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



[[Page 6217]]

Vol. 90

Friday,

No. 11

January 17, 2025

Part III





 Department of Transportation





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National Highway Traffic Safety Administration





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49 CFR Part 571





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

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

[[Page 6218]]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

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


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

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

ACTION: Final rule.

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

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

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

FOR FURTHER INFORMATION CONTACT: For technical issues, Ian MacIntire, 
General Engineer, Special Vehicles & Systems Division within the 
Division of Rulemaking, at (202) 493-0248 or [email protected]. For 
legal issues, Paul Connet, Attorney-Advisor, NHTSA Office of Chief 
Counsel, at (202) 366-5547 or [email protected] or Evita St. Andre, 
Attorney-Advisor, NHTSA Office of Chief Counsel, at (617) 494-2767 or 
[email protected]. The mailing address of these officials is: 
National Highway Traffic Safety Administration, 1200 New Jersey Avenue 
SE, Washington, DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

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

I. Executive Summary

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

[[Page 6219]]

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

II. Background

A. Overview of GTR No. 13

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

B. April 2024 NPRM

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

[[Page 6220]]

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

C. How the Final Rule Differs From the NPRM

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

III. Summary of Comments

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

IV. Response to Comments on Proposed Requirements

A. Deviation From GTR No. 13

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

[[Page 6221]]

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

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

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

[[Page 6222]]

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

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

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

[[Page 6223]]

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

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

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

[[Page 6224]]

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

[[Page 6225]]

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

[[Page 6226]]

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

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

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

[[Page 6227]]

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

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

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

[[Page 6228]]

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

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

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

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

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

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

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

[[Page 6229]]

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

[[Page 6230]]

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

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

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

[[Page 6231]]

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

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

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

[[Page 6232]]

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

[[Page 6233]]

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

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

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

[[Page 6234]]

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

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

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

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

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

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

[[Page 6235]]

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

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

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

    \22\ See https://www.energy.gov/eere/fuelcells/doe-technical-targets-onboard-hydrogen-storage-light-duty-vehicles.
---------------------------------------------------------------------------

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

[[Page 6236]]

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

[[Page 6237]]

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

[[Page 6238]]

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

[[Page 6239]]

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

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

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

[[Page 6240]]

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

[[Page 6241]]

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

    \24\ SAE J2579_201806. Standard for Fuel Systems in Fuel Cell 
and Other Hydrogen Vehicles. https://www.sae.org/standards/content/j2579_201806/.
---------------------------------------------------------------------------

Comments Received
    Luxfer Gas Cylinders commented that the proposed test is time-
consuming and expensive to conduct. It stated that for large 800 liter 
containers, there is only one test lab that can conduct the test. It 
stated that the cost of testing exceeds $500,000. It questioned if 
NHTSA proposing to evaluate containers using the proposed test 
procedures.
Agency Response
    NHTSA is aware of the burden of the proposed test. FMVSS establish 
minimum safety requirements and the FMVSS test procedures establish how 
the agency would verify compliance. However, manufacturers are not

[[Page 6242]]

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

[[Page 6243]]

with a soapy solution. TesTneT raised concerns about hydrogen 
permeation risks in enclosed spaces, pointing out that hydrogen can 
leak out over time, making it difficult to accumulate in dangerous 
amounts.
    Newhouse commented that NHTSA's proposed permeation rate of 46 mL/
L/h at 55 [deg]C is unreasonably low and noted several issues, such as 
considering worst-case scenarios and ventilation assumptions. Newhouse 
suggested allowing a higher limit of 100 percent of the lower 
flammability limit (LFL), or 4 percent hydrogen in air, and questioned 
the use of 55 [deg]C as a peak temperature, stating that a lower 
average would be more representative. Newhouse also recommended 
increasing the allowable permeation rate to 184 mL/L/h at 55 [deg]C and 
noted that the probability of failure remains low, even with more 
conventional ventilation rates in garage spaces.
    FORVIA acknowledged that different methods can accurately measure 
leakage and permeation and suggested that guidance on measurement could 
be provided outside the FMVSS text. It was open to considering 
localized leak requirements but noted that the submersion method, 
though simple, may require more accurate measurements near the limits. 
It indicated that omitting this test for field surveillance would be 
acceptable, as production containers typically exhibit far less 
leakage. H2MOF proposed exempting all-metal containers from the static 
gas leak/permeation test and suggested that procedures from industry 
standards be used for guidance.
Agency Response
    NHTSA is maintaining the extreme temperature static gas pressure 
leak/permeation test as proposed, without the localized leak limit. The 
commenters did not provide any explanation for the safety need of the 
localized leak limit. Commenters did not provide any evidence that 
omitting the localized leakage requirement is less stringent when there 
is also an overall permeation limit applied to the CHSS as a whole.
    Furthermore, commenters did not provide sufficient explanation of 
how, if included, the localized leakage limit could be made more 
objective. Some commenters suggested using analytical chemistry 
equipment such as mass spectrometers. However, these types of 
instruments are highly complex, and additional research would be needed 
by NHTSA before they could be used to objectively quantify a leak. Even 
if the agency determined that mass spectrometers were viable for 
detecting localized leaks, the agency would still need to consider the 
safety need being addressed by the requirement.
    NHTSA is not changing the overall permeation rate of 46 mL/L/h 
based on the comments. This permeation limit is found in GTR No. 13 and 
is widely accepted by the industry as an appropriate permeation limit. 
Well-developed rationale for this limit is provided in GTR No. 13 and 
in the NPRM.\26\ In particular, the conservative 25 percent LFL limit 
accounts for concentration non-homogeneities that may be present, and 
the choice of 55 [deg]C is a worst-case temperature condition, not one 
that is expected to occur commonly. Permeation is higher at higher 
temperatures, so NHTSA considered this worst-case condition when 
evaluating the permeation limit. This permeation limit is also applied 
in the industry standard SAE J2579_201806. The commenters did not 
establish sufficient rationale for NHTSA to deviate from the 
established 46 mL/L/h.
---------------------------------------------------------------------------

    \26\ See 89 FR 27522 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

    NHTSA is not exempting CHSS with all-metal containers from the 
extreme temperature static gas pressure leak/permeation test. All-metal 
containers must demonstrate the same level of performance and safety as 
other containers. NHTSA is not replacing the proposed test with either 
of the standards recommended by H2MOF. The commenter did not establish 
any justification for why doing so would improve safety, nor did it 
provide any detailed information regarding the alternative standards.
d. Residual Pressure Test & Residual Strength Burst Test
Background
    The residual pressure test and residual strength burst test are 
conducted in the same manner and for the same reasons discussed above 
for the test for performance durability.
Comments Received
    Auto Innovators stated support for NHTSA's proposal to harmonize 
these requirements with GTR No. 13.
Agency Response
    NHTSA is maintaining the residual pressure test and residual 
strength burst test as proposed.
10. Test for Service Terminating Performance in Fire
Background
    NHTSA proposed a fire test based closely on the GTR No. 13 Phase 2 
fire test. The updates to the fire test by the IWG of GTR No. 13 Phase 
2 focused on improving the repeatability and reproducibility across 
test laboratories. Two significant improvements to the fire test are 
(1) the use of a pre-test checkout procedure and (2) basic burner 
specifications. The pre-test checkout requires conducting a preliminary 
fire exposure on a standardized steel container to verify that 
specified fire temperatures can be achieved for the localized and 
engulfing fire segments of the test prior to conducting the fire test 
on a CHSS. During this pre-test checkout, the fuel flow is adjusted to 
achieve fire temperatures within the specified limits as measured on 
the surface of the pre-test steel container. The use of a pre-test 
steel container instead of an actual CHSS improves the accuracy and 
repeatability of the test because it avoids possible container material 
degradation that could affect the temperature measurements.
Comments Received
    Luxfer Gas Cylinders commented that the recent changes introduced 
in GTR No. 13 regarding the fire test are ``excessive'' and do not 
enhance test performance. Luxfer stated that the pre-test using a steel 
container is only relevant when the steel container matches the size of 
the composite container being tested. For larger containers, such as 
those used in heavy vehicles, Luxfer stated that the pre-test becomes 
unnecessary. Luxfer and H2MOF both suggested that NHTSA consider 
adopting the Bonfire test from NGV 2 2019, ``Compressed natural gas 
vehicle fuel containers.'' \27\ Additionally, Luxfer expressed concerns 
about the increased costs of the new GTR No. 13 fire test. It 
questioned whether NHTSA intends to apply this test to containers that 
have been withdrawn from service.
---------------------------------------------------------------------------

    \27\ See https://webstore.ansi.org/standards/csa/csaansingv2019.
---------------------------------------------------------------------------

    Agility commented that the fire source and pre-test procedures in 
GTR No. 13 do not accurately represent vehicle fire scenarios, 
particularly for heavy applications. It highlighted that the fire 
source width is set at 500 mm regardless of the container's diameter 
and that the temperature requirements focus solely on the area beneath 
and directly on the container surface. Agility further pointed out the 
lack of

[[Page 6244]]

requirements for measuring temperatures around the container, which is 
where remotely mounted PRDs are typically located.
Agency Response
    NHTSA acknowledges the comments regarding the proposed fire test 
based on GTR No. 13 Phase 2 but does not find them persuasive enough to 
warrant any significant changes to the proposed test procedures. 
Specifically, the concern that the pre-test checkout using a steel 
cylinder is only relevant if it matches the size of the composite 
container is not valid. The pre-test checkout procedure is designed to 
ensure the consistency of fire temperature measurements, which can be 
achieved regardless of the difference in size between the pre-test 
container and the actual CHSS. The objective of the pre-test checkout 
is to verify the fire conditions produce the specified temperatures, 
which improves the accuracy and repeatability of the test across 
different laboratories.
    Regarding the commenters' suggestions to adopt the fire test in NGV 
2 2019, NHTSA is aware of ANSI NGV 2 2019, but the GTR No. 13 fire test 
remains more representative of real-world conditions. The proposed fire 
test procedure based on GTR No. 13 includes both localized and 
engulfing fire stages, which are designed based on actual vehicle fire 
data, as discussed in the NPRM.\28\ The proposed fire test procedure is 
the most realistic fire test available that is representative of a 
range of possible real-world vehicle fires. The NGV 2 fire test does 
not provide the same level of comprehensiveness as the standard. The 
NGV 2 fire test does not include any pre-test procedures to improve 
repeatability and reproducibility, nor does it include a localized fire 
exposure. The fire test procedure, on the other hand, provides a 
rigorous, repeatable test that accounts for both localized and 
engulfing fire conditions, addressing various fire exposure scenarios. 
Due to the large volumes of hydrogen stored on hydrogen fueled 
vehicles, NHTSA maintains that the proposed fire test procedure is 
needed to ensure vehicles are designed with a high level of performance 
in fire conditions. NHTSA further notes that the pre-test checkout 
includes temperature specifications for the bottom, sides, and top of 
the pre-test container.
---------------------------------------------------------------------------

    \28\ See 89 FR 27523 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

    Regarding the concern about increased costs, vehicle manufacturers 
are already designing their vehicles to meet or exceed the requirements 
of the proposed fire test based on GTR No. 13, so NHTSA does not expect 
significant increased costs from implementing the proposed fire test. 
Regarding applying the requirements to containers that have been 
withdrawn from service, NHTSA purchases new vehicles at the point of 
sale for compliance testing. NHTSA does not conduct compliance testing 
on used vehicles or equipment.
a. Burner Specification
Background
    To further improve test reproducibility, a burner configuration is 
defined with localized and engulfing fire zones. These specifications 
allow the fire test to be performed without a burner development 
program. NHTSA explained in the NPRM that it believes that the use of a 
standardized burner configuration is a practical way of conducting fire 
testing and should reduce variability in test results through 
commonality in hardware.\29\ Flexibility is provided to adjust the 
length of the engulfing fire zone to match the CHSS length, up to a 
maximum of 1.65 m. The width of the burner, however, is fixed at 500 mm 
for all fire tests, regardless of the width or diameter of the CHSS 
container to be tested, so that each CHSS is evaluated with the same 
fire condition regardless of size. The length of the localized fire 
zone is also fixed to 250 mm for all fire tests. NHTSA sought comment 
on a specification for the burner rail tubing shape and size, which can 
affect the spacing between the nozzle tips.
---------------------------------------------------------------------------

    \29\ See 89 FR 27527 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

Comments Received
    MEMA expressed concerns that the burner specifications in FMVSS No. 
308 S6.2.5.3 are more rigid than those in GTR No. 13, which specifies a 
larger burner assembly, allowing for the testing of larger hydrogen 
storage containers. MEMA suggested that the proposed limitations could 
create challenges for testing and qualifying hydrogen pressure vessels 
for the U.S. market, requesting that NHTSA to align more closely with 
GTR No. 13. MEMA also recommended revising the language in FMVSS No. 
308 S6.2.5.2(c)(2) regarding nozzle orientation to avoid potential 
confusion and align with GTR No. 13, which targets the lowest elevation 
of the CHSS.
    Auto Innovators recommended harmonizing with GTR No. 13, stating 
that industry standards already establish 1.65 meters as the length of 
the engulfing fire zone. Auto Innovators recommended maintaining the 
basic burner design from GTR No. 13. TesTneT commented that rails 
measuring 50 mm square, spaced at 100 mm, provide optimal nozzle tip 
spacing. It stated that the square rail is crucial for proper burner 
tip installation, and any deviation in rail size could reduce burner 
temperatures.
    FORVIA emphasized the importance of maintaining equivalence with 
GTR No. 13, urging NHTSA to keep the burner configuration consistent 
with phase 2 of GTR No. 13. It cautioned that any changes to the burner 
specification could lead to ``serious dis-harmonization'' and result in 
the need for double testing for products sold across different regions.
Agency Response
    In both GTR No. 13 and the proposed FMVSS No. 308, the burner width 
is between 450 millimeters and 550 millimeters in width. The additional 
length mentioned by TesTneT of 100 mm is intended to be a tolerance. 
Tolerances are discussed below. However, to ensure the maximum possible 
burner size consistent with GTR No. 13, FMVSS No. 308 S6.2.5.2(b) has 
been updated to allow the engulfing burner to extend up to a maximum of 
1.75 meters.
    NHTSA has determined there is no need to specify square burner 
rails. While this shape may be the most convenient shape for the burner 
rails, and test labs may prefer square rails, it may be possible to 
construct a burner using non-square rails. If such a burner were to 
meet all burner specifications and satisfy the prescribed temperature 
requirements, it would be considered an acceptable burner. Sufficient 
burner specifications, as well as the pre-test checkout procedure 
ensure the repeatability and reproducibility of the burner.
    GTR No. 13 specifies that ``[t]he pre-test cylinder used for the 
pre-test checkout shall be mounted at a height of 100  5 mm 
above the burner and located over the burner such that nozzles from the 
two centrally-located manifolds are pointing toward the bottom centre'' 
of the pre-test container. NHTSA similarly proposed mounting the pre-
test container ``such that the nozzles from the two center rails are 
pointing toward the bottom center of the pre-test container.'' NHTSA is

[[Page 6245]]

maintaining this language in the final rule. This specification is 
sufficiently objective to ensure repeatability and reproducibility of 
the test. Furthermore, a specification regarding ``elevation'' may be 
ambiguous, and has not been included. For the CHSS fire test, the CHSS 
will be positioned for the localized fire test by orienting the CHSS 
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. NHTSA is 
maintaining this orientation in the final rule.
b. Additional Pre-Test Procedurs for Irregularly Shaped Containers
Background
    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 check out is conducted using the pre-test plate and using the 
burner monitor thermocouples. If the burner monitor thermocouple 
temperatures do not satisfy the specified minimum temperatures, 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 the required minimum 
temperatures. NHTSA 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 did not propose these additional 
pre-test procedures. NHTSA sought comment on this decision.
Comments Received
    Auto Innovators generally agreed with NHTSA's decision to 
streamline pre-test procedures but suggested that clarification is 
needed to ensure that a repeat test is only required if the pre-test 
does not meet the specified requirements. It emphasized that incorrect 
pre-test temperatures could result in over or under testing of the 
CHSS, potentially leading to a false pass or failure.
    FORVIA disagreed with NHTSA's decision, advocating for the 
retention of the existing pre-test procedures for irregularly shaped 
CHSS as specified in GTR No. 13. It stated that consistency across 
global markets is crucial to minimize discrepancies and ensure 
manufacturers follow uniform guidelines. FORVIA acknowledged that the 
additional pre-test procedures might add time but noted that they would 
likely reduce the need for retesting and avoid introducing variables 
that could compromise repeatability. It emphasized that GTR No. 13 
procedures had been validated through significant work, including round 
robin testing, and stated that deviating from these standards could 
undermine the enforceability of failed tests.
    HATCI also stated that the additional pre-test procedures for 
irregularly shaped CHSS are necessary, stating that a lack of uniform 
temperature distribution could negatively affect TRPD activation. It 
stressed the importance of ensuring proper testing for all CHSS designs 
and suggested that the repeatability and reproducibility of the test 
could be reassessed as more irregular containers are introduced. 
TesTneT, on the other hand, agreed with NHTSA's decision, stating that 
additional pre-test procedures are unnecessary.
Agency Response
    NHTSA is not including additional pretest procedures for 
irregularly shaped containers. NHTSA conducted fire testing of large, 
irregularly shaped CHSS according to the proposed test procedure. The 
test was highly successful, with the CHSS TPRD activating within one 
minute of the ignition of the localize burner. The results of this 
testing are summarized in the test report ``GTR No. 13 Fire and 
Closures Tests.'' \30\ These results indicate that additional design-
specific procedures are not required and irregularly shaped CHSS can 
successfully complete the test for service terminating performance in 
fire. The use of the pre-test container is simply to verify the burner 
and is not intended to precisely match the size of the CHSS.
---------------------------------------------------------------------------

    \30\ See the report titled ``GTR No. 13 Fire and Closures 
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be 
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
---------------------------------------------------------------------------

c. Pre-Test Container Length Compared to CHSS
Background
    NHTSA conducted CHSS fire testing to verify the feasibility of the 
test for service termination performance in fire as proposed. In some 
cases during testing, temperatures measured at the burner monitor 
thermocouples did not satisfy the required minimum value for the burner 
monitor temperature during the engulfing fire stage 
(TminENG).\31\ 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 recommended 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 sought comment on 
whether this recommendation should be a specification for the pre-test 
container.
---------------------------------------------------------------------------

    \31\ TminENG 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.
---------------------------------------------------------------------------

Comments Received
    Several commenters disagreed with NHTSA's recommendation to specify 
a length difference between the pre-test container and the CHSS being 
tested. Nikola stated disagreement with the proposal, explaining that 
the pre-test is conducted according to GTR No. 13 and that additional 
specifications on length differences are unnecessary. TesTneT also 
commented that the pre-test container should align with GTR No. 13 and 
argued that since the burner system is uniform, there is no need to 
correlate the pre-test container's length with that of the CHSS. 
TesTneT added that observations regarding the influence of CHSS length 
on pre-test results were incorrect. Auto Innovators similarly 
disagreed, stating that the pre-test container's role is to verify the 
burner and is not directly related to the CHSS size.
    FORVIA expressed opposition as well, recommending that NHTSA keep 
the test procedure equivalent to GTR No. 13. It emphasized that adding 
length specifications would increase both time and costs for pre-
testing, while the existing GTR No. 13 requirements are sufficient to 
ensure reproducible conditions. FORVIA noted that the GTR No. 13 fire 
test procedure had been validated through extensive testing and

[[Page 6246]]

provided significant improvements over previous testing methods for CNG 
and hydrogen containers.
Agency Response
    NHTSA is not including any requirements regarding the difference in 
length for the pre-test container and the CHSS. The recommendation 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, 
will remain a recommendation for future test labs. Following this 
recommendation will not be required as part of the testing, and not 
adhering to the recommendation will not invalidate test results.
d. Pretest Checkout Frequency
Background
    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 
sought comment on the frequency of conducting this pre-test checkout 
for ensuring repeatability of the fire test on CHSS.
Comments Received
    Several commenters responded to NHTSA's inquiry about the frequency 
of the pre-test checkout for CHSS fire testing, with most agreeing that 
additional requirements were unnecessary if no modifications were made 
to the burner or test setup.
    Auto Innovators agreed that a repeat of the pre-test checkout is 
necessary if the burner or test setup is modified but recommended that 
the pre-test be performed at the manufacturer's discretion if no 
modifications have occurred. HATCI similarly commented that the pre-
test checkout should be performed at the manufacturer's discretion. 
Nikola stated that the frequency of the pre-test should be determined 
by the testing agency, in accordance with ISO 17025, ``General 
requirements for the competence of testing and calibration 
laboratories,'' accreditation requirements.
    TesTneT referred to GTR No. 13, noting that the pre-test only needs 
to be conducted once to verify the burner setup, unless modifications 
are made. It emphasized that multiple pre-tests are unnecessary if the 
test stand remains unchanged between tests. FORVIA disagreed with 
adding additional requirements, requesting harmonization with GTR No. 
13 and stating that the pre-test checkout before commissioning and 
following modifications is sufficient. It suggested that any additional 
pre-test checkouts should be at the discretion of the test site 
operator, but recommended not adding further requirements to FMVSS.
Agency Response
    NHTSA reiterates that the pre-test checkout will be performed at 
least once before the commissioning of a new test site and when the 
burner or test setup is modified to accommodate different CHSS 
configurations. NHTSA believes this approach ensures the consistency 
and reliability of testing procedures. No changes are being made to the 
proposed requirements based on the comments.
e. Thermocouple Positioning
Background
    NHTSA proposed positioning the three burner monitor thermocouples 
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 sought comment 
on whether it is preferable to position the burner monitor 
thermocouples relative to the pre-test container or relative to the 
burner.
Comments Received
    Commenters generally supported harmonizing the positioning of the 
burner monitor thermocouples with GTR No. 13 and opposed NHTSA's 
proposal to position the thermocouples relative to the burner.
    HATCI commented that environmental factors, such as wind and 
temperature, could influence test results, recommending alignment with 
GTR No. 13, where thermocouples are positioned relative to the pre-test 
container. Auto Innovators also recommended positioning the 
thermocouples relative to the pre-test container to ensure that 
temperatures measured on the container are representative, and for 
aiding harmonization with GTR No. 13. It further referenced discussions 
during GTR No. 13 Phase 2, highlighting concerns about potential 
thermocouple failure due to material expansion from the test article 
and noted that GTR No. 13 offers solutions, including backup 
thermocouples.
    Nikola stated that the purpose of the test is to measure the heat 
flux to the container and emphasized the importance of adhering to GTR 
No. 13, as the industry standard is to measure heat from the container 
being tested. TesTneT added that the thermocouples are positioned 
relative to both the pre-test container and the burner, placed 25 mm 
below the container and 75 mm above the burner tips, and stated there 
is no preferable alternative position. DTNA stated that the distance of 
the CHSS to the burner is the key factor that drives the 
characterization of the test. DTNA stated that it supports the effort 
in the NPRM to establish repeatable and objective test scenarios. 
FORVIA disagreed with introducing alternative measurements and stressed 
the importance of maintaining equivalency with GTR No. 13 to avoid 
unnecessary confusion. It suggested that any clearer requirements 
should be introduced in GTR No. 13 Phase 3.
Agency Response
    NHTSA will maintain the burner monitor thermocouples 25 mm below 
the pre-test container, as specified in GTR No. 13. NHTSA acknowledges 
TesTneT's 'point that, due to the prescribed height of the pre-test 
container above the burner, specifying a point's distance below the 
pre-test container also specifies that point's distance above the 
burner.
f. Temperature Variation Greater Than 50 [deg]C and the Associated 
Calculations
Background
    The minimum value for the burner monitor temperature during the 
localized fire stage (TminLOC) 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 (TminENG) 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.
    NHTSA sought comment on the possibility of allowing for a wider 
variation than 50 [deg]C below the pre-test temperatures. Furthermore, 
as currently specified, the minimum temperatures TminLOC and 
TminENG would be time-dependent variables because they are 
based on a time-dependent rolling average. Having TminLOC 
and TminENG being time-dependent is complex and would make 
the testing difficult to monitor. NHTSA sought comment on a simpler 
calculation for TminLOC and TminENG that will 
result in constant values for TminLOC and 
TminENG. NHTSA proposed that TminLOC be 
calculated by subtracting 50 [deg]C from the minimum value of the 60-
second rolling average of

[[Page 6247]]

the burner monitor temperature in the localized fire zone of the pre-
test checkout. Similarly, NHTSA proposed that TminENG 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 sought 
comment on whether these revised calculations for TminLOC 
and TminENG should be required.
Comments Received
    Most commenters opposed NHTSA's proposal to allow a wider 
temperature variation or change the calculation method for 
TminLOC and TminENG, instead requesting 
harmonization with GTR No. 13.
    HATCI and Auto Innovators both recommended maintaining the 50 
[deg]C variation requirement from GTR No. 13, stating that wider 
temperature variations could affect test results and impact CHSS 
design. Auto Innovators also requested that NHTSA align with GTR No. 13 
in terms of calculations for TminLOC and TminENG, 
particularly with respect to their time-dependent nature.
    TesTneT commented that the requirements in GTR No. 13 are clear. It 
stated that there is no need to modify the calculations or allow for 
wider temperature variations. It further stated that the revised 
calculations proposed by NHTSA are unnecessary, referencing section 
6.2.5.4.5.4 of GTR No. 13, which establishes the minimum values for 
TminLOC and TminENG.
    FORVIA also disagreed with the proposed changes, urging NHTSA to 
maintain the test procedure equivalent to GTR No. 13 for simplicity. It 
suggested discussing any potential simplifications during the 
development of GTR No. 13 Phase 3 rather than changing the existing 
method.
Agency Response
    NHTSA will maintain calculations for TminLOC and 
TminENG that are aligned with those specified in GTR No. 13, 
and as proposed in FMVSS No. 308 S6.2.5.3(h). NHTSA will not adopt 
wider temperature variations or simplified calculations for 
TminLOC and TminENG relative to GTR No. 13. The 
calculation method in the final rule specifies a 50 [deg]C variation 
from the 60-second rolling average of the burner monitor 
thermocouple(s) during the respective stage of the pre-test checkout. 
NHTSA notes that this method results in time-dependency of 
TminLOC and TminENG. Test labs should plot 
TminLOC and TminENG over time to observe the 
time-dependency of these variables.
g. Vehicle-Specific Shielding
Background
    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 explained in 
the NPRM that it believes that it is important for safety that the CHSS 
itself can withstand fire and safely vent in the event its shielding is 
compromised.\32\ 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 sought 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.
---------------------------------------------------------------------------

    \32\ See 89 FR 27524 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

Comments Received
    Agility commented that there is insufficient justification to 
deviate from GTR No. 13 in this area, stating that damaged vehicle 
shielding could compromise PRDs as well. It stated that vehicle-level 
protection is appropriate for addressing localized fire risks and 
stated that vehicle-specific shielding should not be excluded as it is 
part of the container's fire protection. TesTneT stated concerns that a 
crash could also compromise a CHSS's ability to vent properly in a 
fire, suggesting that the test's length, duration, and intensity are 
somewhat arbitrary. It stated that surviving the test without 
attachments does not necessarily guarantee survival in a real-world 
vehicle fire, which could vary significantly.
    MEMA commented that NHTSA already acknowledges the importance of 
protective attachments in other tests, such as surface damage and 
chemical corrosion tests. MEMA requested that NHTSA allow vehicle-
specific shields where applicable.
    FORVIA strongly opposed excluding vehicle-specific shielding and 
container attachments from CHSS fire testing. It stated that including 
shields in the test provides a more accurate representation of real-
world vehicle fire scenarios. FORVIA stated that if shields are 
excluded, manufacturers may resort to more complex and costly 
protection methods, reducing the practicality of these systems. It 
requested that shields remain part of fire testing to fully assess all 
safety features. FORVIA requested that shields be specified by 
manufacturers, and also stated that it is important to include 
container attachments in the fire test. Nikola stated support for the 
provisions in GTR No. 13 and stated that allowing container attachments 
in the test is appropriate and both options should be permitted.
Agency Response
    NHTSA has considered the comments submitted regarding the inclusion 
of vehicle-specific shielding and container attachments in the test for 
service terminating performance in fire. While several commenters 
advocated for allowing vehicle-specific shielding to be part of the 
fire test, NHTSA maintains its position to exclude vehicle-specific 
shielding from the CHSS fire test.
    It is important that the CHSS itself can withstand fire exposure 
and properly vent in the event of a failure, regardless of any 
additional vehicle-level protection. This approach is based on the 
possibility that vehicle shielding or other protective elements could 
be compromised in real-world scenarios, such as during a crash. If the 
vehicle shielding is damaged or removed, the CHSS must still be able to 
perform its critical safety function without relying on external 
protection. Including vehicle-specific shielding in the test would not 
adequately evaluate the inherent fire resistance and safety performance 
of the CHSS.
    In addition, vehicle-specific shielding introduces unnecessary 
complexity into the testing process which could affect repeatability 
and reproducibility of the results. Testing that focuses on the CHSS 
itself provides a consistent, uniform assessment that is critical to 
safety.
    Some commenters expressed concerns that the exclusion of vehicle-
level protection measures may not fully represent real-world fire 
scenarios. NHTSA recognizes these concerns but emphasizes that the 
primary goal of the fire test is to ensure the resilience of the CHSS 
as an independent system. In the

[[Page 6248]]

event of a crash or severe incident that compromises the vehicle's 
shielding, it is essential that the CHSS be capable of withstanding 
fire exposure and safely venting without the added protection of 
vehicle-level components.
    Furthermore, the proposed fire test procedure, based on GTR No. 13, 
is specifically designed to replicate realistic fire scenarios that 
vehicles may encounter. As detailed in the NPRM, the test includes both 
localized and engulfing fire stages, which reflect actual vehicle fire 
data.\33\ This data-driven approach ensures that the test conditions 
are neither arbitrary nor excessive, but instead provide a realistic 
assessment of the CHSS's performance during a fire.
---------------------------------------------------------------------------

    \33\ See 89 FR 27523 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

    Regarding container attachments, NHTSA clarifies that if the CHSS 
includes container attachments, they may be part of the fire test. 
Container attachments, as defined, are considered part of the CHSS 
itself.
h. Worst-Case Orientation
Background
    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 is subjective. NHTSA instead 
proposed that the CHSS be 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 positioning 
provides a challenging condition where the TPRD(s) may not sense the 
localized fire. NHTSA sought comment on the proposed orientation of the 
CHSS relative to the localized burner.
Comments Received
    TesTneT referenced section 6.2.5.5.2 of GTR No. 13, stating that it 
already provides clear instructions on how to identify a worst-case 
condition. It commented that while NHTSA proposed some challenging 
orientations, these may not necessarily represent the worst-case 
scenario, and there is no need to deviate from the guidance in GTR No. 
13. On the other hand, Nikola agreed with NHTSA's proposed orientation 
of the CHSS relative to the burner.
    Auto Innovators agreed with NHTSA on the need to address the 
subjectivity in defining a ``worst-case'' orientation but stated that 
this issue is already addressed in GTR No. 13, which offers clear 
instructions for identifying such conditions. It stated that while 
NHTSA's proposal may represent a challenging condition, it may not 
always be considered the worst-case scenario.
Agency Response
    NHTSA is maintaining the CHSS positioning specifications as 
proposed. NHTSA believes that its test procedure aligns well with the 
requirements of GTR No. 13 and will provide the level of safety 
intended by GTR No. 13's ``worst-case'' orientation. Further, NHTSA 
believes that the final standard will simplify determining the 
orientation for compliance testing.
    NHTSA disagrees with the commenters that GTR No. 13 provides clear 
instruction on how a worst-case condition is identified. GTR No. 13 
paragraph 6.2.5.5.2 states ``the CHSS test article shall be rotated 
relative to the localized burner to minimize the ability to [sic] TPRDs 
to sense the fire and respond. Shields, panels, wraps, structural 
elements and other features added to the container shall be considered 
when establishing the worst-case orientation relative to the localized 
fire as parts and features intended to protect sections of the 
container but can (inadvertently) leave other potions or joints/seams 
vulnerable to attack and/or hinder the ability of TPRDs to respond. For 
CHSS where the manufacturer has opted to include vehicle-specific 
features (as defined in paragraph 6.2.5.1.), the CHSS test article is 
oriented relative to the localized burner to provide the worst-case 
fire exposure identified for the specific vehicle.'' This specification 
requires the subjective judgement of the test lab and is therefore not 
objectively enforceable.
i. Jet Flame Measurement
Background
    Jet flames occurring anywhere other than a TPRD outlet, such as the 
container walls or joints, cannot exceed 0.5 meters in length. NHTSA 
sought comment on how to accurately measure jet flames.
Comments Received
    Nikola stated that because most jet fires exceed 0.5 meters, the 
presence of jet fire would result in a flame exceeding the length limit 
and be a clear test failure. However, it suggested that, if needed, the 
test facility can measure the jet flame length using video capture. 
Auto Innovators recommended using camera systems or similar imaging 
devices, such as infrared, to identify the length of jet flames. 
TesTneT commented that fire tests at its facility are monitored using 
several video cameras, and the flame length can be measured by 
comparing it to the known diameter of the container as seen in the 
videos. FORVIA also stated that jet flames are visible in practice, and 
the length can be measured by placing an object with a known length 
near the TPRD outlet and comparing the jet flame length to this object 
in video or pictures taken during the test.
Agency Response
    NHTSA will maintain the jet flame requirement as proposed. Jet 
flames occurring anywhere other than a TPRD outlet, such as the 
container walls or joints, may not exceed 0.5 meters in length. This 
0.5 meter limit aligns with GTR 13, as requested by many commenters, 
and seeks to minimize the safety risk because this is both the 
threshold at which a jet flame is clearly distinguishable from other 
flames present during testing and the point where the risk of spread to 
the surroundings increases significantly.
    NHTSA appreciates the comments regarding the measurement of jet 
flames using video capture, reference objects of known length, and 
thermal imaging technologies to accurately measure jet flame length 
during testing. NHTSA agrees that these methods offer practical ways to 
assess flame length in a manner that is consistent with real-time 
observations during testing.
    At this time, however, NHTSA will not prescribe a specific 
measurement methodology in the regulatory text. Instead, the method of 
measurement will be left to the discretion of the testing facility. 
Test laboratories are encouraged to use suitable techniques for 
ensuring compliance with the 0.5-meter jet flame requirement.
j. Heat Release Rate (HRR/A)
Background
    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. NHTSA 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

[[Page 6249]]

sufficient to ensure repeatability and reproducibility of the test. 
Therefore, NHTSA did not propose specifications for HRR/A. NHTSA sought 
comment on that decision.
Comments Received
    Auto Innovators disagreed with NHTSA's decision, recommending that 
HRR/A specifications be maintained to ensure test repeatability and 
reproducibility. It pointed out that the HRR/A specifications in GTR 
No. 13 were introduced to address inconsistencies observed in round-
robin testing between labs. It argued that without HRR/A 
specifications, the amount of heat energy delivered during testing 
could vary, potentially leading to inconsistent test results. HATCI 
also disagreed, stating that the absence of HRR/A specifications could 
cause variability in the energy delivered during testing, affecting the 
outcome. It recommended that NHTSA adopt the HRR/A specifications in 
GTR No. 13 to avoid this issue.
    Nikola supported maintaining the GTR No. 13 specification for HRR/
A, noting that the test has already been validated and used by several 
test labs globally. TesTneT also disagreed with NHTSA's decision, 
stating that HRR/A is important to the fire test because temperature 
measurements alone cannot always be relied upon. It explained that 
during testing, events like hydrogen venting or coatings dripping onto 
thermocouples can disturb temperature readings, and HRR/A provides a 
way to ensure that fire conditions remain consistent despite such 
disturbances. In contrast, H2MOF agreed with NHTSA's approach not to 
specify HRR/A.
Agency Response
    NHTSA is not including specifications for HRR/A. Such a 
specification 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.
    Failure to satisfy a temperature specification will result in an 
invalid test. Simply adding an additional specification related to HRR/
A will not resolve a failure to meet the temperature specifications. If 
the specified temperatures are not met, the test will be invalid 
regardless of whether an HRR/A specification is present and satisfied.
k. Wind Speed and Shielding
Background
    When testing is conducted outdoors, wind shielding is required to 
prevent wind from interfering with the flame temperatures. 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. Additionally, for 
consistency, the wind shielding used for the pre-test checkout must be 
the same as that for the CHSS fire test. NHTSA sought 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 sought comment on limiting wind speed 
during testing to an average wind velocity during testing to 2.24 
meters/second, as in FMVSS No. 304.\34\
---------------------------------------------------------------------------

    \34\ FMVSS No. 304, ``Compressed natural gas fuel container 
integrity,'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
---------------------------------------------------------------------------

Comments Received
    DTNA supported including wind shielding specifications in the 
regulatory text, stating that wind is critical to the spread of fire 
and that clear wind velocity limits would ensure reproducibility of 
test results. Glickenhaus agreed with NHTSA's proposal to limit wind 
speed to 2.24 meters per second, while HATCI recommended adding 
language to ensure wind does not affect flame direction or 
temperatures. HATCI also sought clarity on where wind speed 
measurements should be taken, recommending they occur between the wind 
shield and the test specimen, with the wind speed at the measuring 
point being near 0 meters per second.
    In contrast, Nikola commented that maintaining the correct 
temperature profile is sufficient and aligned with GTR No. 13, making 
wind speed specifications irrelevant. TesTneT argued that specifying 
wind speed is unnecessary, as the requirement to meet temperature 
specifications already accounts for wind interference. It added that 
wind gusts could momentarily exceed the limit, potentially invalidating 
the test, even if temperature conditions were maintained. TesTneT also 
noted that its use of a large diameter pipe for testing eliminates wind 
effects without needing a wind speed specification.
    MEMA stated a wind speed limit would be impractical, and that the 
fire itself could create an updraft, complicating efforts to limit wind 
speed. MEMA expressed concern that this requirement would cause 
deviations between GTR No. 13 and FMVSS No. 308, and requested that 
NHTSA eliminate the wind speed limit, instead recommending that wind 
speed only be measured and recorded, consistent with GTR No. 13. FORVIA 
also opposed the wind speed limit, stating it introduces unnecessary 
complexities and technical challenges, such as determining where and 
how to measure wind speed. It noted that wind can be unpredictable and 
suggested that industry practices, which involve conducting tests under 
calm conditions and recording wind speed, are sufficient to address 
this issue. FORVIA stated that the pre-test checkout already addresses 
draft effects from both external wind and the fire itself, making wind 
speed limits unnecessary.
Agency Response
    NHTSA is not including additional specification for wind or wind 
speed. FMVSS No. 308 requires that wind shielding be used for outdoor 
fire test sites. It also requires that the separation between the pre-
test container and the walls of the wind shields be at least 0.5 
meters. This standard requires test facilities to provide sufficient 
protection against wind to prevent an impact on test results.
    NHTSA is not including a requirement that air temperature, wind 
speed, and/or wind direction be measured and recorded if testing 
conducted outdoors. If these parameters are not used to conduct the 
test or determine the test result, then there is no reason to require 
them to be recorded. Manufacturers and test labs may wish to retain 
this information for their own purposes, but collecting this 
information is not a specific requirement of the test for service 
terminating performance in fire. As some commenters noted, the burner 
monitor temperature specifications already account for wind 
interference. If the temperature requirements are met during testing, 
this result indicates that wind is not interfering with the test to 
such a degree that would significantly affect the results.
11. Tests for Performance Durability of Closure Devices
Background
    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

