------------------

Other than fire and vehicle crash, testing of the stresses
compounded in a series is required.\59\ This 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. For example, a container that was dropped during
installation could thereafter be exposed to road wear, long term
parking, fueling stresses, and environmental exposures. Accordingly,
the proposed test for performance durability arranges these external
stresses in a sequential application representing a severe in-service
permutation of the stresses. The test sequence is as follows:
---------------------------------------------------------------------------

\59\ This is in contrast to industry standards, wherein
performance is evaluated after the application of a single stress
factor in order to identify which stress factors cause failure.

<bullet> Proof pressure test
<bullet> Drop test
<bullet> Surface damage test
<bullet> Chemical exposure test and ambient-temperature pressure
cycling test
<bullet> High temperature static pressure test
<bullet> Extreme temperature pressure cycling test
<bullet> Residual pressure test
<bullet> Residual strength burst test

The test for performance durability is illustrated in Figure-4.

[[Page 27515]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.003

Figure-4: Illustration of the Test for Performance Durability

For similar reasons as those explained above for the baseline
tests, the cycling pressure force on containers is applied
hydraulically with non-corrosive fluid such as water or a mixture of
anti-freeze and water to prevent freezing. This allows for improved
test lab safety and faster pressurization and depressurization rates
which decreases the cost to conduct the tests.
a. Proof Pressure Test
The proof pressure test is typically done by the manufacturer
before sale of the container. The proof pressure test is performed to
confirm that the container will not leak nor burst due to a simple
over-pressurization event to 150 percent NWP. The test pressure of 150
percent NWP is selected because fueling stations are expected to
provide over-pressure protection of 150 percent NWP. A proof pressure
test is a stress factor that can in some cases result in micro-cracks
appearing in the container. Micro-cracks may weaken a tank's wall
strength, causing the potential for leaks or a burst during the proof
pressure test or the subsequent performance durability testing.
Therefore, it is important that all containers experience proof
pressure.
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 proposes 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. However, it is not expected
that a second application will result in significantly more stress to
the container than a single proof pressure test. NHTSA seeks comment on
conducting the proof pressure test on all containers.
b. Drop Test
The drop test is conducted to simulate dropping the container
during handling or installation. Consistent with GTR No. 13, the
unpressurized container may be dropped in any one of several
orientations such as horizontal, vertical, or at a 45[deg] angle. In
the case of a non-cylindrical or asymmetric container, the horizontal
and vertical axes may not be clear. In such cases, 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 seeks 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.
The surface onto which the container is dropped must be a smooth,
horizontal, uniform, dry, concrete pad or other flooring type with
equivalent hardness. The drop height of 1.8 meters is selected to
represent a drop from a forklift during installation. The four possible
drop orientations are illustrated in Figure-5 below.

[[Page 27516]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.004

Figure-5: The Four Possible Drop Orientations

GTR No. 13 specifies a potential energy of at least 488 J during
the vertical drops, along with a maximum drop height of 1.8 m, and a
minimum drop height of 0.1 m. It is possible that a drop involving a
very lightweight container could not simultaneously satisfy both the
488 J minimum energy and the 1.8 m maximum height. The IWG of GTR No.
13 Phase 2 resolved this conflict by specifying the vertical drop test
potential energy of at least 488 J, with an overriding limitation that
the drop height not exceed 1.8 m in any case. In the case of a
lightweight container that would require a drop height over 1.8 m to
reach 488 J of drop energy, the container should be dropped from 1.8 m,
regardless of the potential energy. Similarly, a very heavy container
could reach a potential energy \60\ of 488 J while being less than 0.1
m above the drop surface. In this case, the container should be dropped
from the 0.1 m minimum drop height.
---------------------------------------------------------------------------

\60\ Potential energy is calculated as the product of container
mass, gravitational acceleration, and the height from the center of
gravity of the container to the surface onto which the container is
dropped.
---------------------------------------------------------------------------

For the angled drop, the container is dropped from any angle
between 40[deg] and 50[deg] from the vertical orientation with the
center of any shut-off valve interface location downward. However, if
the lowest point of the container is closer to the ground than 0.6 m,
the drop angle is changed such that the lowest point of the container
is 0.6 m above the ground and the center of gravity is 1.8 m above the
surface onto which it is dropped. This may result in a drop angle
greater than 50[deg] from the vertical orientation.
The drop test is conducted with an unpressurized container because
the risk of dropping is primarily aftermarket during vehicle repair
where a new storage system, or an older system removed during vehicle
service, is dropped from a forklift during handling. Additionally, drop
testing conducted by NHTSA under various conditions indicated that an
unpressurized container is more susceptible to damage in the drop test
than a pressurized container.\61\
---------------------------------------------------------------------------

\61\ DOT HS_812_988. Hydrogen Container Performance Testing,
<a href="https://rosap.ntl.bts.gov/view/dot/62645">https://rosap.ntl.bts.gov/view/dot/62645</a>.
---------------------------------------------------------------------------

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 seeks comment on
including container attachments for the drop test.
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. To address this possibility, NHTSA proposes
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.
c. Surface Damage Test
The surface damage test applies cuts and impacts to the surface of
the container. The cuts on the surface simulate abrasions that can
occur due to container mounting hardware or straps. The impacts
simulate on-road impacts, such as flying gravel. The surface damage
test consists of two linear cuts and five pendulum impacts.
The linear cuts are created with a saw. The first cut is 0.75
millimeters to 1.25 millimeters deep and 200 to 205 millimeters long.
The second cut is 1.25 millimeters to 1.75 millimeters deep and 25
millimeters to 28 millimeters long. The second cut is only applied if
the container is to be affixed to the vehicle by compressing its
composite surface.
GTR No. 13 allowed all-metal containers to be exempt from the
linear cuts because (1) metal is scratch resistant compared to non-
metal, and (2) metal containers can be so thin that the cuts would
fully penetrate the container. NHTSA's proposal includes this
exemption, but NHTSA seeks 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.
The impacts are created with a pendulum impactor consisting of a
pyramid with equilateral faces and square base, and with the summit and
edges being rounded to a radius of 3 mm. The impact of the pendulum
occurs with a nominal impact energy of 30 J. Prior to the impacts, the
container is preconditioned at -40 [deg]C to simulate a worst-case
temperature environment. The temperature of -40 [deg]C was selected
based on industry standards.\62\ We note that weather records show
temperatures

[[Page 27517]]

of -40 [deg]C can occur in northern locations of the United States.\63\
---------------------------------------------------------------------------

\62\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles.
\63\ Canadian Climate Normals, <a href="https://climate.weather.gc.ca/climate_normals/index_e.html">https://climate.weather.gc.ca/climate_normals/index_e.html</a>.
---------------------------------------------------------------------------

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. However, NHTSA is concerned that 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 is not proposing a specification involving
the accessibility of the container surface. Instead, NHTSA proposes
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. 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. Container attachments that cannot
be removed are included for the test. NHTSA seeks comment on including
container attachments for the surface damage test.
In accordance with GTR No. 13, NHTSA proposes specifying 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 is not proposing
this distinction for pendulum impact location for containers with
multiple permanently interconnected chambers because NHTSA is concerned
that it may be less stringent (and thus, potentially less protective of
safety) than when impacts are to the same chamber where the cuts were
applied. NHTSA seeks 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.
d. Chemical Exposure and Ambient Pressure Cycling Test
Consistent with GTR No. 13, the chemical exposure test exposes the
container to a range of chemicals that might be encountered in on-road
service:
<bullet> Sulfuric acid at 19 percent in water to simulate battery
acid.
<bullet> Sodium hydroxide at 25 percent in water to simulate lye.
<bullet> Methanol at 5 percent in gasoline to simulate fueling
station fluids.
<bullet> Ammonium nitrate at 28 percent in water to simulate
fertilizer.
<bullet> Methanol at 50 percent in water to simulate windshield-
washer fluid.
A pad of glass wool saturated with one of the chemicals listed
above is applied to each of the pendulum impact locations from the
surface damage test. This is done to simulate each chemical exposure in
an area where on-road damage has degraded the container's protective
coating. The chemicals are applied with glass wool fibers to keep them
in place and reduce evaporation.
After the chemical exposures are in place, pressure cycling
commences. 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. Of the total cycles, 60 percent are conducted with the
chemical exposures in place, and at ambient temperature (5 [deg]C to 35
[deg]C). All but the final 10 of these chemical exposure cycles are
conducted from low pressure of 2 MPa to high pressure of 125 percent
NWP, as in the baseline initial pressure cycle test. These cycles
simulate extended vehicle use after impact damage and exposure to
chemicals.
The final 10 chemical exposure cycles are conducted to a high
pressure of 150 percent NWP to simulate fueling station over-
pressurization. After completing chemical exposure cycles, the chemical
exposure pads are removed, and the exposed areas are washed with water
to remove excess chemicals.
The chemical exposure test is a test in which container attachments
may improve performance by shielding the container from the chemical
exposures. Container attachments will be included in the chemical
exposure test unless they were removed prior to the surface damage
test. NHTSA seeks comment on including container attachments for the
chemical exposure test.
e. High Temperature Static Pressure Test
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. This test simulates an extended exposure to high static
pressure and temperature, which is a condition that could occur in the
case of a vehicle parked for an extended period of time. The primary
risk associated with prolonged parking at high pressure and temperature
is stress rupture. However, the stress rupture condition cannot be
directly replicated because the relevant time period is years to
decades. Alternatively, experimental data on the tensile stress failure
of strands representative of those used in container composite wrapping
showed that: 64 65
---------------------------------------------------------------------------

