Federal Motor Vehicle Safety Standards; FMVSS No. 305a Electric-Powered Vehicles: Electric Powertrain Integrity Global Technical Regulation No. 20 Incorporation by Reference

Federal RegisterDec 20, 2024

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Parts 561 and 571

[Docket No. NHTSA-2024-0091]

RIN 2127-AM43

Federal Motor Vehicle Safety Standards; FMVSS No. 305a Electric-Powered Vehicles: Electric Powertrain Integrity Global Technical Regulation No. 20 Incorporation by Reference

AGENCY:

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

ACTION:

Final rule.

SUMMARY:

Consistent with a Global Technical Regulation on electric vehicle safety, NHTSA is establishing Federal Motor Vehicle Safety Standard (FMVSS) No. 305a to replace FMVSS No. 305, “Electric-powered vehicles: Electrolyte spillage and electrical shock protection.” Among other improvements, FMVSS No. 305a applies to light and heavy vehicles and includes performance requirements for the propulsion battery. NHTSA is also establishing a new regulation, part 561, “Documentation for Electric-powered Vehicles,” that requires manufacturers to compile risk mitigation documentation and to submit standardized emergency response information to assist first and second responders handling electric vehicles.

DATES:

Effective date:

This final rule is effective February 18, 2025.

IBR date:

The incorporation by reference of certain publications listed in the rule is approved by the Director of the Federal Register as of February 18, 2025.

Compliance dates:

The compliance date is December 22, 2025, for the emergency response documentation requirements. For all other requirements, the compliance date is September 1, 2027, for vehicles with a gross vehicle weight rating of 4,536 kilograms (kg) or less and September 1, 2028, for vehicles with a gross vehicle weight rating over 4,536 kg. Small-volume manufacturers, final-stage manufacturers, and alterers are provided an additional year to comply with the requirements beyond the dates identified above. Optional early compliance is permitted.

Petitions for Reconsideration:

Petitions for reconsideration of this final rule must be received no later than February 3, 2025.

ADDRESSES:

Petitions for reconsideration of this final rule must refer to the docket and notice number set forth above and be submitted to the Administrator, National Highway Traffic Safety Administration, 1200 New Jersey Avenue SE, West Building, Washington, DC 20590. All petitions received will be posted without change to

http://www.regulations.gov,

including any personal information provided.

Confidential Business Information:

If you wish to submit any information under a claim of confidentiality, you should submit 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 a copy, from which you have deleted the claimed confidential business information, to Docket Management at the address given above. When you send a submission 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). Please see further information in the Regulatory Notices and Analyses section of this preamble.

Privacy Act:

The petition will be placed in the docket. Anyone is able to search the electronic form of all submissions to any of our dockets by the name of the individual submitting the submission (or signing the comment, if submitted on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the

Federal Register

published on April 11, 2000 (Volume 65, Number 70; Pages 19477-78) or you may visit

https://www.transportation.gov/individuals/privacy/privacy-act-system-records-notices.

Docket:

For access to the docket to read background documents or comments received, go to

https://www.regulations.gov

at any time or to 1200 New Jersey Avenue SE, West Building, Room W12-140, Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. Telephone: (202) 366-9826.

FOR FURTHER INFORMATION CONTACT:

For technical issues, you may contact Ms. Lina Valivullah, Office of Crashworthiness Standards; Telephone: (202) 366-8786; Email:

Lina.Valivullah@dot.gov;

Facsimile: (202) 493-2739. For legal issues, you may contact Ms. K. Helena Sung, Office of Chief Counsel; Telephone: (202) 366-2992; Email:

Helena.Sung@dot.gov;

Facsimile: (202) 366-3820. The mailing address of these officials is: National Highway Traffic Safety Administration, 1200 New Jersey Avenue, SE, Washington, DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary

II. Background

a. Overview of FMVSS No. 305

b. Overview of GTR No. 20

c. Statutory Authority

d. Overview of the Final Rule Requirements

e. Changes From the NPRM to the Final Rule

III. Summary of Comments

IV. Response to Comments on Proposed Requirements

a. Expanding Applicability of FMVSS No. 305a to Heavy Vehicles

1. Normal Vehicle Operations and Requirements for the REESS

2. Post-Crash Safety for Heavy School Buses

3. Post-Crash Safety for Other Heavy Vehicles

b. General Specifications Relating to Crash Testing

1. Low Energy Option for Capacitors

2. Assessing Fire or Explosion in Vehicle Post-Crash Test

3. Assessing Post-Crash Voltage Measurements

4. Electrolyte Leakage

c. Vehicle Controls for Safe REESS Operation

1. Vehicle- and Component-Level Testing

2. State of Charge (SOC)

3. Breakout Harness Location

4. Over-Temperature Test

5. Overcurrent Protection

6. Venting and Visual Inspection

d. Mitigating Risk of Thermal Propagation Due to Internal Short Within a Single Cell in the REESS

e. Thermal Event Warning

f. Vehicle Control Malfunction Warning

g. Protection Against Water Exposure

h. Miscellaneous GTR No. 20 Provisions Not Proposed

1. Vibration and Thermal Shock and Cycling

2. Fire Resistance

3. Low State of Charge

i. Low-Speed Vehicles

j. Emergency Response Information

k. Documentation Requirements

l. Compliance Dates

V. Response to Comments on Issues Not Discussed in the NPRM

a. Future Battery Chemistries

b. Marking and Labeling

c. Test Laboratories

d. Other Electrical Specifications

e. Static Rollover

VI. Rulemaking Analyses and Notices

I. Executive Summary

NHTSA is issuing this final rule to achieve two goals. First, NHTSA is establishing FMVSS No. 305a, “Electric-powered Vehicles: Electric Powertrain

Integrity,” to upgrade and replace existing FMVSS No. 305. The new FMVSS No. 305a has all the requirements of FMVSS No. 305 and expands its applicability to vehicles with a gross vehicle weight rating (GVWR) greater than 4,536 kilograms (kg) (10,000 pounds (lb)). FMVSS No. 305a also adds requirements and test procedures covering new aspects of electric vehicle safety, such as performance requirements for the propulsion battery system, also referred to as the Rechargeable Electrical Energy Storage System (REESS). NHTSA is also establishing a new regulation, 49 CFR part 561 (part 561), “Documentation for Electric-powered Vehicles,” to require that manufacturers submit, at NHTSA's request, documentation addressing safety risk mitigation under specified scenarios to demonstrate that they considered, assessed, and mitigated risks for safe operation of the vehicle. Manufacturers are also required to submit documentation to ensure both first

and second

responders have access to vehicle-specific information about extinguishing REESS fires and mitigating safety risks associated with stranded energy

when responding to emergencies. The restructured and upgraded FMVSS No. 305a will facilitate future updates to the standard as battery technologies and charging systems continue to evolve.

“First responder” means a person with specialized training such as a law enforcement officer, paramedic, emergency medical technician, and/or firefighter, who is typically one of the first to arrive and provide assistance at the scene of an emergency.

“Second responder” means a worker who supports first responders by cleaning up a site, towing vehicles, and/or returning services after an event requiring first responders.

Stranded energy is the energy remaining inside the REESS after a crash or other incident.

The second goal is to further NHTSA's effort to harmonize the Federal Motor Vehicle Safety Standards under the Economic Commission for Europe 1998 Global Agreement (“1998 Agreement”). The efforts of the U.S. and other contracting parties to the 1998 Agreement culminated in the establishment of Global Technical Regulation (GTR) No. 20, “Electric Vehicle Safety.”

FMVSS No. 305 already incorporates a substantial portion of GTR No. 20's requirements due to a previous NHTSA rulemaking. In 2017, NHTSA amended FMVSS No. 305 to include electrical safety requirements from GTR No. 13, “Hydrogen and fuel cell vehicles,” pertaining to electric vehicle performance during normal vehicle operation and post-crash.

Because GTR No. 13's provisions for electric vehicles were later incorporated into what would become GTR No. 20, the 2017 final rule that adopted GTR No. 13's provisions adopted what later became many of the requirements of GTR No. 20. That 2017 rulemaking, however, did not expand the applicability of FMVSS No. 305 to include heavy vehicles nor did it include requirements for the REESS. This final rule largely adopts these and other GTR No. 20 requirements.

GTR No. 20,

https://unece.org/fileadmin/DAM/trans/main/wp29/wp29wgs/wp29gen/wp29registry/ECE-TRANS-180a20e.pdf.

GTR No. 13 only applied to light vehicles. Normal vehicle operations include operating modes and conditions that can reasonably be encountered during typical operation of the vehicle, such as driving, parking, standing in traffic with the vehicle in drive mode, and charging. Final rule, 82 FR 44950, September 27, 2017.

The notice of proposed rulemaking (NPRM) preceding this final rule was published on April 15, 2024. The comment period closed on June 14, 2024. After carefully reviewing the comments, NHTSA is adopting the proposed requirements with some changes from the NPRM. Commenters to the NPRM commented on the applicability to heavy vehicles; vehicle-level testing; technical details on documentation requirements; test procedures for evaluating fire risk mitigation; warning in the case of a thermal event in the battery pack; and water exposure safety. NHTSA addresses the comments in this final rule with minor changes to the regulatory text. These changes include edits to definitions and test procedures for clarity and accuracy, addition of a provision to exempt out-of-reach rooftop charging systems from direct contact protection requirements, and new regulation part 561 for documentation requirements and emergency response information requirements.

High Level Summary of the Final Rule

FMVSS No. 305 currently only applies to passenger cars and to multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kg (10,000 lb) or less (“light vehicles”). Consistent with GTR No. 20, FMVSS No. 305a expands the current applicability of FMVSS No. 305 to vehicles with a GVWR greater than 4,536 kg (10,000 lb) (“heavy vehicles”). Under the final FMVSS No. 305a, light vehicles will be subject to requirements carried over from FMVSS No. 305 that ensure the safety of the electrical system during normal vehicle operations and after a crash (post-crash). They will also be subject to new requirements for the REESS. Heavy vehicles will be subject to the requirements for electrical system safety during normal vehicle operations and to requirements for the REESS. However, except for heavy school buses, they will not be subject to post-crash requirements. Heavy school buses (GVWRs greater than 4,536 kg (10,000 lb)) will be subject to the requirements for electrical system safety during normal vehicle operations and to the requirements for the REESS, and will have to meet post-crash test requirements to ensure the vehicles protect against unreasonable risk of electric shock and risk of fire after a crash. The post-crash tests are the same tests described in FMVSS No. 301 for heavy school buses (impacted at any point and at any angle by a moving contoured barrier).

FMVSS No. 305a also includes new and comprehensive performance requirements and risk mitigation strategies for safety of the REESS. These REESS requirements will apply to all vehicles, regardless of GVWR. A REESS provides electric energy for propulsion and may include necessary ancillary systems for physical support, thermal management, electronic controls, and casings. The requirements set a level of protection of the REESS against external fault inputs, ensure the REESS operations are within the manufacturer-specified functional range, and increase the likelihood of safe operation of the REESS and other electrical systems of the vehicle during and after water exposure during normal vehicle operations.

The final rule addresses some aspects of REESS safety through documentation measures, consistent with GTR No. 20. “Documentation measures” means a list of information provided by manufacturers, at NHTSA's request, that demonstrates that they considered, assessed, and mitigated identified risks for safe operation of the vehicle. The final rule's documentation requirements address: (a) safety risk mitigation associated with charging and discharging during low temperature; (b) providing a warning if there is a malfunction of vehicle controls that manage REESS safe operation; (c)

providing a warning if there is a thermal event in the REESS;

and (d) safety risk mitigation for thermal runaway and propagation due to an internal short circuit of a single cell. The GTR takes a documentation approach to these aspects of safety because of the rapidly evolving electric vehicle technologies and the variety of available REESS and electric vehicle designs. NHTSA agrees that there are currently no objective test procedures in these specified areas that are not design restrictive given the current state of knowledge. Thus, until test procedures and performance criteria can be developed for all vehicle powertrain architectures, 49 CFR part 561 will require manufacturers to submit documentation to NHTSA, at NHTSA's request, that identifies all known safety hazards, describes their risk mitigation strategies for the safety hazards, and, if applicable, describes how they provide a warning to address a safety hazard. The purpose of the documentation approach is two-fold. Given the variation of battery design and design specific risk mitigation systems, the documentation requirement will be a means of ensuring that each manufacturer has identified safety risks and safety risk mitigation strategies. The requirement provides a means for NHTSA to learn of the risks associated with the REESS, understand how the manufacturer is addressing the risks, and oversee those safety hazards. This approach is battery technology neutral, not design restrictive, and is intended to evolve over time as battery technologies continue to rapidly evolve. It is an interim measure intended to ensure that manufacturers will identify and address the safety risks of the REESS until such time as objective performance standards can be developed that can be applied to all applicable REESS designs.

The NPRM proposed to include a thermal warning requirement and a corresponding test procedure. After consideration of comments, the final rule specifies an additional documentation requirement in part 561 for the REESS thermal event warning instead of a corresponding test procedure with the warning requirement.

As part of NHTSA's battery initiative and in response to a 2020 NTSB recommendation,

the NPRM proposed to include in FMVSS No. 305a a requirement that vehicle manufacturers submit to NHTSA standardized emergency response guides (ERGs) and rescue sheets for each vehicle make, model, and model year. The uploaded ERGs and rescue sheets will be publicly available on NHTSA's website for easy searchable access. ERGs and rescue sheets communicate vehicle-specific information related to fire, submersion, and towing, as well as the location of components in the vehicle that may expose the vehicle occupants or rescue personnel to risks, the nature of a specific function or danger, and devices or measures which inhibit a dangerous state. The final rule adopts the proposed requirement to submit standardized emergency response information to a NHTSA website in part 561. The standardized information will be available and understandable to first and second responders so they can easily refer to vehicle-specific rescue information en route to or at the scene of a crash or fire event and respond to the emergency quickly and safely.

“Safety risks to emergency responders from lithium-ion battery fires in electric vehicles,” Safety Report NTSB/SR-20/01, PB2020-101011, National Transportation Safety Board,

https://www.ntsb.gov/safety/safety-studies/Documents/SR2001.pdf.

NHTSA is issuing this final rule pursuant to and in accordance with its authority under the National Traffic and Motor Vehicle Safety Act (Safety Act). Under 49 United States Code (U.S.C.) Chapter 301, Motor Vehicle Safety (49 U.S.C. 30101

et seq.

), the Secretary of Transportation is responsible for prescribing motor vehicle safety standards that are practicable, meet the need for motor vehicle safety, and are stated in objective terms. The Safety Act also authorizes NHTSA to require manufacturers to retain certain records and/or make information available to NHTSA. Section 30166 of the Act provides NHTSA the ability to request and inspect manufacturer records that are necessary to enforce the prescribed regulations. NHTSA is authorized by delegation to issue regulations to carry out the agency's duties of ensuring vehicle safety.

49 U.S.C. 322(a); 49 CFR 1.95.

NHTSA believes there are no notable costs associated with this final rule. This final rule closely mirrors the electrical safety provisions of GTR No. 20, which have been voluntarily implemented by manufacturers in this country. The agency believes that the finalized safety standards are widely implemented by manufacturers of light and heavy electric vehicles and heavy electric school buses. Manufacturers are also already providing emergency response information to the National Fire Protection Association (NFPA); under part 561, they would just have to standardize the format and submit the information to NHTSA.