[[Page 6250]]

devices for compressed hydrogen vehicle fuel containers,'' \35\ and 
CSA/ANSI HGV 3.1-2022, ``Fuel System Components for Compressed Hydrogen 
Gas Powered Vehicles.'' \36\ The GTR No. 13 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 proposed these requirements to be consistent with GTR No. 13, 
NHTSA sought 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. NHTSA 
requested that if commenters believe another approach or subset of 
tests is appropriate and meets the need for safety, that they provide 
specific detail on (1) the alternate approach or subset of tests and 
(2) how it meets the need for safety adequately.
---------------------------------------------------------------------------

    \35\ See https://webstore.ansi.org/standards/csa/csaansihprd2021.
    \36\ See https://webstore.ansi.org/standards/csa/csaansihgv2015r2019.
---------------------------------------------------------------------------

    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 sought 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.
Comments Received
    Auto Innovators expressed support for maintaining consistency with 
GTR No. 13 for the tests for performance and durability of closure 
devices. Luxfer Gas Cylinders commented that obtaining 13 TPRDs for 
testing would not be difficult and stated that the associated costs and 
time were not burdensome when compared to container testing. Nikola 
also supported adherence to GTR No. 13.
    WFS commented that the tests in GTR No. 13, Phase 2, are already 
aligned with industry standards such as CSA/ANSI HPRD 1 and CSA/ANSI 
HGV 3.1, and that these GTR No. 13 tests were chosen by the IWG of GTR 
No. 13 Phase 2 as the minimum required to ensure safety. WFS also 
suggested that FMVSS could potentially include a provision allowing 
closure devices compliant with relevant industry standards to be 
considered compliant with FMVSS requirements, except for occasional 
spot checks by NHTSA. FORVIA commented that while the proposed testing 
numbers are necessary for initial component validation and type 
certification due to their safety relevance, these numbers may not be 
needed for field surveillance testing. FORVIA suggested limiting the 
sample number to one per test and allowing NHTSA to focus selectively 
on specific tests at its discretion.
Agency Response
    Based on the comments, NHTSA is maintaining the proposed test 
requirements. The commenters indicated the tests are not overly 
burdensome and the number of tests has already been minimized to cover 
essential safety aspects. NHTSA received no alternative proposals or 
specific data showing how a reduced subset of the tests would 
adequately meet safety needs. Since commenters did not provide any 
evidence for removing tests, NHTSA will maintain the original testing 
scope as proposed to ensure safety and maintain consistency with GTR 
No. 13. Additionally, there is no option to certify compliance with any 
FMVSS requirement by simply stating compliance with a set of industry 
standards. Manufacturers must certify direct compliance with the 
applicable FMVSS.
a. Hydrogen Impurities and Testing With Inert Gas
Background
    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:
     Hydrogen gas compliant with SAE J2719_202003, ``Hydrogen 
Fuel Quality for Fuel Cell Vehicles,'' or
     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
     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 is critical for fuel cell operation; however, 
these contaminants 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 than or equal to 1 part per million particulate. NHTSA 
sought 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 sought comment on whether testing with a non-
reactive gas instead of hydrogen reduces test stringency.
Comments Received
    Auto Innovators stated the levels of impurities are important and 
that other impurities are addressed and limited in SAE J2719. Nikola 
agreed that no other impurities would impact the closure device tests. 
WFS stated that hydrogen with a purity of 99.97 percent and the 
specified water and particulate limits would be adequate, as additional 
impurity limits in SAE J2719 are relevant only to fuel cell 
performance.
    On the subject of testing with inert gas, comments were mixed. 
Agility noted that test stringency could vary depending on the specific 
test, citing a bonfire test as an example where replacing hydrogen 
could be less stringent. Conversely, Agility commented that using inert 
gases would not affect the stringency of TPRD flow rate measurements. 
Auto Innovators suggested that testing with hydrogen, helium, or a non-
reactive gas mixture containing detectable helium, in line with GTR No. 
13, would be acceptable as long as the test conditions, such as 
pressure levels and cycle numbers, remained unchanged. HATCI expressed 
similar support, stating that using a non-reactive gas under consistent 
conditions should not reduce stringency.
    Nikola commented that helium is an appropriate replacement for 
hydrogen in tests, as it does not compromise test stringency and 
facilitates testing procedures. WFS recommended aligning FMVSS with GTR 
No. 13, which lists acceptable gases such as hydrogen, helium, and non-
reactive gas mixtures containing detectable helium or hydrogen. WFS 
noted that nitrogen would be suitable for tests involving pressure 
stress, while helium would be appropriate for leak tests. WFS stated

[[Page 6251]]

that these test gas options are consistent with various industry 
standards.
    FORVIA expressed concerns about potential material compatibility 
issues with impurities not specified in the proposed requirements. It 
recommended consulting manufacturers if there are questions about 
compatibility. Additionally, FORVIA commented that while hydrogen tests 
can help assess resistance to hydrogen embrittlement and fatigue, the 
use of alternative gases like dry nitrogen should be suitable.
Agency Response
    NHTSA agrees with commenters that using an inert gas will not 
reduce the stringency of the tests for performance stability of closure 
devices. Therefore, in the final rule, NHTSA has added the option of 
using inert gas for conducting the tests for performance durability of 
closure devices. NHTSA notes there is no bonfire testing included in 
the tests for performance durability of the closure devices, nor any 
similar tests where the flammability of hydrogen would play a 
significant role in the outcome of the test.
    NHTSA does not expect that impurities below 0.03 percent will have 
any meaningful impact on the test results. Therefore, NHTSA is 
maintaining the specification for hydrogen at 99.97 percent purity, 
less than or equal to 5 parts per million of water, and less than or 
equal to 1 part per million particulate. As noted in the NPRM, while 
fuel cells are highly susceptible to impurities, the test for 
performance durability of closure devices does not involve operating or 
testing fuel cells, and therefore, strictly controlling the specifics 
of the impurities below 0.03 percent is of little importance.
b. TPRD
Background
    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 proposed 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 
sought comment on this requirement.
Comments Received
    Auto Innovators stated that it agrees with the agency proposal to 
integrate the TPRD failure assessment as when evaluating other aspects 
of performance. Nikola stated that this requirement aligns with GTR No. 
13, which mandates that the TPRD meet the criteria of each subsequent 
test. Therefore, Nikola stated, if a TPRD fails, the entire test is 
considered failed. Agility and Luxfer Gas Cylinders both stated that 
unintended activation could pose a safety risk, indicating support for 
the proposal.
    WFS, however, recommended leaving the test requirements as they are 
currently written in GTR No. 13, noting that pressure cycling is a 
unique test that involves pressure fluctuations which could directly 
cause TPRD failure. WFS stated that in other tests like corrosion, it 
is difficult to detect TPRD activation until a subsequent leak test, 
which serves as the main criterion to confirm failure. FORVIA disagreed 
with the proposal, arguing that the concept of ``activation'' is not a 
clear requirement and may be difficult to measure. FORVIA suggested 
that all tests, except for the stress corrosion cracking test, already 
use a leak test as the appropriate pass/fail criterion. For the stress 
corrosion cracking test, FORVIA noted that a separate pass/fail 
criterion is necessary, as exposure to ammonia solution does not 
necessarily cause TPRD activation or leakage.
Agency Response
    NHTSA is maintaining the requirement that the TPRD not activate 
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 TPRD should not 
activate outside of fire-related conditions. Activation during tests 
that do not simulate fire indicates malfunction and poses a safety 
risk. While some commenters suggest relying solely on the leak test, 
this approach does not fully address the hazards of unintended TPRD 
discharge. Unintended activation is a critical failure mode that 
warrants a direct requirement. Thus, the requirement to treat TPRD 
activation as a test failure is necessary to ensure safety.
    A separate test to detect TPRD activation is not necessary. A TPRD 
activation event will be evident to the test lab during the existing 
tests. TPRD activation is a significant event that will be clear 
through visual observation or other monitoring methods already in place 
during the tests.
(1) Pressure Cycling Test
Background
    The NPRM proposed that one TPRD unit undergo 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 noted that 
this number of cycles is higher than the maximum 11,000 pressure cycles 
applied to containers. NHTSA sought comment on the need for 15,000 
pressure cycles for TPRDs.
Comments Received
    Commenters generally supported NHTSA's proposal to require 15,000 
pressure cycles for TPRDs, aligning with GTR No. 13. Auto Innovators 
recommended that NHTSA maintain consistency with GTR No. 13 and stated 
that the 15,000-cycle requirement is harmonized with other industry 
standards. Agility also supported the proposal, stating that 15,000 
cycles are consistent with industry standards.
    Nikola commented that GTR No. 13 and the industry have agreed on 
this higher standard for TPRDs as a safety measure. WFS noted that 
during the development of GTR No. 13 Phase 2, Task Force 3 (TF3) 
recognized the need for a higher cycle count for primary closure 
components compared to containers. WFS stated that TF3 decided to 
harmonize TPRD cycle requirements with industry standards, establishing 
15,000 cycles to provide a slightly higher safety margin. WFS pointed 
out that TF3 applied the same approach to check valve pressure cycle 
requirements.
    FORVIA expressed support for the proposed 15,000 pressure cycles, 
noting that the recently updated UN ECE R134 also mandates 15,000 
cycles, aligning with GTR No. 13 Phase 2 and the NHTSA proposal. FORVIA 
suggested maintaining this standard as a safety margin and considering 
any revisions during Phase 3 of GTR No. 13.
Agency Response
    Consistent with GTR No. 13, and based on the comments received, 
NHTSA is maintaining 15,000 pressure cycles for TPRDs. NHTSA emphasizes 
that maintaining the 15,000 pressure cycle requirement for TPRDs is 
consistent with both GTR No. 13 and other relevant standards such as 
HPRD-

[[Page 6252]]

1.\37\ As noted by multiple commenters, TPRDs are critical safety 
components, and subjecting them to a slightly higher cycle count 
compared to containers provides an added safety margin, which is 
appropriate given their role in preventing catastrophic failures.
---------------------------------------------------------------------------

    \37\ See, https://webstore.ansi.org/standards/csa/csaansihprd2021.
---------------------------------------------------------------------------

(2) Accelerated Life Test
Background
    NHTSA proposed the accelerated life test consistent with GTR No. 
13. This test verifies that a TPRD will activate at its intended 
activation temperature, but also will not activate prematurely due to a 
long-duration exposure to elevated temperature that is below its 
activation temperature.
Comments Received
    Auto Innovators recommended NHTSA remain consistent with the 
requirements of GTR No. 13.
Agency Response
    NHTSA is maintaining the accelerated life test as proposed.
(3)Temperature Cycling Test
Background
    NHTSA proposed the temperature cycling test consistent with GTR No. 
13. This test verifies that a TPRD can withstand extreme temperatures 
while in service.
Comments Received
    Auto Innovators recommended NHTSA remain consistent with the 
requirements of GTR No. 13.
Agency Response
    NHTSA is maintaining the temperature cycling test as proposed.
(4) Salt Corrosion Resistance Test
Background
    NHTSA sought comment on the clarity and objectivity of the salt 
corrosion resistance test procedure. NHTSA asked that if commenters had 
suggestions on how to change the salt corrosion resistance test 
procedure, that they explain how their suggested changes improve the 
clarity and objectivity, and how they continue to meet the need for 
safety represented by this test.
Comments Received
    Auto Innovators and Nikola both recommended maintaining alignment 
with GTR No. 13. WFS also advised against changes, stating that the 
procedure aligns with existing industry standards in North America. WFS 
acknowledged that the 100-day test duration is more extensive compared 
to previous tests, such as a 144-hour salt spray test, but noted that 
this longer test reflects best practices adopted by U.S. automakers and 
integrated into industry standards for primary closure devices.
    FORVIA cautioned against adding additional criteria such as 
staining or pitting resistance, stating that these are cosmetic issues 
that are almost inevitable in aggressive salt corrosion conditions. It 
stated that GTR No. 13 specifies criteria like cracking, softening, and 
swelling, and that a requirement that TPRDs must not show signs of 
physical degradation would adequately addresses concerns about pitting 
and corrosion levels that could impact the device's function. FORVIA 
stated that the salt corrosion resistance test is a sufficient minimum 
baseline.
Agency Response
    Based on the comments received, NHTSA is maintaining the salt 
corrosion test as proposed. In GTR No. 13 and in the proposed standard, 
after the salt corrosion exposure, the TPRD units are subjected to the 
leak test, benchtop activation test, and flow rate test. Neither GTR 
No. 13 nor the standard container requirements related to cracking, 
softening, swelling, or physical degradation. NHTSA is not including 
such requirements in the standard for the salt corrosion test. 
Subjecting the TPRD to the leak test, benchtop activation test, and 
flow rate test is sufficient to evaluate the performance of the TPRD 
after the salt corrosion test exposure.
(5) Vehicle Environment Test
Background
    The vehicle environment test exposes the TPRD to the following 
fluids for 24 hours each: 19 percent sulfuric acid, 10 percent ethanol, 
and 50 percent methanol. GTR No. 13 does not specify the method of 
exposure to these chemical solutions. NHTSA sought comment on the 
exposure method. GTR No. 13 further specifies that ``cosmetic changes 
such as pitting or staining are not considered failures.'' NHTSA sought 
comment on including this specification and noted that pitting can be 
an aggressive form of corrosion which can ultimately lead to component 
failure due to cracking at the pitting site.
Comments Received
    Auto Innovators and HATCI both recommended that NHTSA align with 
GTR No. 13's criteria, which state that cosmetic changes are not 
considered failures. HATCI pointed out that the TPRD undergoes further 
performance evaluations, such as leak and flow rate tests, after the 
vehicle environment test. It stated that these subsequent tests would 
detect any significant degradation in performance caused by corrosion, 
ensuring safety.
    Luxfer Gas Cylinders commented that the 24-hour exposure is not 
aggressive enough to cause pitting and suggested removing references to 
cosmetic changes. Nikola added that pitting and cracking issues are 
associated with the use of brass, which is not commonly used for TPRDs, 
and stated that manufacturers already adhere to these requirements 
since they are harmonized with industry standards. WFS suggested that 
while the language in GTR No. 13 is sufficient, NHTSA could consider 
specifying an exposure method, as outlined in HPRD 1. WFS explained 
that this standard provides two methods--periodic spraying or full 
immersion--and recommended adopting this language if more detail is 
needed. However, WFS agreed that the current approach, which leaves the 
exposure method to the test lab, is also acceptable.
    FORVIA stated that the existing language provides sufficient 
guidance for conducting the test. FORVIA reiterated that cosmetic 
changes, like minor pitting, should not result in failure unless they 
indicate more significant corrosion issues. FORVIA also suggested 
discussing any potential test modifications in the future during GTR 
No. 13 Phase 3 development.
Agency Response
    Consistent with GTR No. 13, NHTSA will include the statement that 
``cosmetic changes such as pitting or staining are not considered 
failures'' in S5.1.5.1(e). Cosmetic changes such as pitting or staining 
that do not affect the performance of the component do not present a 
safety concern and are therefore not considered failures. NHTSA notes 
that, after the vehicle environment test, TPRDs must undergo the leak 
test, benchtop activation test, and flow rate test, as discussed below. 
These subsequent tests are sufficient to ensure the vehicle environment 
test has not degraded the performance of the TPRD.
    NHTSA agrees that either of the exposure methods described by WFS 
would be valid. There could also be other valid exposure methods. 
Therefore, NHTSA will not specify exposure by either immersion or by 
misting, and instead the test facility may determine an appropriate 
exposure method for the component.

[[Page 6253]]

(6) Stress Corrosion Cracking Test
Background
    The stress corrosion cracking test exposes the TPRD 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 sought comment on a more 
direct metric for ammonia concentration specification, such as 20 
weight percent ammonium hydroxide in water.
    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 sought comment on this performance 
requirement and on whether there are alternative requirements for this 
test beyond basic visual inspection, such as subjecting the TPRD to the 
leak test.
Comments Received
    Luxfer Gas Cylinders commented that using a more direct metric for 
ammonia concentration, such as 20 weight percent ammonium hydroxide in 
water, ``would be an improvement.'' It stated that this test is usually 
seen as a material test rather than a component test. Luxfer also 
stated that industry cylinder standards require stress corrosion 
testing specific to the material, which involves sectioning and 
microscopic visual inspection. It suggested that FMVSS No. 308 adopt 
the stress corrosion cracking test specified in ISO 11119, ``Gas 
cylinders--Refillable composite gas cylinders and tubes--Design, 
construction and testing--Part 2: Fully wrapped fibre reinforced 
composite gas cylinders and tubes up to 450 l with load-sharing metal 
liners,'' or ISO 11515, ``Gas cylinders--Refillable composite 
reinforced tubes of water capacity between 450 L and 3000 L--Design, 
construction and testing.'' Luxfer stated that a leak test is not an 
effective method to detect stress corrosion.
    Auto Innovators stated that material requirements for hydrogen 
applications are well established in industry standards. It recommended 
NHTSA refer to GTR No. 13 Phase 2, which outlines material evaluation 
and stress corrosion cracking tests for aluminum alloys. It stated that 
if these standards cannot be adopted as performance requirements, 
alternative measures should be considered.
    HATCI recommended harmonizing with GTR No. 13 Phase 2, in which the 
stress corrosion cracking test is confirmed through visual inspection. 
They cautioned that adding a leak test could lead to failures due to 
affected o-rings rather than actual TPRD issues. HATCI also noted that 
under GTR No. 13, the test only applies to TPRDs containing copper 
alloys and requested clarity on whether NHTSA intends to follow this 
approach.
    WFS suggested no changes to the test procedure in GTR No. 13, 
emphasizing that it is already harmonized with other standards such as 
HPRD 1:21 and ISO 19882, ``Gaseous hydrogen--Thermally-activated 
pressure relief devices for compressed hydrogen vehicle fuel 
containers.'' They commented that third-party laboratories are capable 
of adjusting the moist ammonia concentration and that visual 
examination is the appropriate pass criteria.
    Regarding the proposed concentration metric of 20 weight percent 
ammonium hydroxide, FORVIA disagreed with adding additional measurement 
criteria, noting that these tests are performed in temperature-
controlled laboratories with established procedures. They recommended 
making any new measurement criteria optional and compatible with the 
specific gravity method. FORVIA also stated that a leak test may not be 
appropriate and supported visual inspection as sufficient for 
identifying cracking or delamination, advocating for consistency with 
GTR No. 13.
Agency Response
    Regarding the performance requirement for the stress corrosion 
cracking test, NHTSA has decided to retain the visual inspection 
criterion as the only pass/fail measure. Visual inspection for cracking 
or delamination is the appropriate criteria for determining the results 
of the test. NHTSA considered the possibility of additional testing 
beyond visual inspection, such as leak tests, but concurs with the 
commenters that a leak test may not be the best test to evaluate for 
stress corrosion. Therefore, introducing a leak test would not 
effectively indicate whether stress corrosion cracking has occurred, 
and NHTSA has decided against requiring this additional test.
    NHTSA is not adopting the stress corrosion cracking test in ISO 
11119 or ISO 11515. NHTSA is implementing a stress corrosion cracking 
test aligned with GTR No. 13, as proposed in the NPRM.\38\ This test is 
sufficient to address the risk of stress corrosion cracking in TPRDs 
used in hydrogen vehicles. NHTSA is also not including the humid gas 
stress corrosion cracking testing for aluminum alloys from Part I of 
GTR No. 13. This test is not a requirement in GTR No. 13 and was not 
proposed in the NPRM. Therefore, this test is outside the scope of this 
final rule.
---------------------------------------------------------------------------

    \38\ See 89 FR 27531 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

    Lastly, NHTSA has decided to specify an ammonia concentration 
between 19 weight percent and 21 weight percent ammonium hydroxide 
solution in water as the standard concentration for this test. This 
decision is based on successful testing conducted by NHTSA, which used 
16.7 wt% ammonium hydroxide in water to evaluate closure devices.\39\ 
NHTSA believes specifying between 19 weight percent and 21 weight 
percent ammonium hydroxide in water provides a more practical metric 
for ammonia concentration specification than specific gravity, while 
still mirroring the effect of an ammonia-water mixtures with a specific 
gravity of 0.94. This specification using weight percent also addresses 
the ambiguity regarding the variability of specific gravity due to 
temperature fluctuations. This concentration of between 19 and 21 
weight percent falls with the range of commercially available pre-mixed 
ammonium hydroxide solutions.
---------------------------------------------------------------------------

    \39\ See the report titled ``GTR No. 13 Fire and Closures 
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be 
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.
---------------------------------------------------------------------------

(7) Drop and Vibration Test
Background
    NHTSA proposed the drop and vibration test consistent with GTR No. 
13. TPRDs are first dropped in any one of six different orientations. 
The units are vibrated for 30 minutes along each of the three 
orthogonal axes. The units are vibrated at a resonant frequency which 
is determined by using an acceleration of 1.5 g and sweeping through a 
sinusoidal frequency range of 10 to 500 Hz with a sweep time of 10 
minutes. According to GTR No. 13, the resonance frequency is identified 
by a ``pronounced'' increase in vibration amplitude. However, if the 
resonance frequency is not found, the test is conducted at 40 Hz. NHTSA 
was concerned that specifying a pronounced

[[Page 6254]]

increase in vibration amplitude could be partially subjective. NHTSA 
sought comment on more objective criteria for establishing resonance, 
such as a frequency where the amplitude of the response of the test 
article is at least twice the input energy as measured by response 
accelerometers. Furthermore, the acceleration level was not defined in 
GTR No. 13 for the resonant dwells. NHTSA sought comment on an 
appropriate acceleration level for the resonant dwells.
Comments Received
    Nikola stated that GTR No. 13 already has a defined resonance 
frequency and that the current test procedure is sufficient. WFS 
recommended maintaining the drop and vibration test as harmonized with 
GTR No. 13, noting that it is also consistent with HPRD 1:21 and ISO 
19882. WFS explained that the phrase ``pronounced increase'' was added 
to GTR No. 13 for clarity and stated that a test laboratory with 
vibration testing capabilities should be able to detect resonance, as 
most shaker table software can automatically identify it. WFS stated 
there was no need for additional criteria to establish resonance. 
Regarding the acceleration level for resonant dwells or the 40 Hz 
default, WFS indicated that it should remain at 1.5 g, which is the 
same level as used in the sine sweep portion of the test.
    FORVIA also supported keeping the test procedure harmonized with 
GTR No. 13, stating that while the measurement method is left open in 
the regulation, the definition of a pronounced increase is sufficiently 
precise. FORVIA commented that the test setup must be sensitive enough 
to identify the highest resonance, which is typically not an issue in 
practice. FORVIA expressed confusion over the justification for NHTSA's 
proposal to define resonance as a frequency where the amplitude 
response is at least twice the input energy, preferring to adhere to 
the existing GTR No. 13 criteria.
Agency Response
    NHTSA is maintaining the proposed requirement consistent with GTR 
No. 13. If a resonant frequency cannot be identified, the test is 
conducted at 40 Hz, which is sufficiently objective. As the commenters 
note, test facilities will be able to detect and identify the resonant 
frequency, and therefore NHTSA will allow test facilities to determine 
the appropriate resonant frequency, or otherwise they may use 40 Hz.
(8) Leak Test
Background
    NHTSA proposed the leak test consistent with GTR No. 13. The leak 
test evaluates the TPRD's ability to contain hydrogen at each of the 
following temperatures and pressures:

 Ambient temperature: 5[deg]C to 35[deg]C, test at 2 MPa and 
125 percent NWP
 High temperature: 85[deg]C, test at 2 MPa and 125 percent NWP
 Low temperature: -40[deg]C, test at 2 MPa and 100 percent NWP

    NHTSA sought comment on the need to perform the leak test at 2 MPa 
in addition to the higher pressures.
    The leak evaluation involves observing the pressurized unit for 
hydrogen bubbles while the unit is immersed in the temperature-
controlled fluid. If hydrogen bubbles are observed, the leak rate is 
measured by any method available to the test lab. The total leak rate 
must be less than 10 NmL/h, which represents an extremely low leak 
rate. NHTSA sought comment on the leak rate requirement of 10 NmL/hour, 
noting that this leak rate is much lower than the minimum hydrogen flow 
rate of 3.6 NmL/min necessary for initiating a flame.\40\ NHTSA sought 
comment on objective methods for measuring the leak rate.
---------------------------------------------------------------------------

    \40\ SAE Technical report 2008-01-0726. Flame Quenching Limits 
of Hydrogen Leaks. The paper finds that the lowest possible 
flammable flow is about 0.005 mg/s (3.6 NmL/min).
---------------------------------------------------------------------------

Comments Received
    Agility commented that performing the leak test at higher pressures 
is sufficient and that testing at 2 MPa is unnecessary, as leak rates 
typically decrease with lower pressures. Nikola stated the opposite, 
suggesting that a container is more likely to leak at low pressure and 
low temperatures due to decreased rigidity. HATCI agreed with Agility, 
indicating that testing at the higher pressure is adequate and 
additional testing at 2 MPa does not add to safety assurance. However, 
Auto Innovators supported harmonizing with GTR No. 13, stating it is 
important to evaluate seal performance under both low- and high-
pressure conditions as well as low temperatures.
    DTNA recommended revising the proposed leak rate of 10 NmL/h, 
stating that it is significantly lower than the minimum hydrogen flow 
rate necessary to initiate a flame and suggesting a limit of 3.6 NmL/
min instead. It stated that this higher limit would reduce the risk of 
flame initiation and account for testing variability. Agility, on the 
other hand, supported the 10 NmL/h leak rate, stating that it is 
consistent with HPRD 1 and GTR No. 13, and suggested using pressure 
measurements over time with trace gases as one method to determine 
leakage. Nikola acknowledged that although 10 NmL/h is a low rate, the 
impact could be amplified when considering multiple devices. It 
suggested using bubble tests to confirm the presence of leaks and 
employing mass spectrometers or gasometers to quantify the rate if 
bubbles are detected.
    FORVIA stated disagreement that 10NmL/min is a high leak rate, 
given the potential for multiple leakage points. It noted that this 
rate would be detectable through submersion and bubble tests but 
recommended maintaining consistency with GTR No. 13 for both TPRDs and 
valves. FORVIA supported the inclusion of the low-pressure leak test, 
stating that poor gasket designs can leak at low pressure but may 
become leak-tight at higher pressures.
    WFS also advocated for consistency with GTR No. 13, stating that 
the test accounts for both empty and full container conditions. It 
noted that while the high-pressure condition is typically the most 
severe, low pressure can be a challenging scenario in some cases. WFS 
supported the 10 NmL/h requirement as it aligns with HPRD 1:21 and ISO 
19882 and suggested leaving the choice of measurement methods to the 
testing laboratories, which have various available techniques for 
detecting leakage at these levels.
    MEMA agreed with omitting visual evaluations of bubble formation, 
as proposed by NHTSA, acknowledging the agency's aim to avoid 
subjective assessments. MEMA also supported the proposed maximum leak 
rate of 10 NmL/h.
Agency Response
    NHTSA is maintaining the leak test as proposed. The commenters 
established reasons for conducting the leak test at low pressure in 
addition to high pressure, including gaskets leaking at low pressure 
levels and decreasing container rigidity at low pressures and 
temperatures. Regarding the leakage limit of 10 NmL/h, NHTSA notes that 
there may be more than one TPRD on a vehicle. Therefore, the leakage 
from any single TPRD must be very low and the proposed leakage rate of 
10 NmL/h is a reasonable limit. Based on the comments, NHTSA will leave 
the leakage rate quantification method to the discretion of the test 
lab. As stated by the commenters, possible methods for quantification 
include capturing bubbles or measurement with sensitive hydrogen or 
helium leak detectors.

[[Page 6255]]

(9) Benchtop Activation Test
Background
    Three new TRPD units are tested to establish a baseline activation 
time, which is the average of the activation time of the three new 
TPRDs. TPRD units used in the pressure cycling test, accelerated life 
test, temperature cycling test, salt corrosion resistance test, vehicle 
environment test, and drop and vibration test are also tested in the 
benchtop activation test and these TPRDs must activate within 2 minutes 
of the average activation time established from the tests with the new 
units.
    GTR No. 13 does not provide any information on how to proceed when 
a TPRD does not activate at all during the benchtop activation test. A 
TPRD that does not activate when inserted into the oven or chimney is 
not functioning as intended and therefore presents a safety risk. As a 
result, NHTSA proposed that if a TPRD does not activate within 120 
minutes from the time of insertion into the oven or chimney, the TPRD 
is considered to have failed the test. The time limit of 120 minutes is 
selected based on the maximum possible duration of the CHSS fire test. 
NHTSA sought comment on this requirement.
Comments Received
    Agility supported the proposed 120-minute time limit for TPRD 
activation, describing the rationale as reasonable. Auto Innovators 
also agreed with NHTSA's proposal regarding the failure assessment for 
TPRDs that do not activate within the specified period. However, Nikola 
expressed concern, stating that 120 minutes is too long and dangerous, 
and that the activation window should be limited to 2 minutes beyond 
the baseline established by the new units.
    FORVIA agreed that a TPRD must function as intended and activate 
within a specified time and temperature range. It stated that a failure 
to activate within 120 minutes should be recognizable using sound 
engineering judgment. FORVIA suggested that the lack of an explicit 
time limit in GTR No. 13 might be intentional and recommended clear 
articulation of any additional failure criteria if introduced. It 
argued that such a long activation time is unnecessary, as a TPRD 
taking this long to activate under 600 [deg]C conditions would not pass 
the performance-based fire test.
    WFS disagreed with the 120-minute time limit, recommending that the 
benchtop activation test remain consistent with GTR No. 13. It noted 
that this test is harmonized with HPRD 1:21 and ISO 19882 and differs 
from the CHSS fire test. WFS argued that 120 minutes is excessively 
long for a chimney test, where activation usually occurs within 5 
minutes, and suggested a 10-minute limit as more appropriate. It also 
stated that qualified test labs can determine suitable cut-off times 
and safely vent gas in case of TPRD failure.
Agency Response
    Applying engineering judgment to determine whether a sample has 
passed or failed the benchtop activation test is likely to be 
subjective. In addition, a test lab determining an appropriate ``cut-
off time'' during the benchtop activation test may also be subjective. 
Therefore, NHTSA is maintaining the maximum time limit of 120 minutes 
from insertion into the oven or chimney for the TPRD to activate. Any 
TPRD that does not activate within 120 minutes from insertion into the 
oven or chimney during the benchtop activation test, including any of 
the TPRDs used to establish the baseline activation time, will be 
considered to have failed the test.
    The time limit of 120 minutes is not intended to set the activation 
performance timeframe. Instead, it is simply the maximum amount of time 
the test lab must wait without an activation before declaring the TPRD 
to have failed the test. This standard does not create a dangerous 
situation because TPRDs will likely activate much faster than 120 
minutes, and the CHSS fire test evaluates the performance of the 
overall system in a fire scenario. The CHSS fire test also has a time 
limit of 120 minutes for complete CHSS venting to below 1 MPa.
(10) Flow Rate Test
Background
    The flow rate test evaluates the TPRD for flow capacity of a TPRD. 
Flow rate through the TPRD is measured with the inlet pressurized to 2 
MPa and the outlet unpressurized. The lowest measured flow rate must be 
no less than 90 percent of a baseline flow rate established as the 
measured flow rate of a new TPRD. The number of significant figures 
used in the measurement of flow rate can impact the test result. For 
example, a test flow rate of 1.7 flow units compared against a baseline 
flow rate of 2.0 flow units does not meet the requirement. However, in 
this case, if flow rate were measured using only one significant 
figure, the two flow rates would be identical (2 flow units). As a 
result, NHTSA proposed requiring that the flow rate be measured in 
units of kilograms per minute with a precision of at least 2 
significant digits. NHTSA sought comment on this proposed requirement.
Comments Received
    Auto Innovators and HATCI expressed support for NHTSA's proposal 
regarding the use of flow rate measurement in units of kilograms per 
minute with a precision of at least two significant digits. Nikola also 
agreed with the proposal to use two significant digits. However, 
Agility opposed using mass flow rate units, emphasizing that the 
properties of different gases must be considered in such an approach. 
It stated that the use of percentage difference as specified in GTR No. 
13 is clear and not open to interpretation.
    WFS recommended no changes to the existing procedure in GTR No. 13, 
noting that the test is harmonized with HPRD 1:21 and ISO 19882. It 
argued that specifying units as kilograms per minute is unnecessary 
since most flow tests for hydrogen components are conducted in grams 
per second. It explained that the key aspect of the test is the 
comparison of one TPRD flow rate to another, making the specific units 
less critical. WFS also cautioned that requiring two significant digits 
might suggest a level of precision not achievable with current 
equipment, due to minor flow fluctuations during testing. It added that 
a flow rate measured in grams per second with one significant digit can 
be more precise than a rate in kilograms per hour with two significant 
digits. FORVIA provided a neutral stance but noted that GTR No. 13, 
HPRD 1, and ISO 19882 also use 2 percent.
Agency Response
    NHTSA is maintaining the specification for units of kilograms per 
minute with at least two significant digits. NHTSA conducted testing in 
which these units were used successfully by the test lab to evaluate 
TPRD flowrates.\41\ The test lab used a Coriolis meter to directly 
measure the mass flow rate through each TPRD in units of kg/min. NHTSA 
also notes that units are interchangeable, so other test labs may use 
units such as g/s and simply convert the results to kg/min using the 
appropriate conversion factors, while preserving the significant digits 
in the measurement.
---------------------------------------------------------------------------

    \41\ See the report titled ``GTR No. 13 Fire and Closures 
Tests'' which can be found at: https://downloads.regulations.gov/NHTSA-2024-0006-0002/attachment_4.pdf. This report will also be 
submitted to the National Transportation Library. https://rosap.ntl.bts.gov/.