\64\ SAE Paper 2009-01-0012. Rationale for Performance-based
Validation Testing of Compressed Hydrogen Storage by Christine S.
Sloane.
\65\ Christine S. Sloane, Hydrogen Storage technology--Materials
and Applications, edited by Lennie Klebanoff, Section III-12 with
Figure 12.6 Glass fiber composite strands.
---------------------------------------------------------------------------

<bullet> For the glass fiber composite strands, the probability of
failure for 25 years under tensile stress of 100 percent NWP is
equivalent to 1000 hours under a tensile stress of 125 percent NWP.
<bullet> The time to failure increased when the load was reduced.
<bullet> Carbon fiber composite strands showed greater resistance
to stress rupture than glass fiber composite strands in that a small
reduction in the applied load resulted in a greater increase in time to
failure for the carbon fiber composite strands than for the glass fiber
composite strands.
<bullet> For carbon fiber composite strands, the probability of
failure for 25 years under tensile stress of 100 percent NWP is
approximately equivalent to 500 hours under tensile stress of 125
percent NWP.
An elevated temperature of 85 [deg]C is applied to account for
heat-accelerated deterioration. The temperature of 85 [deg]C represents
an extreme under-hood temperature for a dark/black-colored vehicle
parked outside on asphalt in direct sunlight in 50 [deg]C ambient
conditions.\66\ Including the extreme temperature condition of 85
[deg]C in the high temperature static pressure test ensures that the
container can sustain exposure to 85 [deg]C for 1000 hours under
tensile stress of 125 NWP without experiencing stress rupture.
---------------------------------------------------------------------------

\66\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles.
---------------------------------------------------------------------------

f. Extreme Temperature Pressure Cycling Test
Consistent with GTR No. 13, the extreme temperature pressure
cycling test involves pressure cycling at extreme temperatures and
simulates operation

[[Page 27518]]

(fueling and defueling) in extreme temperature conditions. As mentioned
above, 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. The cold temperature -40 [deg]C is selected to simulate a
worst-case extreme cold environment as explained above for the surface
damage test, and the hot temperature of 85 [deg]C is selected for the
same reasons discussed above for the high temperature static pressure
test. During the cold pressure cycling, the maximum cycling pressure is
only 80 percent NWP. This is because fueling pressures do not reach 100
percent NWP when fueling in extreme cold because as temperature
decreases, pressure also decreases. During the hot pressure cycling,
the maximum cycling pressure is 125 percent NWP for the reasons
discussed above for the baseline initial pressure cycle test.
During the extreme temperature pressure cycling test, the relative
humidity is maintained above 80 percent to represent high humidity that
may foreseeably be encountered in the U.S. Humidity is known to degrade
some materials due to the presence of moisture in humid air. Therefore,
it is important to include the stress factor of humidity in the test
for performance durability.
g. Residual Pressure Test
Consistent with GTR No. 3, the residual pressure test requires
pressurizing the container to 180 percent NWP and holding this pressure
for 4 minutes. The 180 percent NWP hold for 4 minutes is a simulation
of a fueling station pressure regulation failure that results in over-
pressurization of the container. This test is conducted after all other
external stresses have been applied to the container to simulate over-
pressurization near the end of life of the container.67 68
---------------------------------------------------------------------------

\67\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles. Appendix H.
\68\ Christine S. Sloane, Hydrogen Storage technology--Materials
and Applications, edited by Lennie Klebanoff, Section III-12 with
Figure 12.6 Glass fiber composite strands.
---------------------------------------------------------------------------

h. Residual Strength Burst Test
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 effectively
controls the burst pressure degradation rate throughout an extreme
service life. Controlling degradation rate is important because, for
example, a container starting with a very high BP<INF>O</INF>, say 400
percent NWP, but then declining to 180 percent NWP indicates a high
degradation rate. NHTSA is concerned that if such a container were to
be kept in service beyond its intended service life, the high
degradation rate could continue and lead to a high risk of burst.
Therefore, the residual burst strength must be at least 80 percent of
BP<INF>O</INF>. This concept is similar to the requirements for seat
belt webbing in FMVSS No. 209 where both minimum breaking strength
after abrasion (S4.2d) as well as maximum degradation rate after
exposure to light and micro-organisms (S4.2e and S4.2f) are controlled.
6. Test for Expected On-Road Performance
For ensuring safe operations, the CHSS must contain hydrogen
without leakage or burst. The expected on-road performance test ensures
the CHSS is able to effectively contain hydrogen without leakage or
burst. Consistent with GTR No. 13, the test for expected on-road
performance uses on-road operating conditions including fueling and
defueling the container at different ambient conditions with hydrogen
gas at low and high temperatures. The test also includes a static high-
pressure hold during which the CHSS is evaluated for hydrogen leakage
and/or permeation of hydrogen from the CHSS. The container of the CHSS
must withstand 180% NWP hold for 4 minutes and have a burst pressure
that is at least 80 percent of its BP<INF>O</INF> at the end of the
test for expected on-road performance. The test for expected on-road
performance is closely consistent with the industry standard SAE
J2579_201806.\69\
---------------------------------------------------------------------------

\69\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell
and Other Hydrogen Vehicles.
---------------------------------------------------------------------------

While the test for performance durability evaluates the durability
of the container when exposed to external stress factors combined with
hydraulic pressure cycling, the test for expected on-road performance
does not evaluate durability and instead focuses on pneumatic hydrogen
fueling exposure, along with extreme temperature conditions. When
fueling, hydrogen gas increases its temperature due to the Joule
Thomson effect.\70\ As a result, pneumatic testing with hydrogen gas
creates rapid temperature swings within the CHSS that do not occur
during hydraulic cycling. Pneumatic testing also can result in hydrogen
diffusion into materials, which can have deleterious chemical effects
such as hydrogen embrittlement.\71\ Due to these unique stress factors,
a pneumatic test using hydrogen gas is an effective method for
evaluating the susceptibility of the CHSS to hydrogen permeation and
leakage.
---------------------------------------------------------------------------

\70\ For more information, see <a href="https://www.britannica.com/science/Joule-Thomson-effect">https://www.britannica.com/science/Joule-Thomson-effect</a>.
\71\ For more information, see https://www.sciencedirect.com/
topics/engineering/hydrogen-
embrittlement#:~:text=3.7%20Hydrogen%20Embrittlement-
,Hydrogen%20embrittlement%20(HE)%20refers%20to%20mechanical%20damage%
20of%20a%20metal,when%20hydrogen%20atoms%20are%20generated.
---------------------------------------------------------------------------

Again, consistent with GTR No. 13, the test for expected on-road
performance starts with a proof pressure test pressurizing the
container with hydrogen to 150 percent NWP. This is followed by a total
of 500 pressure cycles at various environmental conditions. The 500
cycles are broken up into stages for low temperature cycling, high
temperature cycling, and ambient temperature cycling. Table-3 shows the
number of cycles during each stage, along with other applicable
conditions. After the first 250 cycles, the CHSS is held at high
pressure and temperature for up to 500 hours while it is evaluated for
leakage and/or permeation. After the completion of all 500 cycles, the
CHSS is again held at high pressure and temperature for 500 hours and
evaluated for leakage and/or permeation.
Following this second leakage/permeation evaluation, the container
is pressurized with hydraulic fluid to 180% NWP and held for 4 minutes.
The container then undergoes a residual strength burst test in a
similar manner as that described for the test for performance
durability. Similar to the test for performance durability, the
container's residual burst pressure must be at least 80 percent of
BP<INF>O.</INF> A visual schematic of the test is shown in Figure-6
below.

[[Page 27519]]

Table 3--Summary of the Test for Expected On-Road Performance
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of
Stage of test cycles Ambient conditions Fuel delivery temperature Pressurization medium
--------------------------------------------------------------------------------------------------------------------------------------------------------
Pneumatic proof pressure test to 150% not appliable 5.0 [deg]C to 35.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
NWP. [deg]C.
Low temperature cycling.............. 5 -30.0 [deg]C to -25.0 15.0 [deg]C to 25.0 [deg]C............ Hydrogen gas.
[deg]C.
Low temperature cycling.............. 20 -30.0 [deg]C to -25.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C.
High temperature cycling............. 25 50.0 [deg]C to 55.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C.
80% to 100% relative
humidity.
Ambient temperature cycling.......... 200 5.0 [deg]C to 35.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C.
Static pressure for up to 500 hours not appliable 55.0 [deg]C to 60.0 not appliable......................... Hydrogen gas.
with leak/permeation evaluation. [deg]C.
High temperature cycling............. 25 50.0 [deg]C to 55.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C, 80% to 100%
relative humidity.
Low temperature cycling.............. 25 -30.0 [deg]C to -25.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C.
Ambient temperature cycling.......... 200 5.0 [deg]C to 35.0 -40.0 [deg]C to -33.0 [deg]C.......... Hydrogen gas.
[deg]C.
Static pressure for up to 500 hours not appliable 55.0 [deg]C to 60.0 not appliable......................... Hydrogen gas.
with leak/permeation evaluation. [deg]C.
Residual pressure test............... not applicable not applicable......... not applicable........................ Hydraulic fluid.
Burst test........................... not applicable not applicable......... not applicable........................ Hydraulic fluid.
--------------------------------------------------------------------------------------------------------------------------------------------------------

[GRAPHIC] [TIFF OMITTED] TP17AP24.005

Figure-6: Illustration of the Test for Expected On-Road Performance

a. Proof Pressure Test
The proof pressure test is conducted in the same manner and for the
same reasons discussed above for the test for performance durability.
However, in this test, the container is pressurized to 150 percent NWP
using hydrogen gas which has been pre-cooled to -40.0 [deg]C to -33.0
[deg]C. This is the temperature range to which hydrogen fueling
stations typically pre-cool hydrogen to offset the hydrogen's
temperature increase during fueling.