II. Background

a. Overview of FMVSS No. 305

The purpose of FMVSS No. 305, “Electric-powered vehicles: electrolyte spillage and electrical shock protection,” is to reduce deaths and injuries from electrical shock. The standard applies only to light vehicles (vehicles with a GVWR less than or equal to 4,536 (kg) (10,000 (lb)). The standard's requirements reduce the risk of harmful electric shock: (a) during normal vehicle operation; and (b) in post-crash situations to protect vehicle occupants, and rescue workers and others who may come in contact with the vehicle after a crash. The standard's requirements for the former protect against direct and indirect contact of high voltage sources during everyday operation of the vehicles. The focus of the “in-use” testing (unlike “post-crash” testing) deals with performance criteria that will be assessed without first exposing the vehicle to a crash test. The standard's post-crash test requirements address electrical isolation following frontal, rear, and side impacts of the vehicle, in addition to limiting electrolyte spillage from propulsion batteries.

FMVSS No. 305 already has many of GTR No. 20's requirements for light vehicles, including requirements for electrical safety during normal vehicle operation; post-crash electrolyte spillage; post-crash REESS retention; and most of the GTR's post-crash electrical safety options for high voltage sources.

b. Overview of GTR No. 20

1. The GTR Process

The United States is a contracting party to the Agreement concerning the Establishing of Global Technical Regulations for Wheeled Vehicles, Equipment and Parts which can be fitted and/or be used on Wheeled Vehicles (“1998 Agreement”). This agreement entered into force in 2000 and is administered by the UN Economic Commission for Europe's (UN ECE's) World Forum for the Harmonization of Vehicle Regulations (WP.29). The purpose of this agreement is to establish Global Technical Regulations (GTRs).

In March 2012, UNECE WP.29 formally adopted the proposal to establish GTR No. 20 at its one-hundred-and-fifty-eighth session. NHTSA chaired the development of GTR No. 20 and voted in favor of establishing GTR No. 20.

As a Contracting Party Member to the 1998 Global Agreement that voted in favor of GTR No. 20, NHTSA is obligated to initiate the process used in the U.S. to adopt the GTR as an agency regulation. This process was initiated by the NPRM published on April 15, 2024.

NHTSA is not obligated to adopt the GTR after initiating this process. In deciding whether to adopt a GTR as an FMVSS, NHTSA follows the requirements for NHTSA rulemaking, including the Administrative Procedure Act, the National Traffic and Motor Vehicle Safety Act (Vehicle Safety Act), Presidential Executive Orders, and DOT and NHTSA policies, procedures, and regulations. Among other things, FMVSSs issued under the Vehicle Safety Act “shall be practicable, meet the need for motor vehicle safety, and be stated in objective terms.”

2. GTR No. 20

GTR No. 20 establishes performance-oriented requirements that reduce potential safety risks of electric vehicles while in use and after a crash event. The GTR includes provisions that address electrical shock associated with high voltage circuits of EVs and potential hazards associated with lithium-ion batteries and/or other REESS. One of the principles for developing GTR No. 20 was to address unique safety risks posed by electric vehicles and their components to ensure a safety level equivalent to conventional vehicles with internal combustion engines.

The requirements in GTR No. 20, for Phase 1 in the GTR development process, address issues relating to the safe operation of the REESS, and the mitigation of fire risk and other safety risks associated with the REESS. Phase 2 of the GTR No. 20 development process, which is ongoing, will address issues involving long-term research and verification.

GTR No. 20 applies to all electric-powered vehicles regardless of GVWR, in contrast to FMVSS No. 305, which only applies to light vehicles. FMVSS No. 305 currently includes the majority of GTR No. 20's requirements regarding electric shock protection and applies these only to light vehicles. GTR No. 20 also has safety requirements for the REESS beyond those in FMVSS No. 305. A summary of these additional requirements in GTR No. 20 for the REESS includes:

Safe operation of REESS under the following exposures during normal vehicle operations:

• REESS protection under external fault conditions and extreme operating temperatures:

○ External short circuit

○ Overcharge

○ Over-discharge

○ Overcurrent

○ High operating temperature

○ Low operating temperature

• Management of REESS emitted gases

• Water exposure during vehicle washing and driving through 10-centimeter (cm) deep water on roadway

• Thermal shock and cycling (−40 °C to 60 °C)*

The asterisk notes that the NPRM did not propose to adopt the GTR No. 20 requirement.

• Resistance to short duration external gasoline pool fire *

• Vibration environment during normal vehicle operations *

Warning systems for REESS safe operation in case of:

• Low energy content in REESS *

• REESS control operational failure

• Thermal runaway propagation due to single cell short circuit in REESS

• Thermal event in REESS

• Installation (location) of REESS on the vehicle

This requirement is intended for countries with type approval systems where a generic REESS can be approved separately from the vehicle. A vehicle with a pre-approved REESS that complies with the REESS installation requirement would not have to undergo post-crash safety assessment for approval. This installation requirement would not apply in the U.S. with a self-certification system.

GTR No. 20 includes post-crash requirements but does not specify the crash tests for post-crash evaluation. Instead, the GTR allows contracting parties to apply the crash tests in their regulations. Further, the GTR allows contracting parties to permit regulated entities to comply with post-crash requirements without conducting vehicle crash tests. In place of crash tests, a contracting party may specify tests for “mechanical integrity” and “mechanical shock” of the REESS.

The April 2024 NPRM

proposed to complete the alignment of FMVSS No. 305 with GTR No. 20 by proposing to establish FMVSS No. 305a, which adopts all the requirements in FMVSS No. 305 and extends the standard's electrical safety requirements to heavy vehicles. The NPRM also proposed to adopt the above requirements under normal vehicle operations for the REESS to light and heavy vehicles, except as noted by an asterisk, because requirements for thermal shock and cycling, resistance to short duration external pool fire, and vibration environment are already included under United States Hazardous Materials Regulations (HMR), 49 CFR parts 171 to 180, in accordance with the international lithium battery transportation requirements of UN 38.3, “Transport of dangerous goods: Manual of tests and criteria.” The NPRM proposed adding the post-crash test requirements in FMVSS No. 305 for light vehicles and adding a crash test for all school buses similar to that in FMVSS No. 301, “Fuel system integrity.” The NPRM also proposed a post-crash requirement for no observed fire or explosion in the vehicle for a duration of one hour after the crash test and a low energy post-crash option for capacitors in the electric power train to meet electrical safety requirements.

89 FR 26704 (Apr. 15, 2024).

c. Statutory Authority

et seq.

), the Secretary of Transportation is responsible for prescribing motor vehicle safety standards that are practicable, meet the need for motor vehicle safety, and are stated in objective terms (section 30111(a)). “Motor vehicle safety” is defined in the Safety Act (section 30102(a)(8)) 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.” “Motor vehicle safety standard” means a minimum standard for motor vehicle or motor vehicle equipment performance (section 30102(a)(9)). When prescribing such standards, the Secretary must consider all relevant available motor vehicle safety information (section 30111(b)(1)). The Secretary must also consider whether a proposed standard is reasonable, practicable, and appropriate for the particular type of motor vehicle or motor vehicle equipment for which it is prescribed (section 30111(b)(3)) and the extent to which the standard will further the statutory purpose of reducing traffic accidents and associated deaths and injuries (section 30111(b)(4)). The responsibility for promulgation of FMVSSs is delegated to NHTSA (49 CFR 1.95).

The Safety Act also authorizes NHTSA to require manufacturers to retain certain records and/or make information available to NHTSA. Section 30166 of the Act provides NHTSA the ability to request and inspect manufacturer records that are necessary to enforce the prescribed regulations. NHTSA is also authorized by delegation to issue regulations to

carry out the agency's duties of ensuring vehicle safety.

49 U.S.C. 322(a). This provision states that the Secretary of Transportation may prescribe regulations to carry out the duties and powers of the Secretary. The authority to implement the Vehicle Safety Act has been delegated to NHTSA.

d. Overview of the Final Rule Requirements

Consistent with GTR No. 20, the new FMVSS No. 305a expands the current applicability of FMVSS No. 305 to vehicles with a GVWR greater than 4,536 kg (10,000 lb) (“heavy vehicles”). Under FMVSS No. 305a:

• Light vehicles are subject to requirements carried over from FMVSS No. 305 that ensure the safety of the electrical system during normal vehicle operations and after a crash (post-crash).

They are also subject to new requirements for the REESS.

Current FMVSS No. 305 light vehicle post-crash test requirements (front, side, and rear crashes) are aligned with FMVSS No. 301's light vehicle post-crash test requirements.

• Heavy vehicles are subject to the requirements for electrical system safety during normal vehicle operations and to requirements for the REESS. However, except for heavy school buses, they are not subject to post-crash requirements. This exclusion of heavy vehicles, other than school buses, from crash tests, aligns with similar exclusions in FMVSS No. 301, “Fuel system integrity,” for conventional fuel vehicles and FMVSS No. 303, “Fuel system integrity of compressed natural gas vehicles,” for compressed natural gas vehicles.

• Heavy school buses (GVWRs greater than 4,536 kg (10,000 lb))

are subject to the requirements for electrical system safety during normal vehicle operations and to the requirements for the REESS, and have to meet post-crash test requirements to ensure the vehicles protect against unreasonable risk of electric shock and risk of fire after a crash. The post-crash tests are the same tests described in FMVSS No. 301 for heavy school buses (impacted at any point and at any angle by a moving contoured barrier).

In the school bus safety area, stakeholders, including NHTSA, commonly refer to buses with a GVWR over 4,536 kg (10,000 lb) as “large” school buses.

The post-crash requirements of FMVSS No. 305a for light vehicles and heavy school buses include electric shock protection (there are four compliance options: low voltage, electrical isolation, protective barrier, and low energy for capacitors); REESS retention; electrolyte leakage; and fire safety. The requirements for REESS retention and electrolyte leakage are in FMVSS No. 305, but FMVSS No. 305a enhances some provisions consistent with GTR No. 20. For example, FMVSS No. 305 does not specify that there must be no fire or explosion after a crash test. Electric vehicles may catch fire long after a collision or other occurrence resulting in a fault condition. To account for the potential delayed response, FMVSS No. 305a is prohibiting fire or explosion for a one-hour post-test period.

A substantial portion of FMVSS No. 305a focuses on safety provisions for the propulsion battery, the REESS. FMVSS No. 305a includes comprehensive performance requirements for the REESS. These REESS requirements apply to all vehicles, regardless of GVWR. A REESS provides electric energy for propulsion and may include necessary ancillary systems for physical support, thermal management, electronic controls, and casings. The requirements set a level of protection of the REESS against external fault inputs, ensure the REESS operations are within the manufacturer-specified functional range, and increase the likelihood of safe operation of the REESS and other electrical systems of the vehicle during and after water exposure during normal vehicle operations.

This final rule addresses some aspects of REESS safety through documentation measures, consistent with GTR No. 20, through a new regulation, part 561. “Documentation measures” means a list of information provided by manufacturers, at NHTSA's request, that demonstrates that they considered, assessed, and mitigated identified risks for safe operation of the vehicle. These documentation requirements address: (a) safety risk mitigation associated with charging and discharging during low temperature; (b) providing a warning if there is a malfunction of vehicle controls that manage REESS safe operation; (c) providing a warning if there is a thermal event in the REESS; and (d) safety risk mitigation for thermal runaway and propagation due to an internal short circuit of a single cell. The GTR takes a documentation approach to these aspects of safety because of the rapidly evolving electric vehicle technologies and the variety of available REESS and electric vehicle designs. The Informal Working Group experts that drafted the GTR determined there currently are no objective test procedures to evaluate safety risk mitigation designs or the operations of warnings of a malfunction of vehicle controls in a manner that is not design restrictive.

NHTSA agrees with this approach given the current state of knowledge. Thus, until test procedures and performance criteria can be developed for all vehicle powertrain architectures, manufacturers will be required to submit documentation to NHTSA, at NHTSA's request, that identifies all known safety hazards, describes risk mitigation strategies for the safety hazards, and, if applicable, describes how they provide a warning to address a safety hazard.

The purpose of the documentation approach is two-fold. Given the variation of battery design and design specific risk mitigation systems, the documentation requirement is a means of ensuring that each manufacturer has identified safety risks and safety risk mitigation strategies. The requirement provides a means for NHTSA to learn of the risks associated with the REESS, understand how the manufacturer is addressing the risks, and oversee those safety hazards. This approach is battery technology neutral, not design restrictive, and is intended to evolve over time as battery technologies continue to rapidly evolve. It is an interim measure intended to ensure that manufacturers will identify and address the safety risks of the REESS until such time as objective performance standards can be developed that can be applied to all applicable REESS designs. NHTSA will also acquire information from the submissions to learn about the safety of the REESSs and potentially develop the future performance standards for FMVSS No. 305a. The documentation requirements are based on the approach of GTR No. 20, but NHTSA focused the GTR's documentation requirements to enable the agency to obtain more targeted information from manufacturers.

Section 30166 of the Vehicle Safety Act authorizes the Secretary of Transportation (NHTSA by delegation) the ability to request and inspect manufacturer records that are necessary to enforce the prescribed regulations.

As part of NHTSA's battery initiative,

this final rule also establishes, through regulation, a requirement that vehicle manufacturers submit to NHTSA emergency response guides (ERGs) and rescue sheets for each vehicle make, model, and model year. The purpose of the requirement is to provide information to first and second responders regarding the safe handling of the vehicle in emergencies and for towing and storing operations. The uploaded ERGs and rescue sheets will be publicly available on NHTSA's website for easy searchable access. ERGs and rescue sheets communicate vehicle-specific information related to fire, submersion, and towing, as well as the

location of components in the vehicle that may expose the vehicle occupants or rescue personnel to risks, the nature of a specific function or danger, and devices or measures which inhibit a dangerous state.

https://www.nhtsa.gov/battery-safety-initiative.

NHTSA is requiring standardized formatting of the information. The ERG and rescue sheet requirements include the layout and format specified in ISO-17840, “Road vehicles—Information for first and second responders,” which standardize color-coded sections in a specific order to help first and second responders quickly identify pertinent vehicle-specific rescue information. The standardized information will be available and understandable to first and second responders so they can easily refer to vehicle-specific rescue information enroute to, or at the scene of, a crash or fire event and respond to the emergency quickly and safely.

e. Changes From the NPRM to the Final Rule

In developing this final rule, NHTSA made some modifications to the proposed regulatory requirements in response to comments received and to improve clarity and accuracy of the regulatory text. In addition to typographical corrections, the final rule differs from the April 2024 NPRM in the following ways:

1. Timing of voltage measurements for determining electrical isolation post-crash. The proposal required voltage measurements for assessment of post-crash electrical isolation to be made between 10 to 60 seconds from the time of impact. The final rule requires the voltage measurements for post-crash electrical isolation assessment to be made at least 10 seconds after impact. NHTSA determined that taking all the voltage measurements for determining electrical isolation would typically take more than 60 seconds and since electrical isolation value is not expected to change with time, only specifying a minimum time after impact for making the measurements is sufficient.

2. Definition of State of Charge (SOC). The definition of SOC was updated to clarify that it is the available electric charge in a REESS expressed as a percentage of its normal operating capacity specified by the manufacturer and not as a percentage of the total charge (stored energy) in the REESS.

