The National Highway Traffic Safety Administration (NHTSA) published a Final Rule (FR) in the January 17, 2025 Federal Register (F.R. Vol. 90 No. 11; NHTSA-2024-0090). This FR includes new Standards specifying performance requirements for all motor vehicles that use hydrogen as a fuel source and is based on Global Technical Regulation (GTR) 13, Hydrogen and Fuel Cell Vehicles. The two new Standards are FMVSS 307 - Fuel System Integrity of Hydrogen Vehicles, which specifies requirements for the integrity of the fuel system in hydrogen powered vehicles during normal vehicle operations and after crashes and FMVSS 308 - Compressed Hydrogen Storage System Integrity, which specifies requirements for the Compressed Hydrogen Storage System (CHSS) to ensure the safe storage of hydrogen on board vehicles. The intent is that the two new standards will reduce deaths and injuries from fires due to hydrogen fuel leakages and/or explosion of the hydrogen storage system.
FMVSS 308 applies to all motor vehicles that use compressed hydrogen gas as a fuel source to propel the vehicle, regardless of the vehicle's gross vehicle weight rating (GVWR), except vehicles that are only equipped with cryo-compressed hydrogen storage systems or solid-state hydrogen storage systems to propel the vehicle. Portions of FMVSS 307 also apply to all motor vehicles that use compressed hydrogen gas as a fuel source to propel the vehicle, regardless of the vehicle's GVWR; however, while FMVSS 307's fuel system integrity requirements during normal vehicle operations apply to both light vehicles (vehicles with a GVWR of 4,536kg or less) and to heavy vehicles (vehicles with a GVWR greater than 4,536kg), FMVSS 307's post-crash fuel system integrity requirements apply only to compressed hydrogen-fuelled light vehicles and to all compressed hydrogen-fuelled school buses regardless of GVWR.
NHTSA published a Notice of Proposed Rulemaking (NPRM) on April 17, 2024, seeking comments on the proposed Standards. The NPRM proposed five key performance requirements for hydrogen fuelling receptacles to prevent leakage, incorrect fuelling, and contamination from dirt or water:
- Reverse flow prevention
- Clear labelling
- Positive locking
- Protection against contamination
- Secure placement to avoid crash-related deformations
Other proposed features were:
- An over-pressure protection device
- Hydrogen discharge mechanisms
- Vent lines must be protected from dirt and water
- Hydrogen gas discharge must be directed safely away from critical components like the wheels, doors, and emergency exits
- Protection against flammable conditions (visual warning system that would alert the driver if hydrogen concentrations reached dangerous levels and an automatic shut-off valve closure)
- Hydrogen concentrations in the exhaust system must not exceed set thresholds during normal vehicle operation
Post-crash scenarios (proposal set limits on fuel leakage and specified crash tests to ensure that the hydrogen containers remained intact and that any post-crash hydrogen leakage remained within manageable limits. The proposal allowed a hydrogen leak rate not to exceed 118 normal litres per minute for a duration of 60min after impact).
The NPRM portion for establishing the safety and durability of the CHSS used in hydrogen vehicles outlined performance requirements for the CHSS to prevent leaks, bursts, and other failures during normal vehicle use and under extreme conditions, such as exposure to fire. The proposal included:
- Tests and performance criteria to evaluate the CHSS's resistance to various stress factors that could occur over the vehicle's lifetime. CHSS includes components such as the hydrogen container, check valve, shut-off valve, and TPRD.
- Specific requirements for hydrogen containers, which are the primary components of the CHSS, testing procedures for these containers included hydraulic pressure tests to evaluate burst thresholds, pressure cycling tests to simulate long-term use in service, and tests applying a series of external stress factors such as impact, chemical exposure, high and low temperatures, high pressure hold, and over-pressure along with pressure cycling to assess the container's durability against leak or burst during its lifetime.
- On-road performance test for the entire CHSS to ensure the CHSS contains hydrogen without leak or burst (on-road operating conditions including fuelling and defueling the container at different ambient conditions with hydrogen gas at low and high temperatures, a static high-pressure hold, and an overpressure, designed to replicate the stress factors the system could encounter during a vehicle's operational life).
- Fire exposure testing evaluating whether the CHSS could prevent dangerous hydrogen release or explosion in a vehicle fire scenario, including a localized and engulfing stage.
- Requirements for the CHSS's closure devices (check valves, shut-off valves, and TPRD).
This FR addresses the NPRM comments received and provides rationale for the decisions on the actions taken in the FR. In addition to various editorial and clerical updates made to improve clarity and consistency, areas where the FR differs from the NPRM include:
FMVSS 307:
- Definitions for enclosed or semi-enclosed spaces are more specific and avoid ambiguity
- Removes the requirement for an overpressure protection device
- Removes the requirement that the fuelling receptacle "shall not be mounted to or within the impact energy-absorbing elements of the vehicle."
- Removes the requirements for specific thermally-activated pressure relief device (TPRD) discharge angles
- Eliminates option to use an electronic leak detector in Section S6.6, leaving leak detection liquid as the only applicable test method
- Revises the regulatory text in instances where the NPRM stated that the vehicle is set to the "on" or "run" position (and preventing the vehicle from idling) to instead state that the propulsion system shall be operational
FMVSS 308:
- Excludes cryo-compressed and solid-state hydrogen storage systems from the requirements
- Requires manufacturers to provide the median initial burst pressure for a container (BPo) within fifteen business days instead of five
- Removes requirement to include BPo on the container label
- Removes requirement for container burst pressure variability to be within 10% of BPo
- Changes the requirement that the manufacturer specify the primary constituent of the container to specifying whether the primary constituent of the container is glass fibre composite
- Increases the timeframe from 5 business days to 15 business days for manufacturers to submit vehicle-specific information for testing purposes
- Revises the cycling rate for the baseline initial pressure cycle test to be no more than ten cycles per minute
- Removes the minimum time of 3 min to sustain a visible leak before the baseline initial pressure cycle test can end successfully due to "leak before burst."
- Removes the proof pressure test from both the test for performance durability and the test for expected on-road performance
- Permits the option to conduct the closure tests with an inert gas such as helium instead of hydrogen gas.
The Final Rule effective date is July 16, 2025. The incorporation by reference of certain publications listed in the FR is approved by the Director of the Federal Register as of July 16, 2025. The compliance date is September 1, 2028. Petitions for Reconsideration of this FR must be received by March 3, 2025.