# Federal Motor Vehicle Safety Standards; Fuel System Integrity of Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity; Incorporation by Reference > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-07116 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** April 17, 2024 - **Citation:** 89 FR 27502 ## Text DEPARTMENT OF TRANSPORTATION National Highway Traffic Safety Administration 49 CFR Part 571 [Docket No. NHTSA-2024-0006] RIN 2127-AM40 Federal Motor Vehicle Safety Standards; Fuel System Integrity of Hydrogen Vehicles; Compressed Hydrogen Storage System Integrity; Incorporation by Reference AGENCY: National Highway Traffic Safety Administration (NHTSA), Department of Transportation (DOT). ACTION: Notice of proposed rulemaking (NPRM). SUMMARY: This notice proposes to establish two new Federal Motor Vehicle Safety Standards (FMVSS) specifying performance requirements for all motor vehicles that use hydrogen as a fuel source. The proposed standards are based on Global Technical Regulation (GTR) No. 13. FMVSS No. 307, “Fuel system integrity of hydrogen vehicles,” which would specify requirements for the integrity of the fuel system in hydrogen vehicles during normal vehicle operations and after crashes. FMVSS No. 308, “Compressed hydrogen storage system integrity,” would specify requirements for the compressed hydrogen storage system to ensure the safe storage of hydrogen onboard vehicles. The two proposed standards would reduce deaths and injuries that could occur as a result of fires due to hydrogen fuel leakages and/or explosion of the hydrogen storage system. DATES: You should submit your comments early enough to be received not later than June 17, 2024. In compliance with the Paperwork Reduction Act, NHTSA is also seeking comment on a revision to an existing information collection. For additional information, see the Paperwork Reduction Act Section under the Regulatory Notices and Analyses section below. All comments relating to the information collection requirements should be submitted to NHTSA and to the Office of Management and Budget (OMB) at the address listed in the ADDRESSES section on or before June 17, 2024. Proposed Effective Date: The date 180 days after the date of publication of the final rule in the Federal Register . Proposed Compliance Date: The September 1st that is two years subsequent to the publication of the final rule. ADDRESSES: You may submit comments to the docket number identified in the heading of this document by any of the following methods: • Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the online instructions for submitting comments. • Mail: Docket Management Facility: U.S. Department of Transportation, 1200 New Jersey Avenue SE, West Building Ground Floor, Room W12-140, Washington, DC 20590-0001. • Hand Delivery or Courier: 1200 New Jersey Avenue SE, West Building Ground Floor, Room W12-140, between 9 a.m. and 5 p.m. ET, Monday through Friday, except Federal holidays. • Fax: 202-493-2251. Instructions: All submissions must include the agency name and docket number. Note that all comments received will be posted without change to http://www.regulations.gov, including any personal information provided. Please see the Privacy Act discussion below. We will consider all comments received before the close of business on the comment closing date indicated above. To the extent possible, we will also consider comments filed after the closing date. Docket: For access to the docket to read background documents or comments received, go to http://www.regulations.gov at any time or to 1200 New Jersey Avenue SE, West Building Ground Floor, Room W12-140, Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal Holidays. Telephone: 202-366-9826. Privacy Act: In accordance with 5 U.S.C. 553(c), DOT solicits comments from the public to better inform its decision-making process. DOT posts these comments, without edit, including any personal information the commenter provides, to www.regulations.gov, as described in the system of records notice (DOT/ALL-14 FDMS), which can be reviewed at www.transportation.gov/privacy. In order to facilitate comment tracking and response, we encourage commenters to provide their name, or the name of their organization; however, submission of names is completely optional. Whether or not commenters identify themselves, all timely comments will be fully considered. Confidential Business Information: If you wish to submit any information under a claim of confidentiality, you should submit three copies of your complete submission, including the information you claim to be confidential business information, to the Chief Counsel, NHTSA, at the address given under FOR FURTHER INFORMATION CONTACT . In addition, you should submit two copies, from which you have deleted the claimed confidential business information, to the Docket at the address given above. When you send a comment containing information claimed to be confidential business information, you should include a cover letter setting forth the information specified in our confidential business information regulation (49 CFR part 512). FOR FURTHER INFORMATION CONTACT: For technical issues, Ian MacIntire, General Engineer Special Vehicles & Systems Division within the Division of Rulemaking, at (202) 493-0248 or 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. SUPPLEMENTARY INFORMATION: Table of Contents I. Executive Summary II. Background A. Hydrogen Fueled Vehicles 1. Hydrogen as a Motor Fuel 2. Hydrogen Vehicle Systems B. Global Technical Regulation (GTR) No. 13 1. Overview of the GTR Process 2. History of GTR No. 13 III. Why is NHTSA issuing this proposal? IV. Overview of Proposed Rules A. FMVSS No. 308, “Compressed Hydrogen Storage System Integrity” 1. Compressed Hydrogen Storage System 2. General Requirements for the CHSS 3. Performance Requirements for the CHSS 4. Tests for Baseline Metrics 5. Test for Performance Durability 6. Test for Expected On-Road Performance 7. Test for Service Terminating Performance in Fire 8. Tests for Performance Durability of Closure Devices 9. Labeling Requirements B. FMVSS No. 307, “Fuel System Integrity of Hydrogen Vehicles” 1. Fuel System Integrity During Normal Vehicle Operations 2. Post-Crash Fuel System Integrity C. Lead Time V. Rulemaking Analysis and Notices VI. Public Participation I. Executive Summary Vehicle manufacturers have continued to seek out renewable and clean alternative fuel sources to gasoline and diesel. Compressed hydrogen has emerged as a promising potential alternative because hydrogen is an abundant element in the atmosphere and does not produce tailpipe greenhouse gas emissions when used as a motor fuel. However, hydrogen must be compressed to high-pressures to be an efficient motor fuel, and is also highly flammable, similar to other motor fuels. NHTSA has already set regulations ensuring the safe containment of other motor vehicle fuels such as gasoline in FMVSS No. 301 and compressed natural gas in FMVSS No. 304, and the fuel integrity systems of those systems in FMVSS No. 301 and FMVSS No. 303, respectively. No such standards currently exist in the United States covering vehicles that operate on hydrogen. Accordingly, this document proposes two new Federal Motor Vehicle Safety Standards (FMVSSs) to address safety concerns relating to storage and use of hydrogen in motor vehicles, and to align the safety regulations of hydrogen vehicles with vehicles that operate using other fuel sources. This proposed rule was developed in concert with efforts to harmonize hydrogen vehicle standards with international partners through the Global Technical Regulation (GTR) process, and if adopted, would harmonize the FMVSSs with GTR No. 13, Hydrogen and Fuel Cell Vehicles. This document proposes the creation of two new safety standards: FMVSS No. 307, “Fuel system integrity of hydrogen vehicles,” and FMVSS No. 308, “Compressed hydrogen storage system integrity.” FMVSS No. 307 would regulate the integrity of the fuel system in hydrogen vehicles during normal vehicle operations and after crashes. To this end, it includes performance requirements for the hydrogen fuel system to mitigate hazards associated with hydrogen leakage and discharge from the fuel system, as well as post-crash restrictions on hydrogen leakage, concentration in enclosed spaces, container displacement, and fire. FMVSS No. 308 would regulate the compressed hydrogen storage system (CHSS) itself, and would primarily include performance requirements that would ensure the CHSS is unlikely to leak or burst during use, as well as requirements intended to ensure that hydrogen is safely expelled from the container when it is exposed to a fire. FMVSS No. 308 also specifies performance requirements for different closure devices in the CHSS. NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all motor vehicle that use compressed hydrogen gas as a fuel source to propel the vehicle, regardless of the vehicle's gross vehicle weight rating (GVWR). However, while FMVSS No. 307 fuel system integrity requirements during normal vehicle operations would apply to both light vehicles (vehicles with a GVWR of 4,536 kg or less) and to heavy vehicles (vehicles with a GVWR greater than 4,536 kg), FMVSS No. 307 post-crash fuel system integrity requirements would only apply to compressed hydrogen fueled light vehicles and to all compressed hydrogen fueled school buses regardless of GVWR. While the proposed safety standards are drafted in accordance with GTR No. 13, there are differences between some proposed requirements and test procedures and GTR No. 13. This document highlights these differences and provides reasons for these differences in relevant sections of the preamble, and seeks public comment. II. Background A. Hydrogen Fueled Vehicles 1. Hydrogen as a Motor Fuel In the pursuit of sustainable, renewable, and clean transportation, vehicle manufacturers have continued to expand their pursuits of hydrogen as an alternative fuel source for automobiles. Unlike their gasoline or diesel counterparts, hydrogen-powered vehicles (hydrogen vehicles) do not produce carbon dioxide or other emissions. Furthermore, in contrast with battery electric vehicles, hydrogen vehicles do not require extended recharging from an external electrical source. These advantages, coupled with the relative abundance of hydrogen, make hydrogen vehicles an intriguing alternative to vehicles already offered in the market. Hydrogen vehicles harness the chemical energy within hydrogen using one of two methodologies. The first technique is similar to conventional internal combustion engines (ICE) powered by petroleum products. Hydrogen can be burned in a combustion engine and the energy released from this process used to move pistons that provide mechanical power to the vehicle. The second method utilizes a component called a fuel cell that converts the chemical energy in hydrogen into electricity. In this energy conversion process, hydrogen stored in the vehicle reacts with oxygen in the air to produce water and energy, in the form of electricity, which is then used to power the vehicle's mechanical operations. Hydrogen fuel cell vehicles (HFCVs), which are sometimes also referred to as fuel cell electric vehicles (FCEVs), are capable of continuous electrical generation so long as they have a steady supply of hydrogen fuel and oxygen. One complicating factor of using hydrogen as a mobile fuel source is its relatively low energy density. Compared to gasoline, which has a mass density of 803 grams per liter at 15 °C, uncompressed hydrogen is extremely light, with a mass density of just 0.09 grams per liter at 15 °C, which means a vehicle operating on uncompressed hydrogen will have a significantly shorter range than a comparable gasoline-powered vehicle. To overcome this, hydrogen is compressed to a very high pressure of up to 70 megaPascals (MPa) while stored on a hydrogen vehicle. 1 Hydrogen compressed to 70 MPa at 15 °C has a volumetric energy density of 4.8 mega Joules per liter (MJ/L), which is similar in order of magnitude to gasoline's volumetric energy density of 32 MJ/L. 2 3 1 At atmospheric pressure and ambient temperature, hydrogen is in a gaseous state. The physical state of hydrogen can be changed from gas to liquid through compression and cryogenic cooling, so hydrogen can be stored in both compressed gaseous and liquid forms. However, hydrogen typically exists in gaseous form at essentially all normal usage and storage temperatures. 2 See Patrick Molloy, “Run on Less with Hydrogen Fuel Cells.” RMI, Oct. 2, 2019, https://rmi.org/run-on-less-with-hydrogen-fuel-cells/ . 3 See Department of Energy Hydrogen and Fuel Cell Technologies Office, “Hydrogen Storage,” https://www.energy.gov/eere/fuelcells/hydrogen-storage . While compressed hydrogen is an excellent fuel source due to its high energy density, its high storage pressure and wide limits of flammability ( i.e., concentrations at which a mixture of fuel and air is flammable) raise safety concerns. Specifically, hydrogen is flammable at concentrations ranging from 4 to 75 percent, by volume. 4 By contrast, gasoline limits of flammability when mixed with air are from 1.0 to 7.6 percent, by volume. 5 The velocity at which a hydrogen flame spreads at room temperature and atmospheric pressure is approximately 200 to 300 cm/s, whereas the velocity with which gasoline flames spread under the same conditions is approximately 40 cm/s. 6 7 These characteristics make hydrogen fuel sources more volatile than gasoline, and while NHTSA has existing FMVSS for gasoline vehicle fuel system integrity, no FMVSS yet apply to hydrogen storage and fuel systems. In particular, the safe use of hydrogen vehicles lies in preventing explosion of the hydrogen container(s) and preventing leaks from the container(s) and fuel system which could lead to fire. Given the greater flammability of compressed hydrogen, safety standards applicable to their fuel system integrity are not only reasonable, but necessary. 4 See Hydrogen Compared with Other Fuels, https://h2tools.org/bestpractices/hydrogen-compared-other-fuels . 5 Id. 6 See 6 Things to Remember about Hydrogen vs Natural Gas, https://www.powereng.com/library/6-things-to-remember-about-hydrogen-vs-natural-gas . 7 See Combustion fuels: density, ignition temperature and flame speed, https://thundersaidenergy.com/downloads/combustion-fuels-density-ignition-temperature-and-flame-speed/ . Despite the promise offered by hydrogen vehicles, they are still a diminutive fraction of the fleet. For model year 2022, there were two light hydrogen vehicle models offered for sale in the United States, whose sales by volume represented approximately 0.03% of the overall light vehicle fleet. There were no medium-or heavy-duty 8 hydrogen vehicles offered for sale in the U.S. during the 2022 model year; 9 however, manufacturers continue to state their intentions to explore hydrogen across all fleets. 