6218 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

1See 89 FR 27502 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

2A 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 

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. 

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-systemrecords-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 

Ian.MacIntire@dot.gov. For legal issues, 

Paul Connet, Attorney-Advisor, NHTSA 

Office of Chief Counsel, at (202) 366– 

5547 or Paul.Connet@dot.gov or Evita 

St. Andre, Attorney-Advisor, NHTSA 

Office of Chief Counsel, at (617) 494– 

2767 or Evita.St.Andre@dot.gov. 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

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 postcrash 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 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6219 

3See https://unece.org/sites/default/files/2023- 

07/ECE-TRANS-180-Add.13-Amend1e.pdf. 

4See 89 FR 27502 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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 postcrash fuel system integrity requirements 

apply only to compressed hydrogenfueled 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

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. 

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, shutoff valve, and TPRD, was required to 

meet several durability and safety 

benchmarks throughout its operational 

lifespan. 

The proposal established specific 

requirements for hydrogen containers, 


KHAMMOND on DSK9W7S144PROD with RULES3
6220 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

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. 

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 longterm 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 energyabsorbing 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 vehiclespecific 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 onroad 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). 

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. 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6221 

6Mutual 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. 

7For 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. 

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 selfcertification), and it acknowledges the 

domestic rulemaking and substantive 

legal requirements in the United States. 

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 selfcertification 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 vehiclelevel 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. 

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 


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6222 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

8See 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. 

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 onboard 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 componentspecific 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 typeapproval 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. 

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. 


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9 In this context, ‘‘lines’’ refers to any plumbing, 

piping, and/or connections where hydrogen fuel 

may be present. 

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 multiplechamber 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. 

Similarly, if two conventional highpressure containers share a single shutoff 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 


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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 shutoff 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 


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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, checkvalves, 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), shutoff 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 shutoff 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 ‘‘shutoff 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.’’ 


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10By ‘‘conventional CHSS,’’ we mean a CHSS that 

stores hydrogen in gaseous form at high pressures, 

typically 35 to 70 MPa 

11There 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. 

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 °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 °C and +85 

°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 nonmetallic 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

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 solidstate 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 


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12The 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. 

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. 

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 onboard 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. 


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13Storing 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. 

14See Part 555—Temporary Exemption from 

Motor Vehicle Safety and Bumper Standards, 

https://www.ecfr.gov/current/title-49/part-555. 

15 In this context, ‘‘lines’’ refers to any pluming, 

piping, and/or connections where hydrogen fuel 

may be present. 

Therefore, consistent with GTR No. 

13, NHTSA is maintaining the 

requirement that all CHSS must have an 

NWP of 70 MPa or less.13

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

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 lowpressure 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 lowpressure 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. 

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 backflow 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. 


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16See 89 FR 27518 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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 multicontainer 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 systemlevel 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 checkvalve. 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 manufacturersupplied 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 manufacturerspecified 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 manufacturerspecified 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 


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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. 

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 typeapproval 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 noncompliance. 

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 °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 hightemperature 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 


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17See 89 FR 27511 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-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. 

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 noncompliance. The prospect of noncompliance 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. 

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 


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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 highstrength carbon fiber, it may not be 

sufficient for other materials or thinwalled 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 fourminute 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 


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18The increase from five days to 15 days is 

intended to give manufacturers additional time to 

respond to NHTSA’s request. 

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 loadsharing 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. 

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 


KHAMMOND on DSK9W7S144PROD with RULES3
6234 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

19See 89 FR 27511 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

20See 89 FR 27513 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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. 

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. 

TABLE 1—SERVICE LIFE AND NUMBER OF CYCLES IN THE BASELINE HYDRAULIC PRESSURE CYCLE TEST FOR LIGHT AND

HEAVY VEHICLES

Vehicle type Service life 

(years) 

Number of cycles 

representing maximum 

service life for which 

the container does not 

leak nor burst 

Numbe of cycles for 

which the container 

leaks without burst, or 

does not leak nor 

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 


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21See 89 FR 27512 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

22See https://www.energy.gov/eere/fuelcells/doetechnical-targets-onboard-hydrogen-storage-lightduty-vehicles. 

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

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. 