3. Documentation requirements included in part 561. The NPRM proposed documentation requirements in FMVSS No. 305a for manufacturers to submit, upon request, documentation regarding vehicle and REESS designs to mitigate the risk of vehicle fire and explosion resulting from single cell thermal runaway in the REESS, loss or malfunction of controls managing safe operation of the REESS, and vehicle operations at low temperatures. The NPRM also proposed requiring manufacturers to submit emergency response information to a repository prior to the certification time of the vehicle. The final rule has moved these requirements to part 561 because documentation requirements without corresponding test procedures are better suited in a regulation. Additionally, the final rule requires emergency response information to be submitted to NHTSA's repository before first sale or lease of the vehicle model upon the compliance date.

4. Thermal event warning documentation requirement. The NPRM proposed a test procedure to evaluate the warning function resulting from a thermal event in the REESS. Due to practicability and safety concerns with the proposed test procedure, the final rule specifies an additional documentation requirement in part 561 for the REESS thermal event warning instead of a corresponding test procedure with the warning requirement.

5. Maximum time to conduct driving through standing water test (protection against water exposure). The NPRM proposed a maximum test duration of 5 minutes for the driving through standing water test. Based on NHTSA's recent testing, the final rule extends this time to 10 minutes because of the practicability concerns for conducting the test within 5 minutes for water pools shorter than 500 meters.

7. Exclusion for rooftop charging systems. The final rule excludes those high voltage devices on heavy vehicles not energized except during charging of the REESS, that are installed out of reach on the vehicle rooftop, from direct contact protection requirements. NHTSA inadvertently excluded this carveout for the out of reach high voltage devices from the proposed direct contact protection requirements.

8. Addition of loading specifications. The proposed crash test procedure for heavy school buses inadvertently omitted the loading specifications. Loading specifications matching FMVSS Nos. 301 and 303 have been added to the final regulatory text for completeness.

9. Compliance dates. The final rule adopts the proposed 1-year lead time from the date of publication of the final rule to comply with the emergency response information requirements. The proposed 2-year lead time for complying with all other requirements for light vehicles is largely adopted with a slight date change to align with the beginning of the model year on or after the first September 1 that is at least two years after the publication of the final rule. In response to comments received, the final rule extends the heavy vehicles' lead time to comply with the requirements other than the emergency response information requirements to the first September 1 that is at least three years after the publication of the final rule.

III. Summary of Comments

The NPRM preceding this final rule included requests for comment on several topics, including the post-crash requirements, the thermal event warning performance test, the water exposure tests, the exclusion of some GTR No. 20 requirements, and the documentation requirements. From April 15, 2024, to June 14, 2024, the agency received 38 comments on the NPRM, including one that appears to be an accidental duplicate submission. The comments were generally supportive of the proposed rule, particularly with regard to the collection of standardized emergency response information and harmonization with international regulations. Many commenters suggested modifications to the proposed requirements, including establishing documentation requirements in a separate regulation instead of the FMVSS. Of the 37 unique comments, the majority (26 comments) were submitted by vehicle and component manufacturers and industry associations. Comments were also submitted by standards testing laboratories (3 comments), a government agency (1 comment), and other stakeholders (7 comments).

The vehicle and component manufacturers that provided comments were American Honda Motor Co. (“Honda”), Blue Bird Body Company (“Blue Bird”), Bugatti Rimac d.o.o. (“Bugatti”), Daimler Truck North America (“DTNA”), Eaton Corporation (“Eaton”), Ford Motor Company (“Ford”), Freudenberg Battery Power Systems (“Freudenberg”), Honeywell International (“Honeywell”), Hyundai America Technical Center (“HATCI” or “Hyundai”), Lubrizol Corporation (“Lubrizol”), Lucid Motors (“Lucid”), Navistar, New Flyer of America (“NFA”), Nikola Corporation (“Nikola”), Nissan North America (“Nissan”), Prevost, Rivian Automotive (“Rivian”), Tesla, and Volkswagen Group of America (“Volkswagen”).

The industry associations that provided comments were the Alliance for Automotive Innovation (“Auto Innovators”), Coalition for Safe

Autonomous Vehicles and Electrification (“SAVE Coalition”), Electric Drive Transportation Association (“EDTA”), MEMA Vehicle Suppliers Association (“MEMA”), National Electrical Manufacturers Association (“NEMA”), Truck and Engine Manufacturers Association (“EMA”), and Zero Emission Transportation Association (“ZETA”). Some manufacturers that submitted comments individually indicated that they belong to one of these industry associations and/or stated support for the comments submitted by an industry association.

The standards testing laboratories and associations that provided comments were UL Solutions, the American Council of Independent Laboratories (“ACIL”), and the American Association for Laboratory Accreditation (“A2LA”).

The National Transportation Safety Board (“NTSB”) submitted one comment, expressing strong support for the proposed rulemaking.

The other stakeholders that provided comments were the Center for Auto Safety (“CAS”), Consumer Reports, Creaform/Ametek (“Creaform”), Electric Vehicle Rescue App (“EV Rescue App,” two comments), Michael Lillo, and Kurt Vollmacher.

With regard to heavy vehicles, the commenters generally expressed support for the proposed requirements for heavy school buses. Comments on applying additional requirements to other heavy vehicles were more varied, with some commenters in favor of additional test requirements at the component level or at the vehicle level, and others opposed. One commenter requested that NHTSA add an exemption from the direct contact protection requirements during normal vehicle operation for rooftop charging systems on heavy vehicles.

With regard to post-crash safety, manufacturers expressed support for the inclusion of the low energy option for capacitors. Commenters also generally agreed with the proposed requirement that there be no evidence of fire or explosion for the duration of one hour after each crash test. Comments on the voltage measurement procedure were mixed, with some commenters in agreement and others requesting changes to the test specifications. Honda and Auto Innovators requested removal of the 60-second time limit for post-crash electrical isolation measurements, which would align the specification with GTR No. 20. For electrolyte leakage, commenters said that the updated terminology is appropriate, but the 5-liter maximum leakage requirement is no longer relevant with modern REESS chemistries.

With regard to the proposed requirements for safe operation of the REESS, commenters commented about certain aspects of the proposed test procedures, particularly the state of charge, breakout harness location, and test termination specifications. Many comments from industry disagreed with the agency's exclusion of component-level compliance test options. For the thermal event warning, some commenters also requested implementation of a documentation requirement instead of a test requirement.

For the proposed documentation requirements, some commenters requested clarification of the requirements and implementation in a separate regulation. Most commenters expressed strong support for NHTSA's proposed collection of standardized emergency response information, with a few vehicle manufacturers requesting a modification to the submission timeline. Some also requested extending the compliance date for the other proposed requirements beyond 2 years after publication of the final rule.

IV. Response to Comments on Proposed Requirements

a. Expanding Applicability of FMVSS No. 305a to Heavy Vehicles

1. Normal Vehicle Operations and Requirements for the REESS

Proposed Requirements

Consistent with GTR No. 20, the NPRM proposed to expand the current applicability of FMVSS No. 305 to heavy vehicles. Under FMVSS No. 305a, heavy vehicles (including heavy school buses) would have to meet the same requirements as light vehicles for electrical system safety during normal vehicle operations and for the REESS. The fundamentals for protecting against an electrical shock are the same for light vehicles and heavy vehicles. A failure of a high voltage system may cause injurious electric shock to the human body.

Comments Received

Commenters generally expressed support for applying the expanded electrical system safety requirements during normal vehicle operations to heavy school buses. Comments on applying these requirements to other heavy vehicles were more varied, with some commenters in favor of additional test requirements at the component level or at the vehicle level, and others opposed. MEMA agreed with the inclusion of heavy-duty vehicles without crash testing. Auto Innovators commented that FMVSS No. 305a should not apply to heavy vehicles at this time and more research is needed. Auto Innovators noted that the proposed regulatory requirements that were not previously applicable to heavy vehicles have potential design implications that require thorough consideration by the agency.

EMA disagreed specifically with application of the REESS overcurrent test to heavy vehicles, which were exempted in GTR No. 20. EMA said that NHTSA did not provide justification for applying the overcurrent test requirement to heavy vehicles. EMA also requested that NHTSA include an exemption from GTR No. 20 related to direct contact protection during normal vehicle operation. Specifically, EMA stated that the proposed requirement omitted an important exemption provision for some heavy vehicle applications. Under this provision, conductive connection devices not energized except during charging of the REESS that are located on the roof of the vehicle and out of reach of a person standing outside the vehicle are exempted from direct contact protection requirements. EMA explained that this exemption is necessary for rooftop pantograph charging systems used in some heavy vehicles like transit buses.

Agency Response

The agency is adopting most of the requirements for heavy vehicles as proposed in the NPRM, with one modification. Unlike the NPRM, the final rule excludes direct contact protection requirements from those high voltage devices on heavy vehicles not energized except during charging of the REESS, that are installed out of reach on the vehicle rooftop. NHTSA inadvertently excluded this carveout for high voltage rooftop charging devices on heavy vehicles from the direct contact protection provision in the proposed requirements for FMVSS No. 305a. GTR No. 20 excludes high voltage sources that are not energized except during charging of the REESS from direct contact protection requirements if they are located on the vehicle rooftop such that the wraparound distance from the instep of the vehicle, or the lowest step (if multiple steps are present) of the vehicle, to the high voltage source is at least 3 meters. NHTSA agrees that if the high voltage live parts are not energized except during charging of the REESS and are out of reach for a person standing outside of the vehicle, it is appropriate to exempt those parts from the IPXXB direct contact protection

requirement. NHTSA has included the relevant language in the regulatory text of the final rule.

EMA also requested not applying the overcurrent test to heavy vehicles. The overcurrent test in GTR No. 20 is applicable to light vehicles that have the capability to be charged by an external DC supply. GTR No. 20 states that the overcurrent test for heavy vehicles will be considered in Phase 2, “as it is unclear how to apply on vehicles that have different charging technologies.” GTR No. 20 specifies two methods of conducting the overcurrent test. In the first method, the overcurrent is applied through the external DC supply equipment connected to the vehicle inlet while the vehicle is charging normally. In the second method, the charge current and the overcurrent are applied through a breakout harness connected just outside the REESS. The external DC supply equipment connected to the other end of the breakout harness supplies the normal charge as well as the overcurrent to the REESS. The overcurrent test procedure in FMVSS No. 305a uses the breakout harness method, so any challenges associated with testing via the charging inlet for different charging technologies are avoided. NHTSA evaluated the overcurrent test using the breakout harness and found it to be an easy test to conduct that is practical and feasible for different vehicle types.

Electric Vehicle GTR No. 20 Test Development, Validation, and Assessment, DOT HS 812 092, April 2021,

https://rosap.ntl.bts.gov/view/dot/55584.

Auto Innovators recommended excluding heavy vehicles from FMVSS No. 305a electrical system safety during normal vehicle operations and REESS requirements at this time, citing the need for more research on the implications of these requirements on heavy vehicle designs. Auto Innovators did not provide additional information to support its statement. NHTSA believes the requirements for normal vehicle operations and the REESS in FMVSS No. 305a are basic safety measures that should be included in all electric vehicle designs.

These basic safety measures ensure protection from electric shock and fire originating in the electric powertrain and specifically in the REESS. These measures include electrical isolation, direct and indirect contact protection, protection of the REESS from abuse and external inputs that could damage the REESS over time, and measures to ensure the REESS always operates within its safe operating boundaries. The agency believes that the requirements proposed in the NPRM for heavy vehicles, including the overcurrent test requirement, are relevant and appropriate for heavy vehicle safety and that the test procedures are practicable.

Lithium-ion Battery Safety Issues for Electric and Plug-in Hybrid Vehicles, DOT HS 812 418, October 2017,

https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/12848-lithiumionsafetyhybrids_101217-v3-tag.pdf.

2. Post-Crash Safety for Heavy School Buses

Proposed Requirements

In addition to the requirements for electrical system safety during normal vehicle operations and for the REESS, the NPRM also proposed requirements for post-crash safety of heavy electric school buses. The NPRM proposed use of a moving contoured barrier test, where a barrier traveling at any speed up to 48 km/h (30 mph) impacts the school bus at any point and angle. The crash test requirement aligns FMVSS No. 305a with the requirements for heavy school buses in FMVSS No. 301, “Fuel system integrity,” and FMVSS No. 303, “Fuel system integrity of compressed natural gas vehicles.” The agency did not propose a provision in GTR No. 20 that allows the use of component-level mechanical integrity and mechanical shock tests instead of vehicle crash tests. NHTSA believes that post-crash safety is better evaluated at the system level in a crash test.

Comments Received

Commenters were generally in favor of the proposed crash test requirements for heavy school buses. Commenters NTSB, DTNA, Navistar, and EV Rescue App expressed full support for the expanded requirements for heavy school buses. In particular, NTSB agreed with expanding the post-crash requirements and making full use of the system-level requirements that exist for heavy school buses so the vehicles will be subject to the full intent and scope of FMVSS No. 305a. Bus manufacturers DTNA (Thomas Built Buses) and Navistar (IC Bus) also agreed with the proposed crash test performance requirements, which are consistent with FMVSS No. 301 and FMVSS No. 303. Navistar stated that the proposed requirements for heavy school buses were reasonable and would not add significant cost or weight to the vehicles. EMA noted that the loading requirements should be added to the crash test specifications in S10.2.3. Individual commenter Mr. Lillo also stated general support for enhanced EV school bus safety and suggested conducting time trials for bus evacuation.

One manufacturer disagreed with the proposed requirements for heavy school buses. Blue Bird stated that including multiple post-crash requirements makes FMVSS No. 305a more burdensome than the corresponding requirements for non-electric school buses. Blue Bird also said that the proposed rule would require manufacturers to crash a school bus every time they make a change to the battery pack. Blue Bird requested component-level testing instead of full-vehicle testing.

Agency Response

After reviewing the comments, NHTSA is adopting the crash test and post-crash requirements for heavy school buses as proposed in the NPRM, with the addition of loading specifications. EMA noted that the proposed regulatory text in the NPRM did not state the school bus loading condition for the crash test. This final rule corrects this inadvertent omission; loading specifications matching FMVSS Nos. 301 and 303, as suggested by EMA, have been added to the regulatory text for completeness. With regard to potential fire emergencies, in addition to the requirements of this final rule, electric school buses are subject to FMVSS No. 217, “Bus emergency exits and window retention and release,” which specifies operating forces, opening dimensions, and markings for emergency exits on school buses to facilitate rapid evacuation, and FMVSS No. 302, “Flammability of interior materials,” which specifies burn resistance requirements. NHTSA will also continue to evaluate school bus safety, including school bus evacuation, and update applicable safety standards as technology changes over time.

Most commenters, including bus manufacturers, agreed with the proposed requirements. The dissenting commenter expressed concerns over the testing burden. With regard to the crash test requirements for electric school buses, the dynamic moving contoured barrier test aligns FMVSS No. 305a with FMVSS Nos. 301 and 303, which address post-crash safety of heavy school buses using conventional fuel or compressed natural gas. The four post-crash requirements for FMVSS No. 305a are electric shock protection, REESS retention, electrolyte leakage, and fire safety. These requirements do not necessitate multiple crash tests and can be verified simultaneously. In other words, although there are four post-crash requirements, only one crash test is needed. There are also four compliance options for the electric shock protection requirement to provide flexibility. With regard to repeated full-

vehicle crash testing for component modifications, the FMVSS specifies the procedures that NHTSA uses to evaluate compliance. Manufacturers may use other reasonable methods to certify the compliance of their vehicles, such as simulations and component-level testing, which they may find appropriate when making minor changes. The vehicles must meet the FMVSS when tested by NHTSA according to the test procedures in the standard. For these reasons, the agency is not persuaded by Blue Bird's comments on the test burden of conducting full-vehicle crash tests for school buses. NHTSA maintains that the requirements are reasonable and appropriate for school bus safety and is adopting all proposed requirements for heavy school buses from the NPRM.