8 Medium-duty vehicles have a gross vehicle weight rating (GVWR) greater than 4,536 kg and less than or equal to 11,793 kg. Heavy-duty vehicles have a GVWR greater than 11,793 kg. 9 Toyota has a commercial bus called the Sora that is currently sold in Japan and Europe. 2. Hydrogen Vehicle Systems Hydrogen vehicles—both fuel cell and ICE—share the same basic structure. Hydrogen enters the vehicle through the fueling receptacle, is stored in the CHSS, and is released from the CHSS as needed to power either the combustion engine or fuel cell where the energy stored in hydrogen is converted into mechanical. 10 Figure-1 below shows an example of a hydrogen fuel cell vehicle (HFCV). 11 A diagram of the main elements of a vehicle fuel system is shown in Figure-2. 12 10 The chemical energy stored in the hydrogen fuel is converted into electric energy by the fuel cell, and the resulting electric energy is then be converted into mechanical energy by electric drive motor(s), thereby propelling the vehicle. 11 Note that the vehicle depicted is a fuel cell vehicle. For a hydrogen ICE vehicle, the fuel cell would be replaced with a combustion engine. 12 Figure-2 shows the main elements of a HFCV fuel system. In the case of a hydrogen ICE vehicle, the fuel cell system would be replaced by the ICE, and the electric propulsion management system would be replaced by the vehicle powertrain. EP17AP24.000 Figure-1: Example of a HFCV Design 13 13 For further information on HFCV design, see https://afdc.energy.gov/vehicles/fuel_cell.html, and https://afdc.energy.gov/vehicles/how-do-fuel-cell-electric-cars-work. EP17AP24.001 Figure-2: A Schematic of a HFCV and Its Major Systems a. CHSS During fueling, hydrogen is supplied from the fueling station to the vehicle through the vehicle's fueling receptacle. The hydrogen then flows to the CHSS for storage in the hydrogen container(s). The key functions of the CHSS are to receive compressed hydrogen through a check valve during fueling, contain the hydrogen until needed, and release hydrogen through an electrically activated shut-off valve to the hydrogen delivery system for use in powering the vehicle. The check valve prevents reverse flow in the vehicle fueling line. The shut-off valve between the storage container and the vehicle fuel delivery system controls the fuel flow out of the CHSS and automatically defaults to the closed fail-safe position when unpowered. In the event of a fire impinging on the CHSS, the TPRD provides a controlled release of hydrogen from the CHSS before the high temperature causes a hazardous burst of the container. b. Hydrogen Delivery The hydrogen delivery system transfers hydrogen from the CHSS to the fuel cell system at the proper pressure and temperature for fuel cells to operate. This transfer process is accomplished through a series of flow control valves, pressure regulators, filters, piping, and heat exchangers. c. Fuel Cell System The fuel cell system provides high-voltage electric power to the drive-train and vehicle batteries and capacitors. The fuel cell stack is the electricity-generating component of the fuel cell system. Individual fuel cells are electrically connected in series such that their combined voltage is between 300 and 600 Volts in direct current (VDC). Fuel cell stacks operate at high-voltage, which means a voltage greater than 60 VDC. The high voltage aspect of fuel cells are covered by FMVSS No. 305, “Electric-powered vehicles: electrolyte spillage and electrical shock protection,” and are not considered in this proposal. A typical fuel cell system includes a blower to feed air to the fuel cell system. Most of the hydrogen that is supplied to the fuel cell system is consumed within the fuel cells, but a tiny excess of hydrogen is required to ensure that there is no damage to the fuel cell from a lack of hydrogen, which can cause undesired chemical reactions that damage and degrade the fuel cell. 14 The excess hydrogen is either catalytically removed or vented to the atmosphere in accordance with the requirements discussed below. A fuel cell system also includes auxiliary components to remove heat. Most fuel cell systems are cooled by a mixture of glycol and water. Pumps circulate the coolant between the fuel cells and a radiator. 14 A lack of hydrogen in a fuel cell, also known as hydrogen starvation, occurs when hydrogen fuel is exhausted at the fuel cell anode. This condition can lead to undesired chemical reactions occurring inside the fuel cell which can quickly degrade the fuel cell's catalyst and other components. d. Electric Propulsion and Power Management System The electric power generated by the fuel cell system is supplied to the electric propulsion power management system where it is used to power the electric drive-train that propels the vehicle. The throttle position is used by the drive-train controllers to determine the amount of power to be sent to the drive wheels. Many HFCVs use batteries or ultra-capacitors to supplement the output of the fuel cells. These vehicles may also recapture energy during braking through regenerative braking, which recharges the batteries or ultra-capacitors and thereby maximizes efficiency. 15 15 The electric propulsion and power management system is covered by FMVSS No. 305, “Electric-powered vehicles: electrolyte spillage and electrical shock protection,” and is not considered in this proposal. e. Hydrogen ICE Vehicles Hydrogen ICE vehicles have an ICE instead of a fuel cell system. The ICE engine burns hydrogen to generate mechanical energy to propel the vehicle. These vehicles use a mechanical propulsion system instead of an electric propulsion system. B. Global Technical Regulation (GTR) No. 13 The proposed rule initiates the process of adopting Global Technical Regulation (GTR) No. 13 into the FMVSS. Based on GTR No. 13, this NPRM proposes requirements for the safe onboard storage and utilization of hydrogen in vehicles. 1. Overview of the GTR Process The United States became the first signatory to the 1998 United Nations/Economic Commission for Europe (UNECE) agreement (1998 Agreement). The 1998 Agreement entered into force in 2000 and is administered by the World Forum for Harmonization of Vehicle Regulations working party (WP.29). 16 The 1998 Agreement established the development of global technical regulations (GTRs) regarding the safety, emissions, energy efficiency and theft prevention of wheeled vehicles, equipment and parts. 16 The World Forum was initially named the Working Party on the Construction of Vehicles, a subsidiary of the Inland Transport Committee. It was renamed to the World Forum in 2000. The 1998 Agreement contains procedures for establishing GTRs either through harmonizing existing regulations or developing new regulations. The GTR process provides NHTSA unique opportunities to enhance vehicle safety and improve government efficiency. It assists in developing the best safety practices from around the world, identifying and reducing unwarranted regulatory requirements, and leveraging scarce government resources for research and regulation. The process facilitates our effort to continuously improve and seek high levels of safety, particularly by helping us develop regulations that reflect a global consideration of current and anticipated technology and safety problems. Contracting Parties who vote in favor of a GTR are obligated by the 1998 Agreement to “submit the technical Regulation to the process” used in the country to adopt the requirement into the agency's law or regulation. 17 In the U.S., that process usually commences with an NPRM or Advance NPRM (ANPRM). The 1998 Agreement does not obligate Contracting Parties to adopt the GTR after initiating this process. 18 The 1998 Agreement recognizes that governments have the right to determine whether the global technical regulations established under the Agreement are suitable for their own particular safety needs. Those needs vary from country to country due to differences in laws and in factors such as the traffic environment, vehicle fleet composition, driver characteristics and seat belt usage rates. 17 Article 7, 1998 Agreement, available at https://unece.org/text-1998-agreement. 18 Id. 2. History of GTR No. 13 NHTSA began collaborating with the international community to develop a global technical regulation for hydrogen vehicles in the early 2000s. In 2005, WP.29 agreed to a proposal from Germany, Japan and the United States of America regarding how best to manage the development process for a hydrogen vehicle GTR. Pursuant to the proposal, the United States and Japan were designated co-chairs of an informal working group (IWG) to explore the safety aspects of hydrogen vehicles. In June 2007, WP.29 adopted an action plan prepared by the co-sponsors to develop a GTR for compressed gaseous and liquefied hydrogen fuel vehicles. At the time, no hydrogen vehicles were commercially available. To allow for the advancement of hydrogen technologies, the co-sponsors' action plan split the GTR into two phases. Phase 1 would focus on developing a GTR for hydrogen vehicles based on current best practices. Phase 2 would commence subsequent to Phase 1, and supplement it by assessing any technological advancements and explore ways to harmonize vehicle crash tests to evaluate fuel system integrity. The IWG evaluated existing research and design standards for the development of a hydrogen vehicle GTR. To the extent possible, the group avoided design specific requirements and considered requirements and specification that were supported by research and technically justified. The main areas of focus in Phase 1 were: performance requirements for hydrogen storage systems, high-pressure closures, pressure relief devices, and fuel lines; specifications on limits on hydrogen releases during normal vehicle operations and post-crash; and requirements for electrical isolation and protection against electric shock during normal vehicle operations and post-crash. The draft GTR was recommended by the IWG at the December 2012 session, and GTR No. 13 for Hydrogen and Fuel Cell Vehicles was codified by WP.29 on June 27, 2013, after a 6-year effort, with the United States voting in favor of the GTR. It specified safety-related performance requirements and test procedures with the purpose of minimizing human harm that may occur as a result of fire, burst, or explosion related to the hydrogen fuel system of vehicles, and/or from electric shock caused by a fuel cell vehicle's high voltage power train system. 19 The regulation consists of system performance requirements for compressed hydrogen storage systems (CHSS), CHSS closure devices, and the vehicle fuel delivery system. In Phase 1, the IWG purposefully did not harmonize crash tests and instead elected to have Contracting Parties use their own methodologies. 19 The electrical safety requirements in GTR No. 13 Phase 1 were incorporated into FMVSS No. 305. See 82 FR 44945. Phase 2 was adopted at the 190th Session of WP.29 on June 21, 2023. 20 Phase 2 accomplished several goals, including: broadening of the scope and application of GTR No. 13 to cover heavy-duty/commercial vehicles; harmonizing, clarifying, and expanding the requirements for thermal-pressure relief devices' direction in case of controlled release of hydrogen; strengthening test procedures for containers with pressures below 70 MPa, including comprehensive fire exposure tests; and extending the requirements to 25 years to more accurately capture the expected useful life of vehicles. The U.S. voted in favor of adopting Phase 2 and is proposing to adopt the changes made to GTR No. 13 by Phase 2 with this proposal. 20 A copy of GTR No. 13 as updated by the Phase 2 amendments is available at: https://unece.org/sites/default/files/2023-07/ECE-TRANS-180-Add.13-Amend1e.pdf . III. Why is NHTSA issuing this proposal? As a Contracting Party who voted in favor of GTR No. 13, the United States is obligated under the 1998 Agreement to “submit the technical Regulation to the process” used to adopt the requirement into the agency's law or regulation as a domestic standard. Today's proposal satisfies that obligation. In deciding whether to adopt a GTR as an FMVSS, we follow the procedural and substantive requirements for any other agency rulemaking, including the Administrative Procedure Act, the National Traffic and Motor Vehicle Safety Act (Safety Act) (49 U.S.C. Chapter 301), Presidential executive orders, and DOT and NHTSA policies, procedures, and regulations. 21 Under 49 U.S.C. 30111(a), FMVSSs must be practicable, meet the need for motor vehicle safety, and be stated in objective terms. 22 Section 30111(b) states that, when prescribing such standards, NHTSA must, among other things, consider all relevant, available motor vehicle safety information; consider whether a standard is reasonable, practicable, and appropriate for the types of motor vehicles or motor vehicle equipment for which it is prescribed; and consider the extent to which the standard will further the statutory purpose of reducing traffic crashes and associated deaths and injuries. 21 NHTSA's policies in implementing the 1998 Agreement are published in 49 CFR part 553, appendix C, “Statement of Policy: Implementation of the United Nations/Economic Commission for Europe (UNECE) 1998 Agreement on Global Technical Regulations—Agency Policy Goals and Public Participation.” NHTSA's paramount policy goal under the 1998 Agreement is to “[c]ontinuously improve safety and seek high levels of safety, particularly by developing and adopting new global technical regulations reflecting consideration of current and anticipated technology and safety problems.” 22 “Motor vehicle safety” is defined in the Safety Act as “the performance of a motor vehicle or motor vehicle equipment in a way that protects the public against unreasonable risk of accidents occurring because of the design, construction, or performance of a motor vehicle, and against unreasonable risk of death or injury in an accident, and includes nonoperational safety of a motor vehicle.” 