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-beforeburst 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 timebased 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 leakbefore-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 


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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 


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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, 


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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 nonpressure 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° 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° 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 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6239 

23A copy of GTR No. 13 as updated by the Phase 

2 amendments is available at https://unece.org/ 

transport/documents/2023/07/standards/un-globaltechnical-regulation-no-13-amendment-1. 

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. 

(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 nonremovable 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 fourminute 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 


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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. 


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24SAE J2579_201806. Standard for Fuel Systems 

in Fuel Cell and Other Hydrogen Vehicles. https:// 

www.sae.org/standards/content/j2579_201806/. 

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 °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 °C and the other half 

are conducted at 85 °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

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 


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6242 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

25See 89 FR 27520 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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 lowtemperature pneumatic tests, internal 

temperatures can drop below ¥40 °C, 

sometimes reaching ¥45 °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 °C 

to 85 °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 °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 onroad 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. 

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 wellestablished, 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 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6243 

26See 89 FR 27522 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

27See https://webstore.ansi.org/standards/csa/

csaansingv2019. 

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 °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 °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 °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. Welldeveloped 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 °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. 

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 pretest 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. 

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 


KHAMMOND on DSK9W7S144PROD with RULES3
6244 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

28See 89 FR 27523 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

29See 89 FR 27527 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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 pretest 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 realworld 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. 

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. 

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 disharmonization’’ 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 pretest 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 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6245 

30See 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/. 

31TminENG is calculated by subtracting 50 °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. 

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 pretest 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 designspecific 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. 

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. 

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 


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6246 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

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 pretest 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 °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 °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 °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 °C below the pre-test 

temperatures. Furthermore, as currently 

specified, the minimum temperatures 

TminLOC and TminENG would be timedependent 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 °C from the minimum 

value of the 60-second rolling average of 


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32See 89 FR 27524 (Apr. 17, 2024), available at 

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04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

the burner monitor temperature in the 

localized fire zone of the pre-test 

checkout. Similarly, NHTSA proposed 

that TminENG be calculated by subtracting 

50 °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 °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 °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. 

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 vehiclelevel 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 


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33See 89 FR 27523 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

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 datadriven 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. 

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 worstcase 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 overspecification 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 


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34FMVSS 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. 

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 overspecification 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

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 


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35See https://webstore.ansi.org/standards/csa/

csaansihprd2021. 

36See https://webstore.ansi.org/standards/csa/

csaansihgv2015r2019. 

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. 

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°C to 35°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 nonreactive 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 nonreactive 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 


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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 firerelated 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– 


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

csaansihprd2021. 

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. 

(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. 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6253 

38See 89 FR 27531 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

39See 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/. 

(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 orings 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—Thermallyactivated 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. 

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. 

(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 


KHAMMOND on DSK9W7S144PROD with RULES3
6254 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

40SAE 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). 

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°C to 35°C, 

test at 2 MPa and 125 percent NWP 

• High temperature: 85°C, test at 2 MPa 

and 125 percent NWP 

• Low temperature: ¥40°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. 

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 lowpressure 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. 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6255 

41See 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/. 

(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 °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. 


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6256 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

(11) Atmospheric Exposure Test 

Background 

GTR No. 13 includes an atmospheric 

exposure test to ensure that nonmetallic components that are exposed to 

the atmosphere and provide a fuelcontaining 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 °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 nonmetallic 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 nonmetallic 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 hydrogenfuelled 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 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6257 

42See 89 FR 27530, 27533 (Apr. 17, 2024), 

available at https://www.federalregister.gov/ 

documents/2024/04/17/2024-07116/federal-motorvehicle-safety-standards-fuel-system-integrity-ofhydrogen-vehicles-compressed. 

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°C and 35.0°C, 

100 percent NWP 

• High: 85°C, 125 percent NWP 

• Low: ¥40 °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 shutoff 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 shutoff 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

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. 


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6258 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

(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 shutoff 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 shutoff 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 kW 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 manufacturerset 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 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6259 

43FMVSS 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. 

44The 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. 

45See Global Market Insights: Hydrogen Vehicle 

Market size, https://www.gminsights.com/industryanalysis/hydrogen-vehicle-market#:∼:text=

Hydrogen%20Vehicle%20Market%20size

%20was,expenses%20associated%20with%20

hydrogen%20vehicles. 

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 checkvalves 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. 