3. Post-Crash Safety for Other Heavy Vehicles

Proposed Requirements

The NPRM did not propose crash testing requirements for heavy vehicles other than heavy school buses because there is currently no available test that would be appropriate for these vehicles. The NPRM sought comment on applying a moving contoured barrier crash test to all heavy electric vehicles while acknowledging the cost and practicability constraints. The NPRM also sought comment on component-level tests that are representative of actual impact loads in heavy vehicle crashes and that can be applied to different weight classes of heavy vehicles.

GTR No. 20 provides an option for evaluating post-crash safety of light vehicles using a mechanical integrity test (crush test) of the REESS, with a quasi-static load up to 100 kN. GTR No. 20 also includes a mechanical shock test that evaluates the REESS mountings and fixtures by accelerating and decelerating the REESS installed on a sled system. However, as noted in the NPRM, the loads and accelerations specified in GTR No. 20 may be too low for heavy vehicles. In the absence of additional data to develop appropriate requirements, the NPRM did not propose component-level crash testing of heavy vehicle REESS.

Comments Received

Comments on the potential post-crash requirements for heavy vehicles other than school buses were varied, with some commenters suggesting vehicle-level or component-level tests and others stating additional research is needed. NTSB commented that NHTSA should have proposed the REESS mechanical integrity and mechanical shock test requirements from GTR No. 20 for heavy vehicles, calling the exclusion “unnecessary.” NTSB noted that the component-level tests constitute an established and applicable standard for heavy vehicle REESS that is not design-restrictive. Alternatively, NTSB stated, FMVSS No. 305a could at least include documentation requirements for post-crash safety of the heavy vehicle REESS. MEMA and Eaton also stated support for the inclusion of mechanical integrity and mechanical shock tests with additional isolation criteria.

Heavy vehicle manufacturers, DTNA and Prevost, commented that additional research should be conducted before establishing test requirements for post-crash safety of heavy vehicle REESS. DTNA stated support for the concept of the mechanical integrity test in general, but said that further research is necessary to develop a repeatable, reproducible, and practical test method. Prevost said additional research is needed for mechanical shock testing because accelerations on the REESS are highly design dependent. While Auto Innovators disagreed with application of additional requirements to heavy vehicles in general, Auto Innovators said it did not have significant concerns about applying the mechanical shock test from GTR No. 20 to heavy vehicles and suggested refining the test procedure by defining the acceleration as a function of vehicle mass to provide a more granular method.

Heavy vehicle manufacturer NFA agreed with NHTSA's assessment that component-level tests are more appropriate than full scale crash tests for heavy vehicles due to practicability, as did Navistar and EMA. None of them provided data on crash loads for heavy vehicles; NFA expressly stated that it does not have sufficient data to determine test parameters at this time. NFA pointed to existing standards for mechanical shock testing, stating that it currently uses the mechanical shock requirements of UNECE R100, and noting industry standards for compressed natural gas (CNG) vehicles require that the CNG storage system can endure an inertial load of 8G, which is within the range of the component test procedure from GTR No. 20.

Truck manufacturer Nikola stated that it designed and tested its vehicles based on the moving barrier tests currently in FMVSS Nos. 208, 214, and 305, and recommended that NHTSA likewise use the moving barrier for any heavy vehicle crash test requirements because it is more representative of a passenger vehicle. For mechanical shock testing, Nikola said that test facilities are not currently equipped with a test apparatus capable of testing Nikola's entire REESS or subset. Regarding mechanical integrity testing, Nikola disagreed with establishing a requirement, as it is not required by GTR No. 20 and Nikola already requires its battery pack manufacturers to follow the UL 2580 standard, which includes a crush test.

Tesla commented that component-level testing is inadequate for mechanical integrity and mechanical shock testing, stating that the test will not be representative of the full vehicle, especially if the battery system must be removed from the vehicle for testing. Creaform, a 3D measurement and analysis company, also recommended vehicle-level post-crash requirements for heavy vehicles, saying that vehicle crashes can impose higher loads on an unprotected REESS than quasi-static crush tests, depending on the location of the REESS in the vehicle, and that adjusting the component-level mechanical integrity and mechanical shock test parameters would not cover the risks. Creaform said advanced numerical simulations can serve as a lower-cost alternative to vehicle crash testing. Battery manufacturer Freudenberg also disagreed with component-level mechanical integrity testing, stating it will place undue expectations on the battery enclosure. Freudenberg requested alignment of FMVSS No. 305a with the UNECE regulation, which exempts heavy vehicles from mechanical integrity test requirements.

Agency Response

In the absence of new data, the agency is not adopting post-crash requirements for heavy vehicles other than heavy school buses in FMVSS No. 305a. The agency did not propose post-crash requirements for heavy vehicles other than school buses in the NPRM because additional information is needed to develop requirements that are reasonable, practicable, and appropriate for the vehicles. While NTSB stated that the component-level tests in GTR No. 20 are appropriate, the comment did not provide additional information. NTSB also suggested a documentation requirement for post-crash safety, which was not discussed in the NPRM and is therefore out of scope for this final rule.

Comments from heavy vehicle manufacturers indicated that they currently use industry standards such as UL 2580, “Electric vehicle battery testing and certification,” and other safety regulations in designing their vehicles and procuring battery packs. The industry standards used by manufacturers are convenient tools to

establish best practices in design and generally lack the objectivity needed for FMVSS. Further research will be needed to evaluate and modify such testing standards for inclusion in the FMVSS. Further investigation into heavy vehicle impacts and component-level test specifications would also address commenters' concerns regarding accurate representation of crash forces. As none of the comments provided supporting data, the agency maintains that additional research is necessary to determine appropriate post-crash requirements and acceptability criteria for heavy vehicles other than heavy school buses for future consideration of FMVSS adoption.

b. General Specifications Relating to Crash Testing

The NPRM proposed several general provisions from GTR No. 20 that would apply to various testing and performance requirements. These provisions pertain to light vehicles and heavy school buses subject to the crash testing requirements of the proposed FMVSS No. 305a.

1. Low Energy Option for Capacitors

Proposed Requirements

Currently, FMVSS No. 305 S5.3 requires that vehicles meet one of the following three criteria post-crash: electrical isolation; absence of high voltage; or physical barrier protection. The NPRM proposed to include a post-crash low energy option for capacitors in the electric powertrain that is included in GTR No. 20. Capacitors store electrical energy and may be connected directly to the chassis in some electric power trains. In fuel cell electric vehicles (FCEVs), the high-voltage systems may contain capacitors that are connected to high voltage buses and are not electrically isolated. Such capacitors may be high voltage sources post-crash (because a charged capacitor may not discharge quickly) and may not be able to comply with post-crash electrical safety requirements using the direct and indirect contact protection option or the electrical isolation option. However, capacitors may not pose a safety hazard when contacted, even though they may be high voltage sources post-crash, because they are low energy high voltage sources. NHTSA conducted an analysis of the potential hazard and concluded that the post-crash electrical safety compliance option for capacitors based on an electrical energy of 0.2 Joules or less provides adequate safety from electrical shock and long-term harmful effects on the human body.

Comments Received

Comments on the low energy option for capacitors were positive, with manufacturers expressing support for the inclusion. Tesla agreed that there is no need to fully discharge all the capacitors, and Auto Innovators noted that the option is consistent with GTR No. 20 and other applicable international regulations. Auto Innovators suggested changing the y-capacitor calculation to match ECE 100.03,

noting that the proposed calculation “is inconsistent with ECE practice where the energy of a Y capacitor is the greater of 0.5Cy × V11

2 or 0.5Cy × V2

2.” Auto Innovators also suggested a minor edit to the text of S8.2 to clarify that the inclusion of the low energy specification for capacitors is an additional option for the post-crash electrical safety requirement.

ECE R.100, “Uniform provisions concerning the approval of vehicles with regard to specific requirements for the electric power train,”

https://unece.org/sites/default/files/2024-01/R0100r3e.pdf

MEMA and Eaton commented that the low energy option for capacitors in the powertrain should include additional isolation requirements. MEMA said, “criteria should include an isolation requirement from all parts of battery system to the external power output connectors of the battery pack as is currently included in FMVSS 305 S5.3, as well as avoiding a single point of failure as a standard and best-practice.” Eaton recommended the same criteria. MEMA and Eaton referred to these two additional requirements as “acceptability criteria,” and requested their inclusion in multiple sections.

Agency Response

In response to the comments, the final rule follows the proposal in including a low energy option for capacitors for post-crash electrical safety. However, as detailed below, the final rule adopts the GTR No. 20 method of calculating energy in y-capacitors. In addition, the first paragraph of S8.2 has been edited for clarity and the typographical errors in S8.2(a)(2) have been corrected as suggested by commenters.

Auto Innovators requested changing the y-capacitor energy calculation to that in ECE R.100.03. We note that ECE R.100.03 does not have the post-crash low energy optional method of meeting electric safety requirements because ECE R.100.03 does not address post-crash safety. The post-crash low energy option is available in ECE R.94,

and the method of calculating capacitor energy post-crash is similar to that in GTR No. 20. The NPRM proposed calculating the energy stored in the two y-capacitors at once, assuming that each capacitance is the same, and requiring that the total energy not exceed 0.2 Joules. However, GTR No. 20 calculates the energy in each y-capacitor separately, using the individual capacitance, and requires that the energy in each capacitor does not exceed 0.2 Joules. Because the GTR No. 20 method uses the actual capacitance of each y-capacitor in the corresponding calculation, and therefore more accurately represents the stored energy in each, NHTSA is adopting the method from GTR No. 20 and requiring that the energy in each capacitor not exceed 0.2 Joules.

ECE R.94 Revision 4, “Concerning the Adoption of Harmonized Technical United Nations Regulations for Wheeled Vehicles, Equipment and Parts which can be Fitted and/or be Used on Wheeled Vehicles and the Conditions for Reciprocal Recognition of Approvals Granted on the Basis of these United Nations Regulations,”

https://unece.org/sites/default/files/2024-07/R094r4e.pdf

FMVSS No. 305a includes provisions for electrical isolation. As proposed, the post-crash electrical safety requirements in FMVSS No. 305a are the same as the current requirements in FMVSS No. 305, except for the addition of a low energy option for capacitors to comply with electrical safety requirements. All high voltage sources, including the REESS, need to be either electrically isolated, contactors open resulting in low voltage, or have direct and indirect contact protection. The low energy option for capacitors does not circumvent the requirements for electrical protection, but rather allows for another verification method.

The requirement to ensure no single point of failure (

e.g.,

contact failure) was not discussed in the NPRM and is not in scope of this rulemaking. The FMVSS requirements are written in a manner to not be design restrictive, and therefore do not prescribe a particular connection to the battery due to the variation of battery designs. However, the requirements for the REESS that are included in FMVSS No. 305a for normal vehicle operations and post-crash scenarios verify that the system design provides a requisite level of safety. Comprehensive risk mitigation of potential hazards is further addressed by the documentation requirements. As discussed later in Section IV.n., “Documentation Requirements,” manufacturers are required to demonstrate that they have considered and addressed identified safety risks for their vehicles. Designing separate connections to the battery and avoiding a single point of failure are examples of risk mitigation strategies that could be implemented by manufacturers along

with other protective measures. Additional requirements for the post-crash low energy option for capacitors, beyond those test and documentation requirements discussed above, were not included in the NPRM and so are not in scope for this final rule. NHTSA will continue to study and discuss further requirements for battery safety, including additional requirements for post-crash low energy option for capacitors, during the ongoing efforts on Phase 2 updates to GTR No. 20. Harmonization with the GTR No. 20 Phase 2 updates would be considered in future updates to the FMVSS No. 305a requirements.

2. Assessing Fire or Explosion in Vehicle Post-Crash Test

Proposed Requirements

In accordance with GTR No. 20, NHTSA proposed to include in FMVSS No. 305a a requirement that there be no evidence of fire or explosion for the duration of one hour after the crash test for heavy school buses, and for the duration of one hour after each crash test and subsequent quasi-static rollover test for light vehicles. The assessment of fire or explosion would be verified by inspection without removal of the REESS or any parts of the vehicle.

Comments Received

Commenters generally agreed with the proposed requirement. MEMA, Auto Innovators, Lucid, and Nikola stated support, with Nikola saying that the provision should also apply to heavy vehicles if a crash test requirement is added. Tesla agreed with the proposal as well but requested additional guidance and an explicit evaluation procedure. In contrast to other industry members, SAVE Coalition disagreed with implementing the requirement at the vehicle level because FMVSS Nos. 208, 214, 301, and 303 do not include the same requirement for other types of vehicles. SAVE Coalition said, “If NHTSA's intent is to regulate fire risks from all vehicle systems, that requirement should be applied more generally in a regulation covering all vehicles regardless of powertrain. For the purposes of assessing electric vehicle safety, and to align with GTR 20 and the stated intent in the preamble, this requirement should be clarified to be specific to REESS related fires.”

Agency Response

After considering the comments, NHTSA has decided to adopt the proposed post-crash requirement that there be no evidence of fire or explosion. For electric vehicles, thermal runaway and propagation poses a significant fire risk regardless of electrolyte leakage from the battery pack, so FMVSS No. 305a addresses fire safety assessment directly. The post-crash assessment does not require disassembly of the vehicle or components. Evidence of fire or explosion could include flames, smoke, scorch marks, or other indications. If such evidence were visible at any time within the one-hour inspection period following the crash test, the vehicle would fail to meet the safety requirement. The agency maintains that the requirement is appropriate as written.

Regarding SAVE Coalition's concern that only electric vehicles, not other vehicle types, are subject to post-crash fire assessment, NHTSA would like to explain the FMVSS safety requirements that were cited. FMVSS No. 208, “Occupant crash protection,” and FMVSS No. 214, “Side impact protection,” apply to vehicles regardless of fuel type and address the physical forces and accelerations in a crash; electric and non-electric vehicles must meet the safety requirements in these FMVSSs. Fire resulting from spillage or leakage of combustible fuels is addressed in fuel specific FMVSSs, including FMVSS No. 301, “Fuel system integrity,” and FMVSS No. 303, “Fuel system integrity of compressed natural gas vehicles,” by limiting combustible fuel spillage or leakage. For electric vehicles, FMVSS No. 305a addresses fire safety assessment directly because limiting electrolyte leakage outside of the battery pack is insufficient to address the risk of fire from thermal runaway and propagation in the REESS. Further, it may be difficult to ascertain the origin of a fire observed at the vehicle level, and exempting fires that may originate in or involve other vehicle systems would not be beneficial to safety. For these reasons, the agency is adopting the proposed requirement.