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

[[Page 6256]]

(11) Atmospheric Exposure Test
Background
    GTR No. 13 includes an atmospheric exposure test to ensure that 
non-metallic components that are exposed to the atmosphere and provide 
a fuel-containing seal have sufficient resistance to oxygen. This test 
requires that the component not crack nor show visible evidence of 
deterioration upon exposure to pressurized oxygen for 96 hours at 70 
[deg]C. However, NHTSA is concerned that this test is not objectively 
enforceable because the requirement involves a subjective determination 
of evidence of deterioration. Furthermore, the test would require NHTSA 
to determine which components are non-metallic, exposed to the 
atmosphere, and provide a fuel-containing seal. As a result, this test 
was not included in the proposed FMVSS No. 308. NHTSA sought comment on 
not including the atmospheric exposure test.
Comments Received
    Agility stated that the atmospheric exposure test is appropriate 
for non-metallic materials, but noted that most hydrogen components are 
metallic and would not require such a test. It added that this test 
could be relevant for electrical components with plastic connectors. 
Auto Innovators and HATCI supported NHTSA's proposal to exclude the 
atmospheric exposure test, agreeing with the agency's reasoning. 
Glickenhaus also agreed with the decision, stating that the requirement 
for ``no visible deterioration'' is not objectively measurable and 
should be omitted.
    WFS commented that the atmospheric exposure test is used in various 
industry standards and noted that in third-party laboratories, 
determining cracks in rubber materials during testing has been clear 
for those incompatible with oxygen exposure. WFS indicated that even if 
the test is removed from FMVSS No. 308, manufacturers may still conduct 
the test in line with the requirements of industry standards. FORVIA 
stated that while it believes the test is feasible and visual 
inspection could serve as a pass/fail criterion, it expressed no 
objections if NHTSA decides to remove the test.
Agency Response
    NHTSA is not including the atmospheric exposure test in FMVSS No. 
308. The test criteria are not objectively enforceable, and the 
commenters did not provide any alternative criteria for conducting the 
test with improved objectivity. The commenters also did not provide any 
specific methodology for NHTSA to determine which components are non-
metallic and provide a fuel-containing seal within the closure device 
of interest.
c. Check Valves and Shut-Off Valves
(1) Hydrostatic Strength Test
Background
    The hydrostatic strength test is conducted to ensure the valves can 
withstand extreme pressure of up to 250 percent NWP. Additionally, the 
test also ensures that the burst pressure of the valves exposed to 
various environmental conditions during prior testing is not degraded 
beyond 80 percent of a new unexposed valve's burst pressure.
    In the event of a significant leak, it may become impossible for 
the test laboratory to increase pressure on the valve. This condition 
occurs when any increase in applied pressure is offset by leakage flow, 
thereby negating the pressure increase. If it occurs, it is not 
possible to complete testing. To address this issue, NHTSA proposed 
that valves shall not leak during the hydrostatic strength test, and 
that a leak would constitute a test failure. NHTSA sought comment on 
the requirement that valves not leak during the hydrostatic strength 
test.
Comments Received
    Auto Innovators agreed with NHTSA's proposal to require that valves 
not leak during this test. WFS also supported NHTSA's proposal, 
commenting that leakage during a hydrostatic strength test would 
signify a rupture of the pressure-containing boundary and thus 
constitute a failure. It pointed out that this detail is implied in HGV 
3.1-2022 and further clarified in ISO 19887, ``Gaseous Hydrogen--Fuel 
system components for hydrogen-fuelled vehicles,'' which states: ``The 
components shall be examined to verify that leakage or rupture has not 
occurred.'' WFS added that adopting this language could help with 
clarity and harmonization if NHTSA deems it necessary.
    In contrast, FORVIA disagreed with the proposal, stating that leak 
tightness above 125 percent NWP is not required and that such a 
requirement would not correspond to actual service conditions. It 
suggested that in the event of a leak during hydrostatic testing, there 
should be no test result, and the test should be repeated. FORVIA also 
commented that the leak test should sufficiently address this potential 
failure mode.
Agency Response
    While NHTSA proposed the requirement that the valve not leak during 
the hydrostatic strength test, this requirement is not intended to test 
specifically for leakage above 125 percent NWP. Unlike the leak test, 
the valve will not be submerged in a fluid and observed for bubbles 
from leakage during the hydrostatic strength test. Instead, this 
requirement is intended to avoid a situation where a test lab cannot 
complete testing due to significant leakage from the valve that 
prevents continued pressurization to the required pressures. Even if 
such a test were considered ``no result'' and repeated, the same leak 
could occur with subsequent test samples. Therefore, there needs to be 
a requirement that the valve not leak to an extent that prevents 
continued pressurization in accordance with S6.2.6.2.1(c) during the 
hydrostatic strength test. Accordingly, NHTSA is revising this part of 
the requirement to state the valve ``shall not leak to an extent that 
prevents continued pressurization in accordance with S6.2.6.2.1(c).''
    Regarding adding the language proposed by WFS, NHTSA is revising 
the language as stated above. This is the most clear and concise way to 
state the requirement.
(2) Leak Test
Background
    NHTSA proposed the leak test consistent with GTR No. 13, and 
similar to the leak test discussed above for TPRDs. NHTSA sought 
comment on objective methods for measuring the leak rate.
Comments Received
    Nikola stated that the specified leak rate of 10 NmL/h, while 
applicable to a single point, could accumulate quickly when considering 
multiple leak points throughout the CHSS. WFS commented that the leak 
test is harmonized with industry standards and can be measured using 
various methods, including bubble capture or sensitive hydrogen or 
helium leak detectors capable of measuring levels lower than visible 
bubbles. It stated there is no need for NHTSA to specify a particular 
measurement method, as it can be determined by the testing facility 
based on available equipment.
    FORVIA disagreed with the proposed leak rate of 10 NmL/h, stating 
that it is relatively high, especially if multiple leakage points in 
the vehicle are at this level. It suggested that the leak rate can be 
identified using submersion and bubble tests, but noted that more

[[Page 6257]]

accurate testing methods, such as global accumulation tests, are 
available.
Agency Response
    NHTSA is maintaining the leak test as proposed. NHTSA notes that 
there may be more than one closure device on a vehicle. Therefore, the 
leakage from any single closure device must be very low and the 
proposed leakage rate of 10 NmL/h is a reasonable limit. Based on the 
comments, NHTSA will leave the leakage rate quantification method to 
the test lab. As stated by the commenters, possible methods for 
quantification include capturing bubbles or measurement with sensitive 
hydrogen or helium leak detectors.
(3) Extreme Temperature Pressure Cycling Test
Background
    The extreme temperature pressure cycling test simulates extreme 
temperature conditions that may lead to gas release failures when 
combined with pressure cycling. The total number of operational cycles 
is 15,000 for the check valve, consistent with the 15,000 cycles used 
for the TPRD above. The total number of operational cycles is 50,000 
for the shut-off valve. The higher 50,000 cycles for the shut-off valve 
reflects the multiple pressure pulses the shut-off valve experiences as 
it opens and closes repeatedly during service. In contrast, the check 
valve only experiences a pressure pulse during fueling. NHTSA sought 
comment on the number of pressure cycles for check valves and shut-off 
valves.
    Pressure cycling is conducted at different environmental 
temperatures and pressures:

 Ambient: Between 5.0[deg]C and 35.0[deg]C, 100 percent NWP
 High: 85[deg]C, 125 percent NWP
 Low: -40 [deg]C, 80 percent NWP

    After cycling, each valve is subjected to 24 hours of ``chatter 
flow'' to simulate the chatter condition described above. Chatter flow 
means the application of a flow rate of gas through the valve that 
results in chatter as described above. NHTSA was concerned, however, 
that the application of chatter flow could be partially subjective. 
NHTSA sought comment on the following aspects of the chatter flow test:
     Appropriate methodology or a procedure for inducing 
chatter flow.
     Appropriate instrumentation and criteria to measure and 
quantify chatter flow such as a decibel meter and minimum sound 
pressure level.
     How to proceed in cases where no chatter occurs.
     The specific safety risks that are addressed by the 
chatter flow test.
     The possibility of not including the chatter flow test.
    In the case of shut-off valves, GTR No. 13 specifies that the 
chatter flow test is required only in the case of a shut-off valve 
which functions as a check valve during fueling and that the flow rate 
used to induce chatter should be within the normal operating conditions 
of the valve. However, NHTSA has no way of determining whether a shut-
off valve is functioning as a check valve during fueling or the normal 
operating conditions of the valve. As a result, NHTSA proposed that the 
chatter flow test will apply to all shut-off valves and will not 
specify flow rate limitations for the chatter flow test. NHTSA sought 
comment on this decision.
Comments Received
    Auto Innovators recommended aligning the number of pressure cycles 
with GTR No. 13. FORVIA expressed support for the proposed minimum 
values, confirming that 15,000 cycles for check valves and 50,000 
cycles for shut-off valves are consistent with GTR No. 13. Similarly, 
Nikola commented that safety devices should adhere to higher standards, 
in alignment with GTR No. 13. Agility suggested using 50,000 cycles for 
both check valves and shut-off valves.
    Regarding the chatter flow test, HATCI requested that NHTSA exclude 
this requirement if a CHSS component prevents chatter within the shut-
off valve, suggesting that manufacturers could provide documentation to 
demonstrate this. WFS stated that the test is harmonized with industry 
standards and stated it is sufficiently defined. It commented that GTR 
No. 13 already describes an appropriate methodology for inducing 
chatter flow by specifying a gas flow rate through the valve at the 
level that causes the most chatter. WFS stated that additional 
instrumentation, such as decibel meters, is unnecessary since chatter 
is detectable by ear. WFS also stated that if no chatter occurs during 
the flow test, GTR No. 13 specifies that the 24-hour chatter test is 
not necessary. Regarding the specific safety risks that are addressed 
by the chatter flow test, WFS stated that chatter could lead to 
premature wear and failure of the valve's check functionality. WFS 
recommended keeping the procedure as written in GTR No. 13, noting that 
if a shut-off valve lacks check valve functionality, the test should 
not be required since chatter only occurs during unidirectional flow 
through a check valve.
Agency Response
    NHTSA is maintaining the number of pressure cycles as proposed. For 
the reasons discussed in the NPRM, and confirmed by the commenters, 
15,000 pressure cycles for check-valves and 50,000 pressure cycles for 
shut-off valves are the industry standard for minimum safety of these 
components.\42\
---------------------------------------------------------------------------

    \42\ See 89 FR 27530, 27533 (Apr. 17, 2024), available at 
https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

    NHTSA is maintaining the chatter flow test as proposed. NHTSA will 
leave it to test labs to determine the flowrate that cases the most 
valve flutter. As the commenters note, this determination could be 
accomplished by listening for audible sound changes. In the case of 
valves that do not experience chatter, or vehicles with components that 
prevent chatter, the chatter flow test should not adversely impact the 
test results because these valves will not experience chatter. 
Therefore, a specific exemption is not required for shut-off valves 
that do not experience chatter or for vehicles that have components to 
prevent chatter flow.
    As stated above, NHTSA has no way of determining whether a shut-off 
valve is functioning as a check valve during fueling or the normal 
operating conditions of the valve; therefore NHTSA is maintaining the 
test as proposed. This determination is not expected to adversely 
impact test results because, as stated by the commenters, chatter only 
occurs during unidirectional flow through a check valve. Therefore, if 
a shut-off valve is not functioning as a check valve, it will not 
experience unidirectional flow nor chatter.
(4) Salt Corrosion Resistance Test
Background
    NHTSA proposed a salt corrosion resistance test for check valves 
and shut-off valves equivalent to the salt corrosion resistance test 
for TPRDs discussed above.
Comments Received
    Auto Innovators recommended that NHTSA maintain consistency with 
GTR No. 13. Nikola agreed with the proposal, noting that it is 
harmonized with industry standards.
Agency Response
    Based on the comments received, NHTSA is maintaining the salt 
corrosion test as proposed.

[[Page 6258]]

(5) Vehicle Environment Test
Background
    NHTSA proposed a vehicle environment test for check valves and 
shut-off valves equivalent to the vehicle environment test for TPRDs 
discussed above.
Comments Received
    Auto Innovators recommended that NHTSA remain consistent with GTR 
No. 13. Nikola stated that the tests from GTR No. 13 are aligned with 
industry standards and would be conducted by manufacturers regardless.
Agency Response
    Based on the comments received, NHTSA is maintaining the vehicle 
environment test as proposed.
(6) Atmospheric Exposure Test
Background
    For the reasons discussed above to the TPRD atmospheric exposure 
test, NHTSA did not propose the atmospheric test for check valves and 
shut-off valves.
Comments Received
    Auto Innovators and HATCI both expressed support for NHTSA's 
proposal to not include the atmospheric exposure test for check valves 
and shut-off valves. WFS suggested leaving the requirement in the 
FMVSS, consistent with its feedback on the atmospheric exposure test 
for TPRDs. However, it noted that if NHTSA chooses to remove the test, 
manufacturers will still perform it in accordance with HGV 3.1. FORVIA 
commented that the test is feasible, and a visible inspection could 
serve as a pass/fail criterion, but indicated that it would find it 
acceptable if NHTSA decided to eliminate this test.
Agency Response
    NHTSA is not including the atmospheric exposure test for check 
valves and shut-off valves for the same reasons discussed above for 
TPRDs.
(7) Electrical Tests
Background
    The electrical tests apply to the shut-off valve only. The 
electrical tests evaluate the shut-off valve for:
     Leakage, unintentional valve opening, fire, and/or melting 
after exposure to an abnormal voltage.
     Failure of the electrical insulation between the power 
conductor and casing when the valve is exposed to a high voltage.
    The exposure to abnormal voltage is conducted by applying twice the 
valve's rated voltage or 60 V, whichever is less to the valve for at 
least one minute. After the test, the valve is subject to the leak test 
and leak requirements. The test for electrical insulation is conducted 
by applying 1000 V between the power conductor and the component casing 
for at least two seconds. The isolation resistance between the valve 
and the casing must be 240 k[Omega] or more.
    Some valves may have requirements specified by their manufacturers 
for peak and hold pulse width modulation duty cycle. NHTSA sought 
comment on whether and how to adjust the proposed test procedure to 
account for a manufacturer's specified peak and hold pulse width 
modulation (PWM) duty cycle requirements.
Comments Received
    Commenters provided various perspectives on potential adjustments 
to the proposed test procedure to account for a manufacturer's 
specified peak and hold PWM duty cycle requirements. Auto Innovators 
stated that more information is needed to understand NHTSA's intent, 
emphasizing that ``operation of the valve has no bearing on insulation 
resistance'' and that the insulation resistance should be verified 
between a single conductor and the component casing, regardless of the 
modulation type. HATCI similarly stated that the PWM or peak 
specification is not relevant to the electrical tests, arguing that 
these tests are meant to check compliance under abnormal conditions, 
such as atypical voltages. Agility suggested that any inclusion of PWM 
requirements would go beyond the requirements of GTR No. 13 and would 
require further investigation, adding that it did not recommend 
including such requirements. WFS commented that the test should be 
consistent with GTR No. 13 and noted that peak and hold modulation is 
only applicable when testing to open a valve and keep it open, which is 
not the purpose of this insulation resistance test. WFS stated that the 
coil is not actually energized during this test, as it is similar to a 
Hipot test where one lead is attached to the coil and the other to the 
body to confirm insulation.
    FORVIA stated that NHTSA appears to be proposing new test 
procedures for valves, specifically related to PWM duty cycle 
requirements, and acknowledged concerns about additional certification 
tests to address specific manufacturer-set operational requirements. It 
stated that these operational conditions would already be thoroughly 
evaluated during the manufacturer's Design Validation (DV) and 
Production Validation (PV) phases, where the valve's performance is 
tested against specified requirements. FORVIA concluded that the 
existing DV and PV processes adequately address concerns about PWM duty 
cycles and stated that additional test scenarios are unnecessary. It 
also recommended maintaining equivalence with GTR No. 13 and noted that 
the test is independent of peak/hold or modulation of the voltage, as 
it validates the component's ``electrical robustness.''
Agency Response
    NHTSA is maintaining the electrical tests as proposed. As supported 
by the commenters, NHTSA has determined that procedures to account for 
pulse width modulation specifications are not necessary. The electrical 
tests expose the valve to abnormal voltages and evaluate its insulation 
resistance. The results of these tests will not be affected by PWM 
variations during testing.
(8) Vibration Test
Background
    The vibration test evaluates a valve's resistance to vibration. The 
valve is pressurized to 100 percent NWP and exposed to vibration for 30 
minutes along each of the three orthogonal axes (vertical, lateral, and 
longitudinal). After vibration, the valve shall comply with the leak 
test and the hydrostatic strength test to verify it retains its basic 
ability to contain hydrogen and resist burst due to over-
pressurization. GTR No. 13 also contains a requirement that ``each 
sample shall not show visible exterior damage that indicates that the 
performance of the part is compromised.'' Showing signs of damage is a 
subjective measure and lacks the objectivity needed per the Motor 
Vehicle Safety Act. Therefore, this language was removed.
Comments Received
    Auto Innovators expressed agreement with NHTSA's assessment, 
stating that the lack of an objective measure for evaluating vibrations 
justified the removal of the language. Nikola also indicated its 
agreement with this decision.
Agency Response
    NHTSA is maintaining the vibration test as proposed, which does not 
include the requirement regarding visible exterior damage indicating 
that the performance of the part is compromised.
(9) Stress Corrosion Cracking Test
Background
    NHTSA proposed conducting the stress corrosion cracking test in the

[[Page 6259]]

same manner and for the same reasons discussed above for TPRDs.
Comments Received
    Auto Innovators agreed with NHTSA's proposal.
Agency Response
    NHTSA will maintain an equivalent stress corrosion cracking test 
for check-valves and shut-off valves as the stress corrosion cracking 
test for TPRDs, discussed above.
12. Labeling Requirements
Background
    NHTSA proposed that the container label(s) include the following 
information:
     Manufacturer, serial number, and date of manufacture.
     The statement ``Compressed Hydrogen Only.''
     The container's NWP in MPa and pounds per square inch 
(psi).
     Date when the system should be removed from service.
     BPO in MPa and psi.
Comments Received
    Nikola recommended adding a DOT/FMVSS compliance statement to the 
label. MEMA agreed with NHTSA's proposal to list information such as 
the manufacturer's name and contact details, serial number, NWP, fuel 
type, and the container's service removal date. However, MEMA objected 
to including an inspection schedule on the label. It also pointed out 
that such a requirement is not part of GTR No. 13 and requested NHTSA 
reconsider its inclusion. Glickenhaus noted a lack of sufficient 
information to specify a performance standard for label attachment that 
would prevent localized degradation or stress.
Agency Response
    As discussed above, NHTSA will not require BPO to be 
listed on the container label. NHTSA is maintaining the other labeling 
requirements as proposed. These labeling and inspection requirements 
are consistent with the established labeling requirements for CNG fuel 
containers in FMVSS No. 304.\43\ Having this information on the 
container label will help operators properly maintain their vehicles 
through regular safety inspections.
---------------------------------------------------------------------------

    \43\ FMVSS No. 304, ``Compressed natural gas fuel container 
integrity.'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
---------------------------------------------------------------------------

    Additionally, since FMVSS No. 308 is a vehicle-level standard, the 
DOT/FMVSS compliance statement should be located on the vehicle itself, 
not directly on the container. Lastly, while concerns were raised about 
label attachment durability, label attachment methods are expected to 
be developed based on best practices, and this issue does not affect 
the requirement to specify information on the container label.

C. FMVSS No. 307, ``Fuel System Integrity of Hydrogen Vehicles''

Background
    FMVSS No. 307 sets requirements for the vehicle fuel system to 
mitigate hazards associated with hydrogen leakage and discharge from 
the fuel system, as well as requirements to ensure hydrogen leakage, 
hydrogen concentration in enclosed spaces of the vehicle, and hydrogen 
container displacement are within safe limits post-crash. The fuel 
system integrity requirements for normal vehicle operations would apply 
to all hydrogen-fueled vehicles, while the post-crash fuel system 
integrity requirements only apply to light vehicles and compressed 
hydrogen-fueled school buses regardless of GVWR. NHTSA sought comment 
on the application of FMVSS No. 307 to all vehicles, including heavy 
vehicles (vehicles with a GVWR greater than 4,536 kg (10,000 pounds). 
As proposed, portions of FMVSS No. 307 would apply to all hydrogen 
vehicles regardless of GVWR. However, not all vehicles would be subject 
to crash testing under FMVSS No. 307. As described below, passenger 
cars, multipurpose passenger vehicles, trucks and buses with a GVWR of 
less than or equal to 4,536 kg would be subject to barrier crash 
testing, as would school buses with a GVWR greater than 4,536 kg. Heavy 
vehicles other than school buses with a GVWR greater than 4,536 kg 
would not be subject to crash testing under the proposed standard.
Comments Received
    Agility commented that FMVSS No. 307 should not apply to all 
vehicles, citing significant differences between light and heavy 
vehicles that warrant separate consideration. It stated that while some 
requirements could be the same, fuel system-specific configurations and 
integration into the vehicle body should be addressed separately, given 
the differences in vehicle accelerations and impacts based on GVWR. 
Luxfer Gas Cylinders supported the application of FMVSS No. 307 to all 
vehicles. Auto Innovators stated that while the safety and integrity of 
hydrogen vehicles are priorities regardless of size, it does not 
support the inclusion of heavy vehicles under FMVSS No. 307 at this 
time. Auto Innovators cited the design implications for heavy vehicles, 
which have not been previously subject to such requirements, and called 
for further research to justify this inclusion. It recommended that if 
NHTSA considers including heavy vehicles, a comprehensive regulatory 
impact analysis should be conducted, and a new rulemaking proposal 
issued as either a separate rulemaking notice or a supplemental notice 
of proposed rulemaking. Auto Innovators also stated the need for 
additional research to determine if alternative test procedures are 
required to evaluate heavy vehicle performance and understand the 
potential impact on vehicle design. Nikola stated ``leave it to the OEM 
to decide.''
Agency Response
    NHTSA is maintaining the application of FMVSS No. 307 as proposed, 
consistent with GTR No. 13, which applies to both light and heavy 
vehicles.\44\ While Auto Innovators cited need for more research to 
support application of FMVSS No. 307 to heavy vehicles, Hyundai Motor 
Group noted that heavy commercial vehicles and buses will be important 
types of hydrogen powered vehicles. Indeed, NHTSA and industry expect 
heavy vehicles to comprise a significant portion of the hydrogen fleet. 
In 2023, about 33 percent of hydrogen-powered vehicles were commercial 
vehicles and this percentage is expected to grow in the coming 
years.\45\ Because hydrogen fuel poses risks regardless of a vehicle's 
GVWR, safety need compels that the requirements for normal vehicle 
operation apply to heavy vehicles just as they apply to light vehicles 
so long as the standard is able to be practicable and objective. The 
performance tests under normal vehicle operations adopted in the final 
rule are aligned with GTR No. 13 and have already been implemented for 
hydrogen powered vehicles (regardless of GVWR) in other

[[Page 6260]]

countries.\46\ These tests are simple and can be performed similarly 
for light and heavy vehicles. Therefore, the same minimum safety 
requirements must be applied to all vehicles that use compressed 
hydrogen as a fuel source. Specifically, heavy vehicles must meet the 
same requirements as light vehicles for fueling receptacles, hydrogen 
discharge systems, protection against flammable conditions, fuel system 
leakage, and tell-tale warnings provided to the driver. This approach 
also harmonizes with commenters' requests for harmonization with GTR No 
13.\47\
---------------------------------------------------------------------------

    \44\ The scope of GTR No. 13 states that ``[t]his regulation 
applies to all hydrogen-fueled vehicles of Categories 1 and 2 with a 
maximum design speed exceeding 25 km/h.'' ``Category 1 vehicle'' 
means a power-driven vehicle with four or more wheels designed and 
constructed primarily for the carriage of (a) person(s). ``Category 
2 vehicle'' means a power-driven vehicle with four or more wheels 
designed and constructed primarily for the carriage of goods. See 
TRANS-WP29-1045e, Annex 2, https://unece.org/DAM/trans/doc/2005/wp29/TRANS-WP29-1045e.pdf.
    \45\ See Global Market Insights: Hydrogen Vehicle Market size, 
https://www.gminsights.com/industry-analysis/hydrogen-vehicle-
market#:~:text=Hydrogen%20Vehicle%20Market%20size%20was,expenses%20as
sociated%20with%20hydrogen%20vehicles.
    \46\ See ECE R.134, ``Uniform provisions concerning the approval 
of motor vehicles and their components with regard to the safety-
related performance of hydrogen fuelled vehicles,'' https://unece.org/transport/documents/2024/10/standards/addendum-133-regulation-no-134-revision-1.
    \47\ Hyundai and Nikola are already producing vehicles that 
comply with GTR No. 13 fuel system integrity requirements. As of 
October 2024, Nikola has sold 235 fuel cell electric Class 8 heavy-
duty trucks in the United States. About 70 Hyundai Class 8 XCIENT 
fuel cell trucks have already been sold in the United States.
---------------------------------------------------------------------------

    Furthermore, NHTSA will not leave it to vehicle manufacturers to 
decide whether to apply FMVSS No. 307 to their vehicles. Allowing 
manufacturers to decide whether to apply FMVSS No. 307 to their 
vehicles would not be consistent with the application of other FMVSS.
    As discussed below, NHTSA agrees more research would be beneficial 
before the crash test requirements of FMVSS No. 307 are applied to all 
heavy vehicles. Hyundai suggested post-crash requirements similar to 
that proposed for heavy school buses. EMA suggested use of component 
level tests, while Nikola stated it is developing its own crash test 
requirements based on the FMVSS No. 214 side impact moving barrier 
crash test. This final rule only requires heavy vehicles to comply with 
the fuel system integrity requirements under normal vehicle operations. 
As discussed below, NHTSA is considering conducting research on post-
crash requirements for heavy vehicles and will consider the commenters' 
suggestions on this matter.
1. Enclosed or Semi-Enclosed Spaces Definition
Background
    GTR No. 13 defines ``enclosed or semi-enclosed spaces' as ``the 
special volumes within the vehicle (or the vehicle outline across 
openings) that are external to the hydrogen system (storage system, 
fuel cell system, internal combustion engine (ICE) and fuel flow 
management system) and its housings (if any) where hydrogen may 
accumulate (and thereby pose a hazard).'' NHTSA proposed a similar 
definition of ``enclosed or semi-enclosed spaces means the volumes 
external to the hydrogen fuel system such as the passenger compartment, 
luggage compartment, and space under the hood.'' NHTSA also proposed 
defining that ``hydrogen fuel system means the fueling receptacle, 
CHSS, fuel cell system or internal combustion engine, fuel lines, and 
exhaust systems.''
Comments Received
    EMA raised concerns about the proposed definition of ``enclosed or 
semi-enclosed spaces,'' calling it ambiguous and a departure from 
NHTSA's intent to harmonize with GTR No. 13. It commented that NHTSA's 
use of ``such as'' implies a non-exhaustive list, potentially 
encompassing unintended areas outside the vehicle's hydrogen system. It 
cited various references in the NPRM where NHTSA repeatedly linked 
``enclosed or semi-enclosed spaces'' to volumes that allow hydrogen 
accumulation. EMA highlighted specific alleged problems with the 
proposed definition's broadness, such as in the fueling receptacle 
requirements of S5.1.1, arguing the term's literal interpretation would 
limit receptacle mounting to components within the hydrogen system, 
leading to potentially unsafe situations. Similarly, in section 
S5.1.3.1(c) on pressure relief systems, EMA argued that directing 
hydrogen discharge solely towards the hydrogen system is unsafe. It 
noted that the proposed term appears nine times outside the definition 
in FMVSS No. 307, with several instances relating to hydrogen 
detection. EMA suggested revising the definition to align with GTR No. 
13 or adding a specification that such spaces are where hydrogen can 
accumulate and pose a hazard.
    FORVIA also expressed the need for clearer criteria, recommending 
NHTSA define ``semi-enclosed spaces'' by specifying volumes and 
enclosed sides to avoid testing ambiguities. Meanwhile, Auto Innovators 
opposed the inclusion of ``space under the hood'' in the definition, 
stating it diverged from GTR No. 13.
Agency Response
    NHTSA agrees with the commenters that the proposed definition of 
``enclosed or semi-enclosed spaces'' is vague and ambiguous. To avoid 
ambiguity, NHTSA has revised the definition of enclosed or semi-
enclosed spaces to mean ``the passenger compartment, luggage 
compartment, and space under the hood.'' This definition no longer 
contains the words ``such as,'' so it no longer implies the inclusion 
of ambiguous additional volumes beyond those listed in the definition.
    The ``space under the hood'' is included in the definition of 
enclosed or semi-enclosed spaces because there is a risk of hydrogen 
accumulation under the hood just as there is a risk of hydrogen 
accumulation in the passenger compartment and/or in the luggage 
compartment. If hydrogen were to accumulate heavily in the space under 
the hood, it could result in a fire if an ignition source were present. 
By including the ``space under the hood'' in the definition of enclosed 
or semi-enclosed spaces, the requirements of FMVSS No. 307 S5.1.3(b) 
apply, thereby preventing accumulation of hydrogen to unsafe levels 
under the hood.
    Furthermore, NHTSA believes that including ``space under the hood'' 
in the enclosed and semi-enclose spaces is consistent with GTR No. 13. 
GTR No. 13 defines enclosed or semi-enclosed spaces as ``the special 
volumes within the vehicle (or the vehicle outline across openings) 
that are external to the hydrogen system (storage system, fuel cell 
system, internal combustion engine (ICE) and fuel flow management 
system) and its housings (if any) where hydrogen may accumulate (and 
thereby pose a hazard).'' Space under the hood can be considered a 
special volume within the vehicle, external to the hydrogen system and 
its housings, where hydrogen may accumulate.
2. Fuel System Integrity During Normal Vehicle Operations
a. Fueling Receptacles
Background
    The first proposed requirement for the fueling receptacle was to 
prevent reverse flow to the atmosphere. The second proposed requirement 
was for a label with the statement, ``Compressed Hydrogen Only'' as 
well as the statement ``Service pressure ______ MPa (_____ psig).'' The 
label must also contain the statement, ``See instructions on fuel 
container(s) for inspection and service life.'' The third proposed 
requirement was for positive locking that prevents the disconnection of 
the fueling hose during fueling. The fourth proposed requirement was 
for protection against ingress of dirt and water to protect the fueling 
receptacle from contamination that could lead to degradation of the 
fuel system over time. The fifth proposed requirement was to prevent 
the receptacle from being mounted in a location that would be highly 
susceptible to crash deformations in order to prevent degradation in 
the

[[Page 6261]]

event of a crash. NHTSA also proposed that the receptacle be prevented 
from being mounted in the enclosed or semi-enclosed spaces of the 
vehicle because these areas can accumulate hydrogen.
    NHTSA proposed that the assessment for all five receptacle 
requirements would be by visual inspection. NHTSA sought comment on the 
proposed requirements for the fueling receptacle and on the objectivity 
of assessment by visual inspection.
Comments Received
    Luxfer Gas Cylinders questioned how NHTSA intends to conduct visual 
inspections of the fueling receptacle and inquired about the number of 
receptacles that would be tested annually. It also questioned how 
positive locking would be assessed for the variety of vehicle designs 
in service. Luxfer further commented on the requirement that the 
fueling receptacle should not be mounted in impact energy-absorbing 
areas, stating that since receptacles are typically mounted on a 
vehicle's outer surface for accessibility, any such surface is 
inherently vulnerable in a crash, making this requirement appear 
unnecessary.
    Auto Innovators noted that there is no reference test provided for 
the requirement to prevent reverse flow to the atmosphere and 
recommended using the GTR No. 13 leak test for check valves and shut-
off valves. It also requested clarification on the label location. Air 
Products recommended adding a disconnect switch to fueling receptacles 
for medium and heavy vehicles to prevent starting or drive-away, as 
used in light vehicles. It stated that GTR No. 13 Phase 2 standardizes 
references to fueling receptacle profiles to ensure vehicles are fueled 
only with appropriate pressure classes and prevent cross-fueling with 
other compressed gas dispensing stations. Air products cited standards 
ISO 17268, ``Gaseous hydrogen land vehicle refuelling connection 
devices,'' and SAE J2600, ``Compressed Hydrogen Surface Vehicle Fueling 
Connection Devices,'' in this context.
    HATCI expressed concerns about the lack of space for the proposed 
labeling requirements and recommended omitting additional lines of text 
compared to GTR No. 13. It supported the requirement to prevent ingress 
of water and oil, agreeing that this could affect the closure device 
tests. Nikola and Agility both stated that visual inspection is an 
acceptable means of assessment. FORVIA disagreed with the proposed 
requirements and requested that NHTSA align them exactly with GTR No. 
13.
Agency Response
    Regarding the requirement for the fueling receptacle to not be 
mounted in locations ``highly susceptible to crash deformations,'' the 
proposed requirements do not use the term ``highly susceptible.'' 
Instead, NHTSA proposed that ``[t]he fueling receptacle shall not be 
mounted to or within the impact energy-absorbing elements of the 
vehicle.'' However, in response to concerns raised, NHTSA has 
reconsidered the necessity of this requirement.
    The commenters correctly note that it is generally expected for the 
fueling receptacle to be mounted on the exterior of the vehicle to 
facilitate fuel filling, which inherently exposes it to potential 
damage in the event of a crash. NHTSA agrees that this reality limits 
the effectiveness and practicality of restricting the mounting location 
based on energy-absorbing elements of the vehicle. Given that any 
surface-mounted device, by its nature, could be subject to damage in a 
collision, maintaining the proposed restriction would not significantly 
enhance vehicle safety and could introduce unnecessary design 
constraints.
    Therefore, after careful review, NHTSA has decided to remove the 
requirement that fueling receptacles shall not be mounted in the 
energy-absorbing elements of the vehicle. This decision aligns with the 
practical considerations raised by commenters and reflects the 
understanding that modern vehicle design incorporates various safety 
mechanisms, such as reinforced mounting systems and advanced materials, 
that can adequately protect external components like fueling 
receptacles from damage without the need for this specific regulation. 
NHTSA believes that removing this requirement will not compromise 
safety objectives while allowing for greater flexibility in vehicle 
design.
    NHTSA is maintaining the other fueling receptacle requirements as 
proposed. NHTSA will conduct visual inspection by observation of the 
fueling receptacle, its location within the vehicle, and through basic 
operation of the vehicle such as attaching a fueling nozzle to the 
receptacle to test for positive locking. NHTSA has discretion regarding 
how many vehicles it inspects per year.
    NHTSA notes that the referenced GTR No. 13 leak test outlines the 
check valve and shut-off valve leak test. While a fueling receptacle 
may contain a check valve, the test procedure is not written to 
accommodate fueling receptacles. In addition, testing of CHSS check 
valves is already covered under FMVSS No. 308 S5.1.5.2, and it would be 
redundant to apply the same test to the receptacle. As a result, NHTSA 
is maintaining visual inspection as the evaluation method for the 
requirements of FMVSS No 307 S5.1.1.
    NHTSA is not requiring a disconnect switch to prevent vehicle 
starting and drive away on light duty vehicles. However, vehicle 
manufacturers are free to include this technology in their designs.
    NHTSA is also not including requirements for the fueling receptacle 
profile or setting requirements for different ``Pressure Classes.'' 
Such specification would be design restrictive.
    There is no exact location specified for the location of the 
fueling receptacle label. The presence of this label will be verified 
by visual inspection. Manufacturers may consider this inspection method 
when determining where to locate the label. The additional statement 
``See instructions on fuel container(s) for inspection and service 
life'' is consistent with FMVSS No. 303.\48\ This statement is 
important for the purpose of helping operators properly maintain their 
vehicles through regular safety inspections.
---------------------------------------------------------------------------

    \48\ FMVSS No. 303, ``Fuel system integrity of compressed 
natural gas vehicles,'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.303.
---------------------------------------------------------------------------

    Lastly, NHTSA notes that the fueling receptacle design is not 
standardized by GTR No. 13. The preamble to GTR No. 13 simply 
references industry standards where examples of fueling receptacles can 
be found. This language in GTR No. 13does not constitute a requirement 
or a standardization of the fueling receptacle. NHTSA believes fueling 
receptacle designs may still be evolving. Therefore, while there may be 
safety benefits to standardizing fueling receptable designs, to do so 
at this time would be premature.
b. Over-Pressure Protection for Low-Pressure Systems
Background
    NHTSA proposed GTR No. 13's requirement of over-pressure protection 
for low-pressure systems. Accordingly, the agency proposed requiring 
countermeasures to prevent failure of downstream components in the 
event a pressure regulator fails to properly reduce the fuel pressure 
from the much higher pressure in the CHSS. The activation pressure of 
the overpressure protection device shall be lower than or equal to the 
maximum allowable working pressure for the appropriate

[[Page 6262]]

section of the hydrogen system as determined by the manufacturer. NHTSA 
sought comment on the requirement for an overpressure protection device 
in the fuel system and how to test the performance of such a device.
Comments Received
    Auto Innovators recommended that NHTSA align with GTR No. 13 and 
avoid requiring an additional test. It stated that the main areas of 
GTR No. 13 cover CHSS, high-pressure closures, PRD, fuel lines, 
electrical safety, and performance and other subsystem requirements in 
the vehicle. It commented that the proposed overpressure protection 
falls under the ``Hydrogen Delivery'' system of a hydrogen fuel cell 
vehicle, which it stated should be outside the scope of this 
regulation. Auto Innovators noted that while low-pressure systems are 
not covered by GTR No. 13, it clearly defines overpressure protection 
for these systems as ensuring that ``the hydrogen system downstream of 
a pressure regulator shall be protected against overpressure due to the 
possible failure of the pressure regulator,'' which each manufacturer 
will verify. Thus, it stated that there is no need to add this 
requirement to FMVSS No. 307.
    HATCI supported NHTSA's proposal to harmonize with GTR No. 13 and 
agreed that an overpressure protection device should be included in the 
system. However, it stated that evaluating every overpressure 
protection device in a system would need to end with regulator failure 
and compromise the whole system. It suggested that if such evaluation 
is necessary, the device's operation could be verified at the component 
level by applying a reverse pressure. Agility found the requirement 
acceptable and proposed testing the component on a bench by measuring 
its activation pressure. It also noted the possibility of testing it on 
the vehicle by deliberately exposing a PRD to its activation pressure, 
though it cautioned that this exposure could pose risks to vehicle 
safety.
    Nikola commented that no additional test is needed since this 
component falls outside the scope of the regulation. FORVIA agreed with 
keeping alignment to GTR No. 13 Phase 2 and recommended using visual 
inspection as the test procedure. It argued that conducting an actual 
test on the vehicle would be difficult due to vehicle-dependent 
factors.
Agency Response
    Based on the comments received, NHTSA is removing the requirement 
for an overpressure protection device in the fuel system. There is no 
test available to evaluate the performance of the over-pressure 
protection device, and therefore the proposed requirement that ``the 
activation pressure of the over-pressure protection device be lower 
than or equal to the maximum allowable working pressure for the 
respective downstream section of the hydrogen system'' is 
unenforceable. Simply requiring a device to be present with no test to 
evaluate its performance does not improve safety, and therefore, the 
requirement for an over-pressure protection device has been removed.
c. Hydrogen Discharge Systems
(1) TPRD Discharge Direction
Background
    Consistent with GTR No. 13, NHTSA proposed that the TPRD vent line 
be protected from ingress of dirt or water to prevent contamination 
that could degrade or compromise the TPRD. NHTSA proposed several 
requirements related to the TPRD vent discharge direction, requiring 
that the TPRD discharge must not be directed towards nor impinge upon:
    1. Any enclosed or semi-enclosed spaces where hydrogen could 
unintentionally accumulate, such as the trunk, passenger compartment, 
or engine compartment.
    2. The vehicle wheel housing.
    3. Hydrogen containers.
    4. Rechargeable electrical energy storage system (REESS).
    5. Any emergency exit(s) or service door(s).
    In addition to these requirements, NHTSA proposed an additional 
requirement to protect potential occupants attempting to exit the 
vehicle or first responders approaching the vehicle. This requirement 
stated that hydrogen vented through the TPRD(s) be directed upwards 
within 20[deg] of vertical relative to the level surface or downwards 
within 45[deg] of vertical relative to the level surface. NHTSA sought 
comment on this additional requirement for TPRD discharge direction, 
and on the proposed discharge angles.
Comments Received
    Air Products commented that venting downward could be acceptable 
for light vehicles but recommended any downward TPRD vent flow should 
be diffused to minimize a jet fire scenario. It also proposed specific 
considerations for heavy vehicles, suggesting that venting should be 
oriented away from cargo and vertically positioned outside the CHSS 
enclosure and vehicle. It stated the importance of designing vent 
stacks to withstand back pressure, thrust forces, and vehicle 
accidents.
    Air Products also stated that venting high-pressure hydrogen in 
confined areas increases the likelihood of deflagration or detonation. 
It described the possibility of flame impingement at the TPRD outlet 
potentially leading to a cascading effect and larger hydrogen releases. 
It proposed modifications to include ``enclosed or semi-enclosed spaces 
including portions of the CHSS'' as a location the discharge shall not 
impinge upon.
    Agility stated that the proposed requirement for a discharge angle 
within 20 degrees of vertical does not align with existing standards. 
It suggested using the wording from GTR No. 13 and commented that while 
venting within 45 degrees of vertical from the top could be acceptable, 
venting from the bottom at any angle other than vertical could lead to 
horizontal gas/flame plumes, posing risks to passengers and first 
responders. Agility also noted that these requirements could become 
irrelevant in vehicle rollovers.
    Nikola and FORVIA both expressed concerns over the prescriptiveness 
of specifying venting angles. Nikola stated that discussions among 
experts concluded that manufacturers should be given the responsibility 
to determine safe venting designs. It cited GTR No. 13, which only 
specifies prohibited venting directions rather than mandating specific 
angles. FORVIA similarly stated that the topic is highly vehicle-
specific and should be addressed on a case-by-case basis. FORVIA noted 
that the phrase ``not be directed towards'' could be interpreted 
subjectively, leading to compliance challenges. FORVIA agreed with the 
requirements other than the venting direction angles, but recommended 
aligning the wording exactly with GTR No. 13.
    Luxfer Gas Cylinders viewed the proposed requirements as an 
improvement but indicated uncertainty about manufacturers' ability to 
comply. Auto Innovators did not support the proposed requirements in 
S5.1.3.1(b), citing extensive discussions within GTR No. 13 Phase 2, 
which highlighted structural differences among vehicles, especially 
heavy vehicles, that complicate establishing a ``one-size-fits-all'' 
requirement. It stated that prescribing discharge directions could 
limit design flexibility without improving safety. It also recommended 
deleting the proposed S5.1.3.1(c)(5) and