[[Page 27520]]

b. Ambient and Extreme Temperature Gas Pressure Cycling Test
The expected lifetime fueling exposure consists of 500 fuel cycles
from 2 MPa to 125 percent NWP (empty-to-full) under a variety of
ambient fueling temperatures. The number 500 is obtained through a
calculation of expected vehicle lifetime driving range divided by
driving range per full-fueling. This calculation and the data source is
summarized in Table-4.

Table 4--Maximum Number of Full Fueling/Defueling Cycles
------------------------------------------------------------------------
Expected vehicle Expected vehicle Expected worst-
lifetime driving driving range case number of
range per full-fueling full-fueling
------------------------------------------------------------------------
Data source......... Sierra Research 2006-2007 market ..............
Report No. SR data of high
2004-09-04, volume
September 22, passenger
2004. vehicle
manufacturers
in Europe,
Japan, North
America.
Calculation......... 250,000 km 483 km (300 500
(155,000 miles). miles).
------------------------------------------------------------------------

Some vehicles may exceed 500 fuel cycles if partial fueling occurs
in the vehicle lifetime. However, the stress of full fueling exceeds
the stress of partial fueling because of the higher pressure and
temperature change during full-fueling. NHTSA believes that, as a
result, 500 full-fueling cycles should provide robust demonstration of
leak-free fueling capability.
The industry standard SAE J2601_202005 Fueling protocols for light
duty gaseous hydrogen surface vehicles establishes industry-wide
fueling protocols for the fueling of hydrogen into passenger vehicles.
The guidelines include: \72\
---------------------------------------------------------------------------

\72\ SAE J2601_202005. Fueling Protocols for Light Duty Gaseous
Hydrogen Surface Vehicles. <a href="https://www.sae.org/standards/content/j2601_202005/">https://www.sae.org/standards/content/j2601_202005/</a>.

1. The maximum pressure within the vehicle fuel system is 125 percent
NWP
2. Gas temperature within the vehicle fuel system is less than or equal
to 85 [deg]C
3. Fuel flow rate at dispenser nozzle is less than or equal to 60 g/s
4. The dispenser is capable of dispensing fuel at temperatures between
-40 [deg]C and -33 [deg]C

These guidelines are applied at hydrogen fueling stations when
fueling hydrogen vehicles. During the ambient and extreme temperature
gas pressure cycling test, the rate of pressurization must be greater
than or equal to the ramp rate specified by a table of ramp rates based
on SAE J2601_202005, according to the CHSS volume, the ambient
conditions, and the fuel delivery temperature. If the required ambient
temperature is not available in the table, the closest ramp rate value
or a linearly interpolated value is used. This ensures that the fueling
cycles are similar to those that would occur during on-road service.
Table-5 shows the ramp rates based on SAEJ2601_202005, for different
CHSS volume, the ambient conditions, and the fuel delivery temperature.
GTR No. 13 specifies that the pressure ramp rate shall be decreased if
the measured internal temperature in the container exceeds 85 [deg]C.

Table 5--Pressure Ramp Rates for the Test for Expected On-Road Performance
--------------------------------------------------------------------------------------------------------------------------------------------------------
CHSS pressurization rate (MPa/min)
---------------------------------------------------------------------------------------------------
50.0 [deg]C to 55.0 5.0 [deg]C to 35.0 -30.0 [deg]C to -25.0 -30.0 [deg]C to -25.0
CHSS volume (L) [deg]C ambient [deg]C ambient [deg]C ambient [deg]C ambient
conditions -33.0 [deg]C conditions -33.0 [deg]C conditions -33.0 [deg]C conditions 15.0 [deg]C
to -40.0 [deg]C fuel to -40.0 [deg]C fuel to -40.0 [deg]C fuel to 25.0 [deg]C fuel
delivery temperature delivery temperature delivery temperature delivery temperature
--------------------------------------------------------------------------------------------------------------------------------------------------------
50.................................................. 7.6 19.9 28.5 13.1
100................................................. 7.6 19.9 28.5 7.7
174................................................. 7.6 19.9 19.9 5.2
250................................................. 7.6 19.9 19.9 4.1
300................................................. 7.6 16.5 16.5 3.6
400................................................. 7.6 12.4 12.4 2.9
500................................................. 7.6 9.9 9.9 2.3
600................................................. 7.6 8.3 8.3 2.1
700................................................. 7.1 7.1 7.1 1.9
1000................................................ 5.0 5.0 5.0 1.4
1500................................................ 3.3 3.3 3.3 1.0
2000................................................ 2.5 2.5 2.5 0.7
2500................................................ 2.0 2.0 2.0 0.5
--------------------------------------------------------------------------------------------------------------------------------------------------------

Extreme environmental temperatures around the world are summarized
in Table-6. To ensure safety in extremely hot conditions, some fueling
pressure cycles are conducted at 50 [deg]C. To ensure safety in
extremely cold conditions, consistent with GTR No. 13 Phase 2
amendments, some fueling pressure cycles are conducted at -25 [deg]C.
The temperature -25 [deg]C is used instead of -40 [deg]C because
testing at -40 [deg]C is impractical during the test for expected on-
road performance. Specifically, a test apparatus must operate at well
below -40 [deg]C in order to maintain the temperature surrounding the
CHSS at -40 [deg]C. In addition, at -40 [deg]C, test laboratories
encounter difficulties such as freezing valves and failing o-ring
seals. This can significantly increase test cost. Furthermore, testing
conducted by

[[Page 27521]]

NHTSA found that, for the test for expected on-road performance,
testing at -25 [deg]C yields the same results as testing at -40
[deg]C.\73\ This change does not compromise the safety intent of the
test because in-tank gas temperatures will reach -40 [deg]C due to gas
expansion during depressurization. In addition, pressure cycling under
the extreme cold condition of -40 [deg]C is tested separately during
the test for performance durability. Therefore, -25 [deg]C is proposed
as the extreme cold temperature for the test for expected on-road
performance, which is consistent with the Phase 2 amendment to GTR No.
13. In summary, NHTSA is proposing 50 [deg]C for the high temperature
pressure cycles and -25 [deg]C for the cold temperature pressure
cycles.
---------------------------------------------------------------------------

\73\ DOT HS_811_832. Cumulative Fuel System Life Cycle and
Durability Testing of Hydrogen Containers, <a href="https://www.nhtsa.gov/sites/nhtsa.gov/files/811832.pdf">https://www.nhtsa.gov/sites/nhtsa.gov/files/811832.pdf</a>.

Table 6--Extreme Environmental Temperatures Around the World
----------------------------------------------------------------------------------------------------------------
Extremes of
Frequency of sustained ambient
Temperature Areas that occurs exposure to this environmental
temperature (year) temperature used
for this test
----------------------------------------------------------------------------------------------------------------
Around 50 [deg]C...................... desert areas of lower 5 percent................ 50 [deg]C
latitude countries.
Less or equal to -40 [deg]C........... countries north of the 5 percent................ -40 [deg]C
45th parallel.
Less than -30 [deg]C.................. countries north of the 5 percent of vehicle life ..................
45th parallel.
----------------------------------------------------------------------------------------------------------------
Data source: Environment Canada 1971-2000.

As described above, hydrogen fueling stations typically pre-cool
hydrogen to between -40 [deg]C and -33 [deg]C. However, a fueling
station failure could result in the fueling station delivering hydrogen
at ambient temperature. This would lead to very high temperatures
inside the CHSS after a full fueling. To account for this risk, the
first 5 cycles in the ambient and extreme temperature gas pressure
cycling test are conducted with hydrogen fuel at between 15 [deg]C and
25 [deg]C, as opposed to the pre-cooled hydrogen between -40 [deg]C and
-33 [deg]C which is used for the remaining 495 cycles.
All pressure cycles are performed to 100 percent state-of-charge
(SOC). SOC is defined by the ratio of hydrogen density at a given
temperature and pressure to hydrogen density at NWP and 15 [deg]C.\74\
Specifying 100 percent SOC ensures an equivalent quantity of hydrogen
in the CHSS regardless of the resulting temperature and pressure. For
example, 100 percent NWP at 15 [deg]C corresponds to 80 percent NWP at
-40 [deg]C. In either case, however, the CHSS is at 100 percent SOC
(fully fueled).
---------------------------------------------------------------------------

\74\ Since the hydrogen gas density varies nonlinearly with
temperature and pressure, a table is provided in the regulatory text
for hydrogen density at different pressures and temperatures.
---------------------------------------------------------------------------