49 U.S.C. 30102(a)(8). This proposal marks a substantial step in meeting those procedural and substantive requirements. The proposal serves as notice of our intention to adopt the requirements of GTR No. 13 as FMVSS Nos. 307 and 308 and provides an opportunity for the public to comment on the proposed requirements. In accordance with the APA, we seek comment on this proposal to help inform our decision-making, and will take all timely public comments into consideration when deciding whether (and if so, how) to proceed with a final rule, and the appropriateness of any potential modifications to the proposed performance standards that are appropriately within scope of the NPRM. NHTSA tentatively finds that the proposed standards fulfill a clear, if not immediately present, need for motor vehicle safety. The purpose of FMVSS No. 307, “Fuel system integrity of hydrogen vehicles,” and FMVSS No. 308, “Compressed hydrogen storage system integrity,” is to reduce deaths and injuries in hydrogen-powered vehicles occurring from fires that result from leakage after motor vehicle crashes. Hydrogen is highly flammable, with an exceptionally wide limit of flammability in the air and a high burning velocity. If hydrogen leaks from the fuel system, the risk of fire in or near the vehicle is substantial and gravely impairs the safety of vehicle occupants and others within the vicinity of the vehicle. Although the potential safety risk from hydrogen vehicles has not necessarily materialized, due to their current scarcity in the on-road fleet, NHTSA made the same determination about the safety need for fuel system and container integrity systems when it adopted FMVSS No. 301, Fuel system integrity, with the initial FMVSSs adopted in 1968, 23 and in 1994 when NHTSA adopted FMVSS No. 303, Fuel system integrity of compressed natural gas vehicles, 24 and FMVSS No. 304, Compressed natural gas fuel container integrity. 25 NHTSA faced a similar crossroads when developing FMVSS Nos. 303 and 304. Compressed Natural Gas (CNG) vehicles represented a very small portion of the total fleet size when NHTSA finalized the standards. The agency decided that the safety risk posed by CNG necessitated immediate action. 26 Members of the public shared a similar sentiment with the agency and urged quick action at that time to coalesce safety practices. 27 Today's proposal is the logical extension of NHTSA's existing standards that cover vehicles powered by other combustible fuel sources, except, for this NPRM, the agency has been able to draw on and benefit from the work of the international GTR No. 13 community in developing the proposed standards. 23 See 32 FR 2414 (February 3, 1967). 24 See 59 FR 19648 (April 25, 1994). 25 See 59 FR 49010 (September 26, 1994). 26 58 FR 5323 (January 23, 1993) 27 See 59 FR 19648, 19657. We tentatively find the proposed requirements in this NPRM to be practicable. Both automobile and hydrogen container manufacturers provided technical expertise to the IWG on test procedures and determining the boundaries of practicability of requirements during the development of GTR No. 13. Furthermore, GTR No. 13 incorporates a number of voluntary industry standards, which are discussed throughout this preamble, that have been demonstrated as practicable. Given the industry input informing the GTR and that the GTR incorporates current technical standards now used in hydrogen vehicle safety designs, NHTSA believes that the proposed standards are practicable. The 1998 Agreement provides flexibilities to propose alternative technical regulations as necessary to ensure compliance with a jurisdiction's specific legal and safety need requirements. As noted in the forthcoming sections, NHTSA is proposing several modifications to the requirements in GTR No. 13 to conform with the Safety Act requirements for FMVSS, clarify the wording of the regulation, and improve objectivity. The agency believes that this proposed rule is timely. While hydrogen vehicles currently represent less than half a percent of the total sales of light vehicles and are still in the prototypical stage for heavier vehicles, there are several trends that may point to increased growth in the coming years. The slow adoption of hydrogen vehicles can be attributed to both the expense associated with developing a new powertrain and the lack of existing fueling infrastructure. 28 Recent Federal legislation and spending has renewed the country's focus on incentivizing clean vehicles. The Inflation Reduction Act (IRA) allotted billions towards the development of clean vehicles and the infrastructure to support them. Manufacturers can claim credits for building or retooling facilities to build hydrogen-powered vehicles under Qualifying Advanced energy project credit or can claim credits for each hydrogen vehicle produced pursuant to the Advanced manufacturing production credit. 29 Consumers who purchase hydrogen vehicles can qualify for a $7,500 tax credit, and commercial enterprises can claim up to $40,000 for hydrogen fuel cell vehicles. 30 Additionally, producers of clean hydrogen are also eligible for tax credits on a per-gallon basis. 31 This list of incentives is not exhaustive, and NHTSA recognizes that the collective efforts at both the Federal and State level to incentive clean energy in the transportation industry are extensive and underline the importance of establishing safety standards presently, so that they are in place as the vehicles arrive in the marketplace. 28 See, e.g. S. Hardman, E. Shiu, R. Steinberger-Wilckens, and T. Turrentine., Barriers to the adoption of fuel cell vehicles: A qualitative investigation into early adopters attitudes, 95 Transportation Research Part A: Policy and Practice 166-82 (2017). https://www.sciencedirect.com/science/article/abs/pii/S0965856415302408#:~:text=FCVs%20have%20some%20specific%20challenges,and%20balance%20of%20plant%20components. 29 See 26 U.S.C. 48C and 26 U.S.C. 45X, respectively. 30 See 26 U.S.C. 30D and 26 U.S.C. 45W, respectively. 31 26 U.S.C. 45Z. Manufacturers continue to announce new forays into hydrogen vehicles, with some manufacturers citing the IRA as a catalyst for further development of hydrogen-powered vehicles. 32 Hyundai and Toyota, the only two manufacturers with hydrogen vehicles for sale currently in the United States, have announced plans to introduce more consumer hydrogen vehicle lines covering additional body styles and expand their hydrogen vehicle offerings. 33 Other manufacturers have announced plans to introduce their own hydrogen vehicle models, 34 and new entrants to the automotive market are testing prototypes and concept vehicles. 35 Manufacturers have also stated that they are exploring the viability of hydrogen heavy-duty vehicles. 36 32 See, e.g. Elizabeth Sturcken, “Leading companies are using IRA tax credits for clean manufacturing and technology. Are you?” Environmental Defense Fund, June 7, 2023, https://business.edf.org/insights/leading-companies-are-using-ira-tax-credits-for-clean-manufacturing-and-technology-are-you/ . 33 See Remeredzai J. Kuhadzai, “Toyota Hilux Hydrogen Fuel Cell Pickup Prototype Unveiled” https://cleantechnica.com/2023/01/11/toyota-starts-work-on-the-development-of-prototype-hydrogen-fuel-cell-toyota-hilux-pickup/ (Toyota plans to release the Helix only in Japan for the upcoming model year) and Toyota, “PACCAR and Toyota Expand Hydrogen Fuel Cell Truck Collaboration to Include Commercialization.” May 2, 2023, https://pressroom.toyota.com/paccar-and-toyota-expand-hydrogen-fuel-cell-truck-collaboration-to-include-commercialization/; see also Michelle Thompson, “Hyundai hires new exec to help lead hydrogen initiatives.” Repairer Driven News, June 29, 2023. https://www.repairerdrivennews.com/2023/06/29/hyundai-hires-new-exec-to-help-lead-hydrogen-initiatives/. 34 For example, see Ken Silverstein, “Electric Vehicles or Hydrogen Fuel Cell Cars? The Inflation Reduction Act Will Fuel Both.” Forbes, Aug. 10, 2022, https://www.forbes.com/sites/kensilverstein/2022/08/10/electric-vehicles-or-hydrogen-fuel-cell-cars-the-inflation-reduction-act-will-fuel-both/?sh=2841d7634d01; see also Joey Capparella, “Hydrogen-Powered Honda CR-V to Be Built in the U.S. Starting in 2024.” Car and Driver, Nov. 30, 2022. 35 See, Ezra Dyer, “Pininfarina Reveals Pura Vision SUV Concept.” Car and Driver, Aug. 1, 2023, https://www.caranddriver.com/news/a44690183/pininfarina-pura-vision-suv-concept-revealed/ . 36 See Rebecca Martineau, “Fast Flow Future for Heavy-Duty Hydrogen Trucks: Expanded Capabilities at NREL Demonstrate High-Flow-Rate Hydrogen Fueling for Heavy-Duty Applications.” National Renewable Energy Laboratory, June 8, 2022, https://www.nrel.gov/news/program/2022/fast-flow-future-heavy-duty-hydrogen-trucks.html. NHTSA faced a similar crossroads when developing FMVSS Nos. 303 and 304. Compressed Natural Gas (CNG) vehicles represented a very small portion of the total fleet size when NHTSA finalized the standards. The agency decided that the safety risk posed by keeping CNG at a high pressure necessitated an immediate action. 37 Members of the public have shared a similar sentiment with the agency and urged quick action to coalesce safety practices for hydrogen powered vehicles. 38 37 58 FR 5323. 38 See 59 FR 19648, 19657. We believe that the proposed standards would provide regulatory certainty for manufacturers. Given manufacturers' purported interest in expanding their hydrogen offerings and the IRA incentives reducing the comparative costs of hydrogen vehicles, adopting safety regulations now would provide manufacturers clarity on how to design new vehicle lines. Further, having hydrogen safety standards in place should assist in alleviating the trepidation consumers have of newer technologies, whereas a failure to adequately address safety concerns in the earliest stages of development could have a negative impact on the deployment of this new technology. Manufacturers have also informed NHTSA that they would like to see the agency coordinate and harmonize hydrogen standards with other nations. 39 This proposal would accomplish all of these tasks. 39 See, e.g. NHTSA-2004-18039-0020 at 17. IV. Overview of Proposed Safety Standards The safe use of compressed hydrogen in vehicles lies primarily in preventing explosion of the hydrogen container(s) and preventing fuel leaks which could lead to fire or explosion. The leakage of hydrogen from the fuel system during normal vehicle operations and post-crash can pose safety hazards (fire or explosion) to vehicle occupants and the surroundings. In order to address the fire and explosion hazards associated with hydrogen vehicles, NHTSA is proposing to set performance requirements for the CHSS and the overall fuel system that are generally consistent with GTR No. 13. GTR No. 13, Section 5.1, “Compressed hydrogen storage system,” specifies performance-based CHSS requirements which address documented on-road stress factors. These stress factors include those identified in CNG vehicle containers as well as those that are unique to containment of high-pressure hydrogen. These requirements were developed to demonstrate the CHSS's capability to perform critical functions throughout service, including fueling/defueling events, parking under extreme vehicle and environmental conditions, environmental exposures, and performance in fire without explosion. GTR No. 13, Section 5.2, “Vehicle fuel system,” includes performance requirements to prevent and mitigate hydrogen leak from the fuel system and to warn vehicle occupants in the event of hydrogen concentration in the vehicle above flammable limits during normal vehicle operations and post-crash. Similar to how NHTSA originally established CNG standards, we are proposing to implement GTR No. 13 by establishing two new FMVSSs that would specify minimum performance standards for vehicles that use compressed hydrogen gas as a motor fuel. 40 FMVSS No. 308, “Compressed hydrogen storage system integrity,” would set out requirements for CHSS integrity. FMVSS No. 307, “Fuel system integrity of hydrogen vehicles,” would set out in-use and post-crash requirements for the overall fuel system, including the CHSS, hydrogen delivery system, and fuel cell. 40 The standards proposed in this document would not apply to vehicles that use liquified hydrogen as a motor fuel. NHTSA is proposing that FMVSS Nos. 307 and 308 apply to all hydrogen-powered vehicles. This is a departure from Phase 1 of GTR No. 13 which only applies to hydrogen powered light vehicles. As discussed below, the IWG of GTR No. 13 Phase 2 has expanded the applicability of the standard to hydrogen powered heavy vehicles. With the exception of crash tests for heavy vehicles, NHTSA finds that the technical standards in GTR No. 13 are practicable for heavy vehicles and address the same safety need found in light vehicles. Note that, consistent with GTR No. 13, NHTSA is proposing that FMVSS No. 308 be a vehicle-level standard, rather than an equipment standard. 41 Some performance requirements and test procedures for the CHSS in FMVSS No. 308 are specific to the vehicle design and to its gross vehicle weight rating. NHTSA is aware this is a departure from FMVSS No. 304 that is an equipment standard which applies to CNG containers sold as replacement parts for CNG vehicles. At this time, hydrogen vehicle manufacturers are strictly controlling the CHSS installed in their vehicles and replacement parts are obtained from the vehicle manufacturer (similar to electric vehicle batteries). NHTSA will monitor the deployment of hydrogen vehicles and how consumers are replacing parts of the fuel system. Since such data is lacking at this time, NHTSA is proposing FMVSS No. 308 as a vehicle standard, consistent with GTR No. 13. NHTSA will re-evaluate this decision based on comments received and on field data on hydrogen vehicle deployment, repair, and replacement parts. NHTSA seeks comment on whether FMVSS No. 308 should remain a vehicle standard, as well as whether FMVSS Nos. 307 and 308 should be combined into a single standard in the final rule. 41 This is in contrast to FMVSS No. 304, Compressed natural gas fuel container integrity, which is an equipment standard. A. FMVSS No. 308, “Compressed Hydrogen Storage System Integrity” FMVSS No. 308 would set out requirements for the performance of the CHSS and its subcomponents during normal use, with a particular focus on how the CHSS performs in a variety of incidents that a vehicle could experience during its lifetime operations and how well the component withstands usage. NHTSA is proposing that FMVSS No. 308 only be a vehicle standard. As explained in more detail below, some of the proposed requirements are conditional on the vehicle type and characteristics. Without the knowledge of the relevant vehicle, some of the proposed CHSS standards cannot be tested. For these reasons, NHTSA does not intend that the proposed standard should extend to cover replacement parts, even though they would be considered motor vehicle equipment and still subject to NHTSA's safety defect authority, and replacement parts when installed may not take the vehicle out of compliance with the proposed new FMVSS No. 308, per 49 U.S.C. 30122. NHTSA seeks comment on this approach. 