3. Assessing Post-Crash Voltage Measurements

Proposed Requirements

The NPRM proposed that the post-crash voltage measurements in FMVSS No. 305a would be made between 10 seconds and 60 seconds after impact. Using the time of impact to define the measurement period avoids a source of ambiguity present in FMVSS No. 305 and is consistent with the GTR No. 20 test procedure. The voltage measurement and calculation methods in the NPRM are otherwise the same as those currently in FMVSS No. 305.

Comments Received

Comments on the voltage measurement procedure were mixed, with some commenters in agreement and others requesting changes to the test specifications. Manufacturers Nikola, Tesla, and Lucid agreed with the agency's rationale and stated support for the proposed requirements. However, Honda said that the timing language is ambiguous and “could be misinterpreted to mean that the requirements must be met both at 10 seconds and 60 seconds after the impact.” Honda also said that 60 seconds is insufficient for isolation resistance measurements and requested full alignment with GTR No. 20, which does not include the upper time limit for electrical isolation. Auto Innovators provided a similar comment, noting that electrical isolation is stable and requesting removal of the 60-second limit for post-crash isolation measurements.

Auto Innovators commented on the proposed calculation method as well, stating, “the NPRM assumes that V1+V2=Vbat, but this may not be strictly true,” due to multimeter resistance. Auto Innovators provided revised diagrams and formulas and suggested that FMVSS No. 305a provide an electrical isolation compliance option matching ECE 100.03. Bugatti also disagreed with the calculation method for the electrical isolation baseline measurement, saying that it does not address a potential zero-volt measurement across Ro that may occur if Ri is much higher. Bugatti noted that the proposed requirements do not allow the use of a megohmmeter as an alternative method to avoid the zero-volt issue. Bugatti requested clarification and recommended adding the megohmmeter measurement method allowed by ECE 100.03. As with the low energy option for capacitors, Eaton again suggested adding acceptability criteria for battery isolation.

Agency Response

The agency is adopting the proposed requirements with a minor revision for the timing of voltage measurements for assessing electrical isolation post-crash. The proposed requirements stated that the post-crash voltage measurements would be made “between 10 to 60 seconds after impact.” The agency believes that this language is clear but agrees that the time specification should distinguish between compliance options. The post-crash electrical safety requirements include four compliance options: low voltage, electrical isolation, protective barrier, and low energy for

capacitors. After further consideration, the agency agrees that the 60-second time limit is unnecessary for the electrical isolation measurement procedure because the values are static and that harmonization with the GTR No. 20 specification is appropriate. For these reasons, the post-crash test specification has been modified to state that the measurements for the electrical isolation compliance option are made at least 10 seconds after impact, with no upper time limit.

With regard to possible zero-volt measurements in the electrical isolation baseline calculation, the agency does not believe there is an issue. Consistent with GTR No. 20, the minimum resistance of the voltmeter is specified, and a higher resistance R0 can be used if the voltage measurement is very low. The agency has not observed zero-volt measurements in testing using the specified procedures, which were evaluated for practicability and repeatability. The megohmmeter option from UNECE R100 is not incorporated because research has shown that the megohmmeter method may provide different results than the multimeter method. The agency believes inclusion of the megohmmeter option could lead to inconsistent results and would not be beneficial.

Auto Innovators provided an alternate measurement method and calculations for electrical isolation resistance that takes into consideration the resistance of the multimeter used for voltage measurements. Auto Innovators noted that this alternate method is in ECE R.100.03 and requested harmonizing with ECE R.100.03. However, the test method and calculations in ECE R.100.03

are the same as those currently in FMVSS No. 305 and proposed in the NPRM for FMVSS No. 305a. Regardless, the agency will continue evaluating the recommended alternate procedure to determine whether the results and ease of testing support its inclusion in FMVSS No. 305a. The alternate method was not proposed in the NPRM and is therefore out of scope of this rulemaking. If the agency's research supports use of the alternate measurement procedure and calculations, they may be added at a later date. At this time, NHTSA is adopting the method currently in FMVSS No. 305 and proposed in the NPRM for inclusion in FMVSS No. 305a.

See

Annex 5A on page 40 in ECE R.100.03 at

https://unece.org/sites/default/files/2024-01/R0100r3e.pdf

The suggestion to add acceptability criteria for battery isolation to the post-crash requirements was discussed earlier in Section IV.b.1, “Low Energy Option for Capacitors.”

4. Electrolyte Leakage

Proposed Requirements

The NPRM proposed to include a post-crash requirement limiting electrolyte leakage; this requirement is currently in FMVSS No. 305 as “electrolyte spillage” and permits no more than 5 liters of electrolyte spilled or leaked. NHTSA sought comment on the necessity and relevance of such a requirement for current EVs, as well as recommendations regarding electrolyte leakage detection methods and differentiation from other liquids.

Comments Received

Commenters agreed that the updated terminology of “electrolyte leakage” is appropriate but stated that the 5-liter maximum leakage requirement is no longer relevant. Auto Innovators and Nikola both said that leakage outside of the battery pack should not occur with modern EVs and that 5 liters is a very large amount. Auto Innovators stated that there is no reliable method to detect or quantify leakage and recommended that the requirement be removed entirely. Tesla stated that physical characteristics can be used to determine whether electrolyte or coolant has leaked from the vehicle if differentiation is a concern. Nikola suggested that any electrolyte leakage outside of the battery pack should constitute a failure. Blue Bird noted that there are many different forms of electrolytes, including solids and gels, and leakage may not be observed.

Agency Response

This final rule adopts the updated “electrolyte leakage” terminology and the current FMVSS No. 305 requirement for no more than 5 liters of electrolyte leakage post-crash. The cells of lithium-ion batteries in current EVs have small quantities of electrolyte that could leak out of the battery casing rather than spill. The agency agrees with commenters that any electrolyte leakage in EVs using lithium-ion batteries would be significantly lower than the current 5-liter limit in FMVSS No. 305. However, there are other types of batteries with aqueous electrolyte that may be considered for vehicle applications in the future.

At this time, it is unclear whether the 5-liter limit will remain appropriate for future batteries. Specifically for vehicles using a REESS with aqueous electrolyte, GTR No. 20 similarly includes a requirement limiting electrolyte leakage to no more than 5 liters within 60 minutes after the crash test.

Because there is no further information available, the agency is adopting the post-crash electrolyte leakage limit of 5 liters that is consistent with the current requirements in FMVSS No. 305 and GTR No. 20. However, unlike GTR No. 20, the agency is not distinguishing between REESS with different types of electrolyte; the requirements in FMVSS No. 305a are established as battery chemistry-neutral and are applicable to all types of REESS. The agency will continue to review and update the requirements in FMVSS No. 305a over time, as relevant information becomes available.

Sodium ion aqueous batteries (SIAB), which are environmentally benign, provide a promising alternative for safe, cost-effective, and scalable energy storage, with high power density. However, current SIABs have limited output voltage and inadequate energy density for vehicle applications.

GTR No. 20 also requires that no more than 7 percent by volume of the REESS electrolyte shall leak into the passenger compartment. However, as noted in the NPRM, there is no practical way of measuring the quantity by volume of the electrolyte in the REESS to ensure compliance with such a requirement.

While one commenter suggested a requirement for no electrolyte leakage outside of the battery pack, a post-crash requirement prohibiting any electrolyte leakage from the pack was not proposed in the NPRM and is out of scope for this final rule. A post-crash test requirement prohibiting any amount of leakage outside of the battery pack may also be challenging to verify. However, as in FMVSS No. 305, this final rule includes a requirement that no visible trace of electrolyte shall leak into the passenger compartment of the vehicle for occupant safety. This final rule also adopts visual inspection requirements in the tests evaluating safety during normal vehicle operations, including no evidence of electrolyte leakage or venting (without disassembly of the vehicle), as discussed in Section IV.c.6., below.

c. Vehicle Controls for Safe REESS Operation

Overview

The NPRM proposed requirements and associated full-vehicle tests for vehicles to ensure they have controls managing safe REESS operation, specifically overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit protection. These requirements are applicable to light vehicles and heavy vehicles, and are generally aligned with those in GTR No. 20, with minor differences for ease of testing. The NPRM also proposed documentation requirements for low-temperature protection, as in GTR No.

20, because no practical test procedure currently exists.

Commenters addressed a variety of topics related to the requirements for safe REESS operation. The comments submitted by NTSB and Consumer Reports expressed appreciation and support for the requirements to ensure REESS safety and longevity. The comments from industry also expressed general agreement with the requirements for safe REESS operation but disagreed about certain aspects of the test procedures. Specifically, these comments addressed vehicle- and component-level testing, REESS state of charge, breakout harness location, over-temperature testing, overcurrent protection, and venting and visual inspection, as detailed below. Overall vehicle- and component-level testing is addressed below in section IV.c.1. Comments on specific testing provisions for vehicle controls are then addressed in sections IV.c.2 through c.6.

1. Vehicle- and Component-Level Testing

Proposed Requirements

The NPRM proposed vehicle-level testing using a breakout harness connected to a battery tester/cycler to evaluate vehicle controls for safe REESS operation. The test procedures ensure the vehicle controls provide protection against overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit fault conditions. Maintaining the REESS within the manufacturer-specified functional range minimizes the risk of fire and electrical shock. NHTSA proposed vehicle-level testing of the REESS because testing at the equipment level would not evaluate all relevant vehicle controls or any interaction or interference between vehicle controls.

Comments Received

Many comments from industry disagreed with the agency's exclusion of component-level compliance test options, which are included in GTR No. 20 and ECE R100.03. Auto Innovators, Bugatti, EMA, Ford, Honda, Hyundai, Lucid, NFA, Nissan, UL Solutions, and ZETA were among those that requested component-level testing. ZETA stated that manufacturers “could face hurdles in transitioning to vehicle-level testing, including changing logistics, higher costs, and lack of testing equipment availability.” Auto Innovators likewise said that vehicle-level testing would add significant cost without increasing robustness or stringency.

Ford agreed with Auto Innovators, saying that it does not have large enough facilities, and noted that NHTSA did not provide data showing a need for full-vehicle testing. Honda stated that vehicle-level testing requires specialized parts, increases safety risks, and reduces control over test conditions compared to component-level testing. NFA said requiring full-vehicle testing would be burdensome and redundant, because the same pack would be tested multiple times. Hyundai said that the option to conduct testing at the component level would enable manufacturers to iterate on REESS design and safety systems more rapidly. Lucid said, “testing at the component level (REESS) provides the benefit of recreating the worst-case scenario, ideal for safety testing, due to its smaller thermal mass. Vehicle-level testing would also require larger thermal shock chambers than currently used at the REESS-level.” UL Solutions also suggested adding UL 2580 certification as another compliance option, while ZETA further requested that NHTSA allow manufacturers to specify their own boundary conditions for component-level testing because each vehicle model is different.

A few commenters suggested that component-level testing should be allowed under certain conditions or for specific tests. Nissan suggested that NHTSA allow a component-level compliance option if the manufacturer can demonstrate that the test results reasonably reflect the safety performance of the complete REESS under the same conditions. UL Solutions similarly requested that the agency “allow independent testing of the battery if the battery can demonstrate compliance to the requirements without the benefit of the vehicle support systems.” Tesla agreed with most of the proposed test procedures but requested a component-level compliance option for the over-temperature test, as “it would be difficult to characterize real-world driving temperature profiles fully and accurately due to variable drive states.” Nikola stated that vehicle-level testing for overcharge, over-discharge, and over-temperature protection cannot be conducted on hybrid or fuel cell EVs, so those tests should be conducted at the component level.

Agency Response

After reviewing the comments, the agency is adopting the requirements as proposed because vehicle-level testing is supported by NHTSA's research for its practicability and feasibility. NHTSA-funded research independently evaluated, refined, and validated the proposed vehicle-level test procedures for various types of electric vehicles (HEV, PHEV, and BEV).

NHTSA conducted additional research to evaluate capabilities in compliance test laboratories and practicability of vehicle level tests.

The test program demonstrated the ease of conducting tests at the vehicle level using breakout harnesses connected to a battery cycler/tester for the external inputs to the REESS without having to remove the REESS from the vehicle to conduct component-level tests. Evaluating REESS operation at the vehicle level is consistent with other FMVSSs and ensures the entire system is captured, including input from different subsystems and any interaction or interference between vehicle controls, and is most representative of real-world conditions. A vehicle level test also ensures that the boundary conditions are appropriate and would not be challenged in the event of a compliance test failure. NHTSA's initial research for test procedure development for electric vehicles was done with the whole vehicle and not with individual components in the vehicle.

The comments did not demonstrate that component-level testing of the REESS would provide the same comprehensive evaluation, nor that full-vehicle tests cannot be conducted on all applicable vehicles.

System-Level RESS Safety and Protection Test Procedure Development, Validation, and Assessment-Final Report,” DOT HS 812 782,

https://rosap.ntl.bts.gov/view/dot/42551

Test reports and laboratory test procedures are available in the docket NHTSA-2021-0029.

https://www.regulations.gov/docket/NHTSA-2021-0029/document,

Docket ID, NHTSA-2021-0029-0001, NHTSA-2021-0029-0002, and NHTSA-2021-0029-0003.

Safety Performance of Rechargeable Energy Storage Systems, DOT HS 812 717, 2019,

https://rosap.ntl.bts.gov/view/dot/40791

In contrast to comments that vehicle-level tests are burdensome, overly costly, and require additional safety measures, NHTSA's testing program revealed the ease of conducting testing at the vehicle level multiple times on the same vehicle without significant cost. The overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit test procedures in FMVSS No. 305a are non-destructive, are conducted at ambient temperatures, and can be conducted sequentially on the same vehicle, minimizing the time and cost of testing. The tests also include multiple end conditions for design flexibility. The agency maintains that the requirements are appropriate to replicate and confirm real-world vehicle operations and do not constitute an undue burden on manufacturers.

We understand manufacturers may conduct testing for various scenarios beyond the requirements of FMVSS No. 305a, and such testing may be conducted at the vehicle level and/or the component level. FMVSSs establish minimum safety requirements and the FMVSS test procedures provide notice to establish how the agency would verify compliance. However, this does not mean that manufacturers must conduct the exact test in the FMVSS to certify their vehicles. The Safety Act requires manufacturers to ensure their vehicles comply with all applicable FMVSSs and to certify compliance of their vehicles with all applicable FMVSSs, and the Safety Act specifies that manufacturers may not certify compliance if, in exercising reasonable care, the manufacturer has reason to know the certificate is false or misleading. A manufacturer may use component-level tests to certify its vehicles if they exercise reasonable care in doing so. In other words, a manufacturer must ensure that its vehicles will meet the requirements of FMVSS No. 305a when NHTSA tests the vehicles in accordance with the test procedures specified in the standard, but the manufacturer may use different test procedures to do so.

2. State of Charge (SOC)

Proposed Requirements

Initial SOC ranges were specified for each of the proposed test procedures for vehicles to ensure they have controls managing safe REESS operations. Some of the SOC ranges differed from those in GTR No. 20 for practicability and ease of conducting the tests. For the overcharge, over-temperature, and external short-circuit tests, the REESS is initially at 90 to 95 percent SOC. For the over-discharge test, the REESS is initially at 10 to 15 percent SOC. For the over-current test, the REESS is initially at 40 to 45 percent SOC.