[[Page 6263]]

(6), because these requirements are inconsistent with GTR No. 13 and 
because the intent is not clear.
Agency Response
    NHTSA acknowledges commenters' stated concerns that setting 
specific discharge angles was extensively discussed during GTR No. 13 
Phase 2, and that the Informal Working Group ultimately chose not to 
include such specific requirements due to the complexities involved, 
especially given that vehicles--especially larger vehicles--have 
heterogenous designs and that a specific approach that works for some 
vehicles may not work for other vehicles. NHTSA also acknowledges that 
in certain situations, such as vehicle rollovers, angle requirements 
could become less relevant. After reviewing the comments and 
considering the real-world scenarios presented, NHTSA has decided to 
remove the proposed discharge angle requirements until more information 
is available to determine whether a generalized discharge angle is 
reasonable and beneficial. NHTSA will, however, retain the other TPRD 
discharge direction requirements as proposed. NHTSA notes that the 
requirements specify that ``[t]he hydrogen gas discharge from TPRD(s) 
of the CHSS shall not impinge upon'' as opposed to ``shall not be 
directed towards.''
    NHTSA is not adding any additional requirements based on cargo 
locations within the vehicle or vent stack design at this time. Similar 
to the above discussion, cargo-specific TPRD directional venting 
requirements may be overly prescriptive, and until more data is 
available, it could potentially be unworkable given the variety of 
vehicle designs and cargo configurations or be a suboptimal safety 
solution. Furthermore, requirements for vent stack design, such as 
ensuring mechanical support for thrust forces, are design 
considerations that NHTSA does not intend to regulate and are outside 
the scope of the proposed standards.
    Additionally, there is no need to specify additional portions of 
the CHSS to avoid venting onto, because the requirements list the 
container, which is the main component of the CHSS. Not directing TPRD 
discharge towards the container will effectively avoid the CHSS as 
well, so an additional specification regarding the CHSS would be 
redundant.
    Lastly, NHTSA is retaining the specifications regarding ``emergency 
exit(s) as identified in FMVSS No. 217'' and ``service door(s).'' As 
stated in the NPRM, the purpose of these requirements is to prevent 
safety hazards due to hydrogen discharge from the TPRD that could 
inhibit the ability of passengers to safely exit the vehicle.\49\
---------------------------------------------------------------------------

    \49\ See 89 FR 27536 (Apr. 17, 2024), available at https://www.federalregister.gov/documents/2024/04/17/2024-07116/federal-motor-vehicle-safety-standards-fuel-system-integrity-of-hydrogen-vehicles-compressed.
---------------------------------------------------------------------------

(2) Possible Test To Evaluate TPRD Discharge Direction
Background
    NHTSA proposed that the discharge direction from TPRDs and other 
pressure relief devices be evaluated through visual inspection. NHTSA 
sought comment on whether there is a more appropriate test.
Comments Received
    Nikola recommended relying on a visual inspection for evaluating 
TPRD discharge direction. In contrast, HATCI suggested that NHTSA adopt 
a detailed emission measurement method, which would use the end of the 
valve angle relative to horizontal, instead of solely depending on 
visual inspection.
Agency Response
    NHTSA will maintain visual inspection as the evaluation for TPRD 
discharge direction. It will be clear from the orientation of the TPRD 
and/or the TPRD vent lines where the TPRD discharge is being directed. 
While the suggestion to use valve angle measurements to verify 
compliance is plausible, the commenters did not provide a specific 
procedure for conducting an objective valve angle measurement. If a 
more comprehensive and detailed testing procedure is identified in the 
future, the agency may consider incorporating it in the future.
d. Vehicle Exhaust Systems
Background
    NHTSA proposed the vehicle exhaust requirements outlined in GTR No. 
13. NHTSA proposed that the test procedure be conducted after the 
vehicle has been set to the ``on'' or ``run'' position for at least 
five minutes prior to testing. A hydrogen measuring device is placed in 
the center line of the exhaust within 100 mm from the external 
discharge point. The fuel system would undergo a shutdown, start-up, 
and idle operation to stimulate normal operating conditions. The 
measurement device used should have a response time of less than 0.3 
seconds to ensure an accurate three second moving average calculation. 
Response times higher than 0.3 seconds could result in inaccurate data 
collection because the sensor may not have time to register the true 
concentration levels before recording each data point.
    The time period of three seconds for the rolling average ensures 
that the space around the vehicle remains non-hazardous in the case of 
an idling vehicle in a closed garage. This time period is 
conservatively determined by assuming that a standard size vehicle 
purges the equivalent of a 250 kW (340 HP) fuel cell system.\50\ The 
time is then calculated for a nominal space occupied by a standard 
passenger vehicle (4.6 meters x 2.6 meters x 2.6 meters) to build up to 
25 percent of the LFL, or one percent by volume in air. The time limit 
for this rolling-average situation is determined to be three 
seconds.\51\
---------------------------------------------------------------------------

    \50\ In comparison, the power system output of a Toyota Mirai is 
182 HP.
    \51\ SAE 2578_201408. Recommended Practice for General Fuel Cell 
Vehicle Safety. Appendix C3. https://www.sae.org/standards/content/j2578_201408/.
---------------------------------------------------------------------------

Comments Received
    Luxfer Gas Cylinders questioned how NHTSA intends to ensure 
compliance with these requirements. Auto Innovators expressed support 
for harmonizing the exhaust requirements with GTR No. 13 but suggested 
revising the terminology from ``on'' or ``run'' position to align with 
the GTR standard, which specifies that ``the propulsion system of the 
test vehicle is started, warmed up to its normal operating temperature, 
and left operating for the test duration.'' Nikola stated agreement 
with adopting the requirements in GTR No. 13.
Agency Response
    NHTSA will ensure compliance with the requirements of FMVSS No. 307 
S5.1.2.2, Vehicle exhaust system, by testing vehicles in accordance 
with FMVSS No. 307 S6.5, Test for the vehicle exhaust system. 
Additionally, for the reasons discussed below in section IV.C.2.f., 
Protection against flammable conditions, NHTSA has revised the 
requirement that ``the vehicle shall be set to the `on' or `run' 
position for at least 5 minutes prior to testing, and left operating 
for the test duration.'' The new requirement will specify that ``the 
vehicle propulsion system shall be operated for at least five minutes 
prior to testing and shall continue to operate throughout the test.'' 
This change ensures the safe operation of fuel cell vehicles during 
testing while still meeting the intended objectives of the proposed 
test protocol.

[[Page 6264]]

e. Fuel System Leakage
Background
    GTR No. 13 includes fuel system leakage requirements specifying no 
leakage from the fuel lines. A flammable or explosive condition can 
arise if hydrogen leaks from the fuel lines and accumulates. However, 
the safety risk of a leak applies to the entire fuel system, not only 
to the fuel lines. As a result, NHTSA proposed that the fuel system 
leakage requirement for no leakage apply to the entire hydrogen fuel 
system downstream of the shut-off valve, which includes the fuel lines 
and the fuel cell system. NHTSA further proposed to define fuel lines 
to include all piping, tubing, joints, and any components such as flow 
controllers, valves, heat exchangers, and pressure regulators. From a 
safety standpoint, there is no difference between a leak coming from 
fuel line piping, and a leak coming from a valve, pressure regulator, 
or the fuel cell system itself. Consistent with GTR No. 13, NHTSA 
proposed a strict no leakage standard. NHTSA sought comment on whether 
there is a safe level of hydrogen that may leak, and if so, what would 
be an objective leakage limit and how to accurately quantify hydrogen 
leakage from the fuel system.
    NHTSA proposed to test this requirement using either a gas leak 
detector or leak detecting liquid (bubble test). NHTSA sought comment 
if one of these tests is preferrable. NHTSA also proposed that the test 
be conducted with the fuel system at NWP after having been in the 
``on'' or ``run'' position for at least five minutes. NHTSA sought 
comment on whether alternative conditions would better simulate 
realistic scenarios when downstream lines are more likely to leak.
Comments Received
    Luxfer Gas Cylinders commented that either a gas leak detector or a 
bubble test is acceptable, noting the long-standing effectiveness of 
the bubble test and expressing support for the proposed five-minute 
warm-up period. Ballard Power Systems stated that achieving a strict no 
leakage standard is likely impractical due to the extensive use of 
elastomeric seals and non-metallic materials in fuel cell vehicles. It 
stated that fuel cell stacks typically have a leakage rate around 200 
mL/min hydrogen at the beginning of life, and that standards such as 
HGV 3.1 permit a maximum leak rate of 10 Ncc/h. It recommended 
establishing a leakage requirement that ensures flammable releases are 
negligible, suggesting that gas mixtures with hydrogen concentrations 
below the lower flammability limit do not pose combustion risks. 
Ballard proposed mitigation techniques like enclosing components prone 
to leaks and using ventilation and hydrogen detection to manage non-
flammable releases.
    Auto Innovators disagreed with a strict no leakage requirement, 
stating that leakage can be detected at very low levels well below 
hazardous thresholds using sensitive equipment. It advocated for 
aligning the allowable leakage rate with the single-point leakage 
definition in GTR No. 13. It also supported NHTSA's proposal for the 
five-minute warm-up but suggested adopting GTR No. 13's terminology and 
test conditions. Air Products recommended conducting the leak check at 
1.25 times NWP to align with industry standards.
    HATCI supported harmonizing with GTR No. 13 and advised adopting 
criteria that focus on leak detection at accessible fuel line sections, 
especially at joints, as specified in GTR No. 13 section 6.1.5. HATCI 
also proposed adopting a 3 percent hydrogen concentration limit as a 
flammability condition and suggested clarifying regulatory text 
regarding the vehicle's ``on'' or ``run'' position during testing. 
Agility noted that complete leak-free connections are impossible and 
referenced SAE J1267, which states that ``absolute leak tightness is an 
absolute impossibility.'' It recommended specifying maximum allowable 
leak rates consistent with existing standards, emphasizing that both 
bubble solutions and electronic leak detection are feasible methods.
    Nikola proposed adopting GTR No. 13's leak rate requirement of 
0.005 mg/s and supported the bubble test as a reliable method to check 
for joint leaks, suggesting that more advanced instrumentation be 
required only if a bubble test indicates leakage. Hyzon expressed 
concerns about the subjectivity of bubble testing and recommended that 
NHTSA use additional accurate testing methods, including detection 
devices that meet industry standards. NFA commented that a safe level 
of hydrogen leak should reference standards like SAE technical paper 
2008-01-0726, ``Flame Quenching Limits of Hydrogen Leaks,'' and SAE 
J2579, which limit leak rates to prevent hazardous concentrations. It 
questioned why FMVSS No. 308 would apply a different standard to the 
CHSS compared with the standard that applies to the rest of the fuel 
system. NFA emphasized the practicality of bubble tests for detecting 
localized leaks and noted that metallic ferrule style tube fittings can 
be validated to be bubble-tight.
    FORVIA suggested revising the wording of the proposal to specify 
``no detectable leakage'' based on a test method or minimum measurement 
sensitivity. DTNA argued that a zero percent leak rate is not feasible 
due to hydrogen's chemical properties and current measurement 
technology limitations. It proposed a leak rate below 3.6 NmL/min, 
which it stated is the lowest flow necessary for flame initiation.
Agency Response
    NHTSA has determined that a demonstratable ``no leakage'' standard 
as evaluated by a bubble test is consistent with GTR No. 13, which 
specifies that ``the hydrogen fueling line downstream of the main shut-
off valve(s) shall not leak.'' GTR No. 13 does not provide any leakage 
limit in either section 5.2.1.5 or 6.1.5. Thus, NHTSA's application of 
a demonstratable no-leakage requirement as evaluated by a bubble test 
aligns with GTR No. 13.
    NHTSA acknowledges the concerns regarding the practicality of 
achieving a true no-leakage standard, noting that very low levels of 
hydrogen leakage may occur due to the tiny size of hydrogen molecules 
and the materials and sealing technologies used in hydrogen fuel 
systems. However, NHTSA emphasizes that any detectable hydrogen leakage 
poses potential safety risks. Even minimal levels of hydrogen leakage 
present the possibility of gas accumulation in enclosed spaces, which 
could create hazardous conditions. Multiple individual points of 
leakage could produce an additive effect where the cumulative leakage 
rate becomes significant.
    In response to suggestions that NHTSA define specific test methods 
for leak detection, the proposed regulation already includes objective 
test procedures for verifying compliance with the no-leakage 
requirement in FMVSS No. 307 S6.6. As such, suggestions to include 
additional specificity in test methods are redundant, as the regulation 
already addresses this concern. Furthermore, NHTSA is not including in 
S6.6 the statement ``primarily at joints'' that is found in GTR No. 13. 
This language is unnecessary, as NHTSA will be able to evaluate joints 
as well as other portions of the fuel system for leakage regardless of 
whether this language is included or not. Additionally, it is not 
possible to define a fuel system leakage limit based on a concentration 
of hydrogen in the surrounding air, as some commenters

[[Page 6265]]

suggested. Doing so would require several assumptions to be made 
regarding factors such as the volume of air in which the hydrogen may 
accumulate, the location of leakage points relative to the air volume, 
number of leakage points, and the possibility of air-exchange rates.
    To address concerns about the high sensitivity of leak detection 
equipment, NHTSA has decided to remove the option of using an 
electronic leak detector and will instead require the use of the bubble 
test method exclusively. As some commenters noted, the bubble test has 
been effectively used for decades and provides a practical, reliable 
means of visually detecting leaks. This method, which is less sensitive 
than advanced electronic leak detectors, is based on simple visual 
observation as to the expansion and/or propagation of bubbles and is 
not dependent on the subjective opinions of individuals. It addresses 
the need for an objective evaluation of leakage while acknowledging the 
concerns about detecting insignificant background levels of hydrogen 
that do not present a direct hazard. The bubble test will allow for a 
practical assessment of compliance with the no-leakage requirement 
without the possibility of test equipment detecting harmless levels of 
hydrogen. If no leakage is detectable using the bubble test specified 
in S6.6, then the vehicle will be deemed to have acceptable 
performance. To further clarify this standard, FMVSS No. 307 S5.1.4 has 
been revised to read: ``When tested in accordance with S6.6, the 
hydrogen fuel system downstream of the shut-off valve(s) shall not 
exhibit observable leakage.'' Adding the words ``exhibit observable 
leakage'' clarifies that leaks which do not result in observable bubble 
expansion during the S6.6 test procedure are not considered failures.
    Additionally, for the reasons discussed below in section IV.C.2.f., 
Protection against flammable conditions, NHTSA has revised the 
requirement that ``the vehicle shall be set to the `on' or `run' 
position for at least 5 minutes prior to testing, and left operating 
for the test duration.'' If the vehicle is not a fuel cell vehicle, it 
shall be warmed up and kept idling. If the test vehicle has a system to 
stop idling automatically, measures shall be taken to prevent the 
engine from stopping.'' The new requirement will specify that ``the 
vehicle propulsion system shall be operated for at least five minutes 
prior to testing and shall continue to operate throughout the test.'' 
This change ensures the safe operation of fuel cell vehicles during 
testing while still meeting the intended objectives of the proposed 
test protocol.
f. Protection Against Flammable Conditions
Background
    NHTSA proposed requiring a visual warning within 10 seconds in the 
event that the hydrogen concentration in an enclosed or semi-enclosed 
space exceeds 3.0 percent (75 percent of the LFL). Additionally, 
consistent with GTR No. 13, NHTSA proposed requiring the shut-off valve 
to close within 10 seconds if at any point the concentration in an 
enclosed or semi-enclosed space exceeds 4.0 percent (the LFL).
    GTR No. 13 provides two options for evaluating this requirement. 
The first option is to use a remote-controlled release of hydrogen to 
simulate a leak, along with laboratory-installed hydrogen concentration 
detectors in the enclosed or semi-enclosed spaces. The laboratory-
installed hydrogen concentration detectors are used to verify that the 
required warning and shut-off valve closure occur at the appropriate 
hydrogen concentrations in the enclosed or semi-enclosed spaces. GTR 
No. 13 allows for the remote-controlled release of hydrogen to be drawn 
from the vehicle's own CHSS. Therefore, by using this option, it is 
possible for a vehicle to meet the requirements without a built-in 
hydrogen concentration detector. This objective is accomplished by the 
vehicle monitoring hydrogen outflow from its CHSS. The vehicle can then 
trigger the required warning and shut-off valve closure if significant 
hydrogen outflow from the CHSS is detected that is not accounted for by 
fuel cell hydrogen consumption.
    The second option for evaluating the requirement is to use an 
induction hose and a cover to apply hydrogen test gas directly to the 
vehicle's built-in hydrogen concentration detector(s) within the 
enclosed or semi-enclosed spaces. Test gas with a hydrogen 
concentration of 3.0 to 4.0 percent is used to verify the warning, and 
test gas with a hydrogen concentration of 4.0 to 6.0 percent is used to 
verify the closure of the shut-off valve. The warning and shut-off 
valve closure must occur within 10 seconds of applying the respective 
test gas to the detector. The warning is verified by visual inspection, 
and the shut-off valve closure can be verified by monitoring the 
electric power to the shut-off valve or by the sound of the shut-off 
valve activation.
    This second option indirectly requires the presence of at least one 
hydrogen concentration detector in the enclosed or semi-enclosed spaces 
that can detect the hydrogen test gas and trigger the warning and shut-
off valve closure at appropriate hydrogen concentration levels. NHTSA 
proposed this second option as the only test method in FMVSS No. 307, 
which would thereby require each vehicle to have at least one built-in 
hydrogen concentration detector. NHTSA sought comment on requiring 
built-in hydrogen concentration detectors and on the reliability of the 
required warning and shut-off valve closure for vehicles that do not 
have built-in hydrogen concentration detectors.
    In addition to the above requirement regarding a warning and shut-
off valve closure, GTR No. 13 includes a requirement that any failure 
downstream of the main hydrogen shut off valve shall not result in any 
level of hydrogen concentration in the passenger compartment. This 
requirement is evaluated by applying a remote-controlled release of 
hydrogen simulating a leak in the fuel system, along with laboratory-
installed hydrogen concertation detectors in the passenger compartment. 
After remote release of hydrogen, GTR No. 13 requires that the hydrogen 
concentration in the passenger compartment not exceed 1.0 percent. The 
number, location, and flow capacity of the release points for the 
remote-controlled release of hydrogen are determined by the vehicle 
manufacturer.
    NHTSA instead proposed that the remote-controlled release of 
hydrogen shall not result in a hydrogen concentration exceeding 3.0 
percent in the enclosed or semi-enclosed spaces of the vehicle 
(including the passenger compartment). NHTSA sought comment on this 
requirement and on specific test procedures for initiating a remote-
controlled release of hydrogen in a vehicle.
    To evaluate this requirement, NHTSA proposed that a hydrogen 
concentration detector be installed in any enclosed or semi-enclosed 
space where hydrogen may accumulate from the simulated hydrogen 
release. After the remote-controlled release of hydrogen, the hydrogen 
concentration would be measured continuously using the laboratory-
installed hydrogen concertation detector. The test would be completed 
five minutes after initiating the simulated leak or when the hydrogen 
concentration does not change for three minutes, whichever is longer. 
Five minutes was selected as the minimum time for monitoring the 
hydrogen concentration because five

[[Page 6266]]

minutes is generally considered a sufficient time frame for vehicle 
occupants to evacuate in the event of an emergency.
Comments Received
    Agility commented that using built-in hydrogen detectors is 
feasible and analogous to requirements for liquified natural gas (LNG) 
vehicle systems. It emphasized the need for electronic detection due to 
hydrogen's odorless nature, comparing it to the established reliability 
of natural gas sensors. Agility also stated that any remote release of 
hydrogen should not be built into every vehicle directly, citing 
potential safety risks and increased costs. Instead, it recommended 
using separate testing equipment operated by qualified personnel.
    Luxfer Gas Cylinders expressed concern that requiring detectors and 
warnings for all enclosed and semi-enclosed spaces might be excessively 
difficult due to the number of such spaces in both light and heavy 
vehicles. Air Products suggested incorporating passive or mechanical 
ventilation into the CHSS to help dissipate leaks before they 
accumulate to hazardous levels, in addition to other safety measures.
    Glickenhaus raised safety concerns regarding the idling of fuel 
cell electric vehicles during tests, commenting that forcing fuel cell 
vehicles to idle could be dangerous or even impossible depending on the 
fuel cell's minimum output and battery capacity. Glickenhaus stated 
that while hydrogen internal combustion vehicles might idle safely, 
fuel cell vehicles could face significant risks of overcharging or 
electrical failure.
    HATCI sought clarity on specific test requirements. It questioned 
the definition of the air component in the mixed hydrogen gases for 
testing and expressed concerns over the difficulty of obtaining the 
specified mixtures based on geographical availability. Additionally, 
HATCI supported the flexibility in defining release points downstream 
of the shut-off valve, as proposed by NHTSA, allowing manufacturers to 
determine these parameters.
    Nikola recommended not adding an additional 10-second requirement 
for visual warnings beyond what is specified in GTR No. 13. It also 
preferred allowing OEMs to decide how to meet safety requirements 
rather than requiring built-in hydrogen detectors. It requested that 
NHTSA maintain the lower leakage concentration limit of one percent 
inside the passenger compartment to align with GTR No. 13. FORVIA 
disagreed with deviations from GTR No. 13, requesting that NHTSA keep 
the requirements fully aligned and avoid requiring hydrogen detectors 
in enclosed spaces, suggesting that ventilation might suffice as a 
safety measure.
Agency Response
    After careful consideration of the comments received, NHTSA has 
decided to maintain the proposed requirements, with the exception of 
revisions related to the idling requirements, discussed below, and the 
revision to the definition of enclosed and semi-enclosed spaces, 
discussed above.
    Regarding the use of built-in hydrogen detectors, some commenters 
supported their use, drawing parallels to systems required in LNG 
vehicles due to the lack of odorant in the fuel, which makes electronic 
detection necessary. NHTSA has determined that built-in hydrogen 
detectors are critical for safety. Hydrogen's odorless and highly 
flammable properties necessitate on-board hydrogen detection capability 
to mitigate risks. The proposed test method verifies that hydrogen 
detectors can activate a warning and shut-off valve closure within the 
prescribed time frame and concentration thresholds, thereby ensuring 
that vehicles can detect and respond to hydrogen leaks promptly. There 
will not be an excessive number of spaces that will require hydrogen 
detectors because, as discussed above, the definition of ``enclosed and 
semi-enclosed spaces'' has been revised to be very specific, including 
only the passenger compartment, luggage compartment, and space under 
the hood.
    With respect to concerns about remote-controlled hydrogen release 
for testing purposes, some commenters stated that incorporating this 
feature into every vehicle could introduce safety risks or unnecessary 
costs. This is not a correct interpretation of the proposal. FMVSS No. 
307 S6.4.2(b) states that ``[p]rior to the test, the vehicle is 
prepared to simulate remotely controllable hydrogen releases from the 
fuel system or from an external fuel supply.'' This language indicates 
the use of separate, specialized test equipment that is only applied to 
the test vehicle(s) rather than integrating the capability into all 
vehicles.
    Regarding the hydrogen concentration limit in the passenger 
compartment, some commenters advocated for maintaining the 1.0 percent 
limit specified in GTR No. 13, citing it as more conservative. However, 
NHTSA proposed a 3.0 percent limit in the enclosed and semi-enclosed 
spaces (not just the passenger compartment). The 3.0 percent limit 
aligns with the lower flammability limit (LFL) of hydrogen, and 
providing a more balanced requirement across all the enclosed and semi-
enclosed spaces and ensures that hydrogen concentrations remain below 
hazardous levels. NHTSA has therefore chosen to maintain this 
requirement as proposed. Note that the definition for enclosed and 
semi-enclosed spaces has been revised to eliminate ambiguity, as 
discussed above in section IV.C.1.
    Regarding the comment that the components of the air in the mixed 
gas were not defined in S6.4.1(b), this concern is unfounded. The 
proposed regulatory text specifies the required hydrogen concentrations 
in the test gas mixtures: ``The first test gas has any hydrogen 
concentration between 3.0 and 4.0 percent by volume in air to verify 
function of the warning, and the second test gas has any hydrogen 
concentration between 4.0 and 6.0 percent by volume in air to verify 
function of the shut-down.'' NHTSA can clarify that ``air'' refers to 
the natural atmospheric air composition, which is globally consistent 
across the surface of the Earth. Atmospheric air is primarily composed 
of approximately 78% nitrogen, 21% oxygen, and trace amounts of other 
gases such as argon and carbon dioxide. This standard atmospheric 
composition is well understood and used in numerous industrial and 
scientific applications. Therefore, the air component in the hydrogen-
air mixture is inherently defined and does not require additional 
specification or definition within the regulatory text.
    Regarding the time of 10 seconds to activate the warning or the 
shut-off valve closure, GTR No 13 does not contain a time limit for 
activation. The test can continue indefinitely if the warning has not 
come on or the shut-off valve has not closed. NHTSA cannot have a test 
that may continue indefinitely; therefore, the agency is maintain the 
proposed 10-second time limit to activate the warning and close the 
shut-off valve after the respective mixtures of hydrogen gas are 
applied.
    Lastly, concerns were raised about the idling requirements for fuel 
cell vehicles during testing. One commenter emphasized that forcing 
fuel cell vehicles to idle for extended periods could pose significant 
safety risks, including the potential for battery overcharging or fuel 
cell malfunction. NHTSA recognizes these concerns and has revised the 
regulatory language. The new requirement will specify that ``the 
vehicle propulsion system shall be operated for at least five minutes 
prior

[[Page 6267]]

to testing and shall continue to operate throughout the test.'' This 
change ensures the safe operation of fuel cell vehicles during testing 
while still meeting the intended objectives of the proposed test 
protocol.
(1) Wind Control During Testing
Background
    The proposed test procedures in this section would be conducted 
without the influence of any wind. NHTSA sought comment on providing 
more specific wind protection requirements and sought comment on 
limiting the maximum wind velocity during testing to 2.24 meters/
second, as in FMVSS No. 304.\52\
---------------------------------------------------------------------------

    \52\ FMVSS No. 304, ``Compressed natural gas fuel container 
integrity.'' https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B/section-571.304.
---------------------------------------------------------------------------

Comments Received
    Nikola commented that including wind influence in testing would not 
be feasible unless tests were conducted indoors, which would introduce 
additional complexities. It supported using the same wind velocity 
requirement as FMVSS No. 304. Auto Innovators agreed with NHTSA on the 
need to establish more specific wind protection requirements.
Agency Response
    After careful consideration, NHTSA has determined that it will not 
impose specific limits on wind velocity or require wind shielding 
measures as part of the testing protocol. While some commenters 
suggested adopting a wind velocity limit similar to that in FMVSS No. 
304, NHTSA has decided against incorporating explicit wind control 
specifications. Establishing objective wind control requirements, such 
as specifications for shielding or velocity limits, present logistical 
challenges. Furthermore, requiring all tests to be conducted indoors to 
completely eliminate wind effects could introduce additional safety and 
operational difficulties, further complicating the testing process. 
These challenges make prescriptive wind control requirements 
impractical across different test environments.
    Therefore, while NHTSA is maintaining the requirement that ``the 
test shall be conducted without influence of wind,'' the agency will 
allow individual test facilities the discretion to manage wind 
conditions according to their capabilities and procedures. This 
approach offers necessary flexibility, enabling laboratories to conduct 
tests under conditions suited to their operational constraints, while 
still ensuring the accuracy and reliability of test results.
g. Warning for Elevated Hydrogen Concentration
Background
    NHTSA proposed requiring a telltale warning when hydrogen 
concentration exceeds 3.0 percent in the enclosed or semi-enclosed 
spaces of the vehicle. NHTSA also proposed the visual warning be red in 
color and remain illuminated while the vehicle is in operation with 
hydrogen concentration levels exceeding 3.0 percent in enclosed or 
semi-enclosed spaces of the vehicle. The visual warning must be in 
clear view of the driver. For a vehicle with an Automated Driving 
System (ADS) and without manually operated driving controls, the visual 
warning must be in clear view of all the front seat occupants. NHTSA 
sought comment on whether the warning should be in clear view of all 
occupants, including occupants in rear seating positions, in vehicles 
equipped with an ADS. NHTSA also sought comment on whether an auditory 
warning should be required when hydrogen concentration exceeds 3.0 
percent in the enclosed or semi-enclosed spaces of the vehicle.
    NHTSA also proposed that a telltale be activated if the hydrogen 
warning system malfunctions, such as in the case of a circuit 
disconnection, short circuit, sensor fault, or other system failure. 
NHTSA proposed that when the telltale activates for these 
circumstances, it illuminate as yellow to distinguish a malfunction of 
the warning system from that of excess hydrogen concentration.
Comments Received
    Nikola expressed agreement with the proposal. Auto Innovators 
highlighted the need to align with the requirements in FMVSS No. 101, 
``Controls and displays,'' for vehicles equipped with ADS and 
recommended maintaining current placement requirements for visual 
warnings. It noted that defining ``clear view'' lacks objectivity and 
stated that auditory warnings should not be required in ADS-equipped 
vehicles until further research is conducted. It stated that ``near-
term flexibility'' may be needed to prevent consumer confusion. Auto 
Innovators supported the proposed activation criteria and color scheme, 
noting consistency with GTR No. 13.
    DTNA suggested adding an audible warning to supplement the visual 
warning, particularly for heavy vehicles and school buses with complex 
seating arrangements where occupants might not have clear visibility of 
the visual indicator. It stated that an audible warning would be 
essential for crew cabs, trucks with sleeper berths, and school buses, 
where a visual warning alone would not suffice to communicate risk 
effectively. Similarly, Glickenhaus supported the addition of an 
auditory warning and favored the placement of visual warnings in clear 
view of all seating positions in ADS-equipped vehicles.
    HATCI supported harmonization with GTR No. 13 and recommended 
determining visual warning requirements based on a vehicle's automation 
level. It stated that visual warnings should be in the driver's view 
for vehicles at SAE Levels 0 to 3 but more broadly visible for vehicles 
at SAE Levels 4 or 5. However, HATCI advised against requiring auditory 
warnings, citing concerns about potential confusion due to the numerous 
existing auditory alerts.
    NFA supported the inclusion of a visual telltale in red for high 
hydrogen concentration levels, in line with FMVSS No. 307, and agreed 
with the requirement for a yellow malfunction warning. NFA also 
provided context for its current hydrogen detection system, which 
includes warnings at 20 percent and 50 percent of the LFL, indicating 
that its system already meets the proposed standard. Regarding ADS-
equipped vehicles, NFA agreed with NHTSA's proposal as written, noting 
that transit buses are likely to retain an attendant or driver in the 
front seating position due to the additional duties they perform. NFA 
recommended that NHTSA consider how to address the requirements in 
scenarios where no front seat passengers are present.
Agency Response
    After careful consideration, NHTSA is maintaining the proposal as 
originally outlined. With respect to the inclusion of an auditory 
warning, NHTSA agrees that further research is necessary to assess the 
most appropriate auditory alerting mechanisms for hydrogen-fueled 
vehicles. While some commenters advocated for the inclusion of an 
auditory warning, NHTSA has determined that additional research is 
needed to evaluate the use of auditory alerts. For example, the 
possibility of voice alerts may need to be considered. Voice alerts may 
offer a clearer communication of the hazard without contributing to 
confusion. Additionally, NHTSA is cognizant that the proliferation of 
crash avoidance and driving automation systems has resulted in an 
increased number of telltales and auditory alerts, many of which are

[[Page 6268]]

voluntarily added by manufacturers. As such, NHTSA will not require 
auditory warnings at this time. The absence of a requirement for an 
auditory warning does not preclude manufacturers from voluntarily 
including such warnings based on their vehicle-specific configurations.
    Regarding visual warning placement, NHTSA will not adopt specific 
requirements based on SAE automation levels at this time. The scope of 
this final rule is not contingent on a particular vehicle type. NHTSA's 
focus remains on ensuring that the visual warning is in clear view of 
the driver or, for ADS-equipped vehicles without manual controls, in 
view of the front-seat occupants. This approach provides manufacturers 
with flexibility while maintaining safety for occupants in these 
advanced vehicles. This approach is also consistent with past updates 
to the crashworthiness FMVSS to account for ADS-equipped vehicles.\53\ 
The suggestion to include rear-seat occupants in ADS-equipped vehicles 
is not being implemented at this time, as NHTSA believes that further 
consideration is needed to determine the most effective and appropriate 
hydrogen warning systems for rear-seat occupants.
---------------------------------------------------------------------------

    \53\ See 87 FR 18560 (Mar. 30, 2022), available at https://www.federalregister.gov/documents/2022/03/30/2022-05426/occupant-protection-for-vehicles-with-automated-driving-systems.
---------------------------------------------------------------------------

    Finally, regarding the distinction between malfunction and hydrogen 
concentration warnings, NHTSA will retain the proposed color scheme, 
with yellow indicating a system malfunction and red indicating an 
elevated hydrogen concentration. This color differentiation is 
essential to ensure that drivers and occupants can quickly distinguish 
between a system malfunction and an immediate hydrogen-related hazard.
3. Post-Crash Fuel System Integrity
Background
    Consistent with GTR No. 13, NHTSA proposed that the post-crash 
requirements for vehicles that use hydrogen fuel for propulsion power 
only apply to passenger cars, multipurpose passenger vehicles, trucks, 
and buses with a GVWR less than or equal to 4,536 kg (10,000 pounds) 
and to all school buses. NHTSA did not propose that the post-crash 
requirements apply to all heavy vehicles with a GVWR greater than 4,536 
kg (10,000 pounds). NHTSA sought comment on whether heavy vehicles 
should be subject to these proposed post-crash requirements and, if so, 
what crash tests should NHTSA conduct on heavier vehicles.
    NHTSA proposed to use the crash tests equivalent to those applied 
to conventionally fueled vehicles in accordance with FMVSS No. 301. For 
light vehicles with a GVWR under 4,536 kg, these crash tests include an 
80 kilometers per hour (km/h) (~50 miles per hour (mph)) impact of a 
rigid barrier into the rear of the vehicle, a 48 km/h (~30 mph) frontal 
crash test into a rigid barrier, and a 53 km/h (~33 mph) impact of a 
moving deformable barrier into the side of the vehicle. For school 
buses with a GVWR greater than or equal to 4,536 kg, the crash test is 
a moving contoured barrier impact at 48 km/h. NHTSA sought comment on 
whether there are alternative crash tests that should be used for the 
forthcoming proposed regulations.
    NHTSA proposed that there be no fire during the test, and that 
vehicles meet three additional post-crash requirements described by GTR 
No. 13. The first proposed requirement is the volumetric flow of 
hydrogen gas leakage from the CHSS must not exceed an average of 118 
normal liters per minute (NL/min) from the time of vehicle impact 
through a time interval [Delta]t of at least 60-minutes after impact. 
The volumetric leak rate of hydrogen post-crash is determined as a 
function of the pressure in the container before and after the crash 
test. The interval [Delta]t is at least 60 minutes after impact and the 
pressure drop measurement should be at least 5 percent of the pressure 
sensor's full range. Helium may be used in place of hydrogen during 
crash-testing with an allowable leakage limit for helium of 88.5 NL/
min.
    The second requirement is a hydrogen concentration limit set to 
four percent by volume (for helium, this corresponds to a concentration 
of three percent by volume) in enclosed or semi-enclosed spaces. This 
requirement is satisfied if the CHSS shut-off valve(s) are confirmed to 
be closed within five seconds of the crash and there is no hydrogen 
leakage from the CHSS.
    For the purpose of measuring the hydrogen concentration, GTR No. 13 
specifies that data from the sensors shall be collected at least every 
five seconds and continue for a period of 60 minutes. GTR No. 13 also 
discusses filtering of the data to provide smoothing of the data, but 
is unclear about the exact data filtration method to be used. NHTSA 
proposed using a three-data-point rolling average for filtering the 
data steam. Since a data point will be collected at least every five 
seconds, this rolling average will be, at most, a 15-second rolling 
average. NHTSA sought comment on this proposed data filtration method.
    The third proposed requirement is that the container(s) remain 
attached to the vehicle by at least one component anchorage, bracket, 
or any structure that transfers loads from the device to the vehicle 
structure. This requirement is evaluated by visual inspection of the 
container attachment points. NHTSA will evaluate the presence of 
vehicle fire by visual inspection for the duration of the test, which 
includes the time needed to determine fuel leakage from the CHSS.
    In addition to these requirements, NHTSA sought comment on the 
safety need for a heavy vehicle sled test. NHTSA sought input and 
comment with supporting data on implementing a possible alternative 
heavy vehicle impact test for the CHSS. NHTSA sought comment on the 
possibility of including a moving contoured barrier impact test on 
heavy vehicles (other than school buses) in accordance with S6.5 of 
FMVSS No. 301.
Comments Received
    Auto Innovators supported NHTSA's decision to limit the scope of 
FMVSS No. 307 to light vehicles with a GVWR under 10,000 pounds and 
school buses. It requested that NHTSA conduct a regulatory impact 
analysis before including heavy vehicles. Auto Innovators noted that 
heavy vehicles have varied designs and are produced in low volumes, 
making full-scale crash testing complex and potentially cost-
prohibitive. It recommended that if NHTSA considers including heavy 
vehicles, it should issue a new rulemaking proposal through either a 
separate rulemaking notice or supplemental notice of proposed 
rulemaking. Regarding the proposed crash tests, Auto Innovators agreed 
with using existing crash tests for vehicles under 10,000 pounds GVWR, 
stating that existing crash tests are representative of commonly 
occurring crashes in the field and should be suitable for assessing the 
post-crash fuel system integrity of hydrogen vehicles. Auto Innovators 
opposed adding alternative crash tests for hydrogen vehicles without 
supporting data. Auto Innovators also stated that it agrees with 
NHTSA's proposed data filtration method.
    Hyundai concurred with NHTSA's initial decision to apply the post-
crash requirements for heavy vehicles only to school buses but 
highlighted the potential significance of heavy commercial vehicles for 
hydrogen applications. It stated that post-crash fuel system integrity 
should be a