1. Compressed Hydrogen Storage System The CHSS is defined to include all closure surfaces that provide primary containment of high-pressure hydrogen storage. The CHSS is defined to include the hydrogen container, check valve, shut-off valve and thermally-activated pressure relief device (TPRD), which are discussed in the sections below. Figure-3 illustrates a typical CHSS. EP17AP24.002 Figure-3: Typical CHSS a. Hydrogen Container The hydrogen container is the main component of a CHSS. The hydrogen container stores hydrogen at extremely high pressure. On current hydrogen vehicles, hydrogen has typically been stored at a nominal working pressure (NWP) of 35 MPa or 70 MPa, at 15 °C. NWP means the gauge pressure that characterizes the normal operation of the system. Typically, the container is designed for a maximum allowable gas temperature of 85 °C. If the temperature of hydrogen stored at NWP is increased from 15 °C to 85 °C, then the pressure inside the container will rise to the maximum allowable pressure of 25 percent above NWP. 42 A container may consist of a single chamber or multiple permanently interconnected chambers. This allows designers flexibility in the overall shape of the CHSS. 42 This is based on data published in the NIST Chemistry WebBook, Standard Reference Database Number 69, Thermophysical Properties of Fluid Systems (isochoric properties for hydrogen), available at https://webbook.nist.gov/chemistry/fluid/. Most containers used in hydrogen vehicles consist of two layers. The inner liner prevents gas leakage/permeation and is usually made of metal or thermoplastic polymer. The outer layer provides structural integrity and is usually made of metal or thermoset resin-impregnated fiber-reinforced composite. For instance, Type 3 containers consist of a metal liner reinforced with resin impregnated continuous filament, and Type 4 containers consists of a non-metallic liner with resin-impregnated continuous filament. 43 43 The American National Standard for Compressed Natural Gas Fuel Vehicle Containers (2007) classifies containers into Types 1 through 4 as follows: Type 1—Metal. Type 2—Resin impregnated continuous filament with metal liner with a minimum burst pressure of 125 percent of service pressure. This container is hoop-wrapped. Type 3—Resin impregnated continuous filament with metal liner. This container is full-wrapped. Type 4—Resin impregnated continuous filament with a non-metallic liner. GTR No. 13 defines a container as “the pressure-bearing component on the vehicle that stores the primary volume of hydrogen fuel in a single chamber or in multiple permanently interconnected chambers.” NHTSA is proposing a similar definition with the following modifications: • Replace “the vehicle” with “a compressed hydrogen storage system” to clarify that the container is a subcomponent of the CHSS, and therefore a container cannot exist on its own without the other components of the CHSS. • Remove the word “primary” because this introduces ambiguity regarding secondary or tertiary volumes of 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's proposed definition for “container” would be “pressure-bearing component of a compressed hydrogen storage system that stores a continuous volume of hydrogen fuel in a single chamber or in multiple permanently interconnected chambers.” These changes are intended to clarify the definition and provide greater regulatory certainty as to what is considered part of the container. The changes do not alter the substantive requirements. NHTSA seeks comment on the proposed definition for the container. b. Closure Devices GTR No. 13 refers to closure devices as “primary” closure devices. This creates ambiguity about potential secondary or tertiary closure devices. As a result, NHTSA will refer simply to “closure devices.” NHTSA therefore proposes to define the term “closure devices” as “the check valve(s), shut-off valve(s) and thermally activated pressure relief device(s) that control the flow of hydrogen into and/or out of a CHSS,” so it will be clear what components are covered under the standard. NHTSA seeks comment on removal of the word “primary” and on the proposed definition for “closure devices.” (1) TPRD In the event of a fire, the TPRD provides a controlled release of hydrogen from the container before the high temperature from the fire weakens the container and causes a hazardous burst. TPRDs are designed to vent the entire hydrogen content of the container rapidly. These devices are designed to not be reset or reused once they have been activated. (2) Check Valve During fueling, hydrogen enters the CHSS through a check valve. The check valve prevents back-flow of hydrogen into the fueling line or out of the fueling receptacle. (3) Shut-Off Valve A shut-off valve prevents the outflow of stored hydrogen from the container when the vehicle is not operating or when a fault is detected that requires isolation of the CHSS. In GTR No. 13, the shut-off valve is defined as “a valve between the container and the vehicle fuel system that must default to the `closed' position when not connected to a power source.” NHTSA proposes adding the words “electrically activated” to the definition, so that a shut-off valve would be “an electrically activated valve between the container and the vehicle fuel system that must default to the `closed' position when not connected to a power source.” NHTSA seeks comment on the proposed definition of shut-off valve. (4) Container Attachments The CHSS may include container attachments, which are non-pressure bearing parts attached to the container that provide additional support and/or protection to the container. Container attachments may only be removed with the use of tools for the purpose of maintenance and/or inspection. Container attachments include devices such as bump stops to mitigate impacts or shielding to mitigate surface damage to the container. In the GTR No. 13 test procedures, container attachments are included in some tests. Importantly, in some cases, the container attachments provide protection to the container that improves test performance. Including container attachments for testing is discussed in the sections below where applicable and where the container attachments may affect test performance. NHTSA proposes defining container attachments as “non-pressure bearing parts attached to the container that provide additional support and/or protection to the container and that may be removed only with the use of tools for the specific purpose of maintenance and/or inspection.” NHTSA seeks comment on the proposed definition of container attachments. In this definition, the word “temporarily” has been removed from the GTR definition because anything that can be removed temporarily can also be removed permanently. For clarity, NHTSA has also shifted the order of some words relative to the definition in GTR No. 13. 2. General Requirements for the CHSS NHTSA is proposing that the CHSS be required to include the functionality of a TPRD, shut-off valve, and check valve. These functions are required for the reasons stated above. However, NHTSA is aware of CNG vehicles that do not include check valves as part of their CNG storage system. In such CNG vehicles, the check valves are installed upstream between the fueling port and the CNG container, with additional valves to contain high pressure gas. NHTSA seeks comment on whether the check valves should be required as part of the CHSS. The CHSS would be required to have an NWP of 70 MPa or less. This is because working pressures above 70 MPa are currently considered impractical and may pose a safety risk given current known technologies. The energy density of hydrogen does not increase significantly when pressurized above 70 MPa, so there is no significant improvement in hydrogen storage efficiency at pressures above 70 MPa. Pressures above 70 MPa, however, may present a greater safety hazard. As a result, NHTSA proposes that all CHSS must have an NWP less than or equal to 70 MPa. NHTSA seeks comment on this requirement, and specifically asks commenters to identify any technologies that can safely store hydrogen at pressures above 70 MPa. GTR No. 13 provided contracting parties with the discretion to require that the closure devices be mounted directly on or within each container. The relevant safety concern is that the high-pressure lines required to connect remotely-located closure devices with the container could be susceptible to damage or leak. However, the definition of a container is sufficiently broad that it includes such lines as part of the container. These lines will be considered part of the permanently interconnected chambers storing the continuous volume of hydrogen. Thus, any lines connecting to closure devices are themselves part of the container and will be included in the extensive container performance testing discussed below. If a container (which includes any lines connecting to closure devices) can successfully complete the performance testing in FMVSS No. 308, then the risk of failure of the lines has been addressed. Therefore, NHTSA tentatively concludes that it is not necessary to specify that closure devices be mounted directly on or within each container. NHTSA is also concerned that such a specification would be design restrictive. NHTSA is aware of CNG fuel systems where the closure devices are neither on nor within each container, and there have been no reported safety issues with such systems. Therefore, NHTSA is not proposing to include a requirement for closure devices to be on or within each container, and would instead leave the location of closure devices to manufacturer discretion. NHTSA seeks comment on requiring closure devices to be mounted directly on or within each container. 3. Performance Requirements for the CHSS The CHSS would be required to meet specific performance requirements when subjected to the performance tests listed below. The performance tests and the respective performance requirements are discussed in detail in subsequent sections: • Tests for baseline metrics • Test for performance durability • Test for expected on-road performance • Test for service terminating performance in fire • Tests for performance durability of closure devices Several of these tests utilize a manufacturer-supplied value known as BP O . A container's BP O is a design parameter specified by the manufacturer to establish the expected initial burst pressure of the container. It is NHTSA's understanding that BP O , associated with median or midpoint burst pressure for a batch of containers, can vary between batches of containers. Therefore, in order to facilitate compliance testing, NHTSA is proposing that manufacturers specify the BP O associated with each container on the required container label (discussed below). NHTSA seeks comment on this labeling requirement, noting that it is not required by GTR No. 13. 4. Tests for Baseline Metrics The container must be able to withstand high pressurization, as well as pressure cycling, which is a repeated pressurization and depressurization. Both of these stress factors occur during the service life of the vehicle as its fuel system is repeatedly depleted and refilled. Consistent with GTR No. 13, the proposed tests for baseline metrics would include two tests for the container: the baseline initial burst pressure test to evaluate resistance to burst at high pressure, and the baseline initial pressure cycle test to ensure the container is designed to leak before burst 44 and to evaluate its ability to withstand pressure cycling without burst and without leakage within its service life. 44 Leak before burst design of high pressure containers is a common safety feature to ensure a leak will develop before a catastrophic burst will occur. A leak is a less severe failure mode compared to a catastrophic burst of the high pressure container. During the initial burst pressure test, the container must demonstrate that as the pressure is increased inside the container, the point of failure is above a minimum pressure level, discussed below. In other words, the container must demonstrate a minimum burst pressure. Burst pressure is defined as the highest pressure reached inside a container during a burst test which results in structural failure of the container and resultant fluid loss through the container, not including gaskets or seals. Burst pressure is determined by the baseline initial burst pressure test discussed below. During the baseline initial pressure cycle test, the container must withstand pressure cycling that simulates repeated fueling and defueling by increasing the pressure inside the container to a high pressure level, then depressurizing it to low pressure, and repeating that process for a set number of cycles. The container must neither leak nor burst during an initial set of pressure cycles, and must not burst during a set number of pressure cycles beyond the initial set. These requirements are evaluated by the baseline pressure cycle life test discussed below. The physical forces on the load-bearing components of a container are the same regardless of whether the pressure is being applied with hydraulic fluid, hydrogen gas, or any other medium. Therefore, for practicability and safety purposes both tests would be conducted using hydraulic fluid to exert pressure inside the container. 45 Hydraulic fluids, such as water or water with additives, are advantageous for these tests because they reduce the explosion risk associated with pneumatic pressurization. The explosion risk from pneumatic pressurization is high because compression of gas stores pressure-volume energy (PV energy), whereas during hydraulic pressurization with an incompressible fluid, PV energy is negligible. In addition, the incompressible nature of hydraulic fluids means that pressure cycles can be accomplished much faster than pneumatic pressurization cycles. This is important given the high number of cycles required for the baseline pressure cycle test. The use of hydrogen gas pneumatic pressure cycling does introduce stress factors beyond basic pressurization/depressurization, as discussed later, and these are addressed separately in the test for expected on-road performance. Given that hydraulic pressure cycling provides these benefits without compromising the safety or stringency of the proposed standards, hydraulic pressure cycling is used for these tests. 