The first 10 cycles (cold cycles) are performed with the CHSS
stabilized with the external air temperature surrounding the CHSS at -
25 [deg]C at the beginning of the cycle. This ensures there is no
residual heat present from the previous fueling cycle and maximizes the
severity of the cold external temperature. However, the process to
equilibrate a storage system is time-consuming. As a result, the next
15 cycles are performed with an external air temperature surrounding
the CHSS of -25 [deg]C, but without CHSS equilibration to the external
temperature.
The next 25 cycles are performed with an external temperature of 50
[deg]C. For the first 5 of these cycles, the CHSS is stabilized with
the external air temperature surrounding the CHSS at the at the
beginning of the cycle. At this point, the external temperature to the
system is at its hottest, and the CHSS pressure is at its minimum. The
fueling process will then progressively heat the contents of the CHSS
until full (100 percent SOC). At this point, the CHSS reaches its
hottest possible interior temperature. In addition, these 25 cycles are
performed with the relative humidity over 80 percent surrounding the
CHSS. This adds the stress of excessive humidity which is common in
extreme hot climates. Specifically, the high humidity keeps a thin film
of water on surfaces where dissimilar metals may be in contact, such as
valve to tank interfaces or valve body to valve connection interfaces.
This water film adds the necessary conduction path to effect galvanic
corrosion. Galvanic corrosion can cause pitting and other forms of
metal loss which can degrade the strength of materials and impact
sealing surfaces. Therefore, it is important to include the stress
factor of humidity in the test for expected on-road performance
The next 200 cycles are performed with ambient external temperature
of (5 [deg]C to 35 [deg]C). This represents a normal ambient
temperature. After these 200 cycles (at a total cycle count of 250),
the extreme temperature static gas pressure leak/permeation test is
performed. This test is discussed in the next section. However, after
the completion of the permeation test, pressure cycling continues for
an additional 250 cycles.
The first 25 of these additional cycles (cycle count 251-275) are
performed with the extreme hot external temperature of 50 [deg]C. The
next 25 cycles (cycle count 276-300) are performed with the extreme
cold temperature -25 [deg]C. In this series, the order of extreme hot
and cold cycles is switched. This accounts for compounding stress from
transitioning from hot cycling to cold cycling, as opposed to the
previous series, which transitioned from cold to hot. The final 200
cycles (cycle count 301-500) are performed with ambient external
temperature of 5 [deg]C to 35 [deg]C. After the completion of cycling,
the extreme temperature static gas pressure leak/permeation test is
performed for a second time.
GTR No. 13 states that if system controls that are active in
vehicle service prevent the pressure from dropping below a specified
pressure, the test cycles during the ambient and extreme temperature
gas pressure cycling test must not go below that specified pressure. In
addition, GTR No. 13 states that if devices and/or controls are used in
the intended vehicle application to prevent an extreme internal
temperature, the test may be conducted with these devices and/or
controls in place. However, NHTSA's approach to testing involves the
agency independently purchasing (on the open market) and then testing
vehicles. With this approach, NHTSA has no way of determining what
system controls and/or devices are active in the vehicle,

[[Page 27522]]

because this information is typically proprietary and is not publicly
available. As a result, all cycles would be performed with an initial
pressure of between 1 MPa and 2 MPa and extreme internal temperatures
will not be prevented during cycling. Furthermore, and importantly for
safety, this is a condition that could occur in the event the system
controls and/or devices fail in service.
c. Extreme Temperature Static Gas Pressure Leak/Permeation Test
Leak and permeation are risk factors for fire hazards, particularly
when parking in confined spaces such as garages. The extreme
temperature static gas pressure leak/permeation test is designed to
simulate extended parking in a confined space under an elevated
temperature. In these conditions, hydrogen can leak or permeate from
the CHSS and slowly accumulate in the surrounding air. During the
extreme temperature static gas pressure leak/permeation test, the
pressurized CHSS at 100% SOC is held at 55 [deg]C for a period of up to
500 hours. Any hydrogen leakage and/or permeation from the CHSS cannot
exceed the limit of 46 milliliter/hour (mL/h) per liter of CHSS water
capacity. This limit is discussed below. The test may end before 500
hours if three consecutive hydrogen permeation rates separated by at
least 12 hours are within 10 percent of the prior rate because this
indicates a permeation steady state has been reached. NHTSA seeks
comment on how to accurately measure or otherwise determine the
permeation rate from the CHSS.
The leak/permeation limit is characterized by the many possible
combinations of vehicles and garages, and the associated test
conditions. The leak/permeation limit is defined to restrict the
hydrogen concentration from reaching 25 percent lower flammability
limit (LFL) by volume. The LFL of hydrogen is lowest concentration of
hydrogen in which a hydrogen gas mixture is flammable. National and
international standard bodies (such as National Fire Protection
Association [NFPA] and IEC) recognize 4 percent hydrogen by volume in
air as the LFL.\75\ The conservative 25 percent LFL limit accounts for
concentration non-homogeneities and is equivalent to 1 percent hydrogen
concentration in air.76 77
---------------------------------------------------------------------------

\75\ See Gases--Explosion and Flammability Concentration Limits.
<a href="https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html">https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html</a>.
\76\ Data for hydrogen dispersion behavior, garage and vehicle
scenarios, including garage sizes, air exchange rates and
temperatures, and the calculation methodology are found in the
following reference prepared as part of the European Network of
Excellence HySafe: P. Adams, A. Bengaouer, B. Cariteau, V. Molkov,
A.G. Venetsanos, ``Allowable hydrogen permeation rate from road
vehicles,'' <a href="https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf">https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf</a>.
\77\ NFPA 30A-2015, Code for Motor Fuel Dispensing Facilities
and Repair Garages, 7.4.7.1, <a href="https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=30A">https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=30A</a>.
---------------------------------------------------------------------------

Worst case ventilation in structures where hydrogen vehicles can be
parked is expected to be at or below 0.18 air changes per hour, but the
exact design value is highly dependent on the type and location of
structures in which the vehicles are parked. In the case of light
passenger vehicles, an extremely low air exchange rate (of 0.03
volumetric air changes per hour) has been measured in ``tight'' wood
frame structures (with plastic vapor barriers, weather-stripping on the
doors, and no vents) that are sheltered from wind and are very hot (55
[deg]C) with little daily temperature swings that can cause density-
driven infiltration. The resulting discharge limit for a light vehicle
that tightly fits into a garage of 30.4 cubic meters (m\3\) with 0.03
volumetric air exchange per hour is 150 mL/minute (at 115 percent NWP
for full fill at 55 [deg]C), corresponding to no more than 1 percent
hydrogen concentration in air.
In order to determine the leak/permeation limit for the expected
on-road performance test, consistent with GTR No. 13, the vehicle-level
150 mL/min leak/permeation limit is expressed in terms of allowable
leak/permeation for each container in the storage system at 55 [deg]C
and 115 percent NWP. This corresponds to 46 mL/hour(h)/Liter(L)-water-
capacity for each container in the storage system.\78\ The use of this
limit is applicable to light vehicles that are smaller or larger than
the base described above. If, for example, the total water capacity of
the light vehicle storage system is 330 L (or less) and the garage size
is 50 m\3\, then the 46 mL/h/L-water-capacity requirement results in a
steady-state hydrogen concentration of no more than 1 percent. This can
be shown by calculating the allowable discharge from the light vehicle
based on the requirement of 46 mL/h/L per container volume capacity
(that is, 46 mL/h/L x 330L/(60 min/h) = 253 mL/min) which is similar to
the allowable discharge based on the garage size of 50 m\3\ with an air
exchange rate of 0.03 volumetric air exchanges per hour (that is, 150
mL/min x 50 m\3\/30.4 m\3\ = 247 mL/min). Since both results are
essentially the same, the hydrogen concentration in the garage is not
expected to exceed 1 percent for light vehicles with storage systems of
330L (or less) in 50 m\3\ garages.
---------------------------------------------------------------------------

\78\ Data for hydrogen dispersion behavior, garage and vehicle
scenarios, including garage sizes, air exchange rates and
temperatures, and the calculation methodology are found in the
following reference prepared as part of the European Network of
Excellence HySafe: P. Adams, A. Bengaouer, B. Cariteau, V. Molkov,
A.G. Venetsanos, ``Allowable hydrogen permeation rate from road
vehicles,'' <a href="https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf">https://h2tools.org/sites/default/files/2019-08/paper_-_part_1.pdf</a>.
---------------------------------------------------------------------------

Since the discharge limit has been found to be reasonably scalable
depending on the vehicle size, the discharge limit for alternative
vehicle sizes in tight-fitting garages with 0.03 volumetric air
exchanges per hour can be determined from the 150 mL/minute discharge
limit computed above using a scaling factor R computed as:

R = (V<INF>width</INF>+1) (V<INF>height</INF>+0.5)
(V<INF>length</INF>+1)/30.4

where:

V<INF>length</INF>, V<INF>width</INF>, and V<INF>height</INF> are
the dimensions of the vehicle in meters,

Similarly, the use of 46 mL/h/L-water-capacity requirement for
storage system containers is also scalable to larger medium-duty and
heavy-duty vehicles. Figure-7 shows the required volumetric air
exchange rate that would result in less than 25 percent LFL of hydrogen
by volume in garages of various sized vehicles equipped with CHSS that
have no more than a 46 mL/L/H permeation rate. Examples of current or
currently-planned hydrogen vehicles shown in Figure-7 indicate that the
required ventilation rate for garages of large vehicles (buses and
tractor-trailers) is lower than that of small vehicles (passenger
cars). Light hydrogen vehicles which can possibly be parked in tight
garages (with as low as 0.03 volumetric air changes per hour) are
required to have permeation/leak rate less than of 46 mL/hour(h)/
Liter(L)-water-capacity for each container in the vehicle's CHSS.\79\
Even though medium-duty and heavy-duty vehicles are not expected to be
parked in such ``tight'' garages as is the case with light vehicles, in
order to better meet the safety need, we conservatively assume an
equivalent rate of 0.03 volumetric air exchanges for garages of these
vehicles.
---------------------------------------------------------------------------

\79\ This leak/permeation limit for each container ensures that
the hydrogen concentration is lower than 25 percent of the lower
flammability limit (LFL) by volume and the hydrogen concentration in
air is less than 1 percent.