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 hydrogenfueled 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 


KHAMMOND on DSK9W7S144PROD with RULES3
6260 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

46See 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. 

47Hyundai 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. 

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

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 semienclosed 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 semienclosed 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 


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48FMVSS 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. 

event of a crash. NHTSA also proposed 

that the receptacle be prevented from 

being mounted in the enclosed or semienclosed 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 driveaway, 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 energyabsorbing 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. 

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 LowPressure 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 


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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 vehicledependent 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 overpressure protection device, and 

therefore the proposed requirement that 

‘‘the activation pressure of the overpressure 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° of 

vertical relative to the level surface or 

downwards within 45° 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-fitsall’’ 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 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6263 

49See 89 FR 27536 (Apr. 17, 2024), available at 

https://www.federalregister.gov/documents/2024/ 

04/17/2024-07116/federal-motor-vehicle-safetystandards-fuel-system-integrity-of-hydrogenvehicles-compressed. 

50 In comparison, the power system output of a 

Toyota Mirai is 182 HP. 

51SAE 2578_201408. Recommended Practice for 

General Fuel Cell Vehicle Safety. Appendix C3. 

https://www.sae.org/standards/content/j2578_

201408/. 

(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

(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 nonhazardous 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 × 2.6 meters × 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

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. 


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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 bubbletight. 

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 


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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 semienclosed 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 remotecontrolled 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 remotecontrolled 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 remotecontrolled 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 remotecontrolled 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 remotecontrolled 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 


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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 semienclosed 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 onboard 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 


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52FMVSS 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. 

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

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 ADSequipped 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 hydrogenfueled 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 


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53See 87 FR 18560 (Mar. 30, 2022), available at 

https://www.federalregister.gov/documents/2022/ 

03/30/2022-05426/occupant-protection-forvehicles-with-automated-driving-systems. 

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 frontseat 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. 

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 Dt 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 Dt 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 costprohibitive. 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 


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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 systemspecific 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 postcrash 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 roofmounted 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, 


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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 (±a), but the NPRM proposed 

a range between (X-a) and (X+a) 

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 °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 


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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 hydrogenpowered vehicles. It stated that it was 

important to consider the risks 

associated with pressurized hydrogen 

containers, which differ from nonpressurized 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 


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

55 49 U.S.C. Ch. 301: Motor Vehicle Safety, 

https://uscode.house.gov/view.xhtml?

req=granuleid%3AUSC-prelim-title49-chapter301&

edition=prelim. 

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. 

FMVSS No. 308 addresses vehiclespecific 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 vehiclelevel 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. 

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. 


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56NHTSA 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/resourcecentre/stories/revision-of-the-eu-general-safetyregulation. This period of less than 3 years is less 

than the timelines often requested by American 

industry, who often seek much longer lead times. 

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 oneyear 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 preproduction 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 signiÉcant 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 certiÉcation. 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 threeyear 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

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 semienclosed spaces, which are defined in 

the standard, whereas enclosed or semienclosed 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 


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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 nonidentical 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 


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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. 

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 

§ 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

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 


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

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 (InCabinet 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

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 


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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 

■ 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. 

■ 2. Amend § 571.5 by: 

■ a. Redesignating paragraphs (d)(20) 

through (33) as paragraphs (d)(21) 

through (34), respectively; 

■ b. Adding new paragraph (d)(20); 

■ d. Redesignating paragraphs (i)(1) 

through (4) as paragraphs (i)(2) through 

(5), respectively; and 

■ e. Adding new paragraph (i)(1). 

The additions read as follows: 

§ 571.5 Matter incorporated by reference. 

* * * * * 

(d) * * * 

(20) ASTM D1193–06 (Reapproved 

2018), Standard Specification for 

Reagent Water, approved March 15, 

2018, into § 571.308. 

* * * * * 

(i) * * * 

(1) ISO 6270–2:2017(E), Paints and 

Varnishes—Determination of Resistance 

to Humidity—Part 2: Condensation (InCabinet Exposure with Heated Water 

Reservoir), Second edition, November 

2017, into § 571.308. 

* * * * * 

■ 3. Section 571.307 is added to read as 

follows: 

§ 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 nonpressure 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. 


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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 °C. 