45 This is consistent with GTR No. 13. a. Baseline Initial Burst Pressure The baseline initial burst pressure test verifies that the initial burst pressure of a container is both above a minimum specified pressure level and is within 10 percent of the manufacturer specified BP O . The requirement that the container tested must have a burst pressure within ±10 percent of BP O is based on the need to control variability in container production. If a manufacturing process produces containers with highly variable initial burst pressures, there is a possibility of a container with a dangerously low burst pressure. NHTSA seeks comment on the safety need for specifying a limit on burst pressure variability in a batch and whether the 10 percent limit is appropriate; if commenters believe another limit is appropriate, they are asked to provide supporting data. The minimum burst pressure, BP min , in GTR No. 13 Phase 1 was set at 225 percent of NWP for carbon fiber composite containers, and 350 percent NWP for glass fiber composite containers. The value for carbon fiber composite containers was chosen to be a conservative starting point based on experience from CNG vehicles. GTR No. 13 Phase 1 made clear that the burst pressure requirement would be reviewed in Phase 2. The IWG of GTR No. 13 Phase 2 did review data on variability in initial burst pressure and end-of-life burst pressure ( i.e., burst pressure after the test for performance durability, discussed in a later section), and determined that variation in burst pressure is actually low and that a minimum initial burst pressure of 200 percent NWP was appropriate for carbon fiber composite containers. 46 The GTR No. 13 Phase 2 IWG assessment also noted that manufacturers generally design containers to have burst pressures well above the required minimum burst pressure, to ensure that a container can meet the performance requirements of the test for performance durability. These findings suggest it is possible to lower the minimum burst pressure requirement to 200 percent of NWP without reducing safety, because manufacturers will generally be outperforming this requirement anyway. 46 A study was conducted by the Japanese Automobile Research Institute which evaluated the variability of containers' initial burst pressure, as well as the variability in end-of-life burst pressure. The study concluded that variability among the containers was low, and therefore a minimum initial burst pressure of 200 percent NWP was acceptable and most consistent with the end-of-life burst pressure requirement. See GTR No. 13 Phase 2 file GTR13-3-03: https://wiki.unece.org/download/attachments/58525915/GTR13-3-03%20Initial%20burst%20pressure%20requirement%20_3rd%20GTR13%20IWG_June2018.pdf?api=v2. Furthermore, a 200 percent minimum initial burst pressure can be supported when coupled with the following requirements from the proposed test for performance durability (which are discussed in the following section): 47 47 The tests conducted by the Japanese Automobile Research Institute showed that containers with burst pressure which met the BP O ±10 percent requirement and subjected to the durability sequential tests, were able to withstand the end-of-life 180 percent NWP for four minutes and have an end-of-life burst pressure within −20 percent of BP O , even if the minimum initial burst pressure is reduced to 200 percent NWP. • The container must withstand 180 percent NWP for 4 minutes at the end of the test for performance durability. • The minimum burst pressure after the completion of the test for performance durability cannot be lower than 80 percent of BP O . In light of the variability in the minimum burst pressure and the need to meet the above two requirements at the end of the test for performance durability, NHTSA expects that manufacturers will ultimately design the container with an initial burst pressure well above 200 percent NWP. Accordingly, NHTSA believes that proposing BP min to 200 percent NWP, as set forth in GTR No. 13 Phase 2, meets the need for safety. Proposing the BP min to 200 percent NWP facilitates hydrogen vehicle development without unnecessary overdesign of components. NHTSA seeks comment on the proposed BP min of 200 percent NWP instead of the 225 percent NWP specified in GTR No. 13 Phase 1. In the case of containers having glass-fiber as a primary constituent, consistent with GTR No. 13 Phase 2, NHTSA is proposing a higher BP min of 350 percent of NWP because these containers are highly susceptible to stress rupture as compared to carbon fiber containers. Stress rupture is a failure mode that relates to the intrinsic failure probability of the individual fibers that overwrap the container for support. This failure mode can occur when the fibers are held under stress for long periods of time (such as in a continuously pressurized container). 48 The higher BP min of 350 percent of NWP provides protection from the risk of stress rupture in containers having glass-fiber composite as a primary constituent. NHTSA seeks comment on this proposed requirement and how NHTSA can determine if a container has glass-fiber as a primary constituent. NHTSA seeks comment on appropriate criteria to determine the primary constituent in this context. 48 SAE Paper 2009-01-0012. Rationale for Performance-based Validation Testing of Compressed Hydrogen Storage by Christine S. Sloane, available at https://www.sae.org/publications/technical-papers/content/2009-01-0012/. In the case of containers constructed of both glass and carbon fibers, NHTSA proposes to apply the requirements according to the primary constituent of the container as specified by the manufacturer. NHTSA proposes that the manufacturer shall specify upon request, in writing, and within five business days, the primary constituent of the container. NHTSA proposes that the burst pressure of the container, for which the manufacturer fails to specify upon request, in writing, and within five business days, the primary constituent of the container, must not be less than 350 percent of NWP. NHTSA seeks comment on this proposed requirement. The test for performance durability, described below, includes a 1000 hour high-temperature (85 °C) static pressure test, which is designed to evaluate the container's resistance to stress rupture, in combination with other lifetime stress factors. Given that the high-temperature static pressure test is focused directly on evaluating stress rupture risk, and the test for performance durability represents an overall worst-case lifetime of stress factors, regardless of fiber type, NHTSA seeks comment on whether the baseline initial burst pressure test even needs to be included in the standard's requirements. GTR No. 13 specifies that the baseline initial burst pressure test (as well as the initial pressure cycle test described below) be conducted at ambient temperatures between 5 °C and 35 °C. The IWG of GTR No. 13 determined that container burst strength is not affected by using this range of ambient temperature between 5 °C and 35 °C. 49 This temperature range reduces test costs (thus improving the practicability of the proposed requirements) by enabling outdoor testing without special temperature controls. Extreme temperatures are addressed in later tests. 49 See GTR No. 13, Part I, paragraph 81(d)(v). GTR No. 13 requires that the rate of pressurization be less than or equal to 1.4 MPa/s for pressures higher than 150 percent of the nominal working pressure. If the pressurization rate exceeds 0.35 MPa/s at pressures higher than 150 percent NWP, GTR No. 13 also requires that either the container is placed in series between the pressure source and the pressure measurement device, or that the time at the pressure above a target burst pressure exceeds 5 seconds. These requirements are designed to ensure that a pressure sensor will measure the pressure inside the container accurately. The pressurization rate limit ensures the pressure sensor will have enough time to read the pressure level as it rises. Placing the container in series between the pressure source and the pressure sensor ensures that the container will experience the pressure before the sensor, so there is no chance that the pressure sensor could read a pressure level that is not being experienced by the container. However, NHTSA is concerned that the second option that the time at the pressure above the target burst pressure exceeds 5 seconds is unclear and difficult to enforce. For example, it is not clear what pressure the “target burst pressure” is referring to since the pressure may be increasing continuously. Therefore, this option is not being proposed as an alternative and the container will simply be placed in series between the pressure source and the pressure measurement device. NHTSA seeks comment on this decision. b. Service Life and Number of Cycles for the Baseline Initial Pressure Cycle Test for Containers on Light and Heavy Vehicles As discussed above, hydrogen is highly flammable, and therefore, hydrogen containers must not leak during their service life. While hydrogen leakage is a serious safety concern, leaking hydrogen will likely dissipate quickly into the atmosphere given its density, and may or may not ignite/explode, whereas, a hydrogen container burst involves an explosion by definition and is therefore a far worse, catastrophic failure mode that must be prevented under all circumstances regardless of service life. As a result, hydrogen containers are designed to leak before bursting beyond their service lives. This “leak before burst” safety feature is also followed for other high-pressure vehicle fuel containers such as vehicle CNG fuel containers. Systems are typically designed such that the occurrence of leakage should result in vehicle shut down and subsequent repair or removal of the container from service, thereby preventing a burst of the container from occurring. The baseline pressure cycle test requirement is designed to provide an initial check for resistance to leak or burst due to pressure cycling during service, and a check that the container does in fact leak before burst after the container service life has been exceeded. Accordingly, the baseline initial pressure cycle test requires the container to (i) not leak or burst for a specified number of pressure cycles that are meant to represent maximum container service life, and (ii) leak before burst for a specified number of pressure cycles beyond the maximum service life. In the case of (i), the IWG of GTR No. 13 Phase 1 gave contracting parties the option of selecting either 5,500, 7,500, or 11,000 cycles as the expected maximum service life containers. In the case of (ii), the GTR explains that a greater number of pressure cycles (22,000) that far exceeds service life of containers is used to ensure that a container should leak before bursting during the expected service life. GTR No. 13 provides several examples of the maximum number of empty-to-full fueling cycles for vehicles under extreme service. These examples are described below and summarized in Table-1. • Sierra Research Report No. SR2004-09-04 for the California Air Resource Board (2004) reported on vehicle lifetime distance traveled by scrapped California vehicles, which all showed lifetime distances traveled below 350,000 miles. Based on these figures and 200-300 miles driven per full fueling, the maximum number of lifetime empty-to-full fuelings can be estimated as 1,200-1,800. • Transport Canada reported that required emissions testing in British Columbia, Canada, in 2009 showed the five most extreme usage vehicles had odometer readings in the 500,000-600,000 miles range. Using the reported model year for each of these vehicles, this corresponds to less than 300 full fuelings per year, or less than one full fueling per day. Based on these figures and 200-300 miles driven per full fueling, the maximum number of empty-to-full fuelings can be estimated as 1,650-3,100. • The New York City (NYC) taxicab fact book reports extreme usage of 200 miles in a shift and a maximum service life of five years. 50 Less than 10 percent of vehicles remain in service as long as five years. The average mileage per year is 72,000 for vehicles operating two shifts per day and seven days per week. There is no record of any vehicle remaining in high usage through-out the full 5-year service life. However, if a vehicle were projected to have fueled as often as 1.5-2 times per day and to have remained in service for the maximum 5-year NYC taxi service life, the maximum number of fuelings during the taxi service life would be 2,750-3,600. 50 New York City taxicab fact book, Schaller Consulting (2006), http://www.schallerconsult.com/taxi/taxifb.pdf. • Transport Canada reported a survey of taxis operating in Toronto and Ottawa that showed common high usage of 20 hours per day, seven days per week with daily driving distances of 335-450 miles. Vehicle odometer readings were not reported. In the extreme worst-case, it might be projected that if a vehicle could remain at this high level of usage for seven years (the maximum reported taxi service life); then a maximum extreme driving distance of 870,000-1,200,000 miles is projected. Based on 200-300 miles driven per full fueling, the projected full-usage 15-year number of full fuelings could be 2,900-6,000. Table 1—Expected Vehicle Usage Data Summary Data source Lifetime traveling distance (miles) Distance per full-fueling (mile) Number of lifetime empty-to-full filling Sierra Research Report No. SR2004-09-04: California vehicles 350,000 200-300 1,200-1,800. Transport Canada: Vehicle fleet &Taxi 500,000-600,000 200-300 1,650-3,100. The New York City (NYC) taxicab fact book: Taxi usage 360,000 (5 year life) N/A (Fueling frequency 1.5-2 times/day) 2750-3600 (5 year life). Transport Canada: Taxi usage 870,000-1,200,000 200-300 2,900-6,000. Based on these examples, the IWG of GTR No. 13 Phase 1 set the minimum number of pressure cycles before leak at 5,500. The maximum number of cycles before leak was set at 11,000 cycles, which corresponds to a vehicle that remains in service with two full fuelings per day for 15 years (expected lifetime vehicle mileage of 2.2-3.3 million miles). The last example above shows it is possible for a high usage taxi to experience 6,000 fueling cycles during seven years of service. Taxi service is representative of the most demanding circumstances a light vehicle will experience, so this example is considered worst-case. Furthermore, such a vehicle could be subsequently resold and experience further fuelings beyond 6,000. As a result, the IWG of GTR No. 13 Phase 2 concluded that the choice of 5,500 cycles is not sufficient for containers on light vehicles. However, NHTSA concludes that the maximum choice of 11,000 cycles is too extreme for light vehicles. A vehicle traveling 2.2-3.3 million miles is unrealistic even for the most extreme service life for light vehicles. Accordingly, NHTSA proposes 7,500 as the number of cycles in the baseline initial pressure cycle test for which the container does not leak or burst. NHTSA believes that 7,500 pressure cycles is a reasonable representation of the maximum service life of a container, and notes that is greater than that presented in Table 1 for the Transport Canada taxi usage data. As discussed above, the worst-case scenario is a container failure by burst. To ensure the container leaks before burst beyond the maximum service life, the container is pressure cycled beyond the 7,500 cycles (representing maximum service life) until leak occurs without burst or up to a maximum of 22,000 hydraulic pressure cycles. For vehicles with nominal on-road driving range of 300 miles per full-fueling, 22,000 hydraulic pressure cycles correspond to over 6 million miles, which is beyond extreme on-road vehicle lifetime range. The analysis summarized above considered light vehicles with a service life of 15 years. When conducting their analysis, the IWG of GTR No. 13 Phase 1 had limited information available on lifetime vehicle mileage and fuelings. In addition, hydrogen vehicles were a new technology and there was very little field experience available to draw upon. As a result, the IWG of GTR No. 13 Phase 1 was conservative in setting the number of cycles for the baseline initial cycle test. In the analysis provided above, short periods of extreme service were extrapolated to a full 15-year service life. This is not a realistic assumption because vehicles generally cannot last in extreme service for a full 15 years. To address this issue, the IWG of GTR No. 13 Phase 2 reviewed new data on the number of vehicle miles traveled. The analysis was also expanded to include heavy vehicles in addition to light vehicles. 