---------------------------------------------------------------------------

[[Page 27523]]

While it is foreseeable that medium-duty and heavy-duty vehicles may be
parked in more open (naturally-ventilated) or mechanically-ventilated
spaces, the 46 mL/h/L-water-capacity requirement for storage system
containers provides a safety margin in the event of mechanical
ventilation failures.
[GRAPHIC] [TIFF OMITTED] TP17AP24.006

Figure-7: Required Volumetric Air Exchange Rate (Ventilation Rate) of
Enclosed Space Surrounding a Hydrogen Vehicle That Results in Less Than
25 Percent Lower Flammability Limit of Hydrogen by Volume

In addition to the required leak/permeation limit discussed above,
GTR No. 13 also includes a localized leak requirement. This requirement
is based on the SAE technical paper 2008-01-0726, Flame Quenching
Limits of Hydrogen Leaks.\80\ This paper states that the lowest
possible flammable flow for hydrogen is about 0.005 milligrams per
second (mg/s) (3.6 normal millilitres per minute (NmL/min)).\81\ As a
result, if a hydrogen permeation rate over 0.005 mg/s is detected, a
localized leak test ensures that the hydrogen is not all emanating from
the same localized area of the container. This leak test is conducted
as a bubble test. In a bubble test, a surfactant solution is applied
across the CHSS and the tester observes for the formation of bubbles in
the solution resulting from any leaks. If bubbles are detected, the
test lab estimates the leak rate based on the average size of the
bubbles and the number of bubbles generated per unit of time.
---------------------------------------------------------------------------

\80\ SAE Technical report 2008-01-0726. Flame Quenching Limits
of Hydrogen Leaks. Figure 3 to Figure 9. <a href="https://www.sae.org/publications/technical-papers/content/2008-01-0726/">https://www.sae.org/publications/technical-papers/content/2008-01-0726/</a>.
\81\ A normal milliliter, also known as a standard cubic
centimeter, represents the volume a gas would occupy at standard
temperature (0 [deg]C) and standard pressure (1 atmosphere).
---------------------------------------------------------------------------

However, NHTSA is concerned that this requirement would not meet
the Safety Act requirement for FMVSSs to be objective, due to the
subjective estimation of bubble sizes. Therefore, the localized leak
requirement has not been included in FMVSS No. 308. Furthermore, NHTSA
believes that the primary safety risk of accumulating hydrogen is
already addressed by the overall permeation limit of 46 mL/h/L-water-
capacity. NHTSA seeks comment on not including the localize leak
requirement during the extreme temperature static gas pressure leak/
permeation test. If commenters believe it should be included, NHTSA
requests 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.
d. Residual Pressure Test & Residual Strength Burst Test
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.
7. Test for Service Terminating Performance in Fire
Vehicle fire presents a severe risk to the safe containment of
hydrogen. Fire can rapidly degrade the container while simultaneously
increasing the pressure inside the container. To avoid the possibility
of burst, CHSS should be designed to vent their pressurized contents
when exposed to fire. Under the proposed standard, the CHSS must vent
its pressurized hydrogen during the test for service terminating
performance in fire, discussed below, which simulates a vehicle fire.
The CHSS must expel its contents (high pressure hydrogen gas) in a
controlled manner through its TPRD(s) without the occurrence of burst.
A comprehensive examination of CNG container in-service failures
between 2000 and 2008 showed that the majority of fire incidents
occurred on storage systems that did not utilize properly designed
TPRDs.\82\ The in-service failures resulted when TPRDs did not respond
to protect the container due to the lack of adequate heat exposure on
the TPRDs, while a small ``localized'' fire degraded the container wall
elsewhere, eventually causing the container to burst. Prior to GTR. No.
13, localized fire exposure had not been addressed in regulations or
industry standards. The test for service terminating performance in
fire

[[Page 27524]]

addresses both localized and engulfing fires with two respective test
stages.
---------------------------------------------------------------------------

\82\ SAE Technical Paper 2011-01-0251. Establishing Localized
Fire Test Methods and Progressing Safety Standards for FCVs and
Hydrogen Vehicles. <a href="https://www.sae.org/publications/technical-papers/content/2011-01-0251/">https://www.sae.org/publications/technical-papers/content/2011-01-0251/</a>.
---------------------------------------------------------------------------

The test for service terminating performance in fire evaluates the
CHSS. It is possible that vehicle manufacturers may add additional fire
protection features as part of overall vehicle design, and GTR No. 13
includes the option of conducting CHSS fire testing with vehicle
shields, panels, wraps, structural elements, and other features as
specified by the manufacturer. However, adding vehicle-level protection
features is not practical for testing. Furthermore, NHTSA believes that
it is important for safety that the CHSS itself can withstand fire and
safely vent in the event its shielding is compromised--for example, if
a crash damages the shielding, and the shielding was an integral part
of the CHSS's ability to withstand fire, then the CHSS should be able
to vent properly before it explodes. As a result, vehicle-level
protection measures are not evaluated by the test for service
terminating performance in fire. However, if a CHSS includes container
attachments, these attachments are included in the fire test. NHTSA
seeks comment on excluding vehicle-specific shielding and on including
container attachments as part of the fire test, particularly in the
case of container attachments which can be removed using a process
specified by the manufacturer.
The fire test temperature targets set forth in GTR No. 13 are based
on vehicle fire experiments conducted by the Japanese Automobile
Research Institute (JARI).\83\ Some key findings from these vehicle-
level fire experiments are as follows:
---------------------------------------------------------------------------

\83\ Id.
---------------------------------------------------------------------------

<bullet> About 30 to 50 percent of the JARI vehicle fires resulted
in a ``localized'' fire. In these cases, the data indicated the
container could have been locally degraded before TPRDs would have
activated.
<bullet> Thermal gravimetric analysis (TGA) indicated that
composite container materials begin to degrade rapidly at 300 [deg]C.
<bullet> While the vehicle fires often lasted 30-60 minutes, the
period of localized fire container degradation lasted less than 10
minutes.
<bullet> Peak temperatures on the test containers' surfaces reached
700 [deg]C during the localized fire stages.
<bullet> The rise in peak temperature near the end of the localized
fire period often indicated the transition to an engulfing fire.
<bullet> Peak temperatures on the test containers' surfaces reached
1000 [deg]C during the engulfing fire stage.
Based upon these experiments, temperature limits were defined in
GTR No. 13 to characterize the thermal exposure during the localized
and engulfing fire stages:
<bullet> The minimum container surface temperature during the
localized fire stage for the side of the container facing the fire was
set to 450 [deg]C to create a challenging but realistic thermal
condition.
<bullet> The maximum container surface temperature during the
localized fire stage for the side of the container facing the fire and
for the sides of the container was set to 700 [deg]C.
<bullet> The minimum container surface temperature during the
engulfing fire stage on the side of the container facing the fire was
set to 600 [deg]C, because this was the lowest value observed for this
side of the container during the engulfing fire stage.
<bullet> A maximum temperature limit on the bottom of the container
during the engulfing stage was not necessary as the temperature is
naturally limited.
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 limits given in Table-7 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.

Table 7--Pre-Test Checkout Temperature Requirements
----------------------------------------------------------------------------------------------------------------
Temperature range on
Fire stage bottom of pre-test Temperature range on sides Temperature range on top of
container of pre-test container pre-test container
----------------------------------------------------------------------------------------------------------------
Localized.................. 450 [deg]C to 700 less than 750 [deg]C........ less than 300 [deg]C.
[deg]C.
Engulfing.................. Average temperatures of Not applicable.............. Average temperatures of the
the pre-test container pre-test container surface
surface measured at measured at the three top
the three bottom locations must be at least
locations must be 100 [deg]C, and when
greater than 600 greater than 750 [deg]C,
[deg]C. must also be less than the
average temperatures of the
pre-test container surface
measured at the three
bottom locations.
----------------------------------------------------------------------------------------------------------------

In addition to temperature requirements, GTR No. 13 also specifies
required heat release rates per unit area (HRR/A) during the localized
and engulfing fire stages. The HRR/A is calculated using the lower
heating value (LHV) of the fuel, which is measured in megajoules of
energy released per kilogram of fuel consumed. To obtain HRR/A, the
fuel flow rate is multiplied by LHV and then divided by the burner
area. GTR No. 13 specifies a standardized calculation for burner area.
NHTSA has considered the specification for HRR/A and determined that it
could result in over-specification of the test parameters, potentially
making it very difficult to conduct the test. In addition, NHTSA
believes that the detailed temperature specifications for the pre-test
container during the pre-test checkout are sufficient to ensure
repeatability and reproducibility of the test.\84\ Therefore, NHTSA is
not proposing specifications for HRR/A. NHTSA seeks comment on this
decision.
---------------------------------------------------------------------------

\84\ Testing conducted to support enhancement of the fire test
specifications in GTR No. 13 Phase 2 indicated that the container
surface temperature specifications in the pre-test container fire
test along with the burner temperatures provided the needed
repeatability and reproducibility of the test.