Comments Received

Several commenters stated that there should be more flexibility in the SOC ranges for the tests. Auto Innovators and Honda stated that the proposed values are too extreme and will likely have already activated the protections. Auto Innovators requested that NHTSA align the starting SOC values with those in GTR No. 20. Nissan suggested setting the starting SOC around the middle of the normal operating range for the overcharge and external short-circuit tests, as in UNECE Regulation No.100, because hybrid vehicles may fall outside the range of normal use if the REESS is initially set between 90 to 95 percent SOC. Bugatti commented similarly, “Prescribing absolute values for SoC of the REESS, without consultation of manufacturer-specified SoC operational windows, may influence test results due to possible risk for the REESS to be out of its normal operating SoC range, even from the beginning of tests.” Bugatti recommended removing SOC values and taking a similar approach to UNECE Regulation No. 100, which references manufacturer-specified SOC.

Agency Response

After reviewing the comments, the agency is adopting the proposed requirements with a minor modification to the definition of SOC to clarify the requirements and address commenters' concerns. The initial SOC specifications in the test procedures refer to the “operating SOC,” or percent charge available under normal operation as it may be displayed to the user. In other words, the charge level for beginning each test is based on the normal functional range of the REESS defined by the manufacturer, not direct measurement of the battery capacity. This distinction was not sufficiently clear in the NPRM, leading to concerns about the validity of the test parameters. However, the specified parameters were tested and validated for different types of electric vehicles, including HEV and PHEV. These tests included vehicle crash tests of battery electric vehicles

and tests of vehicle controls that manage REESS operations and its health.

The initial SOC ranges are intended to minimize the amount of time needed to conduct each test. Starting every test in the middle of the normal operating range rather than the upper or lower portion would lead to longer test times with no added benefit. In the event that the vehicle does not display the operating SOC, the charge level can be estimated using the information provided by the manufacturer.

As an example,

see

page 2-27 of a NCAP crash test report of the 2022 Chevrolet Bolt, which indicates that the voltage range corresponds to the “usable energy” of the battery.

https://nrd-static.nhtsa.dot.gov/reports/vehdb/v10000/v14200/v14218R001.pdf

Electric Vehicle GTR No. 20 Test Development, Validation, and Assessment, DOT HS 812 092, April 2021,

https://rosap.ntl.bts.gov/view/dot/55584

To improve clarity, NHTSA is changing the definition of “State of charge” to mean the available electrical charge in a REESS expressed as a percentage of the normal operating capacity specified by the vehicle manufacturer.

3. Breakout Harness Location

Proposed Requirements

The NPRM proposed to conduct the REESS tests using a breakout harness connected to manufacturer-specified location(s) on the traction side of the REESS on the vehicle's electric powertrain. The manufacturer is required to specify the location(s) for connecting the breakout harness and may also provide an appropriate breakout harness for testing the vehicle. If the manufacturer does not provide a breakout harness, NHTSA will use a generic breakout harness to connect to the traction side of the REESS.

Comments Received

Regarding the overcharge, over-discharge, and overcurrent test procedures, Honda stated that the term “traction side” is too prescriptive and inconsistent with the proposed test procedure in S12.5, which did not include the same specification. Auto Innovators provided the same comment. Prevost requested clarification of the “traction side” designation to make clear which systems and subsystems are considered to be part of the traction side of the REESS and which are not. An example to clarify is whether the charging inlet is part of the “traction side” of the REESS. Prevost further suggested making note of a designated location when it is not specified by the manufacturer.

Agency Response

This final rule adopts the proposed requirements for the breakout harness location(s) as described in the NPRM, with edits for clarity and consistency. The “traction side” of the REESS refers to the connection between the REESS and the transmission, so it does not include the charging inlet. The traction side of the REESS is specified to ensure that external charging and regenerative charging are both captured by the test. Regenerative charging can potentially lead to overcharge conditions even if the vehicle controls prevent overcharging from the charging inlet. The manufacturer is also required to state the connection location(s) because a single location would not work for all vehicles and because connecting the harness to the wrong points of the powertrain could be damaging and/or hazardous. For the test operators' safety, ease of testing, and to prevent damage to the vehicle or test equipment, the manufacturer is required to recommend specific connection location(s). Although the NPRM clearly stated that the manufacturer is required to provide connection locations, the proposed

regulatory text was inconsistent. The text in S12 has been edited to clarify the requirement. Additionally, because the manufacturer is required to provide connection locations, no default locations are necessary. Regarding the exclusion of “traction side” in S12.5, that test is intended to evaluate the response to an external short circuit, so the traction side specification does not apply. Another possible source of confusion could be due to the proposed text for S12.5 referencing “overcharge” instead of “external short-circuit;” the text has been corrected in the final rule.

4. Over-Temperature Protection

Proposed Requirements

The NPRM proposed to include the over-temperature protection requirement and test procedure from GTR No. 20, with minor changes. NHTSA's testing indicated that presoaking the vehicle was not necessary,

so the NPRM proposed to remove presoaking from the procedure to reduce the test time and burden. The test procedure specifies that the test is conducted at ambient temperature, between 10°C and 30°C, with the cooling system disabled or minimized. The vehicle is driven on a chassis dynamometer using the manufacturer-provided drive profile, or with aggressive acceleration and deceleration if an appropriate drive profile is not provided.

NHTSA testing demonstrated that presoaking of the vehicle at elevated temperature does not raise the temperature of the REESS as significantly as by driving the vehicle under high acceleration and deceleration drive modes.

See

System-Level RESS Safety and Protection Test Procedure Development, Validation, and Assessment-Final Report. DOT HS 812 782 October 2019.

https://rosap.ntl.bts.gov/view/dot/42551

Comments Received

Commenters generally agreed with the requirement but recommended changes to some aspects of the test procedure. MEMA stated agreement with the agency's decision to remove presoaking, and Auto Innovators agreed with removing the requirement but said it should be permitted. Auto Innovators also stated that several provisions were overly prescriptive and unnecessary, specifically the directions to conduct the test on a chassis dynamometer and/or in active driving mode, limit the ambient temperature to 30°C, and specify a one-hour time period. Honda also disagreed with the limits on the time period and ambient temperature, stating that there are situations where the battery temperature will not rise unless the ambient temperature rises. EMA also suggested modifying the standard cycle specification to allow a manufacturer supplied drive profile, as “S12.4 (d) requires using an appropriate manufacturers supplied drive profile and (h) should follow the same drive profile or allow for the option to follow the same manufactured supplied drive profile.” In an ex-parte meeting,

Nissan commented that it was unclear whether all three test termination conditions had to be fulfilled to terminate the charge/discharge cycle.

Nissan requested to meet with NHTSA to present information related to the proposed rule. An ex-parte memo has been submitted to the docket (

https://www.regulations.gov/docket/NHTSA-2024-0012

Agency Response

After reviewing the comments, the agency is adopting the proposed requirements with an additional clarification for the manufacturer-provided drive profile. The proposed rule defined an appropriate drive profile by stating that it should raise the temperature of the REESS above the safe operating temperature within one hour. The test procedure specifies that the cooling system is disabled or functionally minimized for testing, but this provision was not stated when defining an appropriate drive profile. The commenters did not specify if the REESS cooling system was minimized in their testing. However, the agency recognizes that some vehicles may not be operable with cooling reduced to a level that would allow the REESS to overheat under the specified test conditions. To address commenters' concerns, if it is not possible to raise the temperature of the REESS without raising the ambient temperature of the vehicle above 30°C, the manufacturer may provide a drive profile that would trigger the over-temperature condition within one hour if the thermal management system were effectively disabled.

For the performance test, the test termination conditions in FMVSS No. 305a are identical to those in GTR No. 20, where the vehicle may be charged and discharged for up to 3 hours. The test time is not limited to one hour and it is not required to trigger the over-temperature protection, to avoid penalizing effective thermal management. The test procedure also does not prohibit presoaking or otherwise specify the starting temperature of the vehicle. However, the test is conducted at ambient temperature to avoid the added cost of testing in a heat chamber. The use of a chassis dynamometer and active driving possible mode of the vehicle are specified to ensure that the vehicle is tested in the normal operating state. The termination conditions were accurately described in the preamble of the NPRM and are the same as those in GTR No. 20. However, the agency agrees that the proposed regulatory text did not clearly indicate only one of the termination conditions needs to be fulfilled to terminate the discharge/charge cycle. The regulatory text specifying the test methods for evaluating vehicle controls managing REESS safe operations (S12) have all been modified to clarify the corresponding termination condition requirements in the final rule.

Section S12.4(h) of the over-temperature test procedure specifies conducting a standard cycle, if allowed by the vehicle. A standard cycle, as defined in GTR No. 20 and FMVSS No. 305a, consists of a standard discharge followed by a standard charge. The NPRM stated that the discharge and charge rates used for the standard cycle would be provided by the vehicle manufacturer. It also specified the alternative charge and discharge rates that would be used if the manufacturer did not provide them. The standard cycle is the same for each of the test procedures addressing safe operation of the REESS and is unrelated to other test specifications. The definition and use of the standard cycle are adopted as proposed.

5. Overcurrent Protection

Proposed Requirements

The NPRM proposed to include the overcurrent protection and test for vehicles capable of charging by direct current (DC) external electricity supply, as in GTR No. 20. During the test, the REESS is charged using the battery tester/cycler in accordance with the manufacturer's recommended charging procedure with the highest normal charge current specified by the manufacturer, or at a rate of C/3 current if none is provided. After charging is initiated, an over-current specified by the manufacturer is supplied, or the current is increased in 10-Ampere steps, until the vehicle over-current protection terminates charging or the temperature gradient of the REESS is within 4°C for a two-hour period. The standard cycle is then performed, if possible, and the test concludes with electrical isolation assessment and a one-hour observation period to assess evidence of electrolyte leakage, venting, fire, or rupture.

Comments Received

EDTA, MEMA, NEMA, and Eaton suggested expanding the overcurrent protection requirements to address battery isolation. NEMA said that the

contactors can weld, leading to a system protection failure and a safety issue, and that GTR No. 20 does not offer adequate overcurrent protection in those cases. Eaton emphasized that contactor failure occurs frequently, as evidenced by recent vehicle recalls, and suggested NHTSA require manufacturers to demonstrate they can fully isolate the positive and negative poles of the battery following a vehicle crash or overcurrent event. EDTA, MEMA, and NEMA made similar comments, requesting battery isolation testing and documentation showing no single point of failure.

Agency Response

After reviewing the comments, the agency is adopting the proposed requirements. NHTSA agrees with commenters that contactor failure can lead to system protection failure and a safety issue. However, we do not see a need to explicitly require “fully isolat[ing] the positive and negative poles of the battery following a vehicle crash or overcurrent event,” as Eaton and other commenters suggested. The test procedures in the FMVSS are established to mitigate safety risks in a manner that is not design restrictive. In the adopted overcurrent test, the overcurrent is applied until either the protection controls terminate charging (contactors open), or a long time has passed without an appreciable change in REESS temperature. Additionally, after the overcurrent is applied, a standard cycle is performed, if possible,

after which no electrolyte leakage, rupture, venting, fire, or explosion is permitted during a one-hour observation period. At the conclusion of the observation period, the electrical isolation is determined in a similar manner as in FMVSS No. 305, using a voltmeter to measure the voltages. The agency believes that the termination criteria for the application of overcurrent and the subsequent evaluations ensure that the main contactors in the REESS are not fused due to the overcurrent and therefore mitigate the safety risk. These requirements are intended to enhance safety while allowing manufacturers design flexibility.

If the contactor opens when the overcurrent is applied, the vehicle will not charge/discharge unless the controls are reset.

NHTSA will continue to research and assess electric vehicle safety issues and the need for additional changes to the overcurrent requirements. NHTSA is also aware of vehicle fires originating at the vehicle charge inlet while the vehicle is being charged. Some of these fires have resulted from faulty connections between the charge connector and the vehicle. As part of NHTSA's Battery Safety Initiative,

the agency continues to evaluate these safety risks and potential future agency actions to mitigate these risks.

https://www.nhtsa.gov/battery-safety-initiative.

6. Venting and Visual Inspection

Proposed Requirements

Venting is the release of excessive internal pressure from a cell or REESS in a manner intended by design to preclude rupture or explosion. Venting during normal vehicle use may result in varying degrees of safety risks to the vehicle occupant. The NPRM proposed that each of the tests evaluating vehicle controls for safe REESS operation (overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit test procedures) would end with the vehicle observed for one hour for evidence of electrolyte leakage, rupture, venting, fire, or explosion, followed by voltage measurements for determining electrical isolation. NHTSA proposed that there be no evidence of electrolyte leakage, venting, or rupture that is verified by visual inspection without disassembly of any part of the vehicle. Visible smoke during and after the test, and/or the presence of soot and/or electrolyte residue in post-test visual inspection, are indicators of venting and electrolyte leakage. The agency acknowledged that research is needed to develop a repeatable, reproducible, and practical method to verify the occurrence of various vented gases and requested comment on the Informal Working Group's continuing work in Phase 2 of the GTR.

Comments Received

As a whole, commenters agreed that venting detection methods are challenging to specify at this time and appropriate sensors are still under development. Auto Innovators stated that the proposed visual inspection requirement is unnecessary because visible venting is unlikely. On the other hand, DTNA agreed with the visual inspection requirement but requested adding a test procedure provision where venting inspection is captured visually and with written description of the findings.

With regard to sensor research, Tesla stated agreement with the agency's assessment that more research is needed, and Nikola said it doesn't have enough to data to recommend the usage of such sensors for general application. For future test requirements, Rivian suggested that the detection method depend on whether the area of concern is the gas venting within the REESS or the risk of occupant/bystander exposure to vented gases. Rivian noted that gas detection outside of the REESS is more challenging than detection inside the REESS and recommended prioritizing carbon monoxide sensors. Auto Innovators suggested focusing on a limited number of critical gases, with an emphasis on release or venting that may impact occupants.

Agency Response

The agency is adopting the proposed requirements for no evidence of electrolyte leakage, rupture, venting, fire, or explosion as determined by visual inspection during a one-hour observation period for each of the vehicle controls for safe REESS operation tests. The commenters agreed that appropriate sensors and procedures for detection of vented gases are not currently available and that more research is needed. NHTSA is continuing to investigate gas detection methods and potential test procedures to address venting of hazardous gases such as carbon monoxide. This research will inform future rulemaking. At this time, the agency believes inclusion of the visual inspection requirement enhances safety protection to limit safety risk to vehicle occupants due to venting and should remain a minimum requirement until quantitative detection methods are fully developed. As with similar standards, the compliance test procedures will include recording of the visual inspection results, using detailed descriptions, video, and/or photographs as appropriate.

d. Mitigating Risk of Thermal Propagation Due to Internal Short Within a Single Cell in the REESS

Proposed Requirements

The NPRM proposed documentation requirements for risk mitigation of thermal propagation events resulting from single-cell thermal runaway (SCTR) due to an internal short circuit within a cell in the REESS. NHTSA's proposed documentation component structure is based on elements from GTR No. 20, ISO-6469-1: Amendment 1

2022-11,

and ISO-26262.

The documentation submitted by the manufacturer is required to include all known risks to vehicle occupants and bystanders, risk assessment, risk management, and risk mitigation strategies in external charging mode, active driving possible mode, and parking mode. The objective of the documentation requirements is for vehicle manufacturers to identify the risks of single-cell thermal runaway and propagation for their REESS type, identify strategies to mitigate those risks, and demonstrate how those strategies work. The manufacturers' assessment and validation of risk mitigation strategies may involve a combination of physical testing and simulations at the component level and/or full vehicle level. The requirements are not design restrictive and apply to REESSs of all types.