51 52 The data shows that the number of cycles presented in GTR No. 13 for light vehicles correspond more appropriately to a 25-year service life. 51 See GTR No. 13 Phase 2 file GTR13-11-12b: The number of cycles, https://wiki.unece.org/download/attachments/123666576/GTR13-9-07%20TF1%20OICA%20GTR13%20Baseline%20Initial%20Cycles.pdf?api=v2 . 52 See GTR No. 13 Phase 2 file GTR13-9-07: Extension of the service life of the container to 25 years, https://wiki.unece.org/download/attachments/140706658/GTR13-11-12b%20TF1%20%20210927%20Estimation%20of%20VMT%20TF1-JAMA.pdf?api=v2 . For heavy vehicles, the new data on the number of vehicle miles traveled that was collected in Phase 2 indicates a higher number of cycles are required for a 25-year service life than that for light vehicles. This is consistent with the fact that heavy vehicles typically travel farther and remain in service longer than light vehicles. Consequently, for heavy vehicle containers, the IWG of GTR No. 13 Phase 2 set the number of pressure cycles representing maximum container service life at 11,000. In accordance with GTR No. 13 Phase 2, NHTSA proposes to require heavy vehicle containers to neither leak nor burst for 11,000 hydraulic pressure cycles, and also to leak without burst (or neither leak nor burst) beyond the 11,000 hydraulic pressure cycles up to a maximum of 22,000 pressure cycles. The proposed service life, number of hydraulic pressure cycles representing the maximum service life for which the container is required not to leak nor burst, and the number of pressure cycles beyond that representing maximum service life of the container for which the container is required to leak without burst or not leak nor burst at all is summarized in Table-2 for light and heavy vehicles. Table 2—Proposed Service Life and Number of Cycles in the Baseline Hydraulic Pressure Cycle Test for Light and Heavy Vehicles Vehicle type Service life (years) Number of cycles representing maximum service life for which the container does not leak nor burst Number 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 seeks comment on the proposed number of cycles in Table-2. NHTSA seeks any additional data available related to vehicle life, lifetime miles travelled, and number of lifetime fuel cycles. c. Details of the Baseline Initial Cycle Test for Containers on Light and Heavy Vehicles The low pressure during each cycle has been set at between 1 MPa to 2 MPa. This is selected to make the test easy to conduct. NHTSA seeks comment whether this low-pressure range is sufficiently wide for test lab efficiency. The high pressure of 125 percent NWP is selected because this is the peak pressure that typically occurs during fueling. Furthermore, this is the high pressure used in the ANSI NGV 2-2007, Compressed Natural Gas Vehicle Fuel Containers, ambient cycling test. 53 53 ANSI NGV 2-2007, Compressed Natural Gas Vehicle Fuel Containers, 16.3 Ambient Cycling Test. https://webstore.ansi.org/standards/csa/ansingv22007 . GTR No. 13 requires three new containers to be tested during the baseline initial pressure cycle test. However, NHTSA does not believe three new containers need to be tested under the U.S. self-certification system where NHTSA buys and tests vehicles and equipment at the point of sale. Therefore, NHTSA has instead decided to base the value on the results of testing any one container for the baseline initial pressure cycle test. NHTSA seeks comment on this decision. 54 Id. GTR No. 13's maximum hydraulic pressure cycle rate of 10 cycles/minute is based on the requirement in ANSI NGV 2-2007 for the ambient cycling test. 54 This pressure cycling rate is selected to allow for efficient compliance testing. Actual fueling cycles for hydrogen vehicles occur more slowly. For these reasons, the container manufacturer may specify a hydraulic pressure cycle profile that will prevent premature failure of the container due to test conditions outside of the container design envelope. Changing the hydraulic cycling profile does not change the stringency of the test or the safety of the container. However, the cycling profile can be important because testing NHTSA conducted resulted in a container failure attributed to a rapid defueling profile that was not representative of defueling rates during normal use. 55 56 NHTSA seeks comment on cycling profiles and whether the pressure cycling profile will significantly affect the test result. NHTSA seeks comment on more specifics of what manufacturers should be allowed to specify regarding an appropriate pressure cycling profile for testing their system. 55 DOT HS_812_988. Hydrogen Container Performance Testing, https://rosap.ntl.bts.gov/view/dot/62645. 56 Details are provided in the technical document “Quantum GTR Pressure Cycle Discussion.pdf” submitted to the docket of this NPRM. A burst may be preceded by an instantaneous moment of leakage, especially if observed in slow motion. Therefore, NHTSA proposes a minimum time of 3 minutes to sustain a visible leak before the test can end successfully due to “leak before burst.” NHTSA seeks comment on this additional requirement. 5. Test for Performance Durability The container must withstand stress factors beyond basic pressurization and pressure cycling without leakage or burst. The container must demonstrate its durability by not leaking or bursting during a service life of pressure cycling that includes the application of external stress factors. The container must also withstand 180 percent NWP for four minutes 57 after the application of all the external stress factors and have a burst pressure that is at least 80 percent of its BP O at the end of a service life that includes external stress factors. This requirement is evaluated by the test for performance durability. The test for performance durability uses the same service life described above for the tests for baseline metrics, along with external stress factors applied to the container. 57 The 180 percent NWP hold for 4 minutes is a simulation of a fueling station pressure regulation failure that results in over pressurization of the container. This test is conducted after all other external stresses have been applied to the container to simulate over-pressurization near the end-of-life of the container. A container is expected to encounter six types of external stress factors: 1. Impact (drop during installation and/or road wear) 2. Static high pressure from long-term parking 3. Over-pressurization from fueling and fueling station malfunction 4. Environmental exposures (chemicals and temperature/humidity) 5. Vehicle fire 6. Vehicle crash The test for performance durability addresses the first four of these external stresses. Fire is addressed in a separate section for fire. Crash performance is addressed through crash testing in FMVSS No. 307. The test for performance durability is closely consistent with the industry standard SAE J2579_201806, Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. 58 58 SAE J2579_201806. Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. https://www.sae.org/standards/content/j2579_201806/ Other than fire and vehicle crash, testing of the stresses compounded in a series is required. 59 This is because a container may experience all of these stresses during its service life, and the safety need for a hydrogen system remains an issue for the vehicle's entire service life. For example, a container that was dropped during installation could thereafter be exposed to road wear, long term parking, fueling stresses, and environmental exposures. Accordingly, the proposed test for performance durability arranges these external stresses in a sequential application representing a severe in-service permutation of the stresses. The test sequence is as follows: 59 This is in contrast to industry standards, wherein performance is evaluated after the application of a single stress factor in order to identify which stress factors cause failure. • Proof pressure test • Drop test • Surface damage test • Chemical exposure test and ambient-temperature pressure cycling test • High temperature static pressure test • Extreme temperature pressure cycling test • Residual pressure test • Residual strength burst test The test for performance durability is illustrated in Figure-4. EP17AP24.003 Figure-4: Illustration of the Test for Performance Durability For similar reasons as those explained above for the baseline tests, the cycling pressure force on containers is applied hydraulically with non-corrosive fluid such as water or a mixture of anti-freeze and water to prevent freezing. This allows for improved test lab safety and faster pressurization and depressurization rates which decreases the cost to conduct the tests. a. Proof Pressure Test The proof pressure test is typically done by the manufacturer before sale of the container. The proof pressure test is performed to confirm that the container will not leak nor burst due to a simple over-pressurization event to 150 percent NWP. The test pressure of 150 percent NWP is selected because fueling stations are expected to provide over-pressure protection of 150 percent NWP. A proof pressure test is a stress factor that can in some cases result in micro-cracks appearing in the container. Micro-cracks may weaken a tank's wall strength, causing the potential for leaks or a burst during the proof pressure test or the subsequent performance durability testing. Therefore, it is important that all containers experience proof pressure. GTR No. 13 states that a container that has undergone a proof pressure test in manufacture is exempt from this test. However, NHTSA may not know whether a container has undergone the proof pressure test. As a result, NHTSA proposes that all containers will be subjected to the proof pressure test as part of the test for performance durability. In the event that a proof pressure test is conducted during manufacture and as part of the tests for performance durability, the container would experience two proof pressure tests. However, it is not expected that a second application will result in significantly more stress to the container than a single proof pressure test. NHTSA seeks comment on conducting the proof pressure test on all containers. b. Drop Test The drop test is conducted to simulate dropping the container during handling or installation. Consistent with GTR No. 13, the unpressurized container may be dropped in any one of several orientations such as horizontal, vertical, or at a 45° angle. In the case of a non-cylindrical or asymmetric container, the horizontal and vertical axes may not be clear. In such cases, the container will be oriented using its center of gravity and the center of any of its shut-off valve interface locations. The two points will be aligned horizontally ( i.e., perpendicular to gravity), vertically ( i.e., parallel to gravity) or at a 45° angle relative to vertical. The center of gravity of an asymmetric container may not be easily identifiable, so NHTSA seeks comment on the appropriateness of using the center of gravity as a reference point for this compliance test and how to properly determine the center of gravity for a highly asymmetric container. The surface onto which the container is dropped must be a smooth, horizontal, uniform, dry, concrete pad or other flooring type with equivalent hardness. The drop height of 1.8 meters is selected to represent a drop from a forklift during installation. The four possible drop orientations are illustrated in Figure-5 below. EP17AP24.004 Figure-5: The Four Possible Drop Orientations GTR No. 13 specifies a potential energy of at least 488 J during the vertical drops, along with a maximum drop height of 1.8 m, and a minimum drop height of 0.1 m. It is possible that a drop involving a very lightweight container could not simultaneously satisfy both the 488 J minimum energy and the 1.8 m maximum height. The IWG of GTR No. 13 Phase 2 resolved this conflict by specifying the vertical drop test potential energy of at least 488 J, with an overriding limitation that the drop height not exceed 1.8 m in any case. In the case of a lightweight container that would require a drop height over 1.8 m to reach 488 J of drop energy, the container should be dropped from 1.8 m, regardless of the potential energy. Similarly, a very heavy container could reach a potential energy 60 of 488 J while being less than 0.1 m above the drop surface. In this case, the container should be dropped from the 0.1 m minimum drop height. 60 Potential energy is calculated as the product of container mass, gravitational acceleration, and the height from the center of gravity of the container to the surface onto which the container is dropped. For the angled drop, the container is dropped from any angle between 40° and 50° from the vertical orientation with the center of any shut-off valve interface location downward. However, if the lowest point of the container is closer to the ground than 0.6 m, the drop angle is changed such that the lowest point of the container is 0.6 m above the ground and the center of gravity is 1.8 m above the surface onto which it is dropped. This may result in a drop angle greater than 50° from the vertical orientation. The drop test is conducted with an unpressurized container because the risk of dropping is primarily aftermarket during vehicle repair where a new storage system, or an older system removed during vehicle service, is dropped from a forklift during handling. Additionally, drop testing conducted by NHTSA under various conditions indicated that an unpressurized container is more susceptible to damage in the drop test than a pressurized container. 