---------------------------------------------------------------------------

[[Page 27525]]

The dimensions of the pre-test steel container for the pre-test
checkout are similar to those of the containers from the JARI vehicle
fire tests. The standard pre-test steel container is fabricated from
12-inch Schedule 40 NPS pipe along with end caps. The diameter of this
---------------------------------------------------------------------------
pipe is 12 inches (304 mm), while the length is:

<bullet> at least 800 mm
<bullet> not greater than 1.65 m
<bullet> greater than or equal to the length of the CHSS to be tested,
unless the CHSS is greater than 1.65 m

The pre-test steel container is instrumented with thermocouples in
the same manner as the containers in the JARI vehicle fire tests and
mounted above the burner in the same manner as the CHSS to be fire
tested. Thermocouples are located along the cylindrical section of the
pre-test container at the bottom surface exposed to the burner flame,
mid-height along the left and right side of the cylindrical surface,
and top surface opposite the direct exposure to the burner flame.
Example thermocouple locations are shown below in Figure-8.
[GRAPHIC] [TIFF OMITTED] TP17AP24.007

Figure-8: Thermocouple Locations for the Pre-Test Checkout

The positioning of the pre-test container relative to the localized
and engulfing zones of the burner in the pre-test checkout must be
consistent with the positioning of the CHSS over the burner that is to
be tested.
The three thermocouples along the bottom (labeled TBL25, TBC25,
TBR25 in Figure-8) are considered burner monitor thermocouples. These
thermocouples are positioned 25 mm below the pre-test container. Since
these thermocouples are intended to monitor the burner, an alternative
would be to position these thermocouples relative to the burner itself.
NHTSA seeks comment on whether it is preferable to position the burner
monitor thermocouples relative to the pre-test container or relative to
the burner.
The pre-test checkout is performed at least once before the
commissioning of a new test site. Additionally, if the burner and test
setup is modified to accommodate a test of different CHSS
configurations than originally defined or serviced, then repeat of the
pre-test checkout is needed prior to performing CHSS fire tests. NHTSA
seeks comment on the frequency of conducting this pre-test checkout for
ensuring repeatability of the fire test on CHSS.
After the pre-test checkout is satisfactorily completed, the steel
pre-test container is removed and the CHSS to be fire tested is mounted
for testing. The CHSS fire test is then conducted with fuel flow
settings identical to the pre-test checkout. The profile of the CHSS
fire test is shown in Figure-9. During the CHSS fire test, the only
thermocouples used are the burner monitor thermocouples, which are
positioned 25 mm below the bottom of the CHSS. Temperatures on the
surface of the CHSS will vary naturally based on interactions with the
flames, and these temperatures are not controlled during the CHSS fire
test. The burner monitor thermocouples are used only to ensure the
burner is producing a fire closely matching the pre-test checkout.
The localized fire continues for a total of 10 minutes and then the
test transitions to the engulfing stage which continues until the test
is complete (test completion is discussed below). The minimum value for
the burner monitor temperature during the localized fire stage
(Tmin<INF>LOC</INF>) is calculated by subtracting 50 [deg]C from the
minimum of the 60-second rolling average of the burner monitor
temperature in the localized fire zone of the pre-test checkout. The
minimum value for the burner monitor temperature during the engulfing
fire stage (Tmin<INF>ENG</INF>) is calculated by subtracting 50 [deg]C
from the minimum of the 60-second rolling average of the average burner
monitor temperature in the engulfing fire zone of the pre-test
checkout.

[[Page 27526]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.008

Figure-9: Temperature Profile of the Fire Test

NHTSA has conducted CHSS fire testing to verify the feasibility of
the test for service termination performance in fire as currently
proposed. Overall, the testing was completed successfully,
demonstrating the feasibility of the proposed test for service
terminating performance in fire. The results of this testing are
summarized in the test report GTR No. 13 Fire and Closures Tests.\85\
---------------------------------------------------------------------------

\85\ See the report titled ``GTR No. 13 Fire and Closures
Tests'' submitted to the docket of this NPRM. This report will also
be submitted to the National Transportation Library. <a href="https://rosap.ntl.bts.gov/">https://rosap.ntl.bts.gov/</a>.
---------------------------------------------------------------------------

In some cases during testing, however, temperatures measured at the
burner monitor thermocouples did not satisfy the required
Tmin<INF>ENG</INF>. NHTSA's testing indicated that the airflow during
the pre-test may be different from that of the CHSS if the pre-test
container length is substantially different from that of the CHSS to be
tested. The difference in air flow between the two tests could cause
differences in fire input to the CHSS compared to the pre-test
container. Therefore, NHTSA recommends that for CHSS of length between
600 mm and 1650 mm, the difference in the length of the pre-test
container and the CHSS be no more than 200 mm. NHTSA seeks comment on
whether this recommendation should be a specification for the pre-test
container.
In addition, NHTSA seeks comment on the requirement for
Tmin<INF>ENG</INF>. In particular, NHTSA seeks comment on allowing for
a wider variation than 50 [deg]C below the pre-test temperatures. A
variation of 50 [deg]C is small in the context of fire temperatures,
and such a small variation limit may make the test more difficult for
test labs to conduct. Furthermore, as currently specified,
Tmin<INF>LOC</INF> and Tmin<INF>ENG</INF> would be time-dependent
variables because they are based on a time-dependent rolling average.
Having Tmin<INF>LOC</INF> and Tmin<INF>ENG</INF> being time-dependent
is complex and would make the testing difficult to monitor. NHTSA seeks
comment on a simpler calculation for T<INF>minLOC</INF> and
T<INF>minENG</INF> that will result in constant values for
Tmin<INF>LOC</INF> and Tmin<INF>ENG</INF>. NHTSA proposes that
Tmin<INF>LOC</INF> be calculated by subtracting 50 [deg]C from the
minimum value of the 60-second rolling average of the burner monitor
temperature in the localized fire zone of the pre-test checkout.
Similarly, NHTSA proposes that Tmin<INF>ENG</INF> be calculated by
subtracting 50 [deg]C from minimum value of the 60-second rolling
average of the average of the three burner monitor temperatures during
the engulfing fire stage of the pre-test checkout. NHTSA seeks comment
on whether these revised calculations for T<INF>minLOC</INF> and
T<INF>minENG</INF> should be required.
GTR No. 13 specifies additional pre-test checkout procedures
intended for irregularly shaped CHSS which are expected to impede air
flow through the burner. These procedures involve constructing a pre-
test plate having similar dimensions to the CHSS to be tested. A second
pre-test checkout is conducted using the pre-test plate and using the
burner monitor thermocouples. If the burner monitor thermocouple
temperatures do not satisfy both Tmin<INF>LOC</INF> and
Tmin<INF>ENG</INF>, then the pre-test plate is raised by 50 mm, and a
third pre-test checkout is conducted. GTR No. 13 specifies that this
process is repeated until burner monitor thermocouple temperatures
satisfy Tmin<INF>LOC</INF> and Tmin<INF>ENG</INF>. NHTSA has considered
this additional pre-test process and determined that it is unnecessary.
The goal of the pre-test checkout is a repeatable and reproducible fire
exposure among different testing facilities. NHTSA has determined there
is no need for design-specific modification to the fire test procedure.
Furthermore, the additional pre-test procedures add considerable
complexity to the test procedure, and as a result could undermine the
repeatability and reproducibility of the fire test. Therefore, NHTSA is
not proposing these additional pre-test procedures. NHTSA seeks comment
on this decision. If commenters believe that the additional pre-test
procedures are necessary, NHTSA requests that they explain (1) how they
would improve the safety outcome of the standard, and (2) how they
would improve the

[[Page 27527]]

repeatability and reproducibility of the fire test.
Liquefied petroleum gas, also known as liquified propane gas or
simply LPG, is the selected fuel for the test burner because it is
globally available and easily controllable to maintain the required
thermal conditions. The use of LPG was deemed adequate by the IWG to
reproduce the thermal conditions on the steel container that occurred
during the JARI vehicle fire tests without concerns of carbon formation
that can occur with other liquid fuels. The relatively low hydrogen to
carbon (H/C) ratio of LPG at approximately 2.67 allows the flame to
display flame radiation characteristics (from carbon combustion
products) more similar to petroleum fires (with a H/C of roughly 2.1)
than natural gas, for example, which has an H/C ratio of approximately
4.0. Also, The LPG flame is more uniform and is easier to control than
natural gas and gasoline flames. For this reason, LPG fuel is the
choice for most testing purposes to improve the repeatability and
reproducibility of the test.
To further improve test reproducibility, a burner configuration is
defined in S6.2.5.1 with localized and engulfing fire zones. The burner
configuration specifications are listed in Table-8 below.

Table-8--Burner Specifications
------------------------------------------------------------------------
Item Description
------------------------------------------------------------------------
Nozzle Type............................ Liquefied petroleum gas fuel
nozzle with air pre-mix.
<bullet> LPG Orifice in Nozzle..... 1 mm <plus-minus> 0.1 mm inner
diameter.
<bullet> Air Ports in Nozzle....... Four holes, 6.4 mm <plus-minus>
0.6 mm inner diameter.
<bullet> Fuel/Air Mixing Tube in 10 mm <plus-minus> 1 mm inner
Nozzle. diameter.
Number of Rails........................ Six.
Center-to-center Spacing of Rails...... 105 mm <plus-minus> 5 mm.
Center-to-center Nozzle Spacing Along 50 mm <plus-minus> 5 mm.
the Rails.
------------------------------------------------------------------------

These specifications allow the fire test to be performed without a
burner development program. NHTSA believes that 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. 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. This
allows test laboratories to reduce burner fuel consumption when testing
small containers. 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. An example of a
typical burner is shown in Figure-10 and Figure-11 below. NHTSA seeks
comment on a specification for the burner rail tubing shape and size,
which can affect the spacing between the nozzle tips.
GTR No. 13 specifies that the CHSS is rotated relative to the
localized burner to minimize the ability for TPRDs to sense the fire
and respond. GTR No. 13 specifies establishing a worst-case based on
the specific CHSS design. However, NHTSA is concerned that establishing
a worst-case based on a specific design may be subjective. NHTSA
instead proposes that the CHSS is positioned for the localized fire by
orienting the CHSS relative to the localized burner such that the
distance from the center of the localized fire exposure to the TPRD(s)
and TPRD sense point(s) is at or near maximum. This provides a
challenging condition where the TPRD(s) may not sense the localized
fire. The engulfing fire zone includes the localized fire zone and
extends along the complete length of the container, in one direction,
towards the nearest TPRD or TPRD sense point, up to a maximum burner
length of 1.65 m. Some examples of possible burner orientations are
shown in Figure-12 and Figure-13. NHTSA seeks comment on the proposed
orientation of the CHSS relative to the localized burner.
BILLING CODE 4910-59-P
[GRAPHIC] [TIFF OMITTED] TP17AP24.009