ISO 6469-1: Third Edition 2019-04 Amendment 1 2022-11, “Electrically propelled road vehicles—Safety specifications—Part 1: Rechargeable energy storage system (RESS),” specifies safety requirements for REESSs, including test methodology for initiating thermal runaway in a cell for the purpose of conducting a thermal runaway propagation test and a format for reporting on risk mitigation strategies of thermal propagation resulting from a thermal runaway in a single cell of an REESS due to an internal short within the cell.

ISO 26262: 2018, “Road vehicles—Functional safety,” provides a comprehensive collection of standards to manage and implement road vehicle functional safety from concept phase to production and operation. The standard provides guidelines for overall risk management, individual component development, production, operation, and service.

Comments Received

There were several comments on SCTR risk mitigation documentation, including multiple requests for clarification. Tesla, HATCI, and Honeywell stated support for the proposed documentation approach. However, HATCI disagreed with the addition of the two new operation modes, stating they are unlikely to add material safety benefits while unnecessarily increasing the test and documentation burden, whereas Honeywell said the addition acknowledges the need to identify distinct risks and mitigations for each operational mode. Nissan suggested that NHTSA add a detailed description of safety risks “such as fire, explosion, or smoke” to enhance clarity regarding the severity of these risks in S13.1. Lubrizol stated strong support for the requirements proposed in the NPRM and provided graphs demonstrating the performance of their fluids for immersed thermal management of the REESS.

Auto Innovators questioned the necessity of the SCTR requirement given the inclusion of other thermal runaway and propagation requirements (

e.g.,

the requirement for a thermal event warning), and asked the agency to provide additional research to support the inclusion of this requirement, though it also said that the proposed reporting requirements appear to be reasonable. Additionally, Auto Innovators said the requirement should not apply to Ni-MH batteries because the electrolyte generally used in Ni-MH batteries is not flammable; Auto Innovators noted that GTR No. 20 and industry standards limited the requirement to flammable electrolyte REESS and that internal short-circuits are less likely in Ni-MH batteries due to greater spacing of the electrodes. Auto Innovators further requested clarification on several aspects of the requirements, including risks, validation strategies, and terminology where the FMVSS deviates from GTR No. 20. Auto Innovators said the term “vehicle power” in the definition of parking mode is ambiguous and could mean any voltage or just high voltage. Auto Innovators also said there should be processes for updates or corrections, the requirements should not be limiting, and providing confidential business information should not be required if the information is subject to public disclosure.

Lucid and NFA also requested further clarification of the requirements. Lucid said, “As proposed, the requirements could lead to either over- or under-reporting. Lucid stresses the importance of delineating the documentation requirement under Part IV, overall evaluation of risk mitigation, to avoid conflation with risk mitigation itself.” NFA likewise suggested that NHTSA define “the requisite detail level within the SCTR Risk Assessment and Mitigation documentation of the Proposal, with the expectation that it aligns with established best practices and industrial standards, such as ISO 26262 or SAE J1739.” NFA also stated that the vehicle manufacturers will need information from the REESS manufacturer and NHTSA should follow the confidential document treatment procedure of 49 CFR part 512 to protect proprietary information. Nikola agreed that it makes sense to not require a warning for SCTR and that a thermal runaway warning should be required. Nikola suggested a battery manufacturer requirement similar to the UL 2580 SCTR test, which forces a cell into thermal runaway. Similar to NFA, Nikola expressed concerns about obtaining proprietary information from battery manufacturers and suggested Confidential Business Information treatment per 49 CFR part 512.

Agency Response

For the final rule, the agency is adopting the proposed risk mitigation documentation requirements. However, instead of including the documentation requirements in FMVSS No. 305a as proposed, this final rule includes the risk mitigation documentation requirements in part 561. The purpose of these documentation requirements is to ensure that manufacturers have considered and addressed the risk of SCTR due to an internal short circuit, as the risk is highly dependent on REESS design and there is no one field-relevant performance test that can be applied to all REESS designs in a repeatable and reproducible manner. NHTSA-funded research examined various existing methods of initiating thermal runaway, including the heating element method, rapid heater method, nail penetration, and laser method, on batteries with a variety of chemistries, formats, and configurations.

The agency's research indicated that the thermal runaway initiation methods may influence the test results and the most appropriate initiation method for a battery may depend on the battery chemistry, format, and configuration. Nikola referenced a private industry developed standard, UL 2580 “Standard for batteries for use in electric vehicles,” as a potential requirement for battery manufacturers. Among other requirements, UL 2580 specifies a test where a single cell is forced into thermal runaway, by any means recommended by the battery manufacturer, with a requirement for no evidence of fire or explosion for 1 hour after initiating thermal runaway. Such a test is not appropriate as a compliance test procedure because some thermal runaway initiation methods employed may require advanced equipment and knowledge of the REESS that is only available to the manufacturer. It is also difficult to establish objectivity and could be design restrictive. However, manufacturers may voluntarily use any or all of the tests in UL 2580 for validating risk mitigation strategies in their documentation submitted to the agency. For these reasons, the agency is not requiring a performance test for thermal runaway of a single cell.

Lamb, J., Torres-Castro, L., Stanley J., Grosso, C, Gray, L., “Evaluation of Multi-Cell Failure Propagation,” Sandia Report SAND2020-2802, March 2020.

https://www.osti.gov/servlets/purl/1605985.

Regarding the need for SCTR risk mitigation requirements given the other requirements in the proposal, including

warning for a thermal event in the REESS, the agency believes a requirement to mitigate the risk of SCTR due to an internal short circuit is needed because: (1) there have been a number of electric vehicle fires in the field resulting from a short circuit within a cell in the REESS of vehicles in parking, charging, and driving modes, (2) none of the performance test requirements for the safe operation of the REESS (overcharge, over-discharge, overcurrent, external short-circuit tests) address SCTR and thermal propagation resulting from an internal short circuit, and (3) the thermal event warning is required when the vehicle is in the active driving possible mode to allow vehicle occupants to safely egress, but does not address prevention of vehicle fire.

With regard to specific battery chemistries, the documentation requirements for SCTR are battery chemistry neutral. Safety risks need to be evaluated and mitigated for all types of vehicle REESS, regardless of chemistry, to minimize the possibility of hazardous conditions. Gas venting, explosion, or other hazards can occur even without flammable electrolyte. The documentation requirements include identification of safety risks and mitigation strategies. If a REESS uses non-flammable electrolyte and the REESS cells have large spacing between electrodes, those elements may be included as primary risk mitigation strategies in the required documentation. Primary risk mitigation strategies include manufacturing quality control to mitigate defects in cells of REESS, REESS design features such as heat sinks, cell spacing, coolant, advanced battery management system with prognostics, and diagnostics systems to manage the health of the cells of an REESS and detect a possible thermal runaway condition before it occurs. Primary risk mitigation strategies reduce the risk of SCTR due to an internal short circuit and the occurrence of thermal propagation that may result from SCTR, while secondary risk mitigation strategies may not reduce the risk of thermal runaway or thermal propagation but reduce the hazards associated with thermal propagation. Secondary risk mitigation strategies include warning systems to vehicle occupants/bystanders and/or notification to emergency personnel in the event of thermal propagation (

e.g.,

automatic notification to 911 operators). The NPRM provided examples of mitigation strategies, but specific strategies are not mandated, allowing flexibility and practicability of various battery chemistry and battery systems without limiting only certain risk mitigation strategies known now. The risk reduction analysis requirement follows industry standard methodology.

ISO 26262, “Road vehicles—Functional safety,” provides a comprehensive collection of standards to manage and implement road vehicle functional safety from concept phase to production and operation. The standard provides guidelines for overall risk management, individual component development, production, operation, and service.

https://webstore.ansi.org/industry/automotive/electric/safety/functional-safety-iso-26262?psafe_param=1&gad_source=1&gclid=Cj0KCQjw99e4BhDiARIsAISE7P_bipjmLqkehMPUorfq0x2h6lAVWmd0GSbo7Z7qRtwAI-Rfd40YBMUaAuMuEALw_wcB

As previously stated, the requirements are based on those from GTR No. 20. NHTSA extended the requirements to include consideration of the external charging and parking modes to ensure safety under all normal vehicle operating conditions. The incremental amount of documentation from adding other operating modes is minimal. The operating modes were defined in the NPRM, with

Parking mode

defined as “the vehicle mode in which the vehicle power is turned off, the vehicle propulsion system and ancillary equipment such as the radio are not operational, and the vehicle is stationary.” Per this definition, both the high-voltage and the low-voltage power are turned off. The regulatory text also describes the information to include in each section of the documentation for completeness, from system diagrams to validation of risk mitigation strategies. As proposed, the required documentation is to be submitted upon request. Documentation containing proprietary information can be submitted as Confidential Business Information (CBI) under 49 CFR part 512 and will be handled accordingly. Documentation submission, regulations, and CBI are discussed further in Section k.

e. Thermal Event Warning

Proposed Requirements

As part of a risk-mitigation approach addressing multiple aspects of electrical system safety, the NPRM proposed a performance requirement for a thermal event warning. The term “thermal event” refers to a condition when the temperature within the REESS is significantly higher (as defined by the manufacturer) than the maximum operating temperature specified by the manufacturer. Thermal events may occur due to moisture and dust accumulation that causes a short circuit at the connections or electronic components within the REESS. A thermal event within a battery pack can be a safety critical event, as it can lead to smoke, fire, and/or explosion. A warning provided when a thermal event within the REESS occurs while the vehicle is in active driving possible mode would reduce the likelihood of occupant exposure to hazardous smoke, fire, and/or explosion. NHTSA also proposed that the visual warnings be provided to all front row occupants for vehicles with automated driving systems without manually operated driving controls.

Comments Received

There were many comments on the proposed thermal event warning test. Comments from Consumer Reports, Lucid, and EMA stated support for the actual audio-visual warning. Consumer Reports also suggested that NHTSA work with manufacturers to ensure all warnings are sufficiently prominent and convey the severity of the event. SAVE Coalition agreed with the warning overall but noted that it was only directed to the driver of the vehicle. To include vehicles equipped with automated driving systems, SAVE Coalition suggested adding, “For a vehicle without manually operated driving controls, the warning must be provided to occupants in all outboard designated seating positions.” On the other hand, Auto Innovators said, “We recommend remove requirements for AVs without manual driving controls; NHTSA has not provided rationale for why any warning needs to be provided to the `front row occupant'; the occupant cannot take any action based on the visual warning.” Honeywell suggested adding an auditory warning requirement for active charging and parking modes to enable relocation of adjacent vehicles, evacuation of building occupants, and alerts to bystanders. ACIL likewise encouraged NHTSA to include requirements for a warning to vehicle occupants and/or bystanders outside the vehicle in the event of thermal propagation.

Some commenters said that the NPRM discussion of “thermal runaway,” “thermal propagation,” and “thermal event” was unclear. Nissan suggested that sections S13.2 and S13.3 for the thermal event warning should be distinct from S13, thermal propagation safety, to ensure clarity and precision in addressing thermal safety risks within the documentation. Nikola said, “NHTSA is proposing to not have a warning for a thermal runaway but to require one for thermal event that is intended to inform occupants to egress the vehicle. The definitions of Thermal event and Thermal Runaway are being

conflated.” NFA likewise stated that there appeared to be a discrepancy in NHTSA's statements about the relevance of SCTR and thermal event warnings.

Many comments disagreed with the parameters of the proposed test requirement. Auto Innovators said the NPRM did not provide references or otherwise explain the test parameters. They noted that battery modifications can be risky and suggested slower heating due to “concerns with the proposed test method of using a heater that abruptly achieves 600C within 30 seconds [which] could result in unstable test conditions.” NFA said that the three-minute timeframe seems arbitrary and uncorrelated with occupant hazard exposure, and suggested using the SCTR thermal propagation criteria from ECE R100. Tesla, HATCI, Honeywell, ZETA, Lucid, Nikola, and Honda all expressed similar concerns over the timing and occurrence of actual thermal runaway and propagation with the proposed test procedure. Some suggested other initiation methods or a ramp of 180 seconds as in GTR No. 20. Nissan said the temperature specification was too high. Honda recommended clarification that the temperature specification refers to the heater temperature, not the REESS temperature. Honda also requested clarification on allowable modifications to the REESS, including replacement of one or more cells with heater equipment preinstalled for accurate test results. Similarly, Bugatti requested “a clear definition of thermal runaway condition and confirmation whether instrumented cells will be allowed to recognize this event,” to ensure that manufacturers have flexibility to accommodate the test equipment if NHTSA does not allow other triggering methods.

Several vehicle and component manufacturers said that the vehicle-level test requirement is unnecessarily dangerous. MEMA said that the test would generate toxic smoke and other potentially unsafe conditions for test personnel, and contradicts other requirements to mitigate or stop thermal runaway. Ford said the heater test is “unnecessarily destructive and burdensome in that it requires the initiation of a thermal runaway to confirm the illumination of a warning light,” and recommended verification using an electronic signal instead. Prevost also expressed safety concerns, noted additional difficulty in testing heavy vehicles, and suggested a subsystem test. EMA suggested a documentation requirement or component-level test, as the full-vehicle test could destroy the vehicle and introduce an unsafe situation. Many other commenters also recommended implementing the documentation requirement from GTR No. 20 due to issues with the proposed test requirement.

Agency Response

After consideration of the comments, the agency is not adopting the proposed performance test requirement for the thermal event warning but is implementing a corresponding documentation requirement in part 561 instead. While the agency maintains the importance of the required thermal event warning, commenters raised concerns about the proposed test method and safety of testing. The agency agrees that additional research is needed to ensure that any performance test for the thermal event warning is well-defined, appropriate for all vehicles, and does not pose an undue risk to test personnel. In turn, the documentation requirements are adopted for the final rule.

The documentation requirements for the audio-visual thermal event warning are similar to those in GTR No. 20. Manufacturers are required to provide documentation to the agency, upon request, with a detailed description of the system for triggering the warning. Specifically, the documentation requirements include parameters and associated threshold levels that are used to indicate a thermal event (

e.g.,

temperature, temperature rise rate, SOC level, voltage drop, electrical current, etc.) to trigger the warning, as well as a system diagram and written explanation describing the sensors and operation of the vehicle controls that manage the REESS in the event of a thermal event.

The primary purpose of the adopted warning is to ensure occupants have sufficient time to exit the vehicle to minimize direct exposure to potential hazards. The warning is to be provided regardless of the cause of the thermal event. A thermal event in the REESS can lead to smoke, fire, and/or explosion, and a warning can reduce the likelihood of occupant exposure to these safety hazards. The audio-visual warning is provided to the driver, or to all front row occupants in the case of autonomous vehicles without manually operated controls, notifying of a thermal event in the REESS when the vehicle is in active driving possible mode. The agency believes this specification is appropriate to ensure the driver or the front row occupants in vehicles with automated driving systems without manually operated controls are alerted of the potential safety hazard to ensure the driver or occupants can stop and exit the vehicle. The front row provision for vehicles with automated driving systems is aligned with other FMVSSs

and may be revised over time. The primary purpose of the adopted warning is to ensure occupants have sufficient time to exit the vehicle to minimize direct exposure to potential hazards. Activation of a warning to bystanders outside the vehicle was not proposed in the NPRM and is not in scope for this final rule. Additionally, further research needs to be conducted to determine the type and efficacy of such a warning to people outside the vehicle.