Normal milliliter means a quantity of 

gas that occupies one milliliter of 

volume when its temperature is 0 °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 °C, as expressed as a percentage 

using equation 1 to this section, where 

r is the density of hydrogen (g/L) at 

pressure (P) in MegaPascals (MPa) and 

temperature (T) in Celsius (°C) as listed 

in table 1 to S4 or linearly interpolated 

therein: 

Equation 1 to § 571.307 S4 

TABLE 1 TO § 571.307 S4 

Temperature 

(°C) 

Pressure 

(MPa) 

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 § 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 threesecond 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. 


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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 semienclosed 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 semienclosed 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, Dt, 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, Dt, 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 § 571.301, is 

impacted from the rear by a barrier that 

conforms to S7.3(b) of § 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 § 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 § 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 (°C), shall be 

measured immediately before the 

impact. The hydrogen gas pressure Pf

(MPa) and temperature, Tf (°C) shall also 

be measured immediately after a time 

interval Dt (in minutes) after impact. 

The time interval, Dt, 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 § 571.307 S6.2.1(a)(2) 

Dt = VCHSS × NWP/1000 × ((-0.027 × 

NWP + 4) × Rs ¥0.21) ¥ 1.7 × 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 § 571.307 S6.2.1(b) 

P0’ = P0 × 288/(273 + T0) 

Equation 4 to § 571.307 S6.2.1(b) 

r0’ = –0.0027 × (P0’)2 + 0.75 × P0’ + 1.07 

Equation 5 to § 571.307 S6.2.1(b) 

M0 = r0’ × VCHSS

(c) The final mass of hydrogen in the 

CHSS, Mf (in grams), at the end of the 

time interval, Dt, 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 (°C) is the measured 

final temperature: 

Equation 6 to § 571.307 S6.2.1(c) 

Pf’ = Pf × 288/(273 + Tf) 

Equation 7 to § 571.307 S6.2.1(c) 

rf’ = –0.0027 × (Pf’)2 + 0.75 × Pf’ + 1.07 

Equation 8 to § 571.307 S6.2.1(c) 

Mf = rf’ × 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: 


KHAMMOND on DSK9W7S144PROD with RULES3
6280 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

Equation 9 to § 571.307 S6.2.1(d) 

VH2 = (Mf¥M0)/Dt × 22.41/2.016 × 

(Ptarget/P0) 

S6.2.2 Post-crash leak test for CHSS 

filled with compressed helium. 

(a) The helium pressure, P0 (MPa), 

and temperature, T0 (°C), shall be 

measured immediately before the 

impact and again immediately after a 

time interval starting from the time of 

impact. The time interval, Dt (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 § 571.307 S6.2.2(a)(2) 

Dt = VCHSS × NWP/1000 × (¥0.028 × 

NWP + 5.5) × Rs¥0.3)¥2.6 × 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 § 571.307 S6.2.2(b) 

P0’ = P0 × 288/(273 + T0) 

Equation 12 to § 571.307 S6.2.2(b) 

r0’ = ¥0.0043 × (P0’)2 + 1.53 × P0’ + 1.49 

Equation 13 to § 571.307 S6.2.2(b) 

M0 = r0’ × VCHSS

(c) The final mass of helium Mf (g) in 

the CHSS at the end of the time interval, 

Dt (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 (°C) is the measured final 

temperature: 

Equation 14 to § 571.307 S6.2.2(c) 

Pf’ = Pf × 288/(273 + Tf) 

Equation 15 to § 571.307 S6.2.2(c) 

rf’ = ¥0.0043 × (Pf’)2 + 1.53 × Pf’ + 

1.49 

Equation 16 to § 571.307 S6.2.2(c) 

Mf = rf’ × 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 § 571.307 S6.2.2(d) 

VHe = (Mf¥M0)/Dt × 22.41/4.003 × 

(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 semienclosed 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. 


KHAMMOND on DSK9W7S144PROD with RULES3
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(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 °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 § 571.307 S7 

Ptarget = NWP × (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. 

■ 4. Section 571.308 is added to read as 

follows: 

§ 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 manufacturersupplied 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 nonpressure 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 °C. 

