On April 15, 2024 the National Highway Traffic Safety Administration (NHTSA) proposed a significant new rule governing electric vehicle (EV) battery safety.  The proposal would implement performance and risk mitigation requirements for EV batteries and require EV manufacturers to submit emergency response information to NHTSA.

The proposed rule would align U.S. Federal Motor Vehicle Safety Standard (FMVSS) requirements with a Global Technical Regulation on EV safety. Comments are due to NHTSA by June 14, 2024.

NHTSA’s Notice of Proposed Rulemaking  (NPRM) would replace the existing FMVSS 305, which covers electrolyte spillage and electrical shock protection for EVs, with a new FMVSS 305a, which would be a broader standard covering EV powertrain  integrity.  The new proposed FMVSS 305a would incorporate many elements of the existing FMVSS 305 and add significant new requirements, such as performance and risk mitigation requirements for the propulsion battery, referred to as the Rechargeable Electrical Energy Storage System or REESS.  NHTSA is also proposing requirements to ensure that emergency responders have access to vehicle-specific information about extinguishing REESS fires and mitigating safety risks associated with stranded energy (energy remaining inside the REESS after a crash or other incident) when responding to emergencies.

New Requirements.  The proposed FMVSS 305a would include the following new requirements:

• Performance Tests: EVs would have to meet performance requirements for safe operation of the REESS under overcharge, over-discharge, over-current, over-temperature, or external short-circuit conditions.  This means that there can be no evidence of electrolyte leakage, rupture (for high-voltage REESSs), venting, fire or explosion under the specified test conditions.
• Water Exposure Protection: NHTSA proposes to adopt a water test requirement, where electrical isolation must be maintained during vehicle washing and when driving through 10 cm-deep standing water.  Notably, NHTSA is not proposing a submersion test requirement.
• Safety Risk Mitigation Documentation: The NPRM would require manufacturers to provide documentation, upon NHTSA request, demonstrating how an EV monitors and controls REESS operations at low temperatures.  Documentation also would be required for safety risk mitigation strategies associated with thermal runaway caused by an internal short-circuit in a single cell of an REESS, called single-cell thermal runaway or SCTR.  SCTR risk mitigation would need to be documented in three vehicle operational modes: external charging, active driving possible, and parking. The documentation would consist of four parts: system analysis identifying conditions that could lead to SCTR; safety risk assessment and mitigation strategies; verification and validation of effective risk mitigation strategies, including vehicle-level assessment results; and an overall evaluation summarizing risk mitigation, including the review/audit process.
• Warning Requirements: An audio and visual warning to the driver would need to be provided in case of a thermal event, and a visual warning would be required if there is an operational failure of any REESS vehicle controls.  Additionally, the NPRM proposes a documentation requirement, under which the vehicle manufacturer would need to validate the functionality of the malfunction warning system.
• Emergency Response Guides: Vehicle manufacturers would be required to submit emergency response guides and rescue sheets in a standardized format for each vehicle make, model and model year, to provide information to emergency responders about safe handling of the vehicle in emergencies and for towing and storing operations.  These documents would be publicly available on NHTSA’s website.

Post-Crash Testing.  The NPRM includes post-crash test requirements that mainly mirror existing requirements in FMVSS 305, such as limiting electrolyte leakage from the battery and requiring the REESS to remain attached to the vehicle following a crash.  In addition, the NPRM would add new post-crash provisions:

•  A fire safety requirement, under which there could be no evidence of fire or explosion for one hour after the crash test.
• A low energy compliance option for capacitors, under which compliance could be demonstrated by meeting a 0.2 Joules electrical energy limit post-crash.
• A requirement that post-crash voltage measurements be made between 10 and 60 seconds after crash impact, in contrast with the current 5 second requirement in existing FMVSS 305.

In addition to the new provisions, existing requirements in FMVSS 305 that ensure electrical system safety during normal vehicle operation would be carried over into the new standard.  These existing requirements protect against contact with high voltage sources during everyday vehicle operation. 

Heavy Vehicles.  Heavy vehicles, which are not currently subject to FMVSS 305, would be subject to both the carried-over provisions from FMVSS 305 and the new requirements of FMVSS 305a.  One exception is that heavy vehicles (other than heavy school buses) would not have to meet the post-crash test requirements for EV safety described above. 

Low Speed Vehicles.  NHTSA has requested comment on applying aspects of the new FMVSS 305a to low-speed vehicles (those that travel under 25 mph).  These vehicles are not subject to the existing FMVSS 305 requirements.  The agency notes in the NPRM that many low-speed vehicles are EVs and that protection against shock and fire may be necessary for these vehicles.

Effective date.  Most requirements of the proposed FMVSS 305a would take effect two years after the final rule is published.  Emergency response information requirements would take effect one year after publication.  Small volume manufacturers, final-stage manufacturers and alterers would be given an additional year to comply with each set of requirements.

Next Steps

Comments on the proposed FMVSS 305a are due to NHTSA by June 14, 2024.  The NPRM can be found here.