[[Page 6269]]

consideration for these vehicles. It stated that the moving deformable 
barrier test for heavy school buses could be adapted to include other 
heavy vehicles. However, if the adaptation would delay the rulemaking, 
Hyundai suggested that NHTSA consider a follow-on rulemaking to address 
heavy vehicle standards once those procedures have been developed.
    Agility agreed with NHTSA's decision to keep the post-crash 
requirements separate for heavy vehicles, stating that these vehicles 
differ significantly from light vehicles and require careful 
consideration and research before establishing specific crash testing 
requirements. It suggested benchmarking existing standards for light 
vehicles as a starting point and adapting similar procedures with 
appropriate performance criteria for heavy vehicle applications. 
Agility proposed focusing on fuel system-specific tests, such as a sled 
test, to account for the complexity of heavy vehicle configurations, 
stating that such tests could yield consistent results independent of 
the vehicle's body type or chassis. It also noted that current 
practices under FMVSS Nos. 303 and 304 have been adequate for heavy CNG 
vehicles and that a sled test could serve as a viable alternative to 
full vehicle crash tests, potentially simplifying the process. Agility 
also supported the use of a 15-second rolling average for data 
filtration.
    DTNA supported NHTSA's decision to exclude heavy vehicles, other 
than school buses, from the proposed post-crash requirements, citing 
the lack of existing comparable crash tests and the high costs of 
conducting full-scale tests for heavy vehicle configurations. DTNA 
recommended a partial vehicle impact test using a moving deformable 
barrier (MDB), which allows for evaluating crash protection components 
like shields and panels without the need for full-vehicle tests. It 
suggested that vehicle simulations could also be used to assess these 
components. DTNA supported retaining the moving contoured barrier test 
for school buses over 10,000 pounds GVWR, as it aligns with current 
FMVSS No. 301 standards. It proposed a simulation similar to the 
Federal Motor Carrier Safety Administration's 30-foot drop test 
requirements outlined in 49 CFR 393.67(e)(1) but advised against 
conducting a 30-foot drop test solely on the container, stating that 
this test would not reflect real-world conditions since hydrogen 
containers often have additional protective components.
    EMA supported component-level testing for heavy vehicles, noting 
that full-scale crash tests would be impractical due to the custom 
designs and low production volumes of these vehicles. It stated that 
international standards such as GTR No. 20, ``Electric Vehicle 
Safety,'' and UN ECE R100, ``Uniform provisions concerning the approval 
of vehicles with regard to specific requirements for the electric power 
train,'' rely on mechanical shock tests at the component level. EMA 
agreed with the inclusion of crash tests for hydrogen-fueled school 
buses, as these tests align with FMVSS No. 301 and provide consistent 
safety standards with liquid-fueled buses. EMA stated that heavy school 
buses have relatively few model offering and vehicle configurations.
    Nikola supported applying side impact tests when the CHSS falls 
within the MDB impact zone defined by FMVSS No. 214, ``Side impact 
protection,'' and suggested allowing manufacturers to determine the 
specific impact zones based on vehicle design. Nikola completed 
frontal, side, and rear impact tests for its own designs and proposed 
that each manufacturer should be responsible for identifying the 
relevant strike zones on its vehicles. Nikola also stated that the 
proposed post-crash CHSS retention and leakage requirements seemed 
reasonable, but it did not see a need for a sled test.
    Hyzon agreed with NHTSA's decision not to introduce new post-crash 
requirements for hydrogen-powered heavy vehicles (HPHV) in FMVSS No. 
307, aligning the standard with GTR No. 13 Phase 2. It stated that 
NHTSA has not set crash test requirements for any other heavy vehicles, 
and there is no justification for unique post-crash requirements 
specifically for HPHVs. Hyzon suggested that further research be 
conducted before considering additional standards. Hyzon suggested 
waiting for more data from GTR No. 13 Phase 3 before deciding on any 
new crash tests.
    Glickenhaus expressed safety concerns about crash testing vehicles 
with hydrogen onboard, stating that the proposed regulations do not 
reference procedures and processes to make that crash test safe. It 
pointed out that while NHTSA typically includes safety protocols in its 
standards, such as substituting Stoddard solvent for gasoline during 
FMVSS No. 301 testing, the proposed regulations under FMVSS Nos. 307 
and 308 would allow crashes with hydrogen or helium. It requested that 
if manufacturers are expected to choose between testing with hydrogen 
or helium, this expectation should be explicitly stated in the 
regulation. Glickenhaus stated that two testing laboratories have 
expressed reluctance to perform crash tests with hydrogen due to safety 
concerns, preferring helium or other inert gases. It argued that if 
these experienced labs are not comfortable testing with hydrogen, it is 
unlikely that manufacturers could safely conduct these tests on their 
own. Additionally, Glickenhaus recommended using thermal imaging 
cameras for fire detection, as hydrogen fires are clear and colorless, 
making them difficult to identify through visual inspection alone.
    NFA commented on the need for mechanical shock testing for heavy 
vehicles but noted a lack of comprehensive data to conclusively assess 
the relevance of a sled test. It stated that both NFA and its CHSS 
manufacturers adhere to the mechanical shock requirements in NGV 6.1, 
``Compressed natural gas (CNG) fuel storage and delivery systems for 
road vehicles,'' which requires 8g inertia loading in all three primary 
axes without failure, and referenced UN ECE R134, which specifies lower 
inertia loading requirements of 6.6g longitudinally and 5g 
transversely. NFA commented that harmonizing regulations across North 
America and Europe would provide consistency. It recommended continuing 
testing at the CHSS component level, including the mounting system, to 
ensure tests reflect real-world installations and establish a baseline 
performance standard applicable to all vehicle types, regardless of 
available crash data. It also suggested that NHTSA allow calculation or 
simulation methods, like Finite Element Analysis, to demonstrate 
compliance to reduce prototyping and testing costs for OEMs. NFA noted 
the infrequency of crashes involving its vehicles and the limited full-
vehicle testing required by current regulations, adding that it 
currently position CHSS in less vulnerable areas, such as roof-mounted 
or protected luggage compartments. However, it stated that if 
sufficient data becomes available to support a performance requirement, 
testing should be standardized at the CHSS component or assembly level 
instead of full-vehicle testing.
    HATCI stated that it supports the Agency's harmonization with GTR 
No. 13 for post-crash fuel system integrity.
Agency Response
    After consideration of the comments received, NHTSA has decided to 
maintain the scope of the post-crash requirements as initially proposed 
for vehicles that use hydrogen fuel for propulsion power, limiting the 
applicability to passenger cars, multipurpose passenger vehicles,

[[Page 6270]]

trucks, and buses with a GVWR of less than or equal to 4,536 kg (10,000 
pounds), as well as all school buses. NHTSA will not extend the post-
crash requirements to include all heavy vehicles with a GVWR greater 
than 4,536 kg at this time.
    NHTSA agrees with the commenters that limiting the post-crash 
requirements to light vehicles with a GVWR of 10,000 pounds or less and 
to all school buses regardless of GVWR is appropriate at this time, as 
it helps minimize the testing burden and addresses the practical 
limitations of conducting full-scale vehicle tests on heavier vehicles. 
NHTSA agrees that more research is needed before considering the 
inclusion of heavy vehicles other than school buses in the post-crash 
requirements, given the complexity of these vehicles and the absence of 
existing crash tests for heavy vehicles. NHTSA is considering future 
research to address the comments that component-level testing, rather 
than full vehicle crash testing, may be appropriate for heavy vehicle 
fuel systems at this time and that benchmarking against existing light 
vehicle crash testing procedures is a reasonable starting point for 
future heavy vehicle applications.
    Furthermore, NHTSA is not implementing a moving contoured barrier 
impact test for heavy vehicles at this time due to the complexity 
associated with developing an objective test applicable to various 
heavy vehicle designs. Further research is needed to determine 
appropriate testing methods for tests involving heavy vehicles, and 
current data is insufficient to justify the inclusion of such tests.
    Regarding the use of helium as an alternative to hydrogen for crash 
testing, NHTSA proposed this option in the regulatory text to provide 
flexibility for manufacturers. NHTSA will maintain the proposal that 
the test gas for compliance testing may be either hydrogen or helium, 
with the choice of test gas being at the manufacturer's option. 
Hydrogen and helium gas have similar leak characteristics, so it is 
expected that a vehicle that meets the performance requirements when 
tested with one gas will also meet the performance requirements when 
tested with the other.
    NHTSA is not currently specifying the use of thermal imaging 
cameras as a means to detect post-crash fire. However, test labs are 
encouraged to use available technology such as thermal cameras or other 
heat detection equipment when evaluating for the presence of post-crash 
fire.

D. Tolerances

Background
    The concept of test parameter tolerances refers to the allowable 
variations in the conditions or parameters under which a test is 
conducted, without impacting the validity or reliability of the test 
results. In regulatory testing, it is often impractical or impossible 
to maintain exact, fixed values for all parameters throughout the 
testing process. Therefore, tolerances are established to allow for 
slight deviations that are considered acceptable within a specified 
range. These tolerances ensure that even though the exact conditions 
may not be strictly identical in each test, the outcomes will remain 
consistent and comparable, as long as they fall within the defined 
tolerance limits. NHTSA proposed test parameter tolerances that are 
generally consistent with the suggested tolerances specified in the GTR 
No. 13. By adopting these established tolerances, NHTSA ensures that 
test conditions remain controlled and reliable while allowing for 
practical flexibility in testing environments.
Comments Received
    TesTneT stated that in its 35 years of experience with hydraulic 
pressure cycle testing, it has not faced issues meeting a low-pressure 
tolerance of 1 MPa. Nikola stated that the proposed low-pressure range 
for container pressure cycling was ``adequate.'' However, Luxfer Gas 
Cylinders commented that the proposed lower limits of 1 MPa to 2 MPa 
for pressure cycling tests are ``too low and too tight.'' Luxfer stated 
that few containers would likely reach 1 or 2 MPa during actual 
service, making the test conditions unrealistic. It also noted 
challenges in maintaining these limits due to industrial testing 
equipment constraints and recommended revising the range to align with 
NGV 2, where cycling occurs between no greater than 10 percent of the 
service pressure and 125 percent of the service pressure.
    Auto Innovators expressed concern over NHTSA's application of GTR 
No. 13 tolerances. It noted that GTR No. 13 specifies target values and 
allowable tolerances ([alpha]), but the NPRM proposed a 
range between (X-[alpha]) and (X+[alpha]) without defining a target. 
Auto Innovators argued that this proposal could compel manufacturers to 
set equipment at either extreme of the range, potentially testing at 
various points in between, which it argued deviates from the test's 
purpose. Auto Innovators cited the low-pressure cycling test, where 
NHTSA proposed a range of ``between 1 MPa and 2 MPa.'' It stated that 
this approach could lead to impractical testing conditions and 
recommended NHTSA align with GTR No. 13. It also provided a table 
listing parameters in GTR No. 13 that use minimum (>=) and maximum (<=) 
values.
    H2MOF proposed setting the lower bound of the pressure cycle at no 
more than 10 percent of the upper cycle, with an absolute maximum of 3 
MPa, in line with the standard ISO 11515. H2MOF stated that the upper 
bound in ISO 11515 is defined as the maximum developed pressure at 65 
[deg]C, or approximately 117 percent of NWP. HATCI generally supported 
harmonizing with GTR No. 13. FORVIA stated that indicators for 
conditions like 85 degrees Celsius should use ``greater than or equal 
to'' and for -40 degrees Celsius, ``less than or equal to.'' It also 
requested maintaining the low-pressure range of 1 MPa to 2 MPa to 
ensure a margin above ambient pressure.
Agency Response
    The use of open-ended tolerances, such as ``greater than or equal 
to'' (>=) and ``less than or equal to'' (<=) symbols, does not provide 
the necessary clarity for conducting robust and consistent tests. The 
use of ``>='' or ``<='' without specific upper or lower limits could 
result in impractical testing conditions, potentially leading to tests 
at unreasonably high or low values that are irrelevant to real-world 
performance or safety objectives. Without a defined range, the test 
could extend to extreme values of temperature or pressure, for example, 
making the test results unrealistic and inconsistent. A specific range 
with both upper and lower bounds is essential to ensure the tests 
reflect conditions relevant to vehicle safety, while also providing a 
controlled and repeatable environment for assessment.
    Furthermore, tolerance ranges allow for slight variation in test 
parameters during testing while maintaining the validity of the 
results. Testing at any point within the proposed range will not affect 
the overall outcome, nor will fluctuations within the range impact the 
results. This concept allows for flexibility within the defined range 
that does not materially affect the test results because the allowed 
variation is small enough to be considered insignificant in relation to 
the overall test objectives.
    NHTSA maintains that the test parameter tolerances proposed in the 
NPRM are generally consistent with GTR No. 13. When GTR No. 13 provides 
an open-ended range, such as ``<= 2 MPa,'' the GTR No. 13 suggested 
tolerance is not listed with ``'' because

[[Page 6271]]

it is not intended to be applied to both sides of range endpoint. 
Instead, the tolerance is only intended to be applied to the open end 
of the range. Hence NHTSA's proposal of between 1 MPa and 2 MPa, based 
on the GTR No. 13 suggested tolerance of 1 MPa.
    GTR No. 13 paragraph 245 provides another example, citing GTR No. 
13 paragraph 6.2.3.5., where the static hold pressure is specified as 
>=125 per cent NWP. In this case, there is a minimum value of the 
range, but no maximum. GTR No. 13 paragraph 245 states that in this 
case, ``the tolerance of 5 percent NWP in the table could be applied, 
which results in a maximum of 130 percent NWP.''
    Hence, for the low-pressure range during hydraulic cycling, NHTSA 
proposed a tolerance of between 1 MPa and 2 MPa, based on the GTR No. 
13 suggested tolerance of 1 MPa. Regarding Luxfer Gas Cylinders' 
comment that the proposed lower limits of 1 MPa to 2 MPa for pressure 
cycling tests are ``too low and too tight,'' NHTSA notes that the test 
tolerances proposed in the NPRM are supported by TestNet's comment that 
in its 35 years of experience with hydraulic pressure cycle testing, it 
has not faced issues meeting a low-pressure of 1 MPa.
    The argument that tolerances would force manufacturers or test labs 
to test at extreme ends of the range, such as the lowest or highest 
allowable point and at all points within the range, is inaccurate. 
NHTSA believes all of the proposed test procedures are robust enough to 
accommodate minor fluctuations in parameters without affecting the 
outcome of the test or repeatability of the results. The entire range 
is designed to ensure consistent and valid test results, regardless of 
where within the range the test is performed, or whether there are 
fluctuations within the range during testing. The parameters, as 
proposed, provide the necessary testing flexibility without sacrificing 
the repeatability and reproducibility of the testing procedure. 
Moreover, the use of a specified range prevents the need for excessive 
precision, which could make testing more difficult and unnecessarily 
increase the burden on test laboratories.

E. General Comments

Background
    NHTSA received several general comments about the proposed 
standard, reflecting broad perspectives on the overall proposal. These 
comments did not address specific technical or procedural issues but 
instead addressed general aspects of the proposed standards.
Comments Received
    An anonymous commenter stated that the establishment of new 
standards for hydrogen fuel systems was an ``excellent next step'' 
given the increasing prevalence of hydrogen-powered vehicles. It stated 
that it was important to consider the risks associated with pressurized 
hydrogen containers, which differ from non-pressurized gasoline or 
diesel containers, and noted that hydrogen is highly flammable, 
particularly in a compressed state. The commenter suggested that 
implementing a safety standard could reduce risks of death and injury 
related to the integrity of these containers.
    Consumer Reports supported the proposed creation of FMVSS Nos. 307 
and 308, stating that while hydrogen fuel cell vehicle sales have been 
limited, manufacturers are making advancements in this technology. It 
described the standards as necessary for both fuel system integrity and 
the compressed hydrogen storage system.
    Auto Innovators echoed this support but also recommended that NHTSA 
revise its proposal to better align with GTR No. 13. It highlighted 
potential challenges due to differences in certification testing, 
especially when tests are conducted in series, which could lead to 
increased costs. Ford similarly supported the proposed standards and 
highlighted its experience in hydrogen technology research. Ford 
endorsed Auto Innovators' call for close alignment with GTR No. 13 and 
stated that GTR No. 13 guides its North American product development. 
Hyundai expressed support for the proposed adoption of FMVSS Nos. 307 
and 308 and agreed with NHTSA's statement that the standards address an 
emerging safety need. Hyundai acknowledged the rationale behind 
deviations from GTR No. 13 but suggested exploring additional ways to 
harmonize with the global regulation, and referred to Auto Innovators' 
comments for specific recommendations.
    Glickenhaus commented that the Department of Transportation (DOT) 
already has extensive regulations prescribing testing and certification 
requirements for compressed hydrogen storage containers used for 
transporting hydrogen on public roads under the Hazardous Materials 
Regulations (HMR) in 49 CFR Subchapter C. It specifically referenced 49 
CFR 172, which lists hazardous materials that include compressed 
hydrogen and hydrogen fuel cell vehicles, and stated that DOT's 
requirements for cryogenic and compressed hydrogen storage containers, 
including their manufacturing, testing, and certification, are outlined 
in 49 CFR part 173. Glickenhaus stated that it does not appear that any 
of these requirements are referenced or incorporated into the container 
requirements for FMVSS No. 308. It suggested that if the pressure 
vessel or components making up a CHSS have already undergone DOT 
hazardous material transportation certification, it could potentially 
reduce additional testing requirements specific to using those 
containers for fuel storage in hydrogen fuel cell vehicles. Glickenhaus 
expressed concern that the lack of harmony between DOT's HMR standards 
for compressed hydrogen containers and FMVSS No. 308's requirements 
could result in a scenario where a container certified for transporting 
hydrogen over roads, ships, and airways in the United States might not 
be legal for use in vehicles on those same roads. Alternatively, it 
stated, if a container were certified under FMVSS No. 308 but not under 
DOT's hazardous materials transport standards, any towing company might 
inadvertently violate hazardous material transportation regulations by 
transporting a hydrogen fuel cell vehicle and its stored hydrogen. It 
stated that it does not want this responsibility to fall to towing 
companies. They stated that they do not want NHTSA to create a 
regulation that would make it a violation of other DOT requirements to 
tow or transport a hydrogen fuel cell vehicle.
    TTP commented that the proposal is not consistent with existing 
FMVSS Nos. 303 and 304, and that the intent is unclear regarding 
establishing standards specifically for fuel systems or for the vehicle 
as a whole. They expressed uncertainty about how the proposed 
standards, if required by new FMVSS, would be enforced and noted that 
testing and verification by NHTSA would be costly and impractical. TTP 
questioned if the intent was to approach enforcement differently from 
the current methodology under FMVSS Nos. 303 and 304. They recommended 
that NHTSA harmonize with existing methodologies and allow industry 
standards to control certification and compliance wherever possible to 
maintain consistency. TTP also stated there are significant differences 
between the production processes for light and heavy vehicle 
applications and that enforcement of the proposals would not be 
practical for both. They stated that

[[Page 6272]]

light vehicle OEMs build a complete vehicle, which simplifies 
homologation due to consistent configurations, whereas the heavy market 
involves a mix of suppliers and intermediate manufacturers, making 
enforcement of vehicle-specific requirements impractical. TTP further 
commented that the proposal does not align with existing industry 
standards for container requirements, such as HGV 2, ``Compressed 
Hydrogen Gas Vehicle Fuel Containers,'' and NGV 2, and stated that some 
proposed requirements may compromise safety or prevent the use of 
containers with good safety records. They stated the proposal is not 
consistent with industry standards for component-level fuel system 
requirements specified in HPRD 1 and HGV 3.1, and they requested 
harmonization with these standards. Additionally, TTP requested 
clarification on whether the intent of the proposed FMVSS Nos. 307 and 
308 would differ from FMVSS Nos. 303 and 304.
Agency Response
    Some commenters raised concerns regarding potential misalignment 
between FMVSS No. 308 and the DOT hazardous materials regulations for 
compressed hydrogen storage systems. The regulation of the 
transportation of hydrogen over roads as cargo within tanker trucks in 
the United States is governed by the PHMSA through 49 CFR Subchapter C- 
Hazardous Materials Regulations (HMR).\54\ PHMSA standards focus on the 
safe transportation of hazardous materials like hydrogen across all 
modes of transport, including trucks, and prioritizes minimizing risks 
during transport and handling of hydrogen, including potential leaks or 
spills. On the other hand, FMVSS Nos. 307 and 308 focus on the fuel 
system integrity of motor vehicles that use compressed hydrogen as a 
fuel source to propel the vehicle with the purpose of reducing deaths 
and injuries occurring from fires that result from hydrogen fuel 
leakage during vehicle operation and after motor vehicle crashes and 
from explosions resulting from the bursting of pressurized hydrogen 
containers.
---------------------------------------------------------------------------

    \54\ https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C.
---------------------------------------------------------------------------

    FMVSS No. 308 addresses vehicle-specific safety needs with a focus 
on vehicle occupant safety that go beyond the PHMSA regulations for the 
transportation of hazardous materials. While PHMSA regulations govern 
hydrogen storage containers during transportation and are designed to 
mitigate safety risks during transport and handling of hydrogen, FMVSS 
No. 308 is specifically designed to ensure safety in the context of 
real-world driving, fueling, and crash conditions. Hydrogen storage 
systems in vehicles used for vehicle propulsion must meet performance 
standards that address risks unique to vehicle operation, including 
repeated fueling in different fueling conditions, dynamic driving 
environments, and potential accidents. Therefore, while DOT regulations 
and FMVSS No. 308 serve related functions, the standards are distinct 
and necessary for their respective purposes.
    Several commenters also questioned the practicality and intent of 
the proposed FMVSS Nos. 307 and 308, particularly in relation to 
existing standards like FMVSS Nos. 303 and 304, which apply to CNG 
systems. NHTSA believes that hydrogen vehicles present distinct safety 
challenges that require specific regulatory measures. The unique 
properties of compressed hydrogen, such as its higher storage pressures 
and greater flammability, necessitate separate performance requirements 
to mitigate the associated risks. Hydrogen fuel systems have 
characteristics that differ significantly from CNG systems, and as a 
result, the proposed standards reflect the distinct differences 
presented by hydrogen. While FMVSS Nos. 303 and 304 remain effective 
for CNG, they are not sufficient to address the safety risks unique to 
hydrogen fueled vehicles.
    Some commenters expressed concerns about the potential lack of 
harmonization between FMVSS Nos. 307 and 308 and GTR No. 13. As 
discussed above, NHTSA acknowledges these concerns but emphasizes that 
the proposed standards have been tailored specifically to address the 
safety needs of hydrogen vehicles in the context of the FMVSS. While 
GTR No. 13 is the primary basis for the proposed FMVSS Nos. 307 and 
308, exact alignment with GTR No. 13 is not possible in FMVSS, for the 
reasons discussed above in section IV.A.
    Similarly, some commenters suggested that existing industry 
standards for component-level fuel system requirements should be used 
as the primary basis for FMVSS Nos. 307 and 308. NHTSA acknowledges the 
value of the standards HGV 2, HGV 3.1, and HPRD 1, and notes that they 
were considered during the development of GTR No. 13. However, FMVSS 
are intended to establish minimum vehicle-level safety performance 
standards, and it is not necessary nor practical to adopt the entirety 
of industry standards into the FMVSS. While industry standards play an 
important role in ensuring the safety of individual components, FMVSS 
Nos. 307 and 308 set baseline requirements for hydrogen fuel systems to 
ensure that they function safely as part of the overall vehicle system. 
NHTSA's focus was in aligning the proposed FMVSS Nos. 307 and 308 with 
GTR No. 23 to enable global harmonization of regulations for hydrogen 
powered vehicles.
    FMVSS establish minimum safety requirements and the FMVSS test 
procedures provide notice to establish how the agency would verify 
compliance. However, this does not mean that manufacturers must conduct 
the exact test in the FMVSS to certify their vehicles. The Motor 
Vehicle Safety Act \55\ requires manufacturers to certify that their 
vehicles meet all applicable FMVSS, and specifies that manufacturers 
may not certify compliance if, in exercising reasonable care, the 
manufacturer has reason to know the certificate is false or misleading. 
A manufacturer may use component-level tests to certify its vehicles if 
it exercises reasonable care in doing so. Manufacturers must ensure 
that their vehicles will meet the requirements of FMVSS Nos. 307 and 
308 when NHTSA tests the vehicles in accordance with the test 
procedures specified in the standards, but manufacturers may use 
different test procedures to do so.
---------------------------------------------------------------------------

    \55\ 49 U.S.C. Ch. 301: Motor Vehicle Safety, https://uscode.house.gov/view.xhtml?req=granuleid%3AUSC-prelim-title49-chapter301&edition=prelim.
---------------------------------------------------------------------------

    In response to concerns about the enforceability of the proposed 
standards, particularly for heavy vehicles with complex production 
processes, NHTSA believes that the proposed FMVSS Nos. 307 and 308 
standards are practical and enforceable across vehicle types. Although 
the heavy vehicle market involves a diverse supply chain with multiple 
intermediate manufacturers, the performance-based nature of these 
standards allows for flexibility in design. The regulations do not 
prescribe specific design solutions but instead set performance 
criteria, which manufacturers can meet using various engineering 
approaches. This adaptability ensures that both light and heavy 
vehicles can comply with the safety requirements without imposing 
impractical regulatory burdens. NHTSA is confident that these standards 
will not result in undue complexity or unnecessary cost in terms of 
enforcement.

[[Page 6273]]

F. Lead Time

Background
    In the NPRM, NHTSA proposed two key dates regarding the 
implementation of FMVSS Nos. 307 and 308. First, the effective date was 
proposed as 180 days after the publication of the final rule in the 
Federal Register. This is the date when the final rule would officially 
go into effect. Second, NHTSA proposed a compliance date for 
manufacturers to fully adhere to the new requirements. The compliance 
date was initially stated as September 1, two years after the 
publication of the final rule. However, in the ``Lead Time'' section, a 
different compliance date was proposed as September 1 in the year 
following the rule's publication. This was a clerical error, as both 
compliance dates should have stated ``the first September 1 that is two 
years after the publication of the final rule.''
Comments Received
    Nikola stated they agree with the rule taking effect the following 
September. EMA commented that heavy vehicle manufacturers would need at 
least five years from the final rule's publication to comply, stating 
that GTR No. 13 Phase 2 had only been recently approved and the 
revision broadened its scope to include heavy vehicles. EMA cited the 
need for manufacturers to evaluate the new requirements, conduct 
validation testing, and potentially redesign components. Similarly, 
Auto Innovators raised concerns about the proposed compliance period, 
suggesting that an additional five years beyond the one-year compliance 
date would be necessary. They noted a lack of harmonization with GTR 
No. 13, which they stated would require significant design, hardware, 
and software adjustments for manufacturers.
    Several commenters, including Auto Innovators, HATCI, and 
Glickenhaus, also pointed out conflicting compliance dates within the 
NPRM. Auto Innovators and HATCI pointed out inconsistencies between the 
Dates section, which stated the compliance date as two years after 
publication, and the Lead Time section, which stated it as one year. 
Both organizations requested additional lead time due to a lack of 
harmonization with GTR No. 13 and the substantial vehicle design 
changes they stated will be required. HATCI requested a compliance date 
of five years from the first September 1 after the final rule's 
publication, and cited potential impacts on pre-production vehicles due 
to a lack of harmonization which will prevent manufacturers from 
utilizing existing hardware and software.
    Glickenhaus requested a three-year extension for low volume 
manufacturers to avoid disruption to current pilot projects. Hyundai 
also recommended a five-year compliance period after the September 1 
following the rule's publication, stating that this is justified by the 
signi[filig]cant number of changes from GTR No. 13 in FMVSS Nos. 307 
and 308, the inclusion of substantive new requirements, and the time 
required for design changes, validation and certi[filig]cation. Hyundai 
also noted that these proposed requirements are generally consistent 
with current industry practices, so there is no immediate safety 
necessity warranting a shorter lead time.
Agency Response
    NHTSA acknowledges the comments regarding the proposed lead time 
and the concerns raised about the inconsistency between the compliance 
dates mentioned in the NPRM. NHTSA acknowledges that the ``Lead Time'' 
section was not updated correctly to reflect the intended proposed 
compliance timeline. To clarify this issue, first, NHTSA confirms that 
the effective date remains as proposed: 180 days after the publication 
of the final rule in the Federal Register.
    Second, in response to commenters' requests for additional lead 
time for the compliance date, particularly from heavy vehicle 
manufacturers and others citing the need for additional time, NHTSA has 
revised the compliance date in the final rule. The final rule will 
adopt a compliance date that will be September 1, 2028, more than 3 
years after the publication of the final rule. This extension provides 
additional time for manufacturers to ensure compliance without causing 
significant disruption.
    However, NHTSA emphasizes that the requirements proposed under 
FMVSS Nos. 307 and 308 are closely aligned with GTR No. 13 and current 
industry practices. Many manufacturers have already implemented safety 
systems and testing procedures that meet the requirements of the final 
rule, and thus an extended lead time beyond the three-year period is 
not necessary. NHTSA is not aware of any peculiarities of the U.S. 
market that would necessitate lead times double or triple the lead 
times in other markets.\56\
---------------------------------------------------------------------------

    \56\ NHTSA knows from its involvement in UN ECE that the lead 
times in other markets are sometimes substantially shorter than 
those often requested by manufacturers in the United States. As an 
example, Europe's General Safety Regulation was adopted in late 2019 
and required that manufacturers equip vehicles with certain vehicle 
safety features by July 2022. See https://www.tuvsud.com/en-us/resource-centre/stories/revision-of-the-eu-general-safety-regulation. This period of less than 3 years is less than the 
timelines often requested by American industry, who often seek much 
longer lead times.
---------------------------------------------------------------------------

V. Other Changes to the Regulatory Text

    A clerical correction was made to the S3 Application section of 
FMVSS No. 308 to add the words ``to propel the vehicle.'' These words 
were included in S3 Application of FMVSS No. 307, but were 
inadvertently omitted from FMVSS No. 308 S3. This edit is editorial in 
nature to improve the clarity of the section, and does not intend to 
change the application of the standard.
    A clerical correction was made to S6.2.2.2(e), deleting the word 
``container'' from ``container manufacture may specify.'' The inclusion 
of the word ``container'' before manufacturer was erroneous since the 
standard is being applied as a vehicle-level standard, as discussed 
above. The section will now simply state that the ``manufacturer may 
specify.''
    A clerical correction was made to the definition of ``hydrogen fuel 
system'' to replace the word ``mean'' with ``means'' for grammatical 
accuracy.
    S5.2.2 was updated to include the words ``The vehicle shall meet at 
least'' to clarify that the vehicle must meet at least one of the 
requirements listed in S5.2.2 (a) though (c).
    S6.1 was updated to include the words ``individual test'' before 
vehicle to clarify that the statement is referring to a specific 
individual test vehicle, not a line or model of vehicle.
    S6.4.2(c) was updated to replace the word ``volumes'' with 
``spaces.'' The section is referring to enclosed or semi-enclosed 
spaces, which are defined in the standard, whereas enclosed or semi-
enclosed volumes are not defined.
    NHTSA replaced all instances of the word ``manufacturer'' with 
``vehicle manufacturer'' to clarify that the vehicle manufacturer is 
responsible for all aspects of the two standards.

VI. Rulemaking Analyses and Notices

Executive Order 12866, Executive Order 13563, and DOT Regulatory 
Policies and Procedures

    We have considered the potential impact of this final rule under 
Executive Order 12866, Executive Order 13563, and DOT Order 2100.6A. 
This final rule is nonsignificant under E.O. 12866 and was not reviewed 
by the Office of Management and Budget. It is also not considered ``of 
special note to the Department'' under DOT Order

[[Page 6274]]

2100.6A, Rulemaking and Guidance Procedures.
    Today, there are only two publicly available vehicle models that 
may be affected by the final rule, which collectively equal less than 
5,000 vehicles sold per model year. Most manufacturers and vehicle 
lines currently in production would be unaffected by this rule. Of 
those vehicles that would be covered by today's standards, we expect 
the compliance cost to be minimal. As discussed earlier, the few 
manufacturers that already offer hydrogen vehicles in the marketplace 
already take safety precautions to attempt to emulate the safety of 
conventional and battery electric vehicles, and adhere to the industry 
guidelines that informed the creation of GTR No. 13. Because the final 
rule is intended to coalesce industry practice and future designs 
through harmonized regulations, we do not expect that the rule would 
pose a significant cost to current manufacturers, or for manufacturers 
that may be planning to enter the market.
    Given NHTSA is establishing these standards during the early 
development of hydrogen vehicles, there is no baseline to compare 
today's rule against. While we anticipate the regulations will promote 
safer hydrogen vehicles, we cannot quantify this benefit with any 
degree of certainty, especially given that we cannot forecast what the 
industry would look like in the absence of our proposed standard. 
Furthermore, most of the safety benefits that will accrue to this rule 
will only be realized when hydrogen vehicles become more prevalent. The 
net present value of these future costs and benefits is minimal.

Regulatory Flexibility Act

    Pursuant to the Regulatory Flexibility Act (5 U.S.C. 601 et seq., 
as amended by the Small Business Regulatory Enforcement Fairness Act 
(SBREFA) of 1996), whenever an agency is required to publish a notice 
of proposed rulemaking or final rule, it must prepare and make 
available for public comment a regulatory flexibility analysis that 
describes the effect of the rule on small entities (i.e., small 
businesses, small organizations, and small governmental jurisdictions). 
The Small Business Administration's regulations at 13 CFR part 121 
define a small business, in part, as a business entity ``which operates 
primarily within the United States.'' (13 CFR 121.105(a)(1)). No 
regulatory flexibility analysis is required if the head of an agency 
certifies the proposed or final rule will not have a significant 
economic impact on a substantial number of small entities. SBREFA 
amended the Regulatory Flexibility Act to require Federal agencies to 
provide a statement of the factual basis for certifying that a proposed 
or final rule will not have a significant economic impact on a 
substantial number of small entities.
    I certify that these standards will not have a significant impact 
on a substantial number of small entities. This action creates FMVSS 
Nos. 307 and 308 to establish minimum safety requirements for the CHSS 
and fuel system integrity of hydrogen vehicles. FMVSS Nos. 307 and 308 
are vehicle standards. We anticipate any burdens of the standard will 
fall onto manufacturers of hydrogen vehicles. NHTSA is unaware of any 
small entities that currently manufacture or are planning to 
manufacture hydrogen vehicles. Furthermore, NHTSA is adopting standards 
similar to those already in place across industry. Thus, we anticipate 
the impacts of this final rule on all manufacturers to be minimal 
regardless of manufacturer size.

Executive Order 13132

    NHTSA has examined this final rule pursuant to Executive Order 
13132 (64 FR 43255, August 10, 1999) and concluded that no additional 
consultation with States, local governments or their representatives is 
mandated beyond the rulemaking process. The Agency has concluded that 
this action would not have ``federalism implications'' because it would 
not have ``substantial direct effects on States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government,'' 
as specified in section 1 of the Executive order. This final rule would 
apply to motor vehicle manufacturers. Further, no State has adopted 
requirements regulating the CHSS or fuel integrity of hydrogen powered 
vehicles. Thus, Executive Order 13132 is not implicated and 
consultation with State and local officials is not required.
    NHTSA rules can preempt in two ways. First, the National Traffic 
and Motor Vehicle Safety Act contains an express preemption provision: 
When a motor vehicle safety standard is in effect under this chapter, a 
State or a political subdivision of a State may prescribe or continue 
in effect a standard applicable to the same aspect of performance of a 
motor vehicle or motor vehicle equipment only if the standard is 
identical to the standard prescribed under this chapter. 49 U.S.C. 
30103(b)(1). It is this statutory command by Congress that preempts any 
non-identical State legislative and administrative law addressing the 
same aspect of performance.
    The express preemption provision described above is subject to a 
savings clause under which compliance with a motor vehicle safety 
standard prescribed under this chapter does not exempt a person from 
liability at common law. 49 U.S.C. 30103(e). Pursuant to this 
provision, State common law tort causes of action against motor vehicle 
manufacturers that might otherwise be preempted by the express 
preemption provision are generally preserved.
    NHTSA rules can also preempt State law if complying with the FMVSS 
would render the motor vehicle manufacturers liable under State tort 
law. Pursuant to Executive Order 13132 and 12988, NHTSA has considered 
whether this rule could or should preempt State common law causes of 
action. The agency's ability to announce its conclusion regarding the 
preemptive effect of one of its rules reduces the likelihood that 
preemption will be an issue in any subsequent tort litigation. To this 
end, the agency has examined the nature (i.e., the language and 
structure of the regulatory text) and objectives of this rule and finds 
that this rule, like many NHTSA rules, would prescribe only a minimum 
safety standard. As such, NHTSA does not intend this NPRM to preempt 
State tort law that would effectively impose a higher standard on motor 
vehicle manufacturers rule. Establishment of a higher standard by means 
of State tort law will not conflict with the minimum standard adopted 
here. Without any conflict, there could not be any implied preemption 
of a State common law tort cause of action.