Figure-10: Example Burner Top View

[[Page 27528]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.010

Figure-11: Example Burner Side View
[GRAPHIC] [TIFF OMITTED] TP17AP24.011

Figure-12: Example Burner Orientations With Single TPRD

[[Page 27529]]

[GRAPHIC] [TIFF OMITTED] TP17AP24.012

Figure-13: Example Burner Orientations With Two TPRDs

BILLING CODE 4910-59-C
When testing is conducted outdoors, wind shielding is required to
prevent wind from interfering with the flame temperatures. In order to
ensure that wind shields do not obstruct the drafting of air to burner,
which could cause variations in test results, the wind shields need to
be at least 0.5 m away from the CHSS being tested. Finally, for
consistency, the wind shielding used for the pre-test checkout must be
the same as that for the CHSS fire test. NHTSA seeks comment on whether
specifications for wind shielding should be provided in the regulatory
text of the standard, and if so, what the specifications should be. As
an additional approach to addressing wind interference with flame
temperatures, NHTSA is considering for the final rule to limit average
wind velocity during testing to 2.24 meters/second, as in FMVSS No.
304.\86\ NHTSA seeks comment on limiting wind speed during testing.
---------------------------------------------------------------------------

\86\ FMVSS No. 304, ``Compressed natural gas fuel container
integrity,'' <a href="https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304">https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304</a>.
---------------------------------------------------------------------------

In order to minimize hazard, jet flames occurring anywhere other
than a TPRD outlet, such as the container walls or joints, cannot
exceed 0.5 meters in length. NHTSA seeks comment on how to accurately
measure jet flames.
Consistent with GTR No. 13, if venting occurs though the TPRD(s),
the venting is required to be continuous so the vent lines do not
experience periodic flow blockages which could interfere with proper
venting. The fire test is completed successfully after the CHSS vents
its contents and the CHSS pressure falls to less than 1 MPa. If the
CHSS has not vented below 1 MPa within 60 minutes for vehicles with a
GVWR of 4,536 kg (10,000 pounds) or less, or 120 minutes for vehicles
with a GVWR over 4,536 kg (10,000 pounds), the CHSS is considered to
have failed the test.
The value of 1 MPa is selected such that the risk of stress rupture
after venting is minimal. The time limits are selected to represent
long-lasting fires such as battery fires or vehicle fires occurring
inside of building structures. The time limit for heavy vehicles is
longer because heavy vehicles are larger in size and often carry cargo
or refuse. Both of these factors tend to prolong fire duration.
8. Tests for Performance Durability of Closure Devices
Like the CHSS, closure devices (like the TPRD, check valve and
shut-off valve) must be durable and maintain their expected operational
capabilities during their lifetime of service. Closure devices must
demonstrate their operability and durability in service by completing a
series of performance tests as discussed below. Closure device
operability and durability is essential for the integrity of the CHSS
because these devices isolate the high-pressure hydrogen from the
remainder of the fuel system and the environment. While the closure
devices are challenged in the CHSS performance tests above, additional
specific tests may further enhance safety. In addition, specific
component testing enables equivalent components to be safely exchanged
in a CHSS.
The tests for performance durability of closure devices in GTR No.
13 are closely consistent with the industry standards CSA/ANSI HPRD 1-
2021, Thermally activated pressure relief devices for compressed
hydrogen vehicle fuel containers, and CSA/ANSI HGV 3.1-2022, Fuel
System Components for Compressed Hydrogen Gas Powered
Vehicles.87 88 The tests for performance durability of
closure devices carry a significant test burden. To evaluate a single
TPRD design, 13 TPRD units are required for a total of 29 individual
tests (some units undergo multiple tests in a sequence). Similarly, to
evaluate a single shut-off valve or check valve, 8 units are required
for a total of 17 individual tests. While NHTSA is proposing these
requirements to be consistent with GTR No. 13, NHTSA seeks comment on
whether testing of this extent is necessary to meet the need for
safety, or whether it is still possible to meet the need for safety
with a less-burdensome test approach or with a subset of the test for
performance durability of closure devices. If commenters believe
another approach or subset of tests is appropriate and meets the need
for safety, NHTSA requests that commenters provide specific detail on

[[Page 27530]]

(1) the alternate approach or subset of tests and (2) how it meets the
need for safety adequately.''
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\87\ See. <a href="https://webstore.ansi.org/standards/csa/csaansihprd2021">https://webstore.ansi.org/standards/csa/csaansihprd2021</a>.
\88\ See. <a href="https://webstore.ansi.org/standards/csa/csaansihgv2015r2019">https://webstore.ansi.org/standards/csa/csaansihgv2015r2019</a>.
---------------------------------------------------------------------------

Furthermore, FMVSS represent minimum performance requirements for
safety. FMVSS does not address issues such as component reliability or
best practices. These considerations are left to industry standards.
NHTSA seeks comment on whether a reduced subset of the tests for
performance durability of closure devices could ensure safety with a
lower overall test burden. In such a subset, only those tests directly
linked to critical safety risks would be included.
The tests for performance durability of closure devices are
conducted on finished components representative of normal production.
To enable outdoor testing without special temperature controls that
would increase testing costs, NHTSA proposes that testing be conducted
at an ambient temperature of 5 [deg]C to 35 [deg]C, unless otherwise
specified. In addition, GTR No. 13 specifies that all tests be
performed using either:
<bullet> Hydrogen gas compliant with SAE J2719_202003, Hydrogen
Fuel Quality for Fuel Cell Vehicles, or
<bullet> Hydrogen gas with a hydrogen purity of at least 99.97
percent, less than or equal to 5 parts per million of water, and less
or equal to 1 part per million particulate, or
<bullet> A non-reactive gas instead of hydrogen.
The standard J2719_202003 specifies maximum concentrations of
individual contaminants such as methane and oxygen. Limiting these
individual contaminants are critical for fuel cell operation, however,
they are unlikely to affect the results of the tests for performance
durability of closure devices.
As a result, FMVSS No. 308 will only require hydrogen with a purity
of at least 99.97 percent, less than or equal to 5 parts per million of
water, and less or equal to 1 part per million particulate. NHTSA seeks
comment on any other impurities that could affect the results of the
tests for performance durability of closure devices.
Using a non-reactive gas for testing would have the benefit of
reducing the test lab safety risk related to handling pressurized
hydrogen. However, it is not clear if replacing hydrogen with a non-
reactive gas reduces stringency and therefore may not adequately
address the safety need. As a result, this option has not been proposed
in FMVSS No. 308. NHTSA seeks comment on whether testing with a non-
reactive gas instead of hydrogen reduces test stringency. If commenters
believe (and can explain) that it does not reduce test stringency,
NHTSA requests that they identify a suitable non-reactive gas to
replace hydrogen, such as helium or nitrogen, and explain why it is
suitable.
a. TPRD
Failure of a TPRD to properly vent in the event of a fire could
lead to burst. Accordingly, TPRDs must demonstrate operability and
durability in service by successfully completing the applicable tests
for performance durability of closure devices. This is a series of TPRD
performance tests with requirements discussed below.
GTR No. 13 does not consider the possibility of the TPRD activating
during the pressure cycling test, temperature cycling test, salt
corrosion test, vehicle environment test, stress corrosion cracking
test, drop and vibration test, or leak test. The temperatures applied
during these tests are not characteristic of fire and therefore should
not cause the TPRD to activate. TPRD activation in the absence of
temperatures characteristic of a fire indicates that the TPRD is not
functioning as intended and presents a safety risk due to the hazards
associated with TPRD discharge. As a result, NHTSA is proposing that if
the TPRD activates at any point during the pressure cycling test,
temperature cycling test, salt corrosion test, vehicle environment
test, stress corrosion cracking test, drop and vibration test, or leak
test, that TPRD will be considered to have failed the test. NHTSA seeks
comment on this proposed requirement.
(1) Pressure Cycling Test
Similar to the CHSS test for expected on-road performance, the
pressure cycling test would evaluate a TPRD's ability to withstand
repeated pressurization and depressurization. One TPRD unit undergoes
15,000 internal pressure cycles with hydrogen gas. While the proposed
15,000 pressure cycles for the TPRD is consistent with GTR No. 13,
NHTSA notes that this number of cycles is higher than the maximum
11,000 pressure cycles applied to containers. NHTSA seeks comment on
the need for 15,000 pressure cycles for TPRDs. The testing is performed
under the conditions shown in Table-9 with a maximum cycling rate of 10
cycles per minute.