Normal milliliter means a quantity of 

gas that occupies one milliliter of 

volume when its temperature is 0 °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 


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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 °C, as expressed as a percentage 

using the equation 1 to this section, 

where r is the density of hydrogen (g/ 

L) at pressure (P) in MegaPascals (MPa) 

and temperature (T) in Celsius (°C) as 

listed below in Table 1 or linearly 

interpolated therein: 

Equation 1 to § 571.308 S4 

TABLE 1 TO § 571.308 S4 

Temperature 

(°C) 

Pressure 

(MPa) 

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 § 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 performance ....................................................................................... CHSS. 

S5.1.4. Test for service terminating performance in fire ........................................................................... CHSS. 

S5.1.5. Tests for performance durability of closure devices ..................................................................... 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 


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

90.0 °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 °C and 

¥40.0 °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 °C and 90.0 

°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. 


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6284 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

Figure 1 to § 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 § 571.308 S5.1.3.1 

Number of cycles Ambient conditions Initial system 

equilibration Fuel delivery temperature Cycle initial and final pressure 

Cycle peak 

pressure 

5 ....................................... ¥30.0 °C to ¥25.0 °C ... ¥30.0 °C to ¥25.0 °C ... 15.0 °C to 25.0 °C .......... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

5 ....................................... ¥30.0 °C to ¥25.0 °C ... ¥30.0 °C to ¥25.0 °C ... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

15 ..................................... ¥30.0 °C to ¥25.0 °C ... not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

5 ....................................... 50.0 °C to 55.0 °C, 80% 

to 100% relative humidity.

50 °C to 55 °C, 80% to 

100% relative humidity.

¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

20 ..................................... 50.0 °C to 55.0 °C, 80% 

to 100% relative humidity.

not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

200 ................................... 5.0 °C to 35.0 °C ............ not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6285 

TABLE 3 TO § 571.308 S5.1.3.1—Continued 

Number of cycles Ambient conditions Initial system 

equilibration Fuel delivery temperature Cycle initial and final pressure 

Cycle peak 

pressure 

Extreme temperature static gas pressure leak/ 

permeation test 

S5.1.3.2.

55.0 °C to 60.0 °C .......... 55.0 °C to 60.0 °C .......... not appliable ................... not appliable ................... 100.0% SOC to 105.0% 

SOC. 

25 ..................................... 50.0 °C to 55.0 °C, 80% 

to 100% relative humidity.

not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

25 ..................................... ¥30.0 °C to ¥25.0 °C ... not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

200 ................................... 5.0 °C to 35.0 °C ............ not appliable ................... ¥40.0 °C to ¥33.0 °C ... 1.0 MPa to 2.0 MPa ....... 100.0% SOC to 105.0% 

SOC. 

Extreme temperature static gas pressure leak/ 

permeation test 

S5.1.3.2.

55.0 °C to 60.0 °C .......... 55.0 °C to 60.0 °C .......... not appliable ................... not appliable ................... 100.0% SOC to 105.0% 

SOC. 

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 °C to 35 °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 


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6286 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

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 °C and 

35.0 °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 °C and 

90.0 °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 °C and 

¥40.0 °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 °C and 35.0 °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 °C and 90.0 

°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 °C and 

¥40.0 °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 kW 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 


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

and 35.0 °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 °C 

and 35.0 °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 °C and 35.0 °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° 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° 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° 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° and 

50° 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 


KHAMMOND on DSK9W7S144PROD with RULES3
6288 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

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° and 50° 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. 

Figure 2 to § 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 °C and 

¥40.0 °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. 


KHAMMOND on DSK9W7S144PROD with RULES3ER17JA25.003</GPH>
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6289 

Figure 3 to § 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 °C and 

35.0 °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 temperaturecontrolled 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 


KHAMMOND on DSK9W7S144PROD with RULES3ER17JA25.004</GPH>
6290 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

value shall be used. The pressure ramp 

rate shall be decreased if the gas 

temperature in the container exceeds 85 

°C. 

TABLE 4 TO § 571.308 S6.2.4.1(c) 

CHSS volume (L) 

CHSS pressurization rate (MPa/min) 

50.0 °C to 55.0 °C 

ambient conditions 

¥33.0 °C to ¥40.0 °C 

fuel delivery 

temperature 

5.0 °C to 35.0 °C 

ambient conditions 

¥33.0 °C to ¥40.0 °C 

fuel delivery 

temperature 

¥30.0 °C to ¥25.0 °C 

ambient conditions 

¥33.0 °C to ¥40.0 °C 

fuel delivery 

temperature 

¥30.0 °C to ¥25.0 °C 

ambient conditions 15.0 

°C to 25.0 °C fuel 

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 fueldemand 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 defueling 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 °C and 

60.0 °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 § 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 the rails ...................................... 45 to 55 millimeter. 