61 61 DOT HS_812_988. Hydrogen Container Performance Testing, https://rosap.ntl.bts.gov/view/dot/62645. The drop test is a test in which container attachments may improve performance by protecting the container when it impacts the ground. Consistent with GTR No. 13, the drop test is conducted on the container with any associated container attachments. NHTSA seeks comment on including container attachments for the drop test. It is possible that the container could experience damage from the drop test that prevents continuing with the remainder of the tests for performance durability. To address this possibility, NHTSA proposes that if any damage to the container following the drop test prevents further testing of the container, the container is considered to have failed the tests for performance durability and no further testing is conducted. c. Surface Damage Test The surface damage test applies cuts and impacts to the surface of the container. The cuts on the surface simulate abrasions that can occur due to container mounting hardware or straps. The impacts simulate on-road impacts, such as flying gravel. The surface damage test consists of two linear cuts and five pendulum impacts. The linear cuts are created with a saw. The first cut is 0.75 millimeters to 1.25 millimeters deep and 200 to 205 millimeters long. The second cut is 1.25 millimeters to 1.75 millimeters deep and 25 millimeters to 28 millimeters long. The second cut is only applied if the container is to be affixed to the vehicle by compressing its composite surface. GTR No. 13 allowed all-metal containers to be exempt from the linear cuts because (1) metal is scratch resistant compared to non-metal, and (2) metal containers can be so thin that the cuts would fully penetrate the container. NHTSA's proposal includes this exemption, but NHTSA seeks comment on whether another objective and practicable procedure exists for evaluating surface abrasions that could apply to all containers, such as, for example, the application of a defined cutting force to the container surface. The impacts are created with a pendulum impactor consisting of a pyramid with equilateral faces and square base, and with the summit and edges being rounded to a radius of 3 mm. The impact of the pendulum occurs with a nominal impact energy of 30 J. Prior to the impacts, the container is preconditioned at −40 °C to simulate a worst-case temperature environment. The temperature of −40 °C was selected based on industry standards. 62 We note that weather records show temperatures of −40 °C can occur in northern locations of the United States. 63 62 SAE J2579_201806. Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. 63 Canadian Climate Normals, https://climate.weather.gc.ca/climate_normals/index_e.html . The surface damage test is a test in which container attachments may improve performance by shielding the container from the impacts. For containers with container attachments, GTR No. 13 specifies that if the container surface is accessible, then the test is conducted on the container surface. However, NHTSA is concerned that determining whether the container surface is accessible is subjective, because “accessible” is not defined in the GTR and could have many potential meanings. Therefore, NHTSA is not proposing a specification involving the accessibility of the container surface. Instead, NHTSA proposes that if the container attachments can be removed using a process specified by the manufacturer, they will be removed and not included for the surface damage test nor for the remaining portions of the test for performance durability. Testing the container without its container attachments is representative of a situation in which installation personnel remove the container attachments and fail to re-install them before the container enters service. Container attachments that cannot be removed are included for the test. NHTSA seeks comment on including container attachments for the surface damage test. In accordance with GTR No. 13, NHTSA proposes specifying the pendulum impacts “on the side opposite from the saw cuts.” For containers with multiple permanently interconnected chambers, GTR No. 13 specifies applying the pendulum impacts to a different chamber to that where the saw cuts were made. However, the agency is not proposing this distinction for pendulum impact location for containers with multiple permanently interconnected chambers because NHTSA is concerned that it may be less stringent (and thus, potentially less protective of safety) than when impacts are to the same chamber where the cuts were applied. NHTSA seeks comment on whether applying the impacts to the opposite side of the same chamber that received the saw cuts may be more stringent than applying the impacts to a separate chamber, and whether including the specification as written in GTR No. 13 would reduce stringency for containers with multiple permanently interconnected chambers relative to containers with a single chamber. d. Chemical Exposure and Ambient Pressure Cycling Test Consistent with GTR No. 13, the chemical exposure test exposes the container to a range of chemicals that might be encountered in on-road service: • Sulfuric acid at 19 percent in water to simulate battery acid. • Sodium hydroxide at 25 percent in water to simulate lye. • Methanol at 5 percent in gasoline to simulate fueling station fluids. • Ammonium nitrate at 28 percent in water to simulate fertilizer. • Methanol at 50 percent in water to simulate windshield-washer fluid. A pad of glass wool saturated with one of the chemicals listed above is applied to each of the pendulum impact locations from the surface damage test. This is done to simulate each chemical exposure in an area where on-road damage has degraded the container's protective coating. The chemicals are applied with glass wool fibers to keep them in place and reduce evaporation. After the chemical exposures are in place, pressure cycling commences. The test for performance durability uses the same number of cycles as required by the baseline initial cycle test before leakage. This is a total of 7,500 cycles for light vehicles or 11,000 cycles for heavy vehicles. Of the total cycles, 60 percent are conducted with the chemical exposures in place, and at ambient temperature (5 °C to 35 °C). All but the final 10 of these chemical exposure cycles are conducted from low pressure of 2 MPa to high pressure of 125 percent NWP, as in the baseline initial pressure cycle test. These cycles simulate extended vehicle use after impact damage and exposure to chemicals. The final 10 chemical exposure cycles are conducted to a high pressure of 150 percent NWP to simulate fueling station over-pressurization. After completing chemical exposure cycles, the chemical exposure pads are removed, and the exposed areas are washed with water to remove excess chemicals. The chemical exposure test is a test in which container attachments may improve performance by shielding the container from the chemical exposures. Container attachments will be included in the chemical exposure test unless they were removed prior to the surface damage test. NHTSA seeks comment on including container attachments for the chemical exposure test. e. High Temperature Static Pressure Test Consistent with GTR No. 13, the high temperature static pressure test involves holding the container for 1000 hours at 85 °C and 125 percent NWP. This test simulates an extended exposure to high static pressure and temperature, which is a condition that could occur in the case of a vehicle parked for an extended period of time. The primary risk associated with prolonged parking at high pressure and temperature is stress rupture. However, the stress rupture condition cannot be directly replicated because the relevant time period is years to decades. Alternatively, experimental data on the tensile stress failure of strands representative of those used in container composite wrapping showed that: 64 65 64 SAE Paper 2009-01-0012. Rationale for Performance-based Validation Testing of Compressed Hydrogen Storage by Christine S. Sloane. 65 Christine S. Sloane, Hydrogen Storage technology—Materials and Applications, edited by Lennie Klebanoff, Section III-12 with Figure 12.6 Glass fiber composite strands. • For the glass fiber composite strands, the probability of failure for 25 years under tensile stress of 100 percent NWP is equivalent to 1000 hours under a tensile stress of 125 percent NWP. • The time to failure increased when the load was reduced. • Carbon fiber composite strands showed greater resistance to stress rupture than glass fiber composite strands in that a small reduction in the applied load resulted in a greater increase in time to failure for the carbon fiber composite strands than for the glass fiber composite strands. • For carbon fiber composite strands, the probability of failure for 25 years under tensile stress of 100 percent NWP is approximately equivalent to 500 hours under tensile stress of 125 percent NWP. An elevated temperature of 85 °C is applied to account for heat-accelerated deterioration. The temperature of 85 °C represents an extreme under-hood temperature for a dark/black-colored vehicle parked outside on asphalt in direct sunlight in 50 °C ambient conditions. 66 Including the extreme temperature condition of 85 °C in the high temperature static pressure test ensures that the container can sustain exposure to 85 °C for 1000 hours under tensile stress of 125 NWP without experiencing stress rupture. 66 SAE J2579_201806. Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. f. Extreme Temperature Pressure Cycling Test Consistent with GTR No. 13, the extreme temperature pressure cycling test involves pressure cycling at extreme temperatures and simulates operation (fueling and defueling) in extreme temperature conditions. As mentioned above, the test for performance durability uses the same number of cycles as required by the baseline initial cycle test before leakage. This is a total of 7,500 cycles for light vehicles or 11,000 cycles for heavy vehicles. The extreme temperature pressure cycling test consists of 40 percent of these total cycles, of which half (20 percent of the total) are conducted at −40 °C and the other half are conducted at 85 °C. The cold temperature −40 °C is selected to simulate a worst-case extreme cold environment as explained above for the surface damage test, and the hot temperature of 85 °C is selected for the same reasons discussed above for the high temperature static pressure test. During the cold pressure cycling, the maximum cycling pressure is only 80 percent NWP. This is because fueling pressures do not reach 100 percent NWP when fueling in extreme cold because as temperature decreases, pressure also decreases. During the hot pressure cycling, the maximum cycling pressure is 125 percent NWP for the reasons discussed above for the baseline initial pressure cycle test. During the extreme temperature pressure cycling test, the relative humidity is maintained above 80 percent to represent high humidity that may foreseeably be encountered in the U.S. Humidity is known to degrade some materials due to the presence of moisture in humid air. Therefore, it is important to include the stress factor of humidity in the test for performance durability. g. Residual Pressure Test Consistent with GTR No. 3, the residual pressure test requires pressurizing the container to 180 percent NWP and holding this pressure for 4 minutes. The 180 percent NWP hold for 4 minutes is a simulation of a fueling station pressure regulation failure that results in over-pressurization of the container. This test is conducted after all other external stresses have been applied to the container to simulate over-pressurization near the end of life of the container. 67 68 67 SAE J2579_201806. Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. Appendix H. 68 Christine S. Sloane, Hydrogen Storage technology—Materials and Applications, edited by Lennie Klebanoff, Section III-12 with Figure 12.6 Glass fiber composite strands. h. Residual Strength Burst Test Consistent with GTR No. 13, the residual strength burst test involves subjecting the end-of-life container to a burst test identical to the baseline initial burst pressure test. The burst pressure at the end of the durability test is required to be at least 80 percent of the BP O specified on the container label. This effectively controls the burst pressure degradation rate throughout an extreme service life. Controlling degradation rate is important because, for example, a container starting with a very high BP O , say 400 percent NWP, but then declining to 180 percent NWP indicates a high degradation rate. NHTSA is concerned that if such a container were to be kept in service beyond its intended service life, the high degradation rate could continue and lead to a high risk of burst. Therefore, the residual burst strength must be at least 80 percent of BP O . This concept is similar to the requirements for seat belt webbing in FMVSS No. 209 where both minimum breaking strength after abrasion (S4.2d) as well as maximum degradation rate after exposure to light and micro-organisms (S4.2e and S4.2f) are controlled. 6. Test for Expected On-Road Performance For ensuring safe operations, the CHSS must contain hydrogen without leakage or burst. The expected on-road performance test ensures the CHSS is able to effectively contain hydrogen without leakage or burst. Consistent with GTR No. 13, the test for expected on-road performance uses on-road operating conditions including fueling and defueling the container at different ambient conditions with hydrogen gas at low and high temperatures. The test also includes a static high-pressure hold during which the CHSS is evaluated for hydrogen leakage and/or permeation of hydrogen from the CHSS. The container of the CHSS must withstand 180% NWP hold for 4 minutes and have a burst pressure that is at least 80 percent of its BP O at the end of the test for expected on-road performance. The test for expected on-road performance is closely consistent with the industry standard SAE J2579_201806. 69 69 SAE J2579_201806. Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles. While the test for performance durability evaluates the durability of the container when exposed to external stress factors combined with hydraulic pressure cycling, the test for expected on-road performance does not evaluate durability and instead focuses on pneumatic hydrogen fueling exposure, along with extreme temperature conditions. When fueling, hydrogen gas increases its temperature due to the Joule Thomson effect. 70 As a result, pneumatic testing with hydrogen gas creates rapid temperature swings within the CHSS that do not occur during hydraulic cycling. Pneumatic testing also can result in hydrogen diffusion into materials, which can have deleterious chemical effects such as hydrogen embrittlement. 71 Due to these unique stress factors, a pneumatic test using hydrogen gas is an effective method for evaluating the susceptibility of the CHSS to hydrogen permeation and leakage. 70 For more information, see https://www.britannica.com/science/Joule-Thomson-effect. 71 For more information, see https://www.sciencedirect.com/topics/engineering/hydrogen-embrittlement#:~:text=3.7%20Hydrogen%20Embrittlement-,Hydrogen%20embrittlement%20(HE)%20refers%20to%20mechanical%20damage%20of%20a%20metal,when%20hydrogen%20atoms%20are%20generated. Again, consistent with GTR No. 13, the test for expected on-road performance starts with a proof pressure test pressurizing the container with hydrogen to 150 percent NWP. This is followed by a total of 500 pressure cycles at various environmental conditions. The 500 cycles are broken up into stages for low temperature cycling, high temperature cycling, and ambient temperature cycling. Table-3 shows the number of cycles during each stage, along with other applicable conditions. After the first 250 cycles, the CHSS is held at high pressure and temperature for up to 500 hours while it is evaluated for leakage and/or permeation. After the completion of all 500 cycles, the CHSS is again held at high pressure and temperature for 500 hours and evaluated for leakage and/or permeation. Following this second leakage/permeation evaluation, the container is pressurized with hydraulic fluid to 180% NWP and held for 4 minutes. The container then undergoes a residual strength burst test in a similar manner as that described for the test for performance durability. Similar to the test for performance durability, the container's residual burst pressure must be at least 80 percent of BP O. A visual schematic of the test is shown in Figure-6 below. Table 3—Summary of the Test for Expected On-Road Performance Stage of test Number of cycles Ambient conditions Fuel delivery temperature Pressurization medium Pneumatic proof pressure test to 150% NWP not appliable 5.0 °C to 35.0 °C −40.0 °C to −33.0 °C Hydrogen gas. Low temperature cycling 5 −30.0 °C to −25.0 °C 15.0 °C to 25.0 °C Hydrogen gas. Low temperature cycling 20 −30.0 °C to −25.0 °C −40.0 °C to −33.0 °C Hydrogen gas. High temperature cycling 25 50.0 °C to 55.0 °C 80% to 100% relative humidity −40.0 °C to −33.0 °C Hydrogen gas. Ambient temperature cycling 200 5.0 °C to 35.0 °C −40.0 °C to −33.0 °C Hydrogen gas. Static pressure for up to 500 hours with leak/permeation evaluation not appliable 55.0 °C to 60.0 °C not appliable Hydrogen gas. High temperature cycling 25 50.0 °C to 55.0 °C, 80% to 100% relative humidity −40.0 °C to −33.0 °C Hydrogen gas. Low temperature cycling 25 −30.0 °C to −25.0 °C −40.0 °C to −33.0 °C Hydrogen gas. Ambient temperature cycling 200 5.0 °C to 35.0 °C −40.0 °C to −33.0 °C Hydrogen gas. Static pressure for up to 500 hours with leak/permeation evaluation not appliable 55.0 °C to 60.0 °C not appliable Hydrogen gas. Residual pressure test not applicable not applicable not applicable Hydraulic fluid. Burst test not applicable not applicable not applicable Hydraulic fluid. EP17AP24.005 Figure-6: Illustration of the Test for Expected On-Road Performance a. Proof Pressure Test The proof pressure test is conducted in the same manner and for the same reasons discussed above for the test for performance durability. However, in this test, the container is pressurized to 150 percent NWP using hydrogen gas which has been pre-cooled to −40.0 °C to −33.0 °C. This is the temperature range to which hydrogen fueling stations typically pre-cool hydrogen to offset the hydrogen's temperature increase during fueling. b. Ambient and Extreme Temperature Gas Pressure Cycling Test The expected lifetime fueling exposure consists of 500 fuel cycles from 2 MPa to 125 percent NWP (empty-to-full) under a variety of ambient fueling temperatures. The number 500 is obtained through a calculation of expected vehicle lifetime driving range divided by driving range per full-fueling. This calculation and the data source is summarized in Table-4. Table 4—Maximum Number of Full Fueling/Defueling Cycles Expected vehicle lifetime driving range Expected vehicle driving range per full-fueling Expected worst-case number of full-fueling Data source Sierra Research Report No. SR 2004-09-04, September 22, 2004 2006-2007 market data of high volume passenger vehicle manufacturers in Europe, Japan, North America Calculation 250,000 km (155,000 miles) 483 km (300 miles) 500 Some vehicles may exceed 500 fuel cycles if partial fueling occurs in the vehicle lifetime. However, the stress of full fueling exceeds the stress of partial fueling because of the higher pressure and temperature change during full-fueling. NHTSA believes that, as a result, 500 full-fueling cycles should provide robust demonstration of leak-free fueling capability. The industry standard SAE J2601_202005 Fueling protocols for light duty gaseous hydrogen surface vehicles establishes industry-wide fueling protocols for the fueling of hydrogen into passenger vehicles. The guidelines include: 72 72 SAE J2601_202005. Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles. https://www.sae.org/standards/content/j2601_202005/ . 1. The maximum pressure within the vehicle fuel system is 125 percent NWP 2. Gas temperature within the vehicle fuel system is less than or equal to 85 °C 3. Fuel flow rate at dispenser nozzle is less than or equal to 60 g/s 4. The dispenser is capable of dispensing fuel at temperatures between −40 °C and −33 °C These guidelines are applied at hydrogen fueling stations when fueling hydrogen vehicles. During the ambient and extreme temperature gas pressure cycling test, the rate of pressurization must be greater than or equal to the ramp rate specified by a table of ramp rates based on SAE J2601_202005, according to the CHSS volume, the ambient conditions, and the fuel delivery temperature. If the required ambient temperature is not available in the table, the closest ramp rate value or a linearly interpolated value is used. This ensures that the fueling cycles are similar to those that would occur during on-road service. Table-5 shows the ramp rates based on SAEJ2601_202005, for different CHSS volume, the ambient conditions, and the fuel delivery temperature. GTR No. 13 specifies that the pressure ramp rate shall be decreased if the measured internal temperature in the container exceeds 85 °C. Table 5—Pressure Ramp Rates for the Test for Expected On-Road Performance 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 1000 5.0 5.0 5.0 1.4 1500 3.3 3.3 3.3 1.0 2000 2.5 2.5 2.5 0.7 2500 2.0 2.0 2.0 0.5 Extreme environmental temperatures around the world are summarized in Table-6. To ensure safety in extremely hot conditions, some fueling pressure cycles are conducted at 50 °C. To ensure safety in extremely cold conditions, consistent with GTR No. 13 Phase 2 amendments, some fueling pressure cycles are conducted at −25 °C. The temperature −25 °C is used instead of −40 °C because testing at −40 °C is impractical during the test for expected on-road performance. Specifically, a test apparatus must operate at well below −40 °C in order to maintain the temperature surrounding the CHSS at −40 °C. In addition, at −40 °C, test laboratories encounter difficulties such as freezing valves and failing o-ring seals. This can significantly increase test cost. Furthermore, testing conducted by NHTSA found that, for the test for expected on-road performance, testing at −25 °C yields the same results as testing at −40 °C. 73 This change does not compromise the safety intent of the test because in-tank gas temperatures will reach −40 °C due to gas expansion during depressurization. In addition, pressure cycling under the extreme cold condition of −40 °C is tested separately during the test for performance durability. Therefore, −25 °C is proposed as the extreme cold temperature for the test for expected on-road performance, which is consistent with the Phase 2 amendment to GTR No. 13. In summary, NHTSA is proposing 50 °C for the high temperature pressure cycles and −25 °C for the cold temperature pressure cycles. 73 DOT HS_811_832. Cumulative Fuel System Life Cycle and Durability Testing of Hydrogen Containers, https://www.nhtsa.gov/sites/nhtsa.gov/files/811832.pdf . Table 6—Extreme Environmental Temperatures Around the World Temperature Areas that occurs Frequency of sustained exposure to this temperature (year) Extremes of ambient environmental temperature used for this test Around 50 °C desert areas of lower latitude countries 5 percent 50 °C Less or equal to −40 °C countries north of the 45th parallel 5 percent −40 °C Less than −30 °C countries north of the 45th parallel 5 percent of vehicle life Data source: Environment Canada 1971-2000. As described above, hydrogen fueling stations typically pre-cool hydrogen to between −40 °C and −33 °C. However, a fueling station failure could result in the fueling station delivering hydrogen at ambient temperature. This would lead to very high temperatures inside the CHSS after a full fueling. To account for this risk, the first 5 cycles in the ambient and extreme temperature gas pressure cycling test are conducted with hydrogen fuel at between 15 °C and 25 °C, as opposed to the pre-cooled hydrogen between −40 °C and −33 °C which is used for the remaining 495 cycles. All pressure cycles are performed to 100 percent state-of-charge (SOC). SOC is defined by the ratio of hydrogen density at a given temperature and pressure to hydrogen density at NWP and 15 °C. 74 Specifying 100 percent SOC ensures an equivalent quantity of hydrogen in the CHSS regardless of the resulting temperature and pressure. For example, 100 percent NWP at 15 °C corresponds to 80 percent NWP at −40 °C. In either case, however, the CHSS is at 100 percent SOC (fully fueled). 74 Since the hydrogen gas density varies nonlinearly with temperature and pressure, a table is provided in the regulatory text for hydrogen density at different pressures and temperatures. The first 10 cycles (cold cycles) are performed with the CHSS stabilized with the external air temperature surrounding the CHSS at −25 °C at the beginning of the cycle. This ensures there is no residual heat present from the previous fueling cycle and maximizes the severity of the cold external temperature. However, the process to equilibrate a storage system is time-consuming. As a result, the next 15 cycles are performed with an external air temperature surrounding the CHSS of −25 °C, but without CHSS equilibration to the external temperature. The next 25 cycles are performed with an external temperature of 50 °C. For the first 5 of these cycles, the CHSS is stabilized with the external air temperature surrounding the CHSS at the at the beginning of the cycle. At this point, the external temperature to the system is at its hottest, and the CHSS pressure is at its minimum. The fueling process will then progressively heat the contents of the CHSS until full (100 percent SOC). At this point, the CHSS reaches its hottest possible interior temperature. In addition, these 25 cycles are performed with the relative humidity over 80 percent surrounding the CHSS. This adds the stress of excessive humidity which is common in extreme hot climates. Specifically, the high humidity keeps a thin film of water on surfaces where dissimilar metals may be in contact, such as valve to tank interfaces or valve body to valve connection interfaces. This water film adds the necessary conduction path to effect galvanic corrosion. Galvanic corrosion can cause pitting and other forms of metal loss which can degrade the strength of materials and impact sealing surfaces. Therefore, it is important to include the stress factor of humidity in the test for expected on-road performance The next 200 cycles are performed with ambient external temperature of (5 °C to 35 °C). This represents a normal ambient temperature. After these 200 cycles (at a total cycle count of 250), the extreme temperature static gas pressure leak/permeation test is performed. This test is discussed in the next section. However, after the completion of the permeation test, pressure cycling continues for an additional 250 cycles. The first 25 of these additional cycles (cycle count 251-275) are performed with the extreme hot external temperature of 50 °C. The next 25 cycles (cycle count 276-300) are performed with the extreme cold temperature −25 °C. In this series, the order of extreme hot and cold cycles is switched. This accounts for compounding stress from transitioning from hot cycling to cold cycling, as opposed to the previous series, which transitioned from cold to hot. The final 200 cycles (cycle count 301-500) are performed with ambient external temperature of 5 °C to 35 °C. After the completion of cycling, the extreme temperature static gas pressure leak/permeation test is performed for a second time. GTR No. 13 states that if system controls that are active in vehicle service prevent the pressure from dropping below a specified pressure, the test cycles during the ambient and extreme temperature gas pressure cycling test must not go below that specified pressure. In addition, GTR No. 13 states that if devices and/or controls are used in the intended vehicle application to prevent an extreme internal temperature, the test may be conducted with these devices and/or controls in place. However, NHTSA's approach to testing involves the agency independently purchasing (on the open market) and then testing vehicles. With this approach, NHTSA has no way of determining what system controls and/or devices are active in the vehicle, because this information is typically proprietary and is not publicly available. As a result, all cycles would be performed with an initial pressure of between 1 MPa and 2 MPa and extreme internal temperatures will not be prevented during cycling. Furthermore, and importantly for safety, this is a condition that could occur in the event the system controls and/or devices fail in service. c. Extreme Temperatu [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-07116. Public record. Not legal advice.