Table 9--Test Conditions
------------------------------------------------------------------------
Temperature
Pressure Number of cycles ([deg]C)
------------------------------------------------------------------------
2 MPa to 150% NWP................. First 10............ 85
2 MPa to 125% NWP................. Next 2,240.......... 85
2 MPa to 125% NWP................. Next 10,000......... 20
2 MPa to 80% NWP.................. Final 2,750......... -40
------------------------------------------------------------------------

The pressure cycling test is designed to replicate fueling events
during service. This is important because over time, repeated fueling
events can produce fatigue failures. NHTSA seeks comment on the number
of TPRD pressure cycles. The first 10 cycles use 150 percent NWP to
replicate over-pressurization events at fueling stations. The remaining
cycles are conducted to 125 percent NWP for the reasons discussed above
for the baseline pressure cycle test.
The test temperature of 85 [deg]C for the first 2,250 cycles and
the test temperature of -40 [deg]C for the final 2,750 cycles are
selected to replicate the extreme hot and cold environments described
above for the test for performance durability. After the completion of
pressure cycling, the TPRD units are subjected to the Leak Test,
Benchtop Activation Test, and Flow Rate Test. These three tests,
discussed below, verify the essential functions of the TPRD.
(2) Accelerated Life Test
A TPRD needs to activate at its intended activation temperature,
but also must not activate prematurely due to a long-duration exposure
to elevated temperature that is below its activation temperature.
Holding the TPRD at an elevated temperature TL could lead to creep
failure of the materials within the TPRD and result in a false
activation. The purpose of the accelerated life test is to evaluate the
TPRD's ability to activate at intended activation

[[Page 27531]]

temperature, while demonstrating resistance to creep failure at
elevated temperatures that are below its activation temperature.
During the test, the TPRD units are pressurized with hydrogen at
125 percent NWP and placed in a temperature-controlled environment. One
unit is tested at the manufacturer's specified activation temperature,
Tf, and one unit is tested at the accelerated life temperature, TL,
given by the expression: \89\
---------------------------------------------------------------------------

\89\ Details are provided in the technical document ``New
equation for calculating accelerated life test temperature.pdf''
submitted to the docket of this NPRM.
[GRAPHIC] [TIFF OMITTED] TP17AP24.013

where [beta] = 273.15 if T is in Celsius and [beta] = 459.67 if T is in
Fahrenheit, T<INF>85</INF> = 85 [deg]C (185 [deg]F), and Tf is the
manufacturer's specified activation temperature. The unit tested at Tf
must activate in less than 10 hours and the unit tested at TL must not
activate in less than 500 hours. The required 500 hours without
activation demonstrates the unit's resistance to creep.
(3) Temperature Cycling Test
Similar to the container and CHSS, the TPRD must be able to
withstand extreme temperatures while in service. A study found that
pressure release devices at extreme cold temperature as low as -40
[deg]C could cause a TPRD gas release failure.\90\ The temperature
cycling test evaluates a TPRD's ability to withstand extreme
temperature conditions that may lead to gas release failures when
combined with pressure cycling. The TPRD is first exposed to 15 thermal
cycles by alternating between hot (85 [deg]C) and cold (-40 [deg]C)
temperature baths. This is to simulate rapid swings in environmental
temperature, which can stress the TPRD through thermal expansion and
contraction. The TPRD is then pressure cycled in the cold bath for 100
cycles at 80 percent NWP to simulate fueling and defueling in an
extreme cold environment. After these stresses have been applied, the
TPRD is subjected to the low-temperature condition Leak Test, Benchtop
Activation Test, and Flow Rate Test. These three tests, discussed
below, verify the essential functions of the TPRD. Only the low-
temperature condition leak test is conducted after the temperature
cycling test because leaks are most likely to occur at low
temperatures.
---------------------------------------------------------------------------

\90\ Livio Gambone et al., Performance testing of pressure
relief devices for NGV cylinders, June 1997.
---------------------------------------------------------------------------

(4) Salt Corrosion Resistance Test
The purpose of the salt corrosion resistance test is to verify that
the TPRD can withstand an extreme external salt corrosion environment.
The test occurs in a chamber designed to coat the TPRD with atomized
droplets of salt solution. This creates a highly corrosive environment.
The chamber cycles through wet and dry stages to maximise corrosion
affects. The parameters for this test, such as the chamber design, the
salts and water used, the salt concentrations, temperatures, humidity
levels and cycle times are all based on HGV 3.1-2022 and HPRD 1-
2021.91 92 93 After the salt corrosion exposure, the TPRD
units are subjected to the Leak Test, Benchtop Activation Test, and
Flow Rate Test. These tests, discussed below, verify the essential
functions of the TPRD. NHTSA seeks comment on the clarity and
objectivity of the salt corrosion resistance test procedure. If
commenters have suggestions on how to change the salt corrosion
resistance test procedure, NHTSA asks that they please explain how
their suggested changes improve the clarity and objectivity, and how
they continue to meet the need for safety represented by this test.
---------------------------------------------------------------------------

\91\ CSA/ANSI HGV 3.1-2022 Fuel System Components For Compressed
Hydrogen Gas Powered Vehicles.
\92\ CSA/ANSI HPRD 1-2021 Thermally activated pressure relief
devices for compressed hydrogen vehicle fuel containers.
\93\ HGV 3.1, HPRD 1, GTR No. 13, and the proposed FMVSS No. 308
reference the standards ASTM D1193-06(2018), Standard Specification
for Reagent Water and ISO 6270-2:2017 Determination of resistance to
humidity. ASTM D1193-06(2018) provides specification for the water
to be used during salt corrosion resistance testing. <a href="https://www.astm.org/d1193-06r18.html">https://www.astm.org/d1193-06r18.html</a>.
ISO 6270-2:2017 provides specifications for the cyclic corrosion
chamber to be used. <a href="https://www.iso.org/standard/64858.html">https://www.iso.org/standard/64858.html</a>.
These two standards would be incorporated by reference into the
proposed FMVSS No. 308. A summary of these two standards is provided
in Section V. Regulatory Analyses and Notices of this notice.
---------------------------------------------------------------------------

(5) Vehicle Environment Test
The purpose of the vehicle environment test is to demonstrate that
the TPRD can withstand exposure to chemicals that might be encountered
during on-road service. Prior to testing, the inlet and outlet ports
are capped because the test is not intended to expose the interior of
the TPRD. The TPRD is then exposed to the following fluids for 24 hours
each at 20 [deg]C:
<bullet> Sulfuric acid at 19 percent in water to simulate battery
acid.
<bullet> Ethanol at 10 percent in gasoline to simulate fueling
station fluids.
<bullet> Methanol at 50 percent in water to simulate windshield-
washer fluid.
The TPRD is exposed to all of fluids separately in a sequence. The
fluids are replenished as needed for complete exposure throughout the
duration of the test. After exposure to each chemical fluid, the unit
is wiped off and rinsed with water to end any reactions that may be
occurring.
GTR No. 13 does not specify the method of exposure to these
chemical solutions. The method described in HPRD 1-2021 is to immerse
the test unit in each fluid.\94\ The duration of 24 hours is based on
industry practices. NHTSA seeks comment on the exposure method.
---------------------------------------------------------------------------

\94\ CSA/ANSI HPRD 1-2021, Thermally activated pressure relief
devices for compressed hydrogen vehicle fuel containers.
---------------------------------------------------------------------------

After the conclusion of the exposures, the TPRD unit is subjected
to the Leak Test, Benchtop Activation Test, and Flow Rate Test. These
tests, discussed below, verify the essential functions of the TPRD. In
addition to these subsequent tests, the TPRD must not show signs of
cracking, softening, or swelling. GTR No. 13 further specifies that
``cosmetic changes such as pitting or staining are not considered
failures.'' NHTSA seeks comment on including this specification, and
notes that pitting can be an aggressive form of corrosion which can
ultimately lead to component failure due to cracking at the pitting
site.
(6) Stress Corrosion Cracking Test
The purpose of the stress corrosion cracking test is to ensure that
the TPRD can resist stress corrosion cracking. Stress corrosion
cracking is the growth of crack formation in a corrosive environment.
It can lead to unexpected and sudden failure of normally ductile metal
alloys subjected to a tensile stress, especially at elevated
temperature. In particular, TPRDs containing copper-based alloys can be
susceptible to stress corrosion cracking in the presence of aqueous
ammonia. This is a significant risk because ammonia can be found in the
natural and vehicle environment.
The TPRD test unit is degreased to remove any protective grease
that may be present. The unit is then exposed for ten days to a moist
ammonia-air mixture maintained in a glass chamber. Under GTR No. 13,
the moist ammonia-air mixture is achieved using an ammonia-water
mixture with specific gravity of 0.94. Specific gravity is affected by
temperature and, therefore, is an inconvenient metric for concentration
specification because concentrations will need to be adjusted for
different temperatures. NHTSA seeks comment on a more direct metric for
ammonia

[[Page 27532]]

concentration specification, such as 20 weight percent ammonium
hydroxide in water.
The chamber is maintained at atmospheric pressure and 35 [deg]C.
This simulates a slightly elevated temperature. In GTR No. 13, the only
requirement to pass the stress corrosion cracking test is that the
components must not exhibit cracking or delaminating due to this test.
NHTSA seeks comment on this performance requirement and whether there
are alternative requirements for this test beyond basic visual
inspection, such as subjecting the TPRD to the leak test.
(7) Drop and Vibration Test
The purpose of the drop and vibration test is to evaluate the
TPRD's ability to withstand drop and vibration. Dropping a TPRD could
occur during installation, and vibration is likely to occur during on-
road service. A TPRD may be dropped in any one of six different
orientations covering the opposing directions of three orthogonal axes:
vertical, lateral and longitudinal. After the drop, the TPRD unit is
examined for damage that would prevent its installation in a test
fixture for vibration according to the manufacturer's instructions. If
damage is present that would prevent installation, the TPRD is
discarded, and it is not considered a test failure. Damage that would
prevent its instal

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