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. 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 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 midheight along the left side of the 

cylindrical surface, 

(3) One thermocouple located midheight 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 § 571.308 S6.2.5.2 

Fire stage Temperature range on bottom of pre-test 

container 

Temperature 

range on 

sides of 

pre-test 

container 

Temperature range on top of pre-test 

container 

Localized ............ 450 °C to 700 °C ......................................................... less than 750 

°C.

less than 300 °C. 

Engulfing ............ Average temperatures of the pre-test container surface measured at the three bottom locations shall 

be greater than 600 °C.

Not applicable.Average temperatures of the pre-test container surface measured at the three top locations shall be 

at least 100 °C, and when greater than 750 °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 °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 °C, 

TminLOC shall be 600 °C. 

(2) The minimum value for the burner 

monitor temperature during the 

engulfing fire stage (TminENG) shall be 

calculated by subtracting 50 °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 °C, 

TminENG shall be 800 °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 

°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. 


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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 °C and 35.0 °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 °C to 90.0 °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 °C to 90.0 °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 °C to 35.0 °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 °C to ¥40.0 °C. 

TABLE 7 TO § 571.308 S6.2.6.1.1 

Number of cycles Low pressure High pressure Sample 

temperature for cycles 

First 10 ................................. 1.0 MPa to 2.0 MPa .......... 150.0% NWP to 155.0% NWP ...................................... 85.0 °C to 90.0 °C. 

Next 2,240 ........................... 1.0 MPa to 2.0 MPa .......... 125.0% NWP to 130.0% NWP ...................................... 85.0 °C to 90.0 °C. 

Next 10,000 ......................... 1.0 MPa to 2.0 MPa .......... 125.0% NWP to 130.0% NWP ...................................... 5.0 °C to 35.0 °C. 

Final 2,750 ........................... 1.0 MPa to 2.0 MPa .......... 80.0% NWP to 85.0% NWP .......................................... ¥45.0 °C to ¥40.0 °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 °C using equation 2 to this section, 

where b = 273.15 °C, TME is 85 °C, and 

Tf is the vehicle manufacturer’s 

specified activation temperature in °C.: 

Equation 2 to § 571.308 S6.2.6.1.2 

(b) The TPRDs are placed in an oven 

or liquid bath maintained within 5.0 °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 °C and 

¥40.0 °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 °C and 90.0 °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 °C and ¥40.0 °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 °C and ¥40.0 °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 § 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 °C to 28.0 °C ........................ 35 percent to 55 percent .............. 470 minutes to 490 minutes 

Transition 55 min to 60 min 

Humid stage ................................... 47.0 °C to 51.0 °C ........................ 95 percent to 100 percent ............ 410 minutes to 430 minutes 

Transition 170 minutes to 190 minutes 

Dry stage ....................................... 55.0 °C to 65.0 °C ........................ less than 30 percent ..................... 290 minutes to 310 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 § 571.5), with a suitable water 

supply conforming to Type IV 


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Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 6293 

requirements in ASTM D1193–06 

(Reapproved 2018) (incorporated by 

reference, see § 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 °C and 

not greater than 65 °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 § 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 °C and 

35.0 °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 °C and 

not more than 40 °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 °C and 35.0 °C; test in accordance 

with S6.2.6.1.8(b) at any pressure 

between 1.5 MPa and 2.5 MPa and then 


KHAMMOND on DSK9W7S144PROD with RULES3
6294 Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 

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 

°C and 90.0 °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 °C and ¥40.0 °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 °C and 605.0 °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 °C and 605.0 °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 °C and 35.0 °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 

°C and 35.0 °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 °C 

and 90.0 °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 

°C and ¥40.0 °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. 


KHAMMOND on DSK9W7S144PROD with RULES3
Federal Register / Vol. 90, No. 11 / Friday, January 17, 2025 / Rules and Regulations 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 


KHAMMOND on DSK9W7S144PROD with RULES3