Executive Order 12988 (Civil Justice Reform)

    When promulgating a regulation, Executive Order 12988 specifically 
requires that the agency must make every reasonable effort to ensure 
that the regulation, as appropriate: (1) Specifies in clear language 
the preemptive effect; (2) specifies in clear language the effect on 
existing Federal law or regulation, including all provisions repealed, 
circumscribed, displaced, impaired, or modified; (3) provides a clear 
legal standard for affected conduct rather than a general standard, 
while promoting simplification and burden reduction; (4) specifies in 
clear language the retroactive effect; (5) specifies whether 
administrative proceedings are to be required before parties may file 
suit in court; (6) explicitly or implicitly defines key terms; and (7) 
addresses other important issues affecting clarity

[[Page 6275]]

and general draftsmanship of regulations.
    Pursuant to this Order, NHTSA notes as follows. The preemptive 
effect of this final rule is discussed above in connection with E.O. 
13132. NHTSA notes further that there is no requirement that 
individuals submit a petition for reconsideration or pursue other 
administrative proceeding before they may file suit in court.

Executive Order 13609 (Promoting International Regulatory Cooperation)

    Executive Order 13609, ``Promoting International Regulatory 
Cooperation,'' promotes international regulatory cooperation to meet 
shared challenges involving health, safety, labor, security, 
environmental, and other issues and to reduce, eliminate, or prevent 
unnecessary differences in regulatory requirements.
    The final rule adopts the technical requirements of GTR No.13, a 
technical standard for hydrogen vehicles adopted by the United Nations 
Economic Commission for Europe (UN ECE) World Forum for Harmonization 
of Vehicle Regulations (WP.29). As a Contracting Party that voted in 
favor of GTR No. 13, NHTSA was obligated to initiate rulemaking to 
incorporate safety requirements and options specified in GTR, which the 
agency satisfied when it published its notice of proposed rulemaking 
NHTSA is not required to finalize the text of the GTR.
    While the final rule does contain some differences from GTR No. 13 
to reflect U.S. law, they are consistent with the regulatory process 
envisioned and encouraged from the outset of GTR No. 13. NHTSA will 
continue to participate with the international community on GTR No. 13 
and evaluate further amendments on their merits as they are adopted by 
WP.29.
    NHTSA has analyzed this final rule under the policies and agency 
responsibilities of Executive Order 13609 and has determined this rule 
would have no effect on international regulatory cooperation.

National Environmental Policy Act

    NHTSA has analyzed this rule for the purposes of the National 
Environmental Policy Act (42 U.S.C. 4321 et. seq.), as amended. In 
accordance with 49 C.F.R Sec.  1.81, 42 U.S.C. 4336, and DOT NEPA Order 
5610.1C, NHTSA has determined that this rule is categorically excluded 
pursuant to 23 CFR 771.118(c)(4) (planning and administrative 
activities, such as promulgation of rules, that do not involve or lead 
directly to construction).
    This rulemaking establishes two new FMVSS, FMVSS No. 307, ``Fuel 
system integrity of hydrogen vehicles,'' which specifies requirements 
for the integrity of the fuel system in hydrogen vehicles during normal 
vehicle operations and after crashes, and FMVSS No. 308, ``Compressed 
hydrogen storage system integrity,'' which specifies requirements for 
the compressed hydrogen storage system to ensure the safe storage of 
hydrogen onboard vehicles. This rulemaking is not anticipated to result 
in any environmental impacts, and there are no extraordinary 
circumstances present in connection with this rulemaking.
    NHTSA expects the changes to new and existing vehicles to be 
minimal, and mitigating the hazards associated with fires that result 
from hydrogen fuel leakage during vehicle operation and after motor 
vehicle crashes and from explosions resulting from the burst of 
pressurized hydrogen containers would result in a public health and 
safety benefit. For these reasons, the agency has determined that 
implementation of this action will not have any adverse impact on the 
quality of the human environment.

Paperwork Reduction Act

    Under the procedures established by the Paperwork Reduction Act of 
1995 (PRA) (44 U.S.C. 3501, et. seq.), Federal agencies must obtain 
approval from the OMB for each collection of information they conduct, 
sponsor, or require through regulations. A person is not required to 
respond to a collection of information by a Federal agency unless the 
collection displays a valid OMB control number. The Information 
Collection Request (ICR) for a revision of a previously approved 
collection described below will be forwarded to OMB for review and 
comment. In compliance with these requirements, NHTSA asks for public 
comments on the following proposed collection of information for which 
the agency is seeking approval from OMB. In this final rule, we are 
finalizing a revision and reinstatement to a previously approved OMB 
collection, OMB Clearance No. 2127-0512, Consolidated Labeling 
Requirements for Motor Vehicles (except the VIN).\57\
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    \57\ In compliance with the requirements of the PRA, NHTSA is 
separately publishing a notice to request comment on NHTSA's 
reinstatement with modification of the previously approved 
information collection request.
---------------------------------------------------------------------------

    Title: Consolidated Labeling Requirements for Motor Vehicles 
(except the VIN).
    OMB Control Number: OMB Control No. 2127-0512.
    Type of Request: Revision of a previously approved collection.
    Type of Review Requested: Regular.
    Requested Expiration Date of Approval: 3 years from the date of 
approval.
    Summary of the Collection of Information: FMVSS No. 307 specifies 
requirements for the integrity of motor vehicle fuel systems using 
compressed hydrogen as a fuel source. Each hydrogen vehicle must have a 
permanent label which lists the fuel type, service pressure, and a 
statement directing vehicle users/operators to instructions for 
inspection and service life of the fuel container. FMVSS No. 308 
specifies requirements for the integrity of compressed hydrogen storage 
systems (CHSS). Each hydrogen container must have a permanent label 
containing manufacturer contact information, the container serial 
number, manufacturing date, date of removal from service, and 
applicable BPO burst pressure. If the proposed requirements 
are made final, we will submit a request for OMB clearance of the 
proposed collection of information and seek clearance prior to the 
effective date of the final rule.
    Description of the likely respondents: Vehicle manufacturers.
    Estimated Number of Respondents: 10.
    Estimated Total Annual Burden Hours: $8,616.
    It is estimated that vehicle manufacturers will provide labels on 
10 different hydrogen vehicle models. Since manufacturers have provided 
CNG vehicles with similar required labels for many years, it is 
estimated that manufacturers will have a generalized label template 
which only requires minor adjustments for hydrogen and population with 
the required information. There is an annual 1.0 hour burden for 
manufacturers to have a Mechanical Drafter put the correct information 
into a label template to create a model specific label. The annual 
burden for this label creation is 10 hours (10 hydrogen vehicle model 
labels * 1 hour per model label) and $478 (10 hydrogen vehicle model 
labels * 1 hour per model label * $33.62 labor rate per hour / 70.3% of 
labor rate as total wage compensation). Manufacturers will also bear a 
cost burden of $1,884 (2,850 hydrogen vehicles * $0.73 per label) for 
the required labels to be attached to the hydrogen vehicles. The 
combined total annual burden to vehicle manufacturers from the 
requirements to have the specified label text on hydrogen vehicles is 
10 hours and $2,362. These hour and cost burdens represent a new

[[Page 6276]]

addition to this information collection request.
    It is estimated that vehicle manufacturers will provide labels on 
10 different hydrogen container models. Since manufacturers have 
provided CNG containers with similar labels for many years, it is 
estimated that manufacturers will have a generalized label template 
which requires only minor adjustments for hydrogen and then population 
with their current contact information, the container serial number, 
manufacturing date, and date of removal from service. There is an 
annual 1.0 hour burden for manufacturers to have a Mechanical Drafter 
put the correct information into a label template to create a model 
specific label. The annual burden for this label creation is 10 hours 
(10 hydrogen container model labels * 1.0 hours per model label) and 
$478 (10 hydrogen container models labels * 1.0 hours per model label * 
$33.62 labor rate per hour / 70.3% of labor rate as total wage 
compensation). Manufacturers will also bear a cost burden of $5,776 
(7,910 hydrogen containers * $0.730 per label) for the required labels 
to be attached to the hydrogen containers. The combined total annual 
burden to vehicle manufacturers from the requirements to have the 
specified label text on hydrogen containers is 10 hours and $6,254. 
These hour and cost burdens represent a new addition to this 
information collection request.

National Technology Transfer and Advancement Act

    Under the National Technology Transfer and Advancement Act of 1995 
(NTTAA) (Pub. L. 104) Section 12(d) of the National Technology Transfer 
and Advancement Act (NTTAA) requires NHTSA to evaluate and use existing 
voluntary consensus standards in its regulatory activities unless doing 
so would be inconsistent with applicable law (e.g., the statutory 
provisions regarding NHTSA's vehicle safety authority) or otherwise 
impractical. Voluntary consensus standards are technical standards 
developed or adopted by voluntary consensus standards bodies. Technical 
standards are defined by the NTTAA as ``performance-based or design-
specific technical specification and related management systems 
practices.'' They pertain to ``products and processes, such as size, 
strength, or technical performance of a product, process or material.''
    Examples of organizations generally regarded as voluntary consensus 
standards bodies include ASTM International, the Society of Automotive 
Engineers (SAE), and the American National Standards Institute (ANSI). 
If NHTSA does not use available and potentially applicable voluntary 
consensus standards, we are required by the Act to provide Congress, 
through OMB, an explanation of the reasons for not using such 
standards.
    Today's final rule establishes standards that are consistent with 
voluntary standards cited above such as SAEJ2579_201806, HPRD-1 2021, 
and HGV 3.1 2022.
    This final rule adopting key aspects of GTR No. 13 is consistent 
with the goals of the NTTAA. This final rule adopts much of a global 
consensus standard. However this final rule includes some minor 
deviations from GTR No. 13. As discussed above, FMVSS must maintain 
objectivity, clarity, and practicability, ensuring that every 
requirement is measurable and enforceable, with unambiguous test 
procedures. These adjustments ensure FMVSS remain clear, objective, and 
enforceable. For example, NHTSA is removing subjective requirements 
such as the TPRD atmospheric exposure test and the and localized leak 
requirement from the ambient and extreme gas permeation test. NHTSA is 
also requiring the testing of only one component for some tests instead 
of multiple components (as specified in GTR No. 13 for assessing 
variability in response), and eliminating duplicative requirements like 
the proof pressure tests. NHTSA has also removed unnecessary 
requirements for burst pressure variability, and removed a requirement 
for an overpressure protection device that had no corresponding 
performance test. NHTSA also selected a more balanced requirement for 
the hydrogen concentration limit in the enclosed and semi-enclosed 
spaces, rather than applying the GTR's zero limit to only the passenger 
compartment.
    The GTR was developed by a global regulatory body and is designed 
to increase global harmonization of differing vehicle standards. The 
GTR leverages the expertise of governments in developing safety 
requirements for hydrogen fueled vehicles. NHTSA's consideration of GTR 
No. 13 accords with the principles of NTTAA as NHTSA's consideration of 
an established, proven regulation has reduced the need for NHTSA to 
expend significant agency resources on the same safety need addressed 
by GTR No. 13.

Incorporation by Reference

    Under regulations issued by the Office of the Federal Register (1 
CFR 51.5(a)), an agency, as part of a proposed rule that includes 
material incorporated by reference, must summarize material that is 
proposed to be incorporated by reference and discuss the ways the 
material is reasonably available to interested parties or how the 
agency worked to make materials available to interested parties. At the 
final rule stage, regulations require that the agency seek formal 
approval, summarize the material that it incorporates by reference in 
the preamble of the final rule, discuss the ways that the materials are 
reasonably available to interested parties, and provide other specific 
information to the Office of the Federal Register.
    NHTSA is incorporating by reference two documents into the Code of 
Federal Regulations. First, NHTSA is incorporating by reference ASTM 
D1193-06 (Reapproved 2018), Standard Specification for Reagent Water. 
ASTM D1193-06 is an industry standard that defines the requirements for 
the purity of water used in laboratories, ensuring that experiments and 
tests are not compromised by water impurities. NHTSA will use a water 
supply conforming to Type IV requirements of ASTM D1193-06 in testing 
the compliance of closure devices with the salt corrosion resistance 
test in 571.308 S6.2.6.1.4.
    NHTSA is also incorporating by reference ISO 6270-2:2017, Paints 
and Varnishes--Determination of Resistance to Humidity--Part 2: 
Condensation (In-Cabinet Exposure with Heated Water Reservoir). ISO 
6270-2:2017 specifies methods for assessing the resistance of materials 
to humidity by focusing on how materials behave when exposed to high 
humidity. ISO 6270-2:2017 provides detailed procedures and materials 
for conducting tests where humidity is the primary variable. NHTSA will 
use the apparatus described within ISO 6270-2:2017 in testing the 
compliance of closure devices with the salt corrosion resistance test 
in 571.308 S6.2.6.1.4.
    All standards incorporated by reference in this rule are available 
for review at NHTSA's headquarters in Washington, DC, and for purchase 
from the organizations promulgating the standards. The ASTM standard is 
also available for review at ASTM's online reading room.\58\
---------------------------------------------------------------------------

    \58\ https://www.astm.org/READINGLIBRARY/.
---------------------------------------------------------------------------

Unfunded Mandates Reform Act

    Section 202 of the Unfunded Mandates Reform Act of 1995 (UMRA), 
Public Law 104-4, requires Federal agencies to prepare a written 
assessment of the costs, benefits, and other effects

[[Page 6277]]

of proposed or final rules that include a Federal mandate likely to 
result in the expenditure by State, local, or tribal governments, in 
the aggregate, or by the private sector, of more than $100 million 
annually (adjusted for inflation with base year of 1995). Adjusting 
this amount by the implicit gross domestic product price deflator for 
the year 2022 results in $177 million (111.416/75.324 = 1.48). This 
rule will not result in a cost of $177 million or more to State, local, 
or tribal governments, in the aggregate, or the private sector. Thus, 
this rule is not subject to the requirements of sections 202 of the 
UMRA.

Executive Order 13045 (Protection of Children From Environmental Health 
and Safety Risks)

    Executive Order 13045, ``Protection of Children from Environmental 
Health and Safety Risks,'' (62 FR 19885, April 23, 1997) applies to any 
proposed or final rule that: (1) Is determined to be ``economically 
significant,'' as defined in E.O. 12866, and (2) concerns an 
environmental health or safety risk that NHTSA has reason to believe 
may have a disproportionate effect on children. If a rule meets both 
criteria, the agency must evaluate the environmental health or safety 
effects of the rule on children and explain why the rule is preferable 
to other potentially effective and reasonably feasible alternatives 
considered by the agency.
    This rulemaking is not subject to the Executive Order because it is 
not economically significant as defined in E.O. 12866.

Executive Order 13211

    Executive Order 13211 (66 FR 28355, May 18, 2001) applies to any 
rulemaking that: (1) is determined to be economically significant as 
defined under E.O. 12866, and is likely to have a significantly adverse 
effect on the supply of, distribution of, or use of energy; or (2) that 
is designated by the Administrator of the Office of Information and 
Regulatory Affairs as a significant energy action. This rulemaking is 
not subject to E.O. 13211 as this rule is not economically significant 
and should not have an adverse effect on the supply of, distribution 
of, or use of energy for the same reasons explained in our discussion 
of Executive Orders 12866 and 13563.

Plain Language

    Executive Order 12866 requires each agency to write all rules in 
plain language. Application of the principles of plain language 
includes consideration of the following questions:
     Have we organized the material to suit the public's needs?
     Are the requirements in the rule clearly stated?
     Does the rule contain technical language or jargon that 
isn't clear?
     Would a different format (grouping and order of sections, 
use of headings, paragraphing) make the rule easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by adding tables, lists, or 
diagrams?
     What else could we do to make the rule easier to 
understand?
    If you have any responses to these questions, please include them 
in your comments on this proposal.

Regulation Identifier Number (RIN)

    The Department of Transportation assigns a regulation identifier 
number (RIN) to each regulatory action listed in the Unified Agenda of 
Federal Regulations. The Regulatory Information Service Center 
publishes the Unified Agenda in April and October of each year. You may 
use the RIN contained in the heading at the beginning of this document 
to find this action in the Unified Agenda.

List of Subjects in 49 CFR Part 571

    Imports, Incorporation by reference, Motor vehicle safety, 
Reporting and recordkeeping requirements, Tires.
    In consideration of the foregoing, NHTSA amends 49 CFR part 571 as 
set forth below.

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

0
1. The authority citation for part 571 continues to read as follows:

    Authority:  49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 CFR 1.95.


0
2. Amend Sec.  571.5 by:
0
a. Redesignating paragraphs (d)(20) through (33) as paragraphs (d)(21) 
through (34), respectively;
0
b. Adding new paragraph (d)(20);
0
d. Redesignating paragraphs (i)(1) through (4) as paragraphs (i)(2) 
through (5), respectively; and
0
e. Adding new paragraph (i)(1).
    The additions read as follows:


Sec.  571.5  Matter incorporated by reference.

* * * * *
    (d) * * *
    (20) ASTM D1193-06 (Reapproved 2018), Standard Specification for 
Reagent Water, approved March 15, 2018, into Sec.  571.308.
* * * * *
    (i) * * *
    (1) ISO 6270-2:2017(E), Paints and Varnishes--Determination of 
Resistance to Humidity--Part 2: Condensation (In-Cabinet Exposure with 
Heated Water Reservoir), Second edition, November 2017, into Sec.  
571.308.
* * * * *

0
3. Section 571.307 is added to read as follows:


Sec.  571.307  Standard No. 307; Fuel system integrity of hydrogen 
vehicles

    S1. Scope. This standard specifies requirements for the integrity 
of motor vehicle hydrogen fuel systems.
    S2. Purpose. The purpose of this standard is to reduce deaths and 
injuries occurring from fires that result from hydrogen fuel leakage 
during vehicle operation and after motor vehicle crashes.
    S3. Application. This standard applies to each motor vehicle 
manufactured on or after September 1, 2028, that uses compressed 
hydrogen gas as a fuel source to propel the vehicle.
    S4. Definitions.
    Check valve means a valve that prevents reverse flow.
    Closure devices mean 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.
    Container means a 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.
    Container attachments mean 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.
    Compressed hydrogen storage system (CHSS) means a system that 
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed 
of a container, container attachments (if any), and all closure devices 
required to isolate the stored hydrogen from the remainder of the fuel 
system and the environment.
    Enclosed or semi-enclosed spaces means the passenger compartment, 
luggage compartment, and space under the hood.
    Fuel cell system means a system containing the fuel cell stack(s), 
air processing system, fuel flow control system, exhaust system, 
thermal management system, and water management system.

[[Page 6278]]

    Fueling receptacle means the equipment to which a fueling station 
nozzle attaches to the vehicle and through which fuel is transferred to 
the vehicle.
    Fuel lines means all piping, tubing, joints, and any components 
such as flow controllers, valves, heat exchangers, and pressure 
regulators.
    Hydrogen concentration means the percentage of the hydrogen 
molecules within the mixture of hydrogen and air (equivalent to the 
partial volume of hydrogen gas).
    Hydrogen fuel system means the fueling receptacle, CHSS, fuel cell 
system or internal combustion engine, fuel lines, and exhaust systems.
    Luggage compartment means the space in the vehicle for luggage, 
cargo, and/or goods accommodation, bounded by a roof, hood, floor, side 
walls being separated from the passenger compartment by the front 
bulkhead or the rear bulkhead.
    Maximum allowable working pressure (MAWP) means the highest gauge 
pressure to which a component or system is permitted to operate under 
normal operating conditions.
    Nominal working pressure (NWP) means the settled pressure of 
compressed gas in a container or CHSS fully fueled to 100 percent state 
of charge and at a uniform temperature of 15 [deg]C.
    Normal milliliter means a quantity of gas that occupies one 
milliliter of volume when its temperature is 0 [deg]C and its pressure 
is 1 atmosphere.
    Passenger compartment means the space for occupant accommodation 
that is bounded by the roof, floor, side walls, doors, outside glazing, 
front bulkhead, and rear bulkhead or rear gate.
    Pressure relief device (PRD) means a device that, when activated 
under specified performance conditions, is used to release hydrogen 
from a pressurized system and thereby prevent failure of the system.
    Rechargeable electrical energy storage system (REESS) means the 
rechargeable energy storage system that provides electric energy for 
electrical propulsion.
    Service door means a door that allows for the entry and exit of 
vehicle occupants under normal operating conditions.
    Shut-off valve means a valve between the container and the 
remainder of the hydrogen fuel system that must default to the 
``closed'' position when unpowered.
    State of charge (SOC) means the density ratio of hydrogen in the 
CHSS between the actual CHSS condition and that at NWP with the CHSS 
equilibrated to 15 [deg]C, as expressed as a percentage using equation 
1 to this section, where [rho] is the density of hydrogen (g/L) at 
pressure (P) in MegaPascals (MPa) and temperature (T) in Celsius 
([deg]C) as listed in table 1 to S4 or linearly interpolated therein:

Equation 1 to Sec.  571.307 S4
[GRAPHIC] [TIFF OMITTED] TR17JA25.000


                                                                                  Table 1 to Sec.   571.307 S4
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                         Pressure (MPa)
                     Temperature ([deg]C)                      ---------------------------------------------------------------------------------------------------------------------------------
                                                                    1        10        20        30        35        40        50        60        65        70        75        80       87.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-40...........................................................       1.0       9.7      18.1      25.4      28.6      31.7      37.2      42.1      44.3      46.4      48.4      50.3      53.0
-30...........................................................       1.0       9.4      17.5      24.5      27.7      30.6      36.0      40.8      43.0      45.1      47.1      49.0      51.7
-20...........................................................       1.0       9.0      16.8      23.7      26.8      29.7      35.0      39.7      41.9      43.9      45.9      47.8      50.4
-10...........................................................       0.9       8.7      16.2      22.9      25.9      28.7      33.9      38.6      40.7      42.8      44.7      46.6      49.2
0.............................................................       0.9       8.4      15.7      22.2      25.1      27.9      33.0      37.6      39.7      41.7      43.6      45.5      48.1
10............................................................       0.9       8.1      15.2      21.5      24.4      27.1      32.1      36.6      38.7      40.7      42.6      44.4      47.0
15............................................................       0.8       7.9      14.9      21.2      24.0      26.7      31.7      36.1      38.2      40.2      42.1      43.9      46.5
20............................................................       0.8       7.8      14.7      20.8      23.7      26.3      31.2      35.7      37.7      39.7      41.6      43.4      46.0
30............................................................       0.8       7.6      14.3      20.3      23.0      25.6      30.4      34.8      36.8      38.8      40.6      42.4      45.0
40............................................................       0.8       7.3      13.9      19.7      22.4      24.9      29.7      34.0      36.0      37.9      39.7      41.5      44.0
50............................................................       0.7       7.1      13.5      19.2      21.8      24.3      28.9      33.2      35.2      37.1      38.9      40.6      43.1
60............................................................       0.7       6.9      13.1      18.7      21.2      23.7      28.3      32.4      34.4      36.3      38.1      39.8      42.3
70............................................................       0.7       6.7      12.7      18.2      20.7      23.1      27.6      31.7      33.6      35.5      37.3      39.0      41.4
80............................................................       0.7       6.5      12.4      17.7      20.2      22.6      27.0      31.0      32.9      34.7      36.5      38.2      40.6
85............................................................       0.7       6.4      12.2      17.5      20.0      22.3      26.7      30.7      32.6      34.4      36.1      37.8      40.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release 
hydrogen gas.
    S5. Hydrogen fuel system.
    S5.1. Fuel system integrity during normal vehicle operations.
    S5.1.1. Fueling receptacle requirements. (a) A compressed hydrogen 
fueling receptacle shall prevent reverse flow to the atmosphere.
    (b) A label shall be affixed close to the fueling receptacle 
showing the following information:
    (1) The statement, ``Compressed hydrogen gas only.''
    (2) The statement, ``Service pressure ______MPa (_____psig).''
    (3) The statement, ``See instructions on fuel container(s) for 
inspection and service life.''
    (c) The fueling receptacle shall ensure positive locking of the 
fueling nozzle.
    (d) The fueling receptacle shall be protected from the ingress of 
dirt and water.
    (e) The fueling receptacle shall not be installed in enclosed or 
semi-enclosed spaces.
    S5.1.2. Hydrogen discharge systems.
    S5.1.2.1. Pressure relief systems. (a) If present, the outlet of 
the vent line for hydrogen gas discharge from the TPRD(s) of the CHSS 
shall be protected from ingress of dirt and water.
    (b) The hydrogen gas discharge from TPRD(s) of the CHSS shall not 
impinge upon:
    (1) Enclosed or semi-enclosed spaces;
    (2) Any vehicle wheel housing;
    (3) Container(s);
    (4) REESS(s);
    (5) Any emergency exit(s) as identified in Sec.  571.217 (FMVSS No. 
217); nor
    (6) Any service door(s).
    S5.1.2.2. Vehicle exhaust system. When tested in accordance with 
S6.5 of this standard, the hydrogen concentration at the vehicle 
exhaust system's point of discharge shall not:
    (a) Exceed an average of 4.0 percent by volume during any moving 
three-second time interval; nor
    (b) Exceed 8.0 percent by volume at any time.
    S5.1.3. Protection against flammable conditions. (a) When tested in 
accordance with S6.4.1 of this standard, a warning in accordance with 
S5.1.6 shall be provided within 10 seconds of the application of the 
first test gas.

[[Page 6279]]

When tested in accordance with S6.4.1, the main shut-off valve shall 
close within 10 seconds of the application of the second test gas.
    (b) When tested in accordance with S6.4.2 of this standard, the 
hydrogen concentration in the enclosed or semi-enclosed spaces shall be 
less than 3.0 percent.
    S5.1.4. Fuel system leakage. When tested in accordance with S6.6 of 
this standard, the hydrogen fuel system downstream of the shut-off 
valve(s) shall not exhibit observable leakage.
    S5.1.5 Tell-tale warning. A warning shall be given to the driver, 
or to all front seat occupants for vehicles without a driver's 
designated seating position, by a visual signal or display text with 
the following properties:
    (a) Visible to the driver while seated in the driver's designated 
seating position or visible to all front seat occupants of vehicles 
without a driver's designated seating position;
    (b) Yellow in color if the warning system malfunctions;
    (c) Red in color if hydrogen concentration in enclosed or semi-
enclosed spaces exceeds 3.0 percent by volume;
    (d) When illuminated, shall be visible to the driver (or to all 
front seat occupants in vehicles without a driver's designated seating 
position) under both daylight and nighttime driving conditions; and
    (e) Remains illuminated when hydrogen concentration in any of the 
vehicle's enclosed or semi-enclosed spaces exceeds 3.0 percent by 
volume or when the warning system malfunctions, and the ignition 
locking system is in the ``On'' (``Run'') position or the propulsion 
system is activated.
    S5.2. Post-crash fuel system integrity. Each vehicle with a gross 
vehicle weight rating (GVWR) of 4,536 kg or less to which this standard 
applies must meet the requirements in S5.2.1 through S5.2.4 when tested 
according to S6 under the conditions of S7. Each school bus with a GVWR 
greater than 4,536 kg to which this standard applies must meet the 
requirements in S5.2.1 through S5.2.4 when tested according to S6 under 
the conditions of S7 of this standard.
    S5.2.1. Fuel leakage limit. If hydrogen gas is used for testing, 
the volumetric flow of hydrogen gas leakage shall not exceed an average 
of 118 normal liters per minute for the time interval, [Delta]t, as 
determined in accordance with S6.2.1 of this standard. If helium is 
used for testing, the volumetric flow of helium leakage shall not 
exceed an average of 88.5 normal litres per minute for the time 
interval, [Delta]t, as determined in accordance with S6.2.2 of this 
standard.
    S5.2.2. Concentration limit in enclosed spaces. The vehicle shall 
meet at least one of the requirements in S5.2.2(a), (b), or (c).
    (a) Hydrogen gas leakage shall not result in a hydrogen 
concentration in the air greater than 4.0 percent by volume in enclosed 
or semi-enclosed spaces for 60 minutes after impact when tested in 
accordance with S6.3 of this standard.
    (b) Helium gas leakage shall not result in a helium concentration 
in the air greater than 3.0 percent by volume in enclosed or semi-
enclosed spaces for 60 minutes after impact when tested in accordance 
with S6.3 of this standard.
    (c) The shut-off valve of the CHSS shall close within 5 seconds of 
the crash.
    S5.2.3. Container displacement. The container(s) shall remain 
attached to the vehicle by at least one component anchorage, bracket, 
or any structure that transfers loads from the container to the vehicle 
structure.
    S5.2.4. Fire. There shall be no fire in or around the vehicle for 
the duration of the test.
    S6. Test Requirements.
    S6.1. Vehicle Crash Tests. A test vehicle with a GVWR less than or 
equal to 4,536 kg, under the conditions of S7 of this standard, is 
subject to any one single barrier crash test of S6.1.1, S6.1.2, and 
S6.1.3. A school bus with a GVWR greater than 4,536 kg, under the 
conditions of S7, is subject to the contoured barrier crash test of 
S6.1.4. A particular vehicle need not meet further test requirements 
after having been subjected and evaluated to a single barrier crash 
test.
    S6.1.1. Frontal barrier crash. The test vehicle, with test dummies 
in accordance with S6.1 of 571.301 of this chapter, traveling 
longitudinally forward at any speed up to and including 48.0 km/h, 
impacts a fixed collision barrier that is perpendicular to the line of 
travel of the vehicle, or at an angle up to 30 degrees in either 
direction from the perpendicular to the line of travel of the vehicle.
    S6.1.2. Rear moving barrier impact. The test vehicle, with test 
dummies in accordance with S6.1 of Sec.  571.301, is impacted from the 
rear by a barrier that conforms to S7.3(b) of Sec.  571.301 and that is 
moving at any speed up to and including 80.0 km/h.
    S6.1.3. Side moving deformable barrier impact. The test vehicle, 
with the appropriate 49 CFR part 572 test dummies specified in Sec.  
571.214 (FMVSS No. 214) at positions required for testing by S7.1.1, 
S7.2.1, or S7.2.2 of Standard 214, is impacted laterally on either side 
by a moving deformable barrier moving at any speed between 52.0 km/h 
and 54.0 km/h.
    S6.1.4. Moving contoured barrier crash. The test vehicle is 
impacted at any point and at any angle by the moving contoured barrier 
assembly, specified in S7.5 and S7.6 in Sec.  571.301, traveling 
longitudinally forward at any speed up to and including 48.0 km/h.
    S6.2. Post-crash CHSS leak test.
    S6.2.1. Post-crash leak test for CHSS filled with compressed 
hydrogen. (a) The hydrogen gas pressure, P0 (MPa), and 
temperature, T0 ([deg]C), shall be measured immediately 
before the impact. The hydrogen gas pressure Pf (MPa) and 
temperature, Tf ([deg]C) shall also be measured immediately 
after a time interval [Delta]t (in minutes) after impact. The time 
interval, [Delta]t, starting from the time of impact, shall be the 
greater of S6.2.1(a)(1) or (2):
    (1) 60 minutes; or
    (2) The time interval calculated with equation 2 to this section, 
where Rs = Ps/NWP, Ps is the pressure 
range of the pressure sensor (MPa), NWP is the Nominal Working Pressure 
(MPa), and VCHSS is the volume of the CHSS (L):

Equation 2 to Sec.  571.307 S6.2.1(a)(2)

[Delta]t = VCHSS x NWP/1000 x ((-0.027 x NWP + 4) x 
Rs -0.21) - 1.7 x Rs

    (b) The initial mass of hydrogen M0 (g) in the CHSS 
shall be calculated from equations 3 through 5 to this section:

Equation 3 to Sec.  571.307 S6.2.1(b)

P0' = P0 x 288/(273 + T0)

Equation 4 to Sec.  571.307 S6.2.1(b)

[rho]0' = -0.0027 x (P0')\2\ + 0.75 x 
P0' + 1.07

Equation 5 to Sec.  571.307 S6.2.1(b)

M0 = [rho]0' x VCHSS

    (c) The final mass of hydrogen in the CHSS, Mf (in 
grams), at the end of the time interval, [Delta]t, shall be calculated 
from equations 6 through 8 to this section, where Pf is the 
measured final pressure (MPa) at the end of the time interval, and 
Tf ([deg]C) is the measured final temperature:

Equation 6 to Sec.  571.307 S6.2.1(c)

Pf' = Pf x 288/(273 + Tf)

Equation 7 to Sec.  571.307 S6.2.1(c)

[rho]f' = -0.0027 x (Pf')\2\ + 0.75 x 
Pf' + 1.07

Equation 8 to Sec.  571.307 S6.2.1(c)

Mf = [rho]f' x VCHSS

    (d) The average hydrogen flow rate over the time interval shall be 
calculated from equation 9 to this section, where VH2 is the 
average volumetric flow rate (normal millilitres per min) over the time 
interval:

[[Page 6280]]

Equation 9 to Sec.  571.307 S6.2.1(d)

VH2 = (Mf-M0)/[Delta]t x 22.41/2.016 x 
(Ptarget/P0)

    S6.2.2 Post-crash leak test for CHSS filled with compressed helium.
    (a) The helium pressure, P0 (MPa), and temperature, 
T0 ([deg]C), shall be measured immediately before the impact 
and again immediately after a time interval starting from the time of 
impact. The time interval, [Delta]t (min), shall be the greater of the 
values in S6.2.2(a)(1) or (2):
    (1) 60 minutes; or
    (2) The time interval calculated with equation 10 to this section, 
where Rs = Ps/NWP, Ps is the pressure 
range of the pressure sensor (MPa), NWP is the Nominal Working Pressure 
(MPa), and VCHSS is the volume of the CHSS (L):

Equation 10 to Sec.  571.307 S6.2.2(a)(2)

[Delta]t = VCHSS x NWP/1000 x (-0.028 x NWP + 5.5) x 
Rs-0.3)-2.6 x Rs

    (b) The initial mass of helium M0 (g) in the CHSS shall 
be calculated from equations 11 through 13 to this section:

Equation 11 to Sec.  571.307 S6.2.2(b)

P0' = P0 x 288/(273 + T0)

Equation 12 to Sec.  571.307 S6.2.2(b)

[rho]0' = -0.0043 x (P0')\2\ + 1.53 x 
P0' + 1.49

Equation 13 to Sec.  571.307 S6.2.2(b)

M0 = [rho]0' x VCHSS

    (c) The final mass of helium Mf (g) in the CHSS at the 
end of the time interval, [Delta]t (min), shall be calculated from 
equations 14 through 16 to this section, where Pf is the 
measured final pressure (MPa) at the end of the time interval, and 
Tf ([deg]C) is the measured final temperature:

Equation 14 to Sec.  571.307 S6.2.2(c)

Pf' = Pf x 288/(273 + Tf)

Equation 15 to Sec.  571.307 S6.2.2(c)

    [rho]f' = -0.0043 x (Pf')\2\ + 1.53 x 
Pf' + 1.49

Equation 16 to Sec.  571.307 S6.2.2(c)

Mf = [rho]f' x VCHSS

    (d) The average helium flow rate over the time interval shall be 
calculated from equation 17 to this section, where VHe is 
the average volumetric flow rate (normal millilitres per min) of helium 
over the time interval:

Equation 17 to Sec.  571.307 S6.2.2(d)

VHe = (Mf-M0)/[Delta]t x 22.41/4.003 x 
(Ptarget/P0)
    S6.3. Post-crash concentration test for enclosed spaces. (a) 
Sensors shall measure either the accumulation of hydrogen or helium 
gas, as appropriate, or the reduction in oxygen.
    (b) Sensors shall have an accuracy of at least 5 percent at 4.0 
percent hydrogen or 3.0 percent helium by volume in air, and a full-
scale measurement capability of at least 25 percent above these 
criteria. The sensor shall be capable of a 90 percent response to a 
full-scale change in concentration within 10 seconds.
    (c) Prior to the crash impact, the sensors shall be located in the 
passenger and luggage compartments of the vehicle as follows:
    (1) At any interior point at any distance between 240 mm and 260 mm 
of the headliner above the driver's seat or near the top center of the 
passenger compartment.
    (2) At any interior point at any distance between 240 mm and 260 mm 
of the floor in front of the rear (or rear most) seat in the passenger 
compartment.
    (3) At any interior point at any distance between 90 mm and 110 mm 
below the top of luggage compartment(s).
    (d) The sensors shall be securely mounted on the vehicle structure 
or seats and protected from debris, air bag exhaust gas and 
projectiles.
    (e) The vehicle shall be located either indoors or in an area 
outdoors protected from direct and indirect wind.
    (f) Post-crash data collection in enclosed spaces shall commence 
from the time of impact. Data from the sensors shall be collected at 
least every 5 seconds and continue for a period of 60 minutes after the 
impact.
    (g) The data shall be compiled into a three-data-point rolling 
average prior to evaluating the applicable concentration limit in 
accordance with S5.2.2(a) or (b) of this standard.
    S6.4. Test procedure for protection against flammable conditions.
    S6.4.1. Test for hydrogen gas leakage detectors. (a) The vehicle 
propulsion system shall be operated for at least five minutes prior to 
testing and shall continue to operate throughout the test.
    (b) Two mixtures of air and hydrogen gas shall be used in the test: 
The first test gas has any hydrogen concentration between 3.0 and 4.0 
percent by volume in air to verify function of the warning, and the 
second test gas has any hydrogen concentration between 4.0 and 6.0 
percent by volume in air to verify function of the shut-down.
    (c) The test shall be conducted without influence of wind.
    (d) A vehicle hydrogen leakage detector located in the enclosed or 
semi-enclosed spaces is enclosed with a cover and a test gas induction 
hose is attached to the hydrogen gas leakage detector.
    (e) The hydrogen gas leakage detector is exposed to continuous flow 
of the first test gas specified in S.6.4.1(b) until the warning turns 
on.
    (f) Then the hydrogen gas leakage detector is exposed to continuous 
flow of the second test gas specified in S.6.4.1(b) until the main 
shut-off valve closes to isolate the CHSS. The test is completed when 
the shut-off valve closes.
    S6.4.2. Test for integrity of enclosed spaces and detection 
systems. (a) The test shall be conducted without influence of wind.
    (b) Prior to the test, the vehicle is prepared to simulate remotely 
controllable hydrogen releases from the fuel system or from an external 
fuel supply. The number, location, and flow capacity of the release 
points downstream of the shut-off valve are defined by the vehicle 
manufacturer.
    (c) A hydrogen concentration detector shall be installed in any 
enclosed or semi-enclosed spaces where hydrogen may accumulate from the 
simulated hydrogen release.
    (d) Vehicle doors, windows and other covers are closed.
    (e) The vehicle propulsion system shall be operated for at least 
five minutes and shall continue to operate throughout the remainder of 
the test.
    (f) A leak shall be simulated using the remote controllable 
function.
    (g) The hydrogen concentration is measured continuously until the 
end of the test.
    (h) The test is completed 5 minutes after initiating the simulated 
leak or when the hydrogen concentration does not change for 3 minutes, 
whichever is longer.
    S6.5. Test for the vehicle exhaust system. (a) The vehicle 
propulsion system shall be operated for at least five minutes prior to 
testing and shall continue to operate throughout the test, except for 
times when the propulsion system becomes deactivated by the steps taken 
during S6.5(c).
    (b) The measuring section of the measuring device shall be placed 
along the centerline of the exhaust gas flow within 100 mm of where the 
exhaust is released to the atmosphere.
    (c) The exhaust hydrogen concentration shall be continuously 
measured during the following steps:
    (1) The fuel cell system shall be shut down.
    (2) The fuel cell system shall be immediately restarted.
    (3) After one minute, the vehicle shall be set to the ``off'' 
position and measurement continues until the until the vehicle shutdown 
is complete.

[[Page 6281]]

    (d) The measurement device shall have a resolution time of less 
than 300 milliseconds;
    (e) The measurement device shall have a measurement response time 
(t0-t90) of less than 2 seconds, where 
t0 is the moment of hydrogen concentration switching, and 
t90 is the time when 90 percent of the final indication is 
reached and shall have a resolution time of less than 300 milliseconds 
(sampling rate of greater than 3.33 Hz).
    S6.6. Test for fuel system leakage. The vehicle CHSS shall be 
filled with hydrogen to any pressure between 90 percent NWP and 100 
percent NWP for the duration of the test for fuel system leakage.
    (a) The vehicle propulsion system shall be operated for at least 
five minutes prior to testing and shall continue to operate throughout 
the test.
    (b) Hydrogen leakage shall be evaluated at accessible sections of 
the hydrogen fuel system downstream of the shut-off valve(s) using a 
leak detecting liquid. Hydrogen gas leak detection shall be performed 
immediately after applying the liquid.
    S7. Test conditions. The requirements of S5.2 shall be met under 
the following conditions. Where a range of conditions is specified, the 
vehicle must be capable of meeting the requirements at all points 
within the range.
    (a) Prior to conducting the crash test, instrumentation is 
installed in the CHSS to perform the required pressure and temperature 
measurements if the vehicle does not already have instrumentation with 
the required accuracy.
    (b) The CHSS is then purged, if necessary, following vehicle 
manufacturer directions before filling the CHSS with compressed 
hydrogen or helium gas, as specified by the vehicle manufacturer.
    (c) The target fill pressure Ptarget shall be calculated 
from equation 18 to this section, where NWP is in MPa, To is 
the ambient temperature in [deg]C to which the CHSS is expected to 
settle, and Ptarget is the target fill pressure in MPa after 
the temperature settles:

Equation 18 to Sec.  571.307 S7

Ptarget = NWP x (273 + To)/288

    (d) The container(s) shall be filled to any pressure between 95.0 
percent and 100.0 percent of the calculated target fill pressure.
    (e) After fueling, the vehicle shall be maintained at rest for any 
duration between 2.0 and 3.0 hours before conducting a crash test in 
accordance with S6.1 of this standard.
    (f) The CHSS shut-off valve(s) and any other shut-off valves 
located in the fuel system downstream hydrogen gas piping shall be in 
normal driving condition immediately prior to the impact.
    (g) The parking brake is disengaged and the transmission is in 
neutral prior to the crash test.
    (h) Tires are inflated to manufacturer's specifications.
    (i) The vehicle, including test devices and instrumentation, is 
loaded as follows:
    (1) A passenger car, with its fuel system filled as specified in 
S7(d), is loaded to its unloaded vehicle weight plus its rated cargo 
and luggage capacity weight, secured in the luggage area, plus the 
necessary test dummies as specified in S6, restrained only by means 
that are installed in the vehicle for protection at its seating 
position(s).
    (2) A multipurpose passenger vehicle, truck, or bus with a GVWR of 
10,000 pounds or less, whose fuel system is filled as specified in 
S7(d), is loaded to its unloaded vehicle weight, plus the necessary 
test dummies as specified in S6 of this standard, plus 136.1 kg, or its 
rated cargo and luggage capacity weight, whichever is less, secured to 
the vehicle and distributed so that the weight on each axle as measured 
at the tire-ground interface is in proportion to its gross axle weight 
rating (GAWR). Each dummy shall be restrained only by means that are 
installed in the vehicle for protection at its seating position(s).
    (3) A school bus with a GVWR greater than 10,000 pounds, whose fuel 
system is filled as specified in S7(d), is loaded to its unloaded 
vehicle weight, plus 54.4 kg of unsecured weight at each designated 
seating position.

0
4. Section 571.308 is added to read as follows:


Sec.  571.308  Standard No. 308; Compressed hydrogen storage system 
integrity

    S1. Scope. This standard specifies requirements for compressed 
hydrogen storage systems used in motor vehicles.
    S2. Purpose. The purpose of this standard is to reduce deaths and 
injuries occurring from fires that result from hydrogen fuel leakage 
during vehicle operation and to reduce deaths and injuries occurring 
from explosions resulting from the burst of pressurized hydrogen 
containers.
    S3. Application. This standard applies to each motor vehicle 
manufactured on or after September 1, 2028, that is equipped with 
compressed hydrogen gas as a fuel source to propel the vehicle. The 
standard does not apply to vehicles that are only equipped with cryo-
compressed hydrogen storage systems and/or solid-state hydrogen storage 
system to propel the vehicle.
    S4. Definitions.
    BPO means the vehicle manufacturer-supplied median burst 
pressure for a batch of new containers.
    Burst means to break apart or to break open.
    Burst pressure means the highest pressure achieved for a container 
tested in accordance with S6.2.2.1 of this standard.
    Check valve means a valve that prevents reverse flow.
    Closure devices mean 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.
    Container means a 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.
    Container attachments mean 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.
    Compressed hydrogen storage system (CHSS) means a system that 
stores compressed hydrogen fuel for a hydrogen-fueled vehicle, composed 
of a container, container attachments (if any), and all closure devices 
required to isolate the stored hydrogen from the remainder of the fuel 
system and the environment.
    Cryo-compressed hydrogen storage system means a system that stores 
hydrogen by compressing it to high pressure while simultaneously 
cooling it to very low temperatures, allowing for a higher density of 
hydrogen storage compared to standard compressed hydrogen systems.
    Hydrogen fuel system means the fueling receptacle, CHSS, fuel cell 
system or internal combustion engine, fuel lines, and exhaust systems.
    Nominal working pressure (NWP) means the settled pressure of 
compressed gas in a container or CHSS fully fueled to 100 percent state 
of charge and at a uniform temperature of 15 [deg]C.
    Normal milliliter means a quantity of gas that occupies one 
milliliter of volume when its temperature is 0 [deg]C and its pressure 
is 1 atmosphere.
    Pressure relief device (PRD) means a device that, when activated 
under specified performance conditions, is used to release hydrogen 
from a

[[Page 6282]]

pressurized system and thereby prevent failure of the system.
    Service life (of a container) means the time frame during which 
service (usage) is authorized by the vehicle manufacturer.
    Shut-off valve means a valve between the container and the 
remainder of the hydrogen fuel system that must default to the 
``closed'' position when unpowered.
    Solid-state hydrogen storage system means a system that stores 
hydrogen at ambient temperatures and low pressures within solid 
materials that can either physically absorb the hydrogen gas or 
chemically combine with it.
    State of charge (SOC) means the density ratio of hydrogen in the 
CHSS between the actual CHSS condition and that at NWP with the CHSS 
equilibrated to 15 [deg]C, as expressed as a percentage using the 
equation 1 to this section, where [rho] is the density of hydrogen (g/
L) at pressure (P) in MegaPascals (MPa) and temperature (T) in Celsius 
([deg]C) as listed below in Table 1 or linearly interpolated therein:

Equation 1 to Sec.  571.308 S4
[GRAPHIC] [TIFF OMITTED] TR17JA25.001


                                                                                  Table 1 to Sec.   571.308 S4
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                         Pressure (MPa)
                     Temperature ([deg]C)                      ---------------------------------------------------------------------------------------------------------------------------------
                                                                    1        10        20        30        35        40        50        60        65        70        75        80       87.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-40...........................................................       1.0       9.7      18.1      25.4      28.6      31.7      37.2      42.1      44.3      46.4      48.4      50.3      53.0
-30...........................................................       1.0       9.4      17.5      24.5      27.7      30.6      36.0      40.8      43.0      45.1      47.1      49.0      51.7
-20...........................................................       1.0       9.0      16.8      23.7      26.8      29.7      35.0      39.7      41.9      43.9      45.9      47.8      50.4
-10...........................................................       0.9       8.7      16.2      22.9      25.9      28.7      33.9      38.6      40.7      42.8      44.7      46.6      49.2
0.............................................................       0.9       8.4      15.7      22.2      25.1      27.9      33.0      37.6      39.7      41.7      43.6      45.5      48.1
10............................................................       0.9       8.1      15.2      21.5      24.4      27.1      32.1      36.6      38.7      40.7      42.6      44.4      47.0
15............................................................       0.8       7.9      14.9      21.2      24.0      26.7      31.7      36.1      38.2      40.2      42.1      43.9      46.5
20............................................................       0.8       7.8      14.7      20.8      23.7      26.3      31.2      35.7      37.7      39.7      41.6      43.4      46.0
30............................................................       0.8       7.6      14.3      20.3      23.0      25.6      30.4      34.8      36.8      38.8      40.6      42.4      45.0
40............................................................       0.8       7.3      13.9      19.7      22.4      24.9      29.7      34.0      36.0      37.9      39.7      41.5      44.0
50............................................................       0.7       7.1      13.5      19.2      21.8      24.3      28.9      33.2      35.2      37.1      38.9      40.6      43.1
60............................................................       0.7       6.9      13.1      18.7      21.2      23.7      28.3      32.4      34.4      36.3      38.1      39.8      42.3
70............................................................       0.7       6.7      12.7      18.2      20.7      23.1      27.6      31.7      33.6      35.5      37.3      39.0      41.4
80............................................................       0.7       6.5      12.4      17.7      20.2      22.6      27.0      31.0      32.9      34.7      36.5      38.2      40.6
85............................................................       0.7       6.4      12.2      17.5      20.0      22.3      26.7      30.7      32.6      34.4      36.1      37.8      40.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    Thermally-activated pressure relief device (TPRD) means a non-
reclosing PRD that is activated by temperature to open and release 
hydrogen gas.
    TPRD sense point means instrumentation that detects elevated 
temperature for the purpose of activating a TPRD.
    S5. Requirements.
    S5.1. Requirements for the CHSS. Each vehicle CHSS shall include 
the following functions: shut-off valve, check valve, and TPRD. Each 
vehicle CHSS shall have a NWP of 70 MPa or less. Each vehicle 
container, closure device, and CHSS shall meet the applicable 
performance test requirements listed in table 2 to this section.

                     Table 2 to Sec.   571.308 S5.1
------------------------------------------------------------------------
            Requirement section                     Test article
------------------------------------------------------------------------
S5.1.1. Tests for baseline metrics........  Container.
S5.1.2. Test for performance durability...  Container.
S5.1.3. Test for expected on-road           CHSS.
 performance.
S5.1.4. Test for service terminating        CHSS.
 performance in fire.
S5.1.5. Tests for performance durability    Closure devices.
 of closure devices.
------------------------------------------------------------------------

    S5.1.1. Tests for baseline metrics.
    S5.1.1.1. Baseline initial burst pressure. The vehicle manufacturer 
shall immediately and irrevocably specify upon request, in writing and 
within 15 business days: whether the primary constituent of the 
container is glass fiber composite. When a new container with its 
container attachments (if any) is tested in accordance with S6.2.2.1 of 
this standard, both of the following requirements shall be met:
    (a) The burst pressure of the container shall not be less than 2 
times NWP.
    (b) The burst pressure of the container having glass-fiber 
composite as a primary constituent shall not be less than 3.5 times 
NWP.
    S5.1.1.2. Baseline initial pressure cycle test. When a new 
container with its container attachments (if any) is hydraulically 
pressure cycled in accordance with S6.2.2.2 of this standard to any 
pressure between 125.0 percent NWP and 130.0 percent NWP,
    (a) Containers for vehicles with a GVWR of 10,000 pounds or less
    (1) Shall not leak nor burst for at least 7,500 cycles, and
    (2) Thereafter shall not burst for an additional 14,500 cycles. If 
a leak occurs while conducting the test as specified in S5.1.1.2(a)(2), 
the test is stopped and not considered a failure.
    (b) Containers for vehicles with a GVWR of over 10,000 pounds
    (1) Shall not leak nor burst for at least 11,000 cycles, and
    (2) Thereafter shall not burst for an additional 11,000 cycles. If 
a leak occurs while conducting the test as specified in S5.1.1.2(b)(2), 
the test is stopped and not considered a failure.
    S5.1.2. Test for performance durability. A new container shall not 
leak nor burst when subjected to the sequence of tests in S5.1.2.1 
through S5.1.2.6. Immediately following S5.1.2.6, and without 
depressurizing the container, the container is subjected to a burst 
test in accordance with S6.2.2.1(c) and (d) of this standard. The burst 
pressure of the container at the end of the sequence of tests in this

[[Page 6283]]

section shall not be less than 0.8 times the BPO value 
specified by the vehicle manufacturer. The sequence of tests and the 
burst pressure test are illustrated in figure 1 to S5.1.2. The vehicle 
manufacturer shall immediately and irrevocably specify upon request, in 
writing and within 15 business days: the BPO of the 
container.
    S5.1.2.1. Drop test. The container with its container attachments 
(if any) is dropped once in accordance with S6.2.3.2 of this standard 
in any one of the four orientations specified in that section. Any 
container with damage from the drop test that prevents further testing 
of the container in accordance with S6.2.3.4 of this standard shall be 
considered to have failed to meet the test for performance durability 
requirements. In the case of an asymmetric container, the vehicle 
manufacturer shall immediately and irrevocably specify upon request, in 
writing, and within 15 business days: the center of gravity of the 
container.
    S5.1.2.2. Surface damage test. The container, except if an all-
metal container, is subjected to the surface damage test in accordance 
with the S6.2.3.3 of this standard. Container attachments designed to 
be removed shall be removed and container attachments that are not 
designed to be removed shall remain in place. Container attachments 
that are removed shall not be reinstalled for the remainder of S5.1.2; 
container attachments that are not removed shall remain in place for 
the remainder of S5.1.2.
    S5.1.2.3. Chemical exposure and ambient-temperature pressure 
cycling test. The container is exposed to chemicals in accordance with 
S6.2.3.4 and then hydraulically pressure cycled in accordance with 
S6.2.3.4 of this standard for 60 percent of the number of cycles as 
specified in S5.1.1.2(a)(1) or (b)(1) as applicable. For all but the 
last 10 of these cycles, the cycling pressure shall be any pressure 
between 125.0 percent NWP and 130.0 percent NWP. For the last 10 
cycles, the pressure shall be any pressure between 150.0 percent NWP 
and 155.0 percent NWP.
    S5.1.2.4. High temperature static pressure test. The container is 
pressurized to any pressure between (or equal to) 125 percent NWP and 
130 percent NWP and held at that pressure no less than 1,000 and no 
more than 1,050 hours in accordance with S6.2.3.5 of this standard and 
with the temperature surrounding the container at any temperature 
between 85.0 [deg]C and 90.0 [deg]C.
    S5.1.2.5. Extreme temperature pressure cycling test. The container 
is pressure cycled in accordance with S6.2.3.6 for 40 percent of the 
number of cycles specified in S5.1.1.2(a)(1) or (b)(1) as applicable. 
The pressure for the first half of these cycles equals any pressure 
between 80.0 percent NWP and 85.0 percent NWP with the temperature 
surrounding the container equal to any temperature between -45.0 [deg]C 
and -40.0 [deg]C. The pressure for the next half of these cycles equals 
any pressure between 125.0 percent NWP and 130.0 percent NWP and the 
temperature surrounding the container equal to any temperature between 
85.0 [deg]C and 90.0 [deg]C and the relative humidity surrounding the 
container not less than 80 percent.
    S5.1.2.6. Residual pressure test. The container is hydraulically 
pressurized in accordance with S6.2.3.1 of this standard to a pressure 
between 180.0 percent NWP and 185.0 percent NWP and held for any 
duration between 240 to 245 seconds.

[[Page 6284]]

[GRAPHIC] [TIFF OMITTED] TR17JA25.002

Figure 1 to Sec.  571.308 S5.1.2. Performance Durability Test; (for 
Illustration Purposes Only)

    S5.1.3. Test for expected on-road performance. When subjected to 
the sequence of tests in S5.1.3.1, the CHSS shall meet the permeation 
and leak requirements specified in S5.1.3.2 and shall not burst. 
Thereafter, the container of the CHSS shall not burst when subjected to 
a residual pressure test in accordance with S5.1.3.3. Immediately 
following the test specified in S5.1.3.3, and without depressurizing 
the container, the container of the CHSS is subjected to a burst test 
in accordance with S6.2.2.1(c) and (d) of this standard. The burst 
pressure of the container at the end of the sequence of tests in this 
section shall not be less than 0.8 times the BPO specified 
by the vehicle manufacturer under S5.1.2.
    S5.1.3.1. Ambient and extreme temperature gas pressure cycling 
test. The CHSS is pressure cycled using hydrogen gas for 500 cycles 
under any temperature and pressure condition for the number of cycles 
as specified in table 3 to S5.1.3.1, and in accordance with the 
S6.2.4.1 of this standard test procedure. A static gas pressure leak/
permeation test performed in accordance with S5.1.3.2 is conducted 
after the first 250 pressure cycles and after the remaining 250 
pressure cycles.

                                                           Table 3 to Sec.   571.308 S5.1.3.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                 Initial system          Fuel delivery        Cycle initial and
          Number of cycles             Ambient conditions         equilibration           temperature           final pressure      Cycle peak pressure
--------------------------------------------------------------------------------------------------------------------------------------------------------
5..................................  -30.0 [deg]C to -25.0   -30.0 [deg]C to -25.0   15.0 [deg]C to 25.0    1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                 [deg]C.                 [deg]C.                                       SOC.
5..................................  -30.0 [deg]C to -25.0   -30.0 [deg]C to -25.0   -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                 [deg]C.                 [deg]C.                                       SOC.
15.................................  -30.0 [deg]C to -25.0   not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
5..................................  50.0 [deg]C to 55.0     50 [deg]C to 55         -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C, 80% to 100%     [deg]C, 80% to 100%     [deg]C.                                       SOC.
                                      relative humidity.      relative humidity.
20.................................  50.0 [deg]C to 55.0     not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C, 80% to 100%                             [deg]C.                                       SOC.
                                      relative humidity.
200................................  5.0 [deg]C to 35.0      not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.

[[Page 6285]]

 
Extreme temperature static gas       55.0 [deg]C to 60.0     55.0 [deg]C to 60.0     not appliable........  not appliable........  100.0% SOC to 105.0%
 pressure leak/permeation test        [deg]C.                 [deg]C.                                                               SOC.
 S5.1.3.2.
25.................................  50.0 [deg]C to 55.0     not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C, 80% to 100%                             [deg]C.                                       SOC.
                                      relative humidity.
25.................................  -30.0 [deg]C to -25.0   not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
200................................  5.0 [deg]C to 35.0      not appliable.........  -40.0 [deg]C to -33.0  1.0 MPa to 2.0 MPa...  100.0% SOC to 105.0%
                                      [deg]C.                                         [deg]C.                                       SOC.
Extreme temperature static gas       55.0 [deg]C to 60.0     55.0 [deg]C to 60.0     not appliable........  not appliable........  100.0% SOC to 105.0%
 pressure leak/permeation test        [deg]C.                 [deg]C.                                                               SOC.
 S5.1.3.2.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    S5.1.3.2. Extreme temperature static gas pressure leak/permeation 
test. When tested in accordance with S6.2.4.2 of this standard after 
each group of 250 pneumatic pressure cycles in S5.1.3.1, the CHSS shall 
not discharge hydrogen more than 46 millilitres per hour (mL/h) for 
each litre of CHSS water capacity.
    S5.1.3.3. Residual pressure test. The container of the CHSS is 
hydraulically pressurized in accordance with S6.2.3.1 to any pressure 
between 1.800 times NWP and 1.850 times NWP and held at that pressure 
for any duration between 240 to 245 seconds.
    S5.1.4. Test for service terminating performance in fire. When the 
CHSS is exposed to the two-stage localized or engulfing fire test in 
accordance with S6.2.5 of this standard, the container shall not burst. 
The pressure inside the CHSS shall fall to 1 MPa or less within the 
test time limit specified in S6.2.5.3(o) of this standard. Any leakage 
or venting, other than that through TPRD outlet(s), shall not result in 
jet flames greater than 0.5 m in length. If venting occurs though the 
TPRD, the venting shall be continuous.
    S5.1.5. Tests for performance durability of closure devices. All 
tests are performed at ambient temperature of 5 [deg]C to 35 [deg]C 
unless otherwise specified.
    S5.1.5.1. TPRD requirements. The TPRD shall not activate at any 
point during the test procedures specified in S6.2.6.1.1, S6.2.6.1.3, 
S6.2.6.1.4, S6.2.6.1.5, S6.2.6.1.6, S6.2.6.1.7, and S6.2.6.1.8 of this 
standard.
    (a) A TPRD subjected to pressure cycling in accordance with 
S6.2.6.1.1 of this standard shall be sequentially tested in accordance 
with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this standard;
    (1) When tested in accordance with S6.2.6.1.8, the TPRD shall not 
exhibit leakage greater than 10 normal milliliters per minute (NmL/
hour).
    (2) When tested in accordance with S6.2.6.1.9 of this standard, the 
TPRD shall activate within no more than 2 minutes of the average 
activation time of three new TPRDs tested in accordance with 
S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10 of this standard, 
the TPRD shall have a flow rate of at least 90 percent of the highest 
baseline flow rate established in accordance with S6.2.6.1.10;
    (b)(1) A TPRD shall activate in less than ten hours when tested at 
the vehicle manufacturer's specified activation temperature in 
accordance with S6.2.6.1.2 of this standard;
    (2) When tested at the accelerated life temperature in accordance 
with S6.2.6.1.2 of this standard, a TPRD shall not activate in less 
than 500 hours and shall not exhibit leakage greater than 10 NmL/hour 
when tested in accordance with S6.2.6.1.8 of this standard;
    (c) A TPRD subjected to temperature cycling testing in accordance 
with S6.2.6.1.3 of this standard shall be sequentially tested in 
accordance with S6.2.6.1.8(a)(3), S6.2.6.1.9, and S6.2.6.1.10 of this 
standard;
    (1) When tested in accordance with S6.2.6.1.8(a)(3) of this 
standard, the TPRD shall not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.1.9 of this standard, the 
TPRD shall activate within no more than 2 minutes of the average 
activation time of three new TPRDs tested in accordance with 
S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10 of this standard, 
the TPRD shall have a flow rate of at least 90 percent of the highest 
baseline flow rate established in accordance with S6.2.6.1.10;
    (d) A TPRD subjected to salt corrosion resistance testing in 
accordance with S6.2.6.1.4 of this standard shall be sequentially 
tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of 
this standard;
    (1) When tested in accordance with S6.2.6.1.8 of this standard, the 
TPRD shall not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.1.9 of this standard, the 
TPRD shall activate within no more than 2 minutes of the average 
activation time of three new TPRDs tested in accordance with 
S6.2.6.1.9;
    (3) When tested in accordance with S6.2.6.1.10 of this standard, 
the TPRD shall have a flow rate of at least 90 percent of the highest 
baseline flow rate established in accordance with S6.2.6.1.10;
    (e) A TPRD subjected to vehicle environment testing in accordance 
with S6.2.6.1.5 of this standard shall not show signs of cracking, 
softening, or swelling, and thereafter shall be sequentially tested in 
accordance with S6.2.6.1.8, S6.2.6.1.9, and S6.2.6.1.10 of this 
standard. Cosmetic changes such as pitting or staining are not 
considered failures.
    (1) When tested in accordance with S6.2.6.1.8 of this standard, the 
TPRD shall not exhibit leakage greater than 10 NmL/hour.
    (2) When tested in accordance with S6.2.6.1.9 of this standard, the 
TPRD shall activate within no more than 2 minutes of the average 
activation time of three new TPRDs tested in accordance with 
S6.2.6.1.9,
    (3) When tested in accordance with S6.2.6.1.10 of this standard, 
the TPRD shall have a flow rate of at least 90 percent of the highest 
baseline flow rate established in accordance with S6.2.6.1.10;
    (f) A TPRD subjected to stress corrosion cracking testing in 
accordance with S6.2.6.1.6 of this standard shall not exhibit visible 
cracking or delaminating;
    (g) A TPRD shall be subjected to drop and vibration testing in 
accordance with

[[Page 6286]]

S6.2.6.1.7 of this standard. If the TPRD progresses beyond 
S6.2.6.1.7(c) to complete testing under S6.2.6.1.7(d), it shall then be 
sequentially tested in accordance with S6.2.6.1.8, S6.2.6.1.9, and 
S6.2.6.1.10 of this standard.
    (1) When tested in accordance with S6.2.6.1.8 of this standard, the 
TPRD shall not exhibit leakage greater than 10 NmL/hour.
    (2) When tested in accordance with S6.2.6.1.9 of this standard, the 
TPRD shall activate within no more than 2 minutes of the average 
activation time of three new TPRDs tested in accordance with 
S6.2.6.1.9,
    (3) When tested in accordance with S6.2.6.1.10 of this standard, 
the TPRD shall have a flow rate of at least 90 percent of the highest 
baseline flow rate established in accordance with S6.2.6.1.10;
    (h) One new TPRD subjected to leak testing in accordance with 
S6.2.6.1.8 of this standard shall not exhibit leakage greater than 10 
NmL/hour;
    (i) Three new TPRDs are subjected to a bench top activation test in 
accordance with S6.2.6.1.9 of this standard. The maximum difference in 
the activation time between any two of the three TPRDs shall be 2 
minutes or less.
    S5.1.5.2. Check valve and shut-off valve requirements. This section 
applies to both check valves and shut-off valves.
    (a) A valve subjected to hydrostatic strength testing in accordance 
with S6.2.6.2.1 of this standard shall not leak to an extent that 
prevents continued pressurization in accordance with S6.2.6.2.1(c) nor 
burst at less than 250 percent NWP;
    (b) A valve subjected to leak testing in accordance with S6.2.6.2.2 
of this standard shall not exhibit leakage greater than 10 NmL/hour;
    (c)(1) A check valve shall meet the requirements when tested 
sequentially as follows:
    (i) The check valve shall reseat and prevent reverse flow after 
each cycle when subjected to 13,500 pressure cycles in accordance with 
S6.2.6.2.3 of this standard to any pressure between 100.0 and 105.0 
percent NWP and at any temperature between 5.0 [deg]C and 35.0 [deg]C;
    (ii) The same check valve shall reseat and prevent reverse flow 
after each cycle when subjected to 750 pressure cycles in accordance 
with S6.2.6.2.3 of this standard to any pressure between 125.0 and 
130.0 percent NWP and at any temperature between 85.0 [deg]C and 90.0 
[deg]C;
    (iii) The same check valve shall reseat and prevent reverse flow 
after each cycle when subjected to 750 pressure cycles in accordance 
with S6.2.6.2.3 of this standard to any pressure between 80.0 and 85.0 
percent NWP and at any temperature between -45.0 [deg]C and -40.0 
[deg]C;
    (iv) The same check valve shall be subjected to chatter flow 
testing in accordance with S6.2.6.2.4 of this standard;
    (v) When tested in accordance with S6.2.6.2.2 of this standard, the 
same check valve shall not exhibit leakage greater than 10 NmL/hour;
    (vi) When tested in accordance with S6.2.6.2.1 of this standard, 
the same check valve shall not leak to an extent that prevents 
continued pressurization in accordance with S6.2.6.2.1(c), nor burst at 
less than 250 percent NWP, nor burst at less than 80 percent of the 
burst pressure of the new unit tested in accordance with S5.1.5.2(a) 
unless the burst pressure of the valve exceeds 400 percent NWP.
    (2) A shut-off valve shall meet the requirements when tested 
sequentially as follows:
    (i) The shut-off valve shall be subjected to 45,000 pressure cycles 
in accordance with S6.2.6.2.3 to any pressure between 100.0 and 105.0 
percent NWP and at any temperature between 5.0 [deg]C and 35.0 [deg]C;
    (ii) The same shut-off valve shall be subjected to 2,500 pressure 
cycles in accordance with S6.2.6.2.3 of this standard to any pressure 
between 125.0 and 130.0 percent NWP and at any temperature between 85.0 
[deg]C and 90.0 [deg]C;
    (iii) The same shut-off valve shall be subjected to 2,500 pressure 
cycles in accordance with S6.2.6.2.3 of this standard to any pressure 
between 80.0 and 85.0 percent NWP and at any temperature between -45.0 
[deg]C and -40.0 [deg]C;
    (iv) The same shut-off valve shall be subjected to chatter flow 
testing in accordance with S6.2.6.2.4 of this standard;
    (v) When tested in accordance with S6.2.6.2.2 of this standard, the 
same shut-off valve shall not exhibit leakage greater than 10 NmL/hour;
    (vi) When tested in accordance with S6.2.6.2.1 of this standard, 
the same shut-off valve shall not leak to an extent that prevents 
continued pressurization in accordance with S6.2.6.2.1(c), nor burst at 
less than 250 percent NWP, nor burst at less than 80 percent of the 
burst pressure of the new unit tested in accordance with S5.1.5.2(a) 
unless the burst pressure of the valve exceeds 400 percent NWP.
    (d) A valve subjected to salt corrosion resistance testing in 
accordance with S6.2.6.1.4 of this standard shall be tested 
sequentially in accordance with S6.2.6.2.2 followed by S6.2.6.2.1 of 
this standard.
    (1) When tested in accordance with S6.2.6.2.2 of this standard, the 
valve shall not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.2.1 of this standard, the 
valve shall not leak to an extent that prevents continued 
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 
250 percent NWP, nor burst at less than 80 percent of the burst 
pressure of the new unit tested in accordance with S5.1.5.2(a) unless 
the burst pressure of the valve exceeds 400 percent NWP.
    (e) A valve subjected to vehicle environment testing in accordance 
with S6.2.6.1.5 of this standard shall not show signs of cracking, 
softening, or swelling and shall be tested sequentially in accordance 
with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard. Cosmetic 
changes such as pitting or staining are not considered failures.
    (1) When tested in accordance with S6.2.6.2.2 of this standard, the 
valve shall not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.2.1 of this standard, the 
valve shall not leak to an extent that prevents continued 
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 
250 percent NWP, nor burst at less than 80 percent of the burst 
pressure of the new unit tested in accordance with S5.1.5.2(a) unless 
the burst pressure of the valve exceeds 400 percent NWP;
    (f) A shut-off valve shall have a minimum resistance of 240 
k[Omega] between the power conductor and the valve casing, and shall 
not exhibit open valve, smoke, fire, melting, or leakage greater than 
10 NmL/hour when subjected to electrical testing in accordance with 
S6.2.6.2.5 followed by leak testing in accordance with S6.2.6.2.2 of 
this standard;
    (g) A valve subjected to vibration testing in accordance with 
S6.2.6.2.6 of this standard shall be tested sequentially in accordance 
with S6.2.6.2.2 followed by S6.2.6.2.1 of this standard.
    (1) When tested in accordance with S6.2.6.2.2 of this standard, the 
valve shall not exhibit leakage greater than 10 NmL/hour;
    (2) When tested in accordance with S6.2.6.2.1 of this standard, the 
valve shall not leak to an extent that prevents continued 
pressurization in accordance with S6.2.6.2.1(c), nor burst at less than 
250 percent NWP, nor burst at less than 80 percent of the burst 
pressure of the new unit tested in accordance with

[[Page 6287]]

S5.1.5.2(a) unless the burst pressure of the valve exceeds 400 percent 
NWP.
    (h) A valve shall not exhibit visible cracking or delaminating when 
subjected to stress corrosion cracking testing in accordance with 
S6.2.6.1.6 of this standard.
    S5.1.6. Labeling. Each vehicle container shall be permanently 
labeled with the information specified in paragraphs S5.1.6(a) through 
(g). Any label affixed to the container in compliance with this section 
shall remain in place and be legible for the vehicle manufacturer's 
recommended service life of the container. The information shall be in 
English and in letters and numbers that are at least 6.35 millimeters 
(\1/4\ inch) high.
    (a) The statement: ``If there is a question about the proper use, 
installation, or maintenance of this compressed hydrogen storage 
system, contact ______,'' inserting the vehicle manufacturer's name, 
address, and telephone number. The name provided shall be consistent 
with the vehicle manufacturer's filing in accordance with 49 CFR part 
566.
    (b) The container serial number.
    (c) The statement: ``Manufactured in ______,'' inserting the month 
and year of manufacture of the container.
    (d) The statement ``Nominal Working Pressure ______MPa 
(_____psig),'' Inserting the nominal working pressure which shall be no 
greater than 70 MPa.
    (e) The statement ``Compressed Hydrogen Gas Only.''
    (f) The statement: ``Do Not Use After ______,'' inserting the month 
and year that mark the end of the vehicle manufacturer's recommended 
service life for the container.
    (g) The statement: ``This container should be visually inspected 
for damage and deterioration after a motor vehicle accident or fire, 
and either: (i) at least every 12 months when installed on a vehicle 
with a GVWR greater than 4,536 kg, or (ii) at least every 36 months or 
36,000 miles, whichever comes first, when installed on a vehicle with a 
GVWR less than or equal to 4,536 kg.''
    S6. Test procedures.
    S6.1. [Reserved]
    S6.2. Test procedures for compressed hydrogen storage.
    S6.2.1. Unless otherwise specified, data sampling for pressure 
cycling under S6.2 shall be at least 1 Hz.
    S6.2.2. Test procedures for baseline performance metrics.
    S6.2.2.1. Burst test. (a) The container is filled with a hydraulic 
fluid.
    (b) The container, the surrounding environment, and the hydraulic 
fluid are at any temperature between 5.0 [deg]C and 35.0 [deg]C.
    (c) The rate of pressurization shall be less than or equal to 1.4 
MPa per second for pressures higher than 1.50 times NWP. If the rate 
exceeds 0.35 MPa per second at pressures higher than 1.50 times NWP, 
then the container is placed in series between the pressure source and 
the pressure measurement device.
    (d) The container is hydraulically pressurized until burst and the 
burst pressure of the container is recorded.
    S6.2.2.2. Pressure cycling test. (a) The container is filled with a 
hydraulic fluid.
    (b) The container surface, or the surface of the container 
attachments if present, the environment surrounding the container, and 
the hydraulic fluid are at any temperature between 5.0 [deg]C and 35.0 
[deg]C at the start of testing and maintained at the specified 
temperature for the duration of the testing.
    (c) The container is pressure cycled at any pressure between 1.0 
MPa and 2.0 MPa up to the pressure specified in the respective section 
of S5. The cycling rate shall be any rate up to 10 cycles per minute.
    (d) The temperature of the hydraulic fluid entering the container 
is maintained and monitored at any temperature between 5.0 [deg]C and 
35.0 [deg]C.
    (e) The vehicle manufacturer may specify a hydraulic pressure cycle 
profile within the specifications of S6.2.2.2(c). Vehicle manufacturers 
shall submit this profile to NHTSA immediately and irrevocably, upon 
request, in writing, and within 15 business days; otherwise, NHTSA 
shall determine the profile. At NHTSA's option, NHTSA shall cycle the 
container within 10 percent of the vehicle manufacturer's specified 
cycling profile.
    S6.2.3. Performance durability test.
    S6.2.3.1. Residual pressure test. The container is pressurized 
smoothly and continually with hydraulic fluid or hydrogen gas as 
specified until the pressure level is reached and held for the 
specified time.
    S6.2.3.2. Drop impact test. The container is drop tested without 
internal pressurization or attached valves. The surface onto which the 
container is dropped shall be a smooth, horizontal, uniform, dry, 
concrete pad or other flooring type with equivalent hardness. No 
attempt shall be made to prevent the container from bouncing or falling 
over during a drop test, except for the vertical drop test, during 
which the test article shall be prevented from falling over. The 
container shall be dropped in any one of the following four 
orientations described below and illustrated in figure 2 to S6.2.3.2.
    (a) From a position within 5[deg] of horizontal with the lowest 
point of the container at any height between 1.800 meters and 1.820 
meters above the surface onto which it is dropped. In the case of a 
non-axisymmetric container, the largest projection area of the 
container shall be oriented downward and aligned horizontally;
    (b) From a position within 5[deg] of vertical with the center of 
any shut-off valve interface location upward and with any potential 
energy of between 488 Joules and 538 Joules. If a drop energy of 
between 488 Joules and 538 Joules would result in the height of the 
lower end being more than 1.820 meters above the surface onto which it 
is dropped, the container shall be dropped from any height with the 
lower end between 1.800 meters and 1.820 meters above the surface onto 
which it is dropped. If a drop energy of between 488 Joules and 538 
Joules would result in the height of the lower end being less than 
0.100 meters above the surface onto which it is dropped, the container 
shall be dropped from any height with the lower end between 0.100 
meters and 0.120 meters above the surface onto which it is dropped. In 
the case of a non-axisymmetric container, the center of any shut-off 
valve interface location and the container's center of gravity shall be 
aligned vertically, with the center of that shut-off valve interface 
location upward;
    (c) From a position within 5[deg] of vertical with the center of 
any shut-off valve interface location downward with any potential 
energy of between 488 Joules and 538 Joules. If a potential energy of 
between 488 Joules and 538 Joules would result in the height of the 
lower end being more than 1.820 meters above the surface onto which it 
is dropped, the container shall be dropped from any height with the 
lower end between 1.800 meters and 1.820 meters above the surface onto 
which it is dropped. If a drop energy of between 488 Joules and 538 
Joules would result in the height of the lower end being less than 
0.100 meters above the surface onto which it is dropped, the container 
shall be dropped from any height with the lower end between 0.100 
meters and 0.120 meters above the surface onto which it is dropped. In 
the case of a non-axisymmetric container, the center of any shut-off 
valve interface location and the container's center of gravity shall be 
aligned vertically, with the center of that shut-off valve interface 
location downward;
    (d) From any angle between 40[deg] and 50[deg] from the vertical 
orientation with the center of any shut-off valve interface location 
downward, and with the container center of gravity between 1.800 meters 
and 1.820 meters above the

[[Page 6288]]

surface onto which it is dropped. However, if the lowest point of the 
container is closer to the ground than 0.60 meters, the drop angle 
shall be changed so that the lowest point of the container is between 
0.60 meters and 0.62 meters above the ground and the center of gravity 
is between 1.800 meters and 1.820 meters above the surface onto which 
it is dropped. In the case of a non-axisymmetric container, the line 
passing through the center of any shut-off valve interface location and 
the container's center of gravity shall be at any angle between 40[deg] 
and 50[deg] from the vertical orientation. If this specification 
results in more than one possible container orientation, the drop shall 
be conducted from the orientation that results in the lowest 
positioning of the center of the shut-off valve interface location.
[GRAPHIC] [TIFF OMITTED] TR17JA25.003

Figure 2 to Sec.  571.308 S6.2.3.2. The Four Drop Orientations; (for 
Illustration Purposes Only)

    S6.2.3.3. Surface damage test. The surface damage test consists of 
surface cut generation and pendulum impacts as described below.
    (a) Surface cut generation: Two longitudinal saw cuts are made at 
any location on the same side of the outer surface of the unpressurized 
container, as shown in Figure 3, or on the container attachments if 
present. The first cut is 0.75 millimeters to 1.25 millimeters deep and 
200 millimeters to 205 millimeters long; the second cut, which is only 
required for containers affixed to the vehicle by compressing its 
composite surface, is 1.25 millimeters to 1.75 millimeters deep and 25 
millimeters to 28 millimeters long.
    (b) Pendulum impacts: Mark the outer surface of the container, or 
the container attachments if present, with five separate, non-
overlapping circles each having any linear diameter between 100.0 
millimeters and 105.0 millimeters, as shown in Figure 3. The marks 
shall be located on the side opposite from the saw cuts, or located on 
a different chamber in the case of a container with more than one 
chamber. Within 30 minutes following preconditioning for any duration 
from 12 hours to 24 hours in an environmental chamber at any 
temperature between -45.0 [deg]C and -40.0 [deg]C, impact the center of 
each of the five areas with a pendulum having a pyramid with 
equilateral faces and square base, and the tip and edges being rounded 
to a radius of between 2.0 millimeters and 4.0 millimeters. The center 
of impact of the pendulum shall coincide with the center of gravity of 
the pyramid. The energy of the pendulum at the moment of impact with 
each of the five marked areas on the container is any energy between 
30.0 Joules and 35.0 Joules. The container is secured in place during 
pendulum impacts and is not pressurized above 1 MPa.

[[Page 6289]]

[GRAPHIC] [TIFF OMITTED] TR17JA25.004

Figure 3 to Sec.  571.308 S6.2.3.3. Locations of Surface Damage for 
S6.2.3.3(a) and Pendulum Impacts for S6.2.3.3(b); (for Illustration 
Purposes Only)

    S6.2.3.4. Chemical exposure and ambient temperature pressure 
cycling test. (a) Each of the 5 areas preconditioned by pendulum impact 
in S6.2.3.3(b) is exposed to any one of five solutions:
    (1) 19 to 21 percent by volume sulfuric acid in water;
    (2) 25 to 27 percent by weight sodium hydroxide in water;
    (3) 5 to 7 percent by volume methanol in gasoline;
    (4) 28 to 30 percent by weight ammonium nitrate in water; and
    (5) 50 to 52 percent by volume methyl alcohol in water.
    (b) The container is oriented with the fluid exposure areas on top. 
A pad of glass wool approximately 0.5 centimeters thick and 100 
millimeters in diameter is placed on each of the five preconditioned 
areas. A sufficient amount of the test fluid is applied to the glass 
wool to ensure that the pad is wetted across its surface and through 
its thickness for the duration of the test. A plastic covering shall be 
applied over the glass wool to prevent evaporation.
    (c) The exposure of the container with the glass wool is maintained 
for at least 48 hours and no more than 60 hours with the container 
hydraulically pressurized to any pressure between 125.0 percent NWP and 
130.0 percent NWP. During exposure, the temperature surrounding the 
container is maintained at any temperature between 5.0 [deg]C and 35.0 
[deg]C.
    (d) Hydraulic pressure cycling is performed in accordance with 
S6.2.2.2 at any pressure within the specified ranges according to 
S5.1.2.3 for the specified number of cycles. The glass wool pads are 
removed and the container surface is rinsed with water after the cycles 
are complete.
    S6.2.3.5. Static pressure test. The container is hydraulically 
pressurized to the specified pressure in a temperature-controlled 
chamber. The temperature of the chamber and the container surface, or 
the surface of the container attachments if present, are held at the 
specified temperature for the specified duration.
    S6.2.3.6. Extreme temperature pressure cycling test. (a) The 
container is filled with hydraulic fluid for each test;
    (b) At the start of each test, the container surface, or the 
surface of the container attachments if present, the hydraulic fluid, 
and the environment surrounding the container are at any temperature 
and relative humidity (if applicable) within the ranges specified in 
S5.1.2.5 of this standard and maintained for the duration of the 
testing.
    (c) The container is pressure cycled from any pressure between 1.0 
MPa and 2.0 MPa up to the specified pressure at a rate not exceeding 10 
cycles per minute for the specified number of cycles;
    (d) The temperature of the hydraulic fluid entering the container 
shall be measured as close as possible to the container inlet.
    S6.2.4. Test procedures for expected on-road performance.
    S6.2.4.1. Ambient and extreme temperature gas pressure cycling 
test. (a) In accordance with table 3 to S5.1.3.1 of this standard, the 
specified ambient conditions of temperature and relative humidity, if 
applicable, are maintained within the test environment throughout each 
pressure cycle. When required in accordance with table 3 to S5.1.3.1, 
the CHSS temperature shall be in the specified initial system 
equilibration temperature range between pressure cycles.
    (b) The CHSS is pressure cycled from any pressure between 1.0 MPa 
and 2.0 MPa up to any pressure within the specified peak pressure range 
in accordance with table 3 to this section. The temperature of the 
hydrogen fuel dispensed to the container is controlled to within the 
specified temperature range within 30 seconds of fueling initiation. 
The specified number of pressure cycles are conducted.
    (c) The ramp rate for pressurization shall be greater than or equal 
to the ramp rate given in table 4 to S6.2.4.1(c) according to the CHSS 
volume, the ambient conditions, and the fuel delivery temperature. If 
the required ambient temperature is not available in table 4 to this 
section, the closest ramp rate value or a linearly interpolated

[[Page 6290]]

value shall be used. The pressure ramp rate shall be decreased if the 
gas temperature in the container exceeds 85 [deg]C.

                                                          Table 4 to Sec.   571.308 S6.2.4.1(c)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                      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
1,000...............................................                      5.0                      5.0                      5.0                      1.4
1,500...............................................                      3.3                      3.3                      3.3                      1.0
2,000...............................................                      2.5                      2.5                      2.5                      0.7
2,500...............................................                      2.0                      2.0                      2.0                      0.5
--------------------------------------------------------------------------------------------------------------------------------------------------------

    (d) The de-fueling rate shall be any rate greater than or equal to 
the intended vehicle's maximum fuel-demand rate. Out of the 500 
pressure cycles, any 50 pressure cycles are performed using a de-
fueling rate greater than or equal to the maintenance de-fueling rate.
    S6.2.4.2. Gas permeation test. (a) A CHSS is filled with hydrogen 
gas to any SOC between 100.0 percent and 105.0 percent and placed in a 
sealed container. The CHSS is held for any duration between 12 hours 
and 24 hours at any temperature between 55.0 [deg]C and 60.0 [deg]C 
prior to the start of the test.
    (b) The permeation from the CHSS shall be determined hourly 
throughout the test.
    (c) The test shall continue for 500 hours or until the permeation 
rate reaches a steady state. Steady state is achieved when at least 3 
consecutive leak rates separated by any duration between 12 hours and 
48 hours are within 10 percent of the previous rate.
    S6.2.5. Test procedures for service terminating performance in 
fire. The fire test consists of two stages: a localized fire stage 
followed by an engulfing fire stage. The burner configuration for the 
fire test is specified in S6.2.5.1. The overall test configuration of 
the fire test is verified using a pre-test checkout in accordance with 
S6.2.5.2 prior to the fire test of the CHSS. The fire test of the CHSS 
is conducted in accordance with S6.2.5.3.
    S6.2.5.1. Burner configuration. (a) The fuel for the burner shall 
be liquefied petroleum gas (LPG).
    (b) The width of the burner shall be between 450 millimeters and 
550 millimeters.
    (c) The length of the burner used for the localized fire stage 
shall be between 200 millimeters and 300 millimeters.
    (d) The length of the burner used for the engulfing fire stage 
shall be in accordance with S6.2.5.3(m).
    (e) The burner nozzle configuration and installation shall be in 
accordance with table 5 to S6.2.5.1. The nozzles shall be installed 
uniformly on six rails.

                   Table 5 to Sec.   571.308 S6.2.5.1
------------------------------------------------------------------------
                  Item                             Description
------------------------------------------------------------------------
Nozzle type............................  Liquefied petroleum gas fuel
                                          nozzle with air pre-mix.
LPG orifice in nozzle..................  0.9 to 1.1 millimeter inner
                                          diameter.
Air ports in nozzle....................  Four (4) holes, 5.8 to 7.0
                                          millimeter inner diameter.
Fuel/Air mixing tube in nozzle.........  9 to 11 millimeter inner
                                          diameter.
Number of rails........................  6.
Center-to-center spacing of rails......  100 to 110 millimeter.
Center-to-center nozzle spacing along    45 to 55 millimeter.
 the rails.
------------------------------------------------------------------------

    S6.2.5.2. Pre-test checkout. (a) The pre-test checkout procedure in 
this section shall be performed to verify the fire test configuration 
for the CHSS tested in accordance with S6.2.5.3.
    (b) A pre-test container is a 12-inch Schedule 40 Nominal Pipe Size 
steel pipe with end caps. The cylindrical length of the pre-test 
container shall be equal to or longer than the overall length of the 
CHSS to be tested in S6.2.5.3, but no shorter than 0.80 m and no longer 
than 1.75 m.
    (c) The pre-test container shall be mounted over the burner:
    (1) At any height between 95 millimeters and 105 millimeters above 
the burner;
    (2) Such that the nozzles from the two center rails are pointing 
toward the bottom center of the pre-test container; and
    (3) Such that the container's position relative to the localized 
and engulfing zones of the burner is consistent with the positioning of 
the CHSS over the burner in S6.2.5.3.
    (d) For outdoor test sites, wind shielding shall be used. The 
separation between the pre-test container and the walls of the wind 
shields shall be at least 0.5 meters.

[[Page 6291]]

    (e) Temperatures during the pre-test check-out shall be measured at 
least once per second using 3.2 millimeter diameter or less K-type 
sheath thermocouples.
    (f) The thermocouples shall be located in sets to measure 
temperatures along the cylindrical section of the pre-test container. 
These thermocouples are secured by straps or other mechanical 
attachments within 5 millimeters from the pre-test container surface. 
One set of thermocouples consists of:
    (1) One thermocouple located at the bottom surface exposed to the 
burner flame,
    (2) One thermocouple located mid-height along the left side of the 
cylindrical surface,
    (3) One thermocouple located mid-height along the right side of the 
cylindrical surface, and
    (4) One thermocouple located at the top surface opposite to the 
burner flame.
    (g) One set of thermocouples shall be centrally located at the 
localized fire zone of the CHSS to be tested as determined in S6.2.5.3. 
Two additional sets of thermocouples shall be spread out over the 
remaining length of the engulfing fire zone of the CHSS to be tested 
that is not part of the localized fire zone of the CHSS to be tested.
    (h) Burner monitor thermocouples shall be located between 20 
millimeters and 30 millimeters below the bottom surface of the pre-test 
container in the same three horizontal locations described in 
S6.2.5.2(g). These thermocouples shall be mechanically supported to 
prevent movement.
    (i) With the localized burner ignited, the LPG flow rate to the 
burner shall be set such that the 60-second rolling averages of 
individual temperature readings in the localized fire zone shall be in 
accordance with the localized stage row in the table below.
    (j) With the entire burner ignited, the LPG flow rate to the burner 
shall be set such that the 60-second rolling averages of individual 
temperature readings shall be in accordance with the engulfing stage 
row in table 6 to S6.2.5.2.

                                       Table 6 to Sec.   571.308 S6.2.5.2
----------------------------------------------------------------------------------------------------------------
                                                              Temperature range on
         Fire stage            Temperature range on bottom     sides of pre-test     Temperature range on top of
                                 of pre-test  container            container             pre-test  container
----------------------------------------------------------------------------------------------------------------
Localized...................  450 [deg]C to 700 [deg]C....  less than 750 [deg]C...  less than 300 [deg]C.
Engulfing...................  Average temperatures of the   Not applicable.........  Average temperatures of the
                               pre-test container surface                             pre-test container surface
                               measured at the three                                  measured at the three top
                               bottom locations shall be                              locations shall be at
                               greater than 600 [deg]C.                               least 100 [deg]C, and when
                                                                                      greater than 750 [deg]C,
                                                                                      shall also be less than
                                                                                      the average temperatures
                                                                                      of the pre-test container
                                                                                      surface measured at the
                                                                                      three bottom locations.
----------------------------------------------------------------------------------------------------------------

    S6.2.5.3. CHSS fire test. (a) The CHSS to be fire tested shall 
include TPRD vent lines.
    (b) The CHSS to be fire tested shall be mounted at any height 
between 95 millimeters and 105 millimeters above the burner.
    (c) CHSS shall be positioned for the localized fire test by 
orienting the CHSS 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.
    (d) When the container is longer than the localized burner, the 
localized burner shall not extend beyond either end of the container in 
the CHSS.
    (e) The CHSS shall be filled with compressed hydrogen gas to any 
SOC between 100.0 percent and 105.0 percent.
    (f) For outdoor test sites, the same wind shielding shall be used 
as was used for S6.2.5.2. The separation between the CHSS and the walls 
of the wind shields shall be at least 0.5 meters.
    (g) Burner monitor temperatures shall be measured below the bottom 
surface of the CHSS in the same positions as specified in S6.2.5.2(h).
    (h) The allowable limits for the burner monitor temperatures during 
the CHSS fire test shall be established based on the results of the 
pre-test checkout as follows:
    (1) The minimum value for the burner monitor temperature during the 
localized fire stage (TminLOC) shall be calculated by 
subtracting 50 [deg]C from the 60-second rolling average of the burner 
monitor temperature in the localized fire zone of the pre-test 
checkout. If the resultant TminLOC exceeds 600 [deg]C, 
TminLOC shall be 600 [deg]C.
    (2) The minimum value for the burner monitor temperature during the 
engulfing fire stage (TminENG) shall be calculated by 
subtracting 50 [deg]C from the 60-second rolling average of the average 
of the three burner monitor temperatures during the engulfing fire 
stage of the pre-test checkout. If the resultant TminENG 
exceeds 800 [deg]C, TminENG shall be 800 [deg]C.
    (i) The localized fire stage is initiated by starting the fuel flow 
to the localized burner and igniting the burner.
    (j) The 10-second rolling average of the burner monitor temperature 
in the localized fire zone shall be at least 300 [deg]C within 1 minute 
of ignition and for the next 2 minutes.
    (k) Within 3 minutes of the igniting the burner, using the same LPG 
flow rate as S6.2.5.2(i), the 60-second rolling average of the 
localized zone burner monitor temperature shall be greater than 
TminLOC as determined in S6.2.5.3(h)(1).
    (l) After 10 minutes from igniting the burner, the engulfing fire 
stage is initiated.
    (m) The engulfing fire zone includes the localized fire zone and 
extends in one direction towards the nearest TPRD or TPRD sense point 
along the complete length of the container up to a maximum burner 
length of 1.65 m.
    (n) Within 2 minutes of the initiation of the engulfing fire stage, 
using the same LPG flow rate as S6.2.5.2(j), the 60-second rolling 
average of the engulfing burner monitor temperature shall be equal or 
greater than TminENG as determined in S6.2.5.3(h)(2).
    (o) The fire testing continues until the pressure inside the CHSS 
is less than or equal to 1.0 MPa or until:
    (1) A total test time of 60 minutes for CHSS on vehicles with a 
GVWR of 10,000 pounds or less or;
    (2) A total test time of 120 minutes for CHSS on vehicles with a 
GVWR over 10,000 pounds.
    S6.2.6. Test procedures for performance durability of closure 
devices.

[[Page 6292]]

    S6.2.6.1. TPRD performance tests. Unless otherwise specified, 
testing is performed with either hydrogen gas 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, or with an inert gas. 
All tests are performed at any temperature between 5.0 [deg]C and 35.0 
[deg]C unless otherwise specified.
    S6.2.6.1.1. Pressure cycling test. A TPRD undergoes 15,000 internal 
pressure cycles at a rate not exceeding 10 cycles per minute. The table 
below summarizes the pressure cycles. Any condition within the ranges 
specified in table 7 to this section may be selected for testing.
    (a) The first 10 pressure cycles shall be from any low pressure of 
between 1.0 MPa and 2.0 MPa to any high pressure between 150.0 percent 
NWP and 155.0 percent NWP. These cycles are conducted at any sample 
temperature between 85.0 [deg]C to 90.0 [deg]C.
    (b) The next 2,240 pressure cycles shall be from any low pressure 
between 1.0 MPa and 2.0 MPa to any high pressure of between 125.0 
percent NWP and 130.0 percent NWP. These cycles are conducted at any 
sample temperature between 85.0 [deg]C to 90.0 [deg]C.
    (c) The next 10,000 pressure cycles shall be from any low pressure 
of between 1.0 MPa and 2.0 MPa to any high pressure between 125.0 
percent NWP and 130.0 percent NWP. These cycles are conducted at a 
sample temperature between 5.0 [deg]C to 35.0 [deg]C.
    (d) The final 2,750 pressure cycles shall be from any low pressure 
between 1.0 MPa and 2.0 MPa to any high pressure between 80.0 percent 
NWP and 85.0 percent NWP. These cycles are conducted at any sample 
temperature between -45.0 [deg]C to -40.0 [deg]C.

                                      Table 7 to Sec.   571.308 S6.2.6.1.1
----------------------------------------------------------------------------------------------------------------
                                                                                            Sample  temperature
          Number of cycles                Low pressure              High pressure               for cycles
----------------------------------------------------------------------------------------------------------------
First 10...........................  1.0 MPa to 2.0 MPa....  150.0% NWP to 155.0% NWP...  85.0 [deg]C to 90.0
                                                                                           [deg]C.
Next 2,240.........................  1.0 MPa to 2.0 MPa....  125.0% NWP to 130.0% NWP...  85.0 [deg]C to 90.0
                                                                                           [deg]C.
Next 10,000........................  1.0 MPa to 2.0 MPa....  125.0% NWP to 130.0% NWP...  5.0 [deg]C to 35.0
                                                                                           [deg]C.
Final 2,750........................  1.0 MPa to 2.0 MPa....  80.0% NWP to 85.0% NWP.....  -45.0 [deg]C to -40.0
                                                                                           [deg]C.
----------------------------------------------------------------------------------------------------------------

    S6.2.6.1.2. Accelerated life test. (a) Two TPRDs undergo testing; 
one at the vehicle manufacturer's specified activation temperature, and 
one at an accelerated life temperature, TL, given in [deg]C using 
equation 2 to this section, where [beta] = 273.15 [deg]C, TME is 85 
[deg]C, and Tf is the vehicle manufacturer's specified activation 
temperature in [deg]C.:

Equation 2 to Sec.  571.308 S6.2.6.1.2
[GRAPHIC] [TIFF OMITTED] TR17JA25.005

    (b) The TPRDs are placed in an oven or liquid bath maintained 
within 5.0 [deg]C of the specified temperature per S6.2.6.1.2(a). The 
TPRD inlets are pressurized with hydrogen to any pressure between 125.0 
percent NWP and 130.0 percent NWP and time until activation is 
measured.
    S6.2.6.1.3. Temperature cycling test. (a) An unpressurized TPRD is 
placed in a cold liquid bath maintained at any temperature between -
45.0 [deg]C and -40.0 [deg]C. The TPRD shall remain in the cold bath 
for any duration not less than 2 hours and not more than 24 hours. The 
TPRD is removed from the cold bath and transferred, within five minutes 
of removal, to a hot liquid bath maintained at any temperature between 
85.0 [deg]C and 90.0 [deg]C. The TPRD shall remain in the hot bath for 
any duration not less than 2 hours and not more than 24 hours. The TPRD 
is removed from the hot bath and, within five minutes of removal, 
transferred back into the cold bath maintained at any temperature 
between -45.0 [deg]C and -40.0 [deg]C.
    (b) Step (a) is repeated until 15 thermal cycles have been 
achieved.
    (c) The TPRD remains in the cold liquid bath for any duration not 
less than 2 and not more than 24 additional hours, then the internal 
pressure of the TPRD is cycled with hydrogen gas from any pressure 
between 1.0 MPa and 2.0 MPa to any pressure between 80.0 percent NWP 
and 85.0 percent NWP for 100 cycles. During cycling, the TPRD remains 
in the cold bath and the cold bath is maintained at any temperature 
between -45.0 [deg]C and -40.0 [deg]C.
    S6.2.6.1.4. Salt corrosion resistance test. (a) Each closure device 
is exposed to a combination of cyclic conditions of salt solution, 
temperatures, and humidity. One test cycle is equal to any duration not 
less than 22 and not more than 26 hours, and is in accordance with 
table 8 to S6.2.6.1.4.

                                      Table 8 to Sec.   571.308 S6.2.6.1.4
----------------------------------------------------------------------------------------------------------------
                    Accelerated cyclic corrosion conditions (1 cycle = 22 hours to 26 hours)
-----------------------------------------------------------------------------------------------------------------
           Cycle condition                   Temperature           Relative humidity          Cycle duration
----------------------------------------------------------------------------------------------------------------
Ambient stage........................  22.0 [deg]C to 28.0      35 percent to 55         470 minutes to 490
                                        [deg]C.                  percent.                 minutes
----------------------------------------------------------------------------------------------------------------
                                           Transition 55 min to 60 min
----------------------------------------------------------------------------------------------------------------
Humid stage..........................  47.0 [deg]C to 51.0      95 percent to 100        410 minutes to 430
                                        [deg]C.                  percent.                 minutes
----------------------------------------------------------------------------------------------------------------
                                      Transition 170 minutes to 190 minutes
----------------------------------------------------------------------------------------------------------------
Dry stage............................  55.0 [deg]C to 65.0      less than 30 percent...  290 minutes to 310
                                        [deg]C.                                           minutes
----------------------------------------------------------------------------------------------------------------

    (b) The apparatus used for this test shall consist of a fog/
environmental chamber as defined in ISO 6270-2:2017(E) (incorporated by 
reference, see Sec.  571.5), with a suitable water supply conforming to 
Type IV

[[Page 6293]]

requirements in ASTM D1193-06 (Reapproved 2018) (incorporated by 
reference, see Sec.  571.5). The chamber shall include a supply of 
compressed air and one or more nozzles for fog generation. The nozzle 
or nozzles used for the generation of the fog shall be directed or 
baffled to minimize any direct impingement on the closure devices.
    (c) During ``wet-bottom'' generated humidity cycles, water droplets 
shall be visible on the samples.
    (d) Steam generated humidity may be used provided the source of 
water used in generating the steam is free of corrosion inhibitors and 
visible water droplets are formed on the samples to achieve proper 
wetness.
    (e) The drying stage shall occur in the following environmental 
conditions: any temperature not less than 60 [deg]C and not greater 
than 65 [deg]C and relative humidity no more than 30 percent with air 
circulation.
    (f) The impingement force from the salt solution application shall 
not remove corrosion and/or damage the coatings of the closure devices.
    (g) The complex salt solution in percent by mass shall be as 
specified in S6.2.6.1.4(g)(1) through (5):
    (1) Sodium Chloride: not less than 0.08 and not more than 0.10 
percent.
    (2) Calcium Chloride: not less than 0.095 and not more than 0.105 
percent.
    (3) Sodium Bicarbonate: not less than 0.07 and not more than 0.08 
percent.
    (4) Sodium Chloride must be reagent grade or food grade. Calcium 
Chloride must be reagent grade. Sodium Bicarbonate must be reagent 
grade. For the purposes of S6.2.6.1.4, water must meet ASTM D1193-06 
(Reapproved 2018) Type IV requirements (incorporated by reference, see 
Sec.  571.5).
    (5) Either calcium chloride or sodium bicarbonate material must be 
dissolved separately in water and added to the solution of the other 
materials.
    (h) The closure devices shall be installed in accordance with the 
vehicle manufacturer's recommended procedure and exposed to the 100 
daily corrosion cycles, with each corrosion cycle in accordance with 
table 8 to S6.2.6.1.4.
    (i) For each salt mist application, the solution shall be sprayed 
as an atomized mist, using the spray apparatus to mist the components 
until all areas are thoroughly wet and dripping. Suitable application 
techniques include using a plastic bottle, or a siphon spray powered by 
oil-free regulated air to spray the test samples. The quantity of spray 
applied should be sufficient to visibly rinse away salt accumulation 
left from previous sprays. Four salt mist applications shall be applied 
during the ambient stage. The first salt mist application occurs at the 
beginning of the ambient stage. Each subsequent salt mist application 
should be applied not less than 90 and not more than 95 minutes after 
the previous application.
    (j) The time from ambient to the wet condition shall be any 
duration not less than 60 and not more than 65 minutes and the 
transition time between wet and dry conditions shall be any duration 
not less than 180 and not more than 190 minutes.
    S6.2.6.1.5. Vehicle environment test. (a) The inlet and outlet 
connections of the closure device are connected or capped in accordance 
with the vehicle manufacturer's installation instructions. All external 
surfaces of the closure device are exposed to each of the following 
fluids for any duration between 24 hours and 26 hours. The temperature 
during exposure shall be any temperature between 5.0 [deg]C and 35.0 
[deg]C. A separate test is performed with each of the fluids 
sequentially on a single closure device.
    (1) Sulfuric acid: not less than 19 and not more than 21 percent by 
volume in water;
    (2) Ethanol/gasoline: not less than 10 and not more than 12 percent 
by volume ethanol and not less than 88 and not more than 90 percent by 
volume gasoline; and
    (3) Windshield washer fluid: not less than 50 and not more than 52 
percent by volume methanol in water.
    (b) The fluids are replenished as needed to ensure complete 
exposure for the duration of the test.
    (c) After exposure to each fluid, the closure device is wiped off 
and rinsed with water.
    S6.2.6.1.6. Stress corrosion cracking test. (a) All components 
exposed to the atmosphere shall be degreased. For check valves and 
shut-off valves, the closure device shall be disassembled, all 
components degreased, and then reassembled.
    (b) The closure device is continuously exposed to a moist ammonia 
air mixture maintained in a glass chamber having a glass cover. The 
exposure lasts any duration not less than 240 hours and not more than 
242 hours. The aqueous ammonia shall have a composition of between 19 
weight percent and 21 weight percent ammonium hydroxide in water. 
Aqueous ammonia shall be located at the bottom of the glass chamber 
below the sample at any volume not less than 20 mL and not more than 22 
mL of aqueous ammonia per liter of chamber volume. The bottom of the 
sample is positioned any distance not less than 30 and not more than 40 
millimeters above the aqueous ammonia and supported in an inert tray.
    (c) The moist ammonia-air mixture is maintained at atmospheric 
pressure and any temperature not less than 35 [deg]C and not more than 
40 [deg]C.
    S6.2.6.1.7. Drop and vibration test. (a) The TPRD is aligned 
vertically to any one of the six orientations covering the opposing 
directions of three orthogonal axes: vertical, lateral and 
longitudinal.
    (b) A TPRD is dropped in free fall from any height between 2.00 
meters and 2.02 meters onto a smooth concrete surface. The TPRD is 
allowed to bounce on the concrete surface after the initial impact.
    (c) Any sample with damage from the drop that results in the TPRD 
not being able to be tested in accordance with S6.2.6.1.7(d) shall not 
proceed to S6.2.6.1.7(d) and shall not be considered a failure of this 
test.
    (d) Each TPRD dropped in S6.2.6.1.7(a) that did not have damage 
that results in the TPRD not being able to be tested is mounted in a 
test fixture in accordance with vehicle manufacturer's installation 
instructions and vibrated for any duration between 30.0 minutes and 
35.0 minutes along each of the three orthogonal axes (vertical, lateral 
and longitudinal) at the most severe resonant frequency for each axis.
    (1) The most severe resonant frequency for each axis is determined 
using any acceleration between 1.50 g and 1.60 g and sweeping through a 
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time 
between 10.0 minutes and 20.0 minutes. The most severe resonant 
frequency is identified by a pronounced increase in vibration 
amplitude.
    (2) If the resonance frequency is not found, the test shall be 
conducted at any frequency between 35 Hz and 45 Hz.
    S6.2.6.1.8. Leak test. Unless otherwise specified, the TPRD shall 
be thermally conditioned to the ambient temperature condition, then 
checked for leakage, then conditioned to the high temperature 
condition, then checked for leakage, then conditioned to low 
temperature, then checked for leakage.
    (a) The TPRD shall be thermally conditioned at test temperatures in 
each of the test conditions and held for any duration between 1.0 hour 
and 24.0 hours. The TPRD is pressurized with hydrogen at the inlet. The 
required test conditions are:
    (1) Ambient temperature: condition the TPRD at any temperature 
between 5.0 [deg]C and 35.0 [deg]C; test in accordance with 
S6.2.6.1.8(b) at any pressure between 1.5 MPa and 2.5 MPa and then

[[Page 6294]]

at any pressure between 125.0 percent NWP and 130.0 percent NWP.
    (2) High temperature: condition the TPRD at any temperature between 
85.0 [deg]C and 90.0 [deg]C; test in accordance with S6.2.6.1.8(b) at 
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure 
between 125.0 percent NWP and 130.0 percent NWP.
    (3) Low temperature: condition the TPRD at any temperature between 
-45.0 [deg]C and -40.0 [deg]C; test in accordance with S6.2.6.1.8(b) at 
any pressure between 1.5 MPa and 2.5 MPa and then at any pressure 
between 100.0 percent NWP and 105.0 percent NWP.
    (b) Following conditioning at each of the specified test 
temperature ranges, the TPRD is observed for leakage while immersed in 
a temperature-controlled liquid at the same specified temperature range 
for any duration between 1.0 minutes and 2.0 minutes at each of the 
pressure ranges listed above. If no bubbles are observed for the 
specified time period, it is not considered a failure. If bubbles are 
detected, the leak rate is measured.
    S6.2.6.1.9. Bench top activation test. (a) The test apparatus 
consists of either a forced air oven or chimney with air flow. The TPRD 
is not exposed directly to flame. The TPRD is mounted in the test 
apparatus according to the vehicle manufacturer's installation 
instructions.
    (b) The temperature of the oven or chimney is at any temperature 
between 600.0 [deg]C and 605.0 [deg]C for any duration between 2 
minutes and 62 minutes prior to inserting the TPRD.
    (c) Prior to inserting the TPRD, pressurize the TPRD to any 
pressure between 1.5 MPa and 2.5 MPa.
    (d) The pressurized TPRD is inserted into the oven or chimney, the 
temperature within the oven or chimney is maintained at any temperature 
between 600.0 [deg]C and 605.0 [deg]C, and the time for the TPRD to 
activate is recorded. If the TPRD does not activate within 120 minutes 
from the time of insertion into the oven or chimney, the TPRD shall be 
considered to have failed the test.
    S6.2.6.1.10. Flow rate test. (a) At least one new TPRD is tested to 
establish a baseline flow rate.
    (b) After activation in accordance with S6.2.6.1.9, and without 
cleaning, removal of parts, or reconditioning, the TPRD is subjected to 
flow testing using hydrogen, air or an inert gas;
    (c) Flow rate testing is conducted with any inlet pressure between 
1.5 MPa and 2.5 MPa. The outlet is at atmospheric pressure.
    (d) Flow rate is measured in units of kilograms per minute with a 
precision of at least 2 significant digits.
    S6.2.6.2. Check valve and shut-off valve performance tests. Unless 
otherwise specified, testing shall be performed with either hydrogen 
gas with a purity of at least 99.97 percent, less than or equal to 5 
parts per million of water, and less than or equal to 1 part per 
million particulate, or with an inert gas. All tests are performed at 
any temperature between 5.0 [deg]C and 35.0 [deg]C unless otherwise 
specified.
    S6.2.6.2.1. Hydrostatic strength test. (a) The outlet opening is 
plugged and valve seats or internal blocks are made to assume the open 
position.
    (b) Any hydrostatic pressure between 250.0 percent NWP and 255.0 
percent NWP is applied using water to the valve inlet for any duration 
between 180.0 seconds and 185.0 seconds. The unit is examined to ensure 
that burst has not occurred.
    (c) The hydrostatic pressure is then increased at a rate of less 
than or equal to 1.4 MPa/sec until component failure. The hydrostatic 
pressure at failure is recorded.
    S6.2.6.2.2. Leak test. Each unit shall be thermally conditioned to 
the ambient temperature condition, then checked for leakage, then 
conditioned to the high temperature condition, then checked for 
leakage, then conditioned to low temperature, then checked for leakage.
    (a) Each unit shall be pressurized to any pressure between 2.0 MPa 
and 3.0 MPa and held for any duration between 1.0 hours and 24.0 hours 
in the specified temperature range before testing. The outlet opening 
is plugged. The test conditions are:
    (1) Ambient temperature: condition the unit at any temperature 
between 5.0 [deg]C and 35.0 [deg]C; test at any pressure between 1.5 
MPa and 2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 
percent NWP.
    (2) High temperature: condition the unit at any temperature between 
85.0 [deg]C and 90.0 [deg]C; test at any pressure between 1.5 MPa and 
2.5 MPa and at any pressure between 125.0 percent NWP and 130.0 percent 
NWP.
    (3) Low temperature: condition the unit at any temperature between 
-45.0 [deg]C and -40.0 [deg]C; test at any pressure between 1.5 MPa and 
2.5 MPa and at any pressure between 100.0 percent NWP and 105.0 percent 
NWP.
    (b) While within the specified temperature and pressure range, the 
unit is observed for leakage while immersed in a temperature-controlled 
liquid held within the same specified temperature range as the test 
condition for any duration between 1.0 minutes and 2.0 minutes at each 
of the test pressures. If no bubbles are observed for the specified 
time period, the sample passes the leak test. If bubbles are detected, 
the leak rate is measured.
    S6.2.6.2.3. Extreme temperature pressure cycling test. (a) The 
valve unit is connected to a test fixture.
    (b) For a check valve, the pressure is applied in six incremental 
pulses to the check valve inlet with the outlet closed. The pressure is 
then vented from the check valve inlet. The pressure is lowered on the 
check valve outlet side to any pressure between 55.0 percent NWP and 
60.0 percent NWP prior to the next cycle.
    (c) For a shut-off valve, the specified pressure is applied through 
the inlet port. The shut-off valve is then energized to open the valve 
and the pressure is reduced to any pressure less than 50 percent of the 
specified pressure range. The shut-off valve shall then be de-energized 
to close the valve prior to the next cycle.
    S6.2.6.2.4. Chatter flow test. The valve is subjected to between 
24.0 hours and 26.0 hours of chatter flow at a flow rate that causes 
the most valve flutter.
    S6.2.6.2.5. Electrical Tests. This section applies to shut-off 
valves only.
    (a) The solenoid valve is connected to a variable DC voltage 
source, and the solenoid valve is operated as follows:
    (1) Held for any duration between 60.0 and 65.0 minutes at any 
voltage between 0.50 V and 1.5 times the rated voltage.
    (2) The voltage is increased to any voltage between 0.5 V to two 
times the rated voltage, or between 60.0 V and 60.5 V, whichever is 
less, and held for any duration between 60.0 seconds and 70.0 seconds.
    (b) Any voltage between 1,000.0 V DC and 1,010.0 V DC is applied 
between the power conductor and the component casing for any duration 
between 2.0 seconds to 4.0 seconds.
    S6.2.6.2.6. Vibration test. (a) The valve is pressurized with 
hydrogen to any pressure between 100.0 percent NWP and 105.0 percent 
NWP, sealed at both ends, and vibrated for any duration between 30.0 
and 35.0 minutes along each of the three orthogonal axes (vertical, 
lateral and longitudinal) at the most severe resonant frequencies.
    (b) The most severe resonant frequencies are determined using any 
acceleration between 1.50 g and 1.60 g and sweeping through a 
sinusoidal frequency range from 10 Hz to 500 Hz with any sweep time 
between 10.0 minutes and 20.0 minutes. The resonance frequency is 
identified by a pronounced increase in vibration amplitude.

[[Page 6295]]

    (c) If the resonance frequency is not found, the test shall be 
conducted at any frequency between 35 Hz and 45 Hz.

    Issued in Washington, DC, under authority delegated in 49 CFR 
1.95 and 501.
Adam Raviv,
Chief Counsel.
[FR Doc. 2024-31367 Filed 1-16-25; 8:45 am]
BILLING CODE 4910-59-P`