See

requirements in S9.2.2 of FMVSS No. 208 with regard to the air bag suppression telltale. The telltale is required to be visible to the front outboard passengers.

Some commenters said the discussion in the NPRM was unclear between the term of thermal event and SCTR and the corresponding warning requirements. Section 2 of the NPRM addressed thermal propagation from SCTR due to an internal short circuit within the cell; this is a specific hazard that can be minimized by risk evaluation and mitigation in design and manufacturing. Risk mitigation includes implementing strategies to prevent SCTR and to isolate a cell that is in thermal runaway to prevent thermal propagation. A warning specifically for SCTR is not required. However, any instance of thermal runaway and propagation that occurs, regardless of the cause, should trigger the thermal event warning for the vehicle occupants' safety. To minimize confusion, the documentation requirements for the thermal event warning and for SCTR risk mitigation are adopted in separate sections of part 561.

f. Vehicle Control Malfunction Warning

Proposed Requirements

The NPRM proposed a documentation requirement for a driver warning in the event of a malfunction of vehicle controls that manages the safe operation of the REESS. The warning documentation requirement is similar to GTR No. 20, with two added provisions, and is an interim measure intended to ensure that manufacturers will identify, address, and validate the effectiveness of their visual warnings that help manage safe REESS operation. This approach is intended to evolve over time as battery technologies and NHTSA's information about the REESS safety risk mitigation strategies evolve.

Comments Received

Comments on the vehicle control malfunction warning documentation requirement were positive. Nikola

agreed with requiring a warning, stating that it already provides malfunction warnings to the driver and documents all the information in the monitoring and diagnostic documents required by the California Air Resources Board for powertrains. Tesla stated support for including the requirements in FMVSS No. 305a because they apply to all REESSs irrespective of crash conditions. HATCI and Auto Innovators also stated support for the proposed documentation requirements. Auto Innovators agreed that there is currently no practical test procedure and stated support for the documentation approach.

Agency Response

The agency is adopting the proposed requirements for a driver warning in the event of a malfunction of vehicle controls that manage the safe operation of the REESS. Commenters agreed that the warning and documentation requirement are appropriate and indicated that they may already maintain and produce such documentation as required by other regulations. For the final rule, the vehicle control malfunction warning requirements are adopted in FMVSS No. 305a and part 561.

g. Protection Against Water Exposure

Proposed Requirements

The NPRM proposed water exposure test requirements, where a vehicle shall maintain electrical isolation resistance after the vehicle is exposed to water under normal vehicle operation, such as in a car wash or while driving through a pool of standing water. As in GTR No. 20, the proposed test procedures specify the use of freshwater. The proposed physical test requirements comprised of two tests. The proposed washing test was similar to that in GTR No. 20, with the addition of exposing the vehicle underbody to the water stream to make the test more representative of vehicle washing. The proposed driving through standing water test was also similar to that in GTR No. 20, but with the maximum test duration reduced from 10 minutes to 5 minutes. Electrical isolation was proposed to be determined at the conclusion of each test, and once again after 24 hours.

The NPRM did not propose to allow the documentation or isolation loss warning compliance options from GTR No. 20 for the water exposure tests. The NPRM requested comment on the proposed test specifications, including water pressure for the washing test. The NPRM also requested comment on water salinity levels for the tests as well as potential test procedures for submersion.

Comments Received

There were a variety of comments on the water exposure requirements. Some commenters agreed with the proposed test procedures, while others requested additional compliance options or changes to the test specifications. For the washing test, Tesla stated support for the proposed test method and recommended keeping the freshwater specification from GTR No. 20. Auto Innovators suggested establishing a maximum test duration and changing the timing of the isolation checks to 12 hours to reduce the time burden. Auto Innovators said the test parameters should not include salinity because it is unnecessary and because a large amount of water will be needed, and the reproducibility of salinity levels is challenging. Nissan also said that using saline in the proposed tests would not significantly impact the evaluation and is unnecessary.

Hyundai requested clarification for the underbody spray distance and angle for the proposed test procedure to ensure the test is clear and repeatable. For water pressure, Eaton agreed with adopting IPX5 for normal driving conditions. NEMA also agreed that IPX5 matches normal conditions but suggested using IPX7 to address submersion concerns. Nikola said, “Increasing the pressure does seem prudent as it will be the standard practice to use a pressure washer to clean the vehicles,” and suggested IPX6.

Eaton stated support for the inclusion of the driving through standing water test. Tesla also agreed with the proposed procedure and suggested keeping the long rectangular pool for ease of defining driving and test evaluation methodologies. As with the washing test, Auto Innovators said there should not be a salinity requirement and requested changing the timing of the isolation checks to 12 hours. Prevost and EMA opposed the driving through standing water test for heavy vehicles. Prevost said, “Since NHTSA suggests improving vehicle washing test by adding the underside of the vehicle to the scope of the test, the driving through standing water tests does not seem to add value to the safety of the vehicle, as the washing test with the underbody included will be a harsher requirement than driving through 10cm of water at 20kph . . . Since facilities providing the infrastructures to perform the driving through standing water test will be scarce, this test would add significant costs while not improving vehicle safety.” EMA likewise stated that the washing test is more aggressive, test facilities for heavy vehicles do not currently exist, and NHTSA should remove the redundant and expensive driving through standing water test for heavy vehicles.

Auto Innovators, Hyundai, Nissan, and NFA requested inclusion of compliance options from GTR No. 20. Hyundai recommended harmonizing with GTR No. 20 and UNECE R100, in which the electrical isolation loss warning system is allowed as a compliance option. Nissan similarly requested a compliance option to harmonize with the UNECE. Auto Innovators asked that NHTSA allow a component-level test compliance option, and transit bus manufacturer NFA specifically requested component-level water exposure safety tests instead of full vehicle tests for heavy buses and motor coaches. NFA asserted that spraying the battery pack directly would constitute a more rigorous test than the proposed full-vehicle tests and said it is open to component-level testing at the IPX6 level.

With regard to submersion concerns, commenters generally agreed that further research is necessary, and some urged NHTSA to commit to a technical amendment. Auto Innovators said that more analysis is needed before determining whether additional test requirements should be implemented and recommended harmonizing with UNECE R100. EDTA recommended that NHTSA commit to a technical amendment and collaborate with stakeholders in collecting data to establish a test requirement addressing real-world flooding scenarios. MEMA, NEMA, and Eaton provided similar comments. Eaton also stated that rigorous test standards would enable the United States to maintain a position of technological leadership and prevent lower-quality imports from entering the market. NEMA said that testing documentation requirements should include water ingress and egress risks. Nikola said that submersion in saline should be compared to the salt spray test in UL2580. Tesla also recommended additional research on salinity. MEMA, NEMA, EDTA, and Eaton further recommended adding a leak check requirement for battery packs at the time of manufacture. MEMA and Eaton specified that the leak checks should include all sealing surfaces and be implemented as a documentation requirement; Eaton said the sealing surfaces between vent valves and the battery housing are often missed in current leak testing practices.

Agency Response

After consideration of the comments, the agency believes the proposed test procedures remains practicable and the requirements mitigate the risk of short circuit or loss of electrical isolation due to water ingress under normal operating scenarios such as driving through standing water on the road or vehicle washing. NHTSA is adopting the proposed requirements with minor changes, including an increase of the standing water test maximum duration from 5 minutes to 10 minutes due to recent NHTSA testing. For the vehicle washing test, the NPRM included a figure from GTR No. 20 to specify the dimensions of the water nozzle and stated that the “nozzle specifications are from IEC 60529 for IPX5 water jet nozzle.” However, the provided figure depicted the nozzle dimensions from IEC 60034, wherein one internal dimension of the nozzle deviates from IEC 60529 by 2 mm. As IEC 60034 is specific to rotating electrical machines, it is more appropriate to use the nozzle specifications from IEC 60529, which was the standard referenced in the text of the NPRM. For these reasons, this final rule contains a corrected figure specifying water nozzle dimensions consistent with IEC 60529.

The NPRM proposed a maximum test duration of 5 minutes for the driving through standing water test instead of GTR No. 20's 10 minutes but also sought comment on the maximum duration. NHTSA conducted the driving through standing water test in August 2024 using a 30-meter length water pool with a 15-meter approach ramp on both ends of the pool.

To accumulate 500 meters of driving through 10 cm of standing water, the vehicle needed to be driven 17 times through the 30-meter water pool. Based on the testing, the agency determined that a test duration of 5 minutes may not be sufficient when the test is conducted using a short water pool. Traversing the entry and exit ramps and turning around between each pass of the water pool adds to the total time necessary to complete the test. NHTSA estimates that 7.5 minutes is sufficient for a water pool length of 30 meters. More time would be needed to complete the test using water pools shorter than 30 meters. The maximum test duration time for conducting the driving through standing water test is 10 minutes in GTR No. 20, which NHTSA agrees is appropriate. Therefore, this final rule adopts a 10-minute time limit for the driving through standing water test.

The testing is described in more detail in a separate document being placed in the docket for this rulemaking.

Some comments addressed other parameters of the vehicle washing test, specifically test time, spray angle, and spray distance. The maximum test time is not stated because the test procedure specifies “washing test duration per square meter of the vehicle surface area is 60 to 75 seconds.” The maximum test time depends on the surface area of the vehicle, which can be measured in square meters and multiplied by 75 seconds per square meter to obtain the maximum test duration for the vehicle. The spray angle provision ensures that all directions are considered for water resistance and is consistent with the IPX5 standard and GTR No. 20. The test procedure states, “The vehicle is sprayed from any direction,” which means the vehicle must be able to meet the test requirements regardless of the angles used. With regard to the spray distance, the proposed requirement said, “the distance from the nozzle to the vehicle surface is 3.0 to 3.2 meters [and] may be reduced, if necessary, to ensure the surface is wet when spraying upwards.” The test procedure includes some adjustment to the nozzle distance because the water stream may not be capable of hitting a vehicle's lower side and bottom (underbody) unless the nozzle is pointed upwards and positioned closer than 3.0 to 3.2 meters from these vehicle surface areas. These provisions are consistent with GTR No. 20. Further, NHTSA believes the proposed testing parameters provide sufficient specification and flexibility for a repeatable test, thus, the agency is adopting the proposed specification.

Regarding the time interval between isolation measurements, Auto Innovators did not provide any supporting data for the request to reduce the minimum wait time to 12 hours. The isolation measurements are conducted immediately after water exposure and after a minimum of 24 hours, which is identical to the GTR No. 20 and ECE R.100 specifications. The agency believes that the 24-hour wait time is appropriate and consistent with observed electric vehicle fires initiating a day or longer after water exposure/submersion.

In the absence of information demonstrating that reducing the time interval between isolation measurements would not significantly alter the test results, the agency is adopting the requirements as proposed.

Overview of NHTSA EV Safety Activities, SAE Government Industry Meeting, January 2023,

https://www.nhtsa.gov/sites/nhtsa.gov/files/2023-03/15874-NHTSA%20SAE%20GIM%202023_final_032223-tag.pdf.

Some commenters supported the addition of a warning option. Although visual warning indicators triggered from an isolation monitoring system could help mitigate safety concerns, NHTSA believes that this approach is not sufficient to solely mitigate a shock or fire hazard caused by the effects of water exposure. Consequently, the agency is not adopting the loss of isolation warning compliance option because warning signals alone are not sufficient for addressing loss of electrical isolation concerns.

Some commenters also requested component-level testing, particularly for heavy vehicles. The agency believes that component-level testing is not as representative of actual conditions as full-vehicle testing. Furthermore, the vehicle washing test does not pose an undue burden.

The agency also disagrees with EMA and Prevost's requests that heavy vehicles be excluded from the driving through standing water test. In support of their position, the two commenters said that test facilities do not accommodate heavy vehicles, it would be very expensive to conduct the test, and the test is redundant. The agency notes that FMVSSs establish minimum safety requirements and the FMVSS test procedures establish how the agency would verify compliance. The Safety Act requires manufacturers to ensure their vehicles comply with all applicable FMVSSs and to certify compliance of their vehicles with all applicable FMVSSs. The Safety Act specifies that manufacturers may not certify compliance if, in exercising reasonable care, the manufacturer has reason to know the certificate is false or misleading. A manufacturer may use component-level tests to certify its vehicles if they exercise reasonable care in doing so. Additionally, while NHTSA agrees that the driving through standing water test may not be as stringent as vehicle washing for certain heavy vehicle configurations with greater ground clearance and/or with the REESS located higher on the vehicle (

e.g.,

on the roof), vehicle configuration is not prescribed by the FMVSS and is left to the discretion of the manufacturer. Both water exposure tests represent reasonable scenarios for normal vehicle operations and establish minimum levels of safety for water exposure of electric vehicles. With the flexibilities afforded to manufacturers to certify compliance, NHTSA disagrees that the cost burden may be excessive for heavy vehicles. Some vehicle manufacturers suggested use of the IPX6

or IPX7 standard instead of IPX5. NHTSA agrees that other standards such as IPX6 or IPX7 may be appropriate for evaluating the water resistance of electric vehicles. However, the corresponding IPX6 or IPX7 test procedures were not proposed in the NPRM and are out of scope for this final rule. While the final rule adopts the proposed requirements corresponding to IPX5, manufacturers are not prohibited from additional test methods beyond the FMVSS specifications and may choose to use the IPX6 or IPX7 standard to evaluate the water resistance of their vehicles.

The commenters agreed that saline should not be specified for the test procedures because it would not significantly affect the results and the salinity level would be difficult to maintain. The commenters also observed that the test procedures of using fresh water would harmonize with international standards. At this time, the agency agrees that generally, water exposure under normal vehicle operation occurs with freshwater; thus, keeping the freshwater specification is appropriate for these tests.

With regard to the battery leak check requirements suggested by some commenters, such requirements were not proposed in the NPRM and are also out of scope for this final rule. Typical leak check procedures require access via one of the vent valves; a requirement to check all sealing surfaces would necessitate a different test method that does not use an opening in the pack. Additionally, research on flood-damaged vehicles has shown that water ingress occurs for a variety of reasons and does not necessarily lead to catastrophic failure.

A Teardown Study of Flood Damaged Electric Vehicles—EV Battery Safety, Part 2, SAE Government Industry Meeting, January 2024,

https://www.nhtsa.gov/document/teardown-study-flood-damaged-electric-vehicles-ev-battery-safety-part-2.

NHTSA recognizes that further research is needed on the field incidences of electric vehicle fires following water exposure, particularly saltwater exposure, in order to establish additional requirements. NHTSA is taking the first step by adopting the proposed water exposure requirements for normal vehicle operations and continues to research salinity, immersion, and test procedures to support the development of future safety requirements and inform potential updates to the FMVSS.

h. Miscellaneous GTR No. 20 Provisions Not Proposed

The NPRM did not propose to require some provisions from GTR No. 20 for vibration, thermal shock and cycling, fire resistance, and low state of charge (SOC) of the REESS during normal vehicle operations. The NPRM requested comment on these exclusions.

j. Vibration and Thermal Shock and Cycling

NPRM Discussion

As stated in the NPRM, GTR No. 20 contains a vibration requirement and test procedure that applies a generic vertical vibration profile to the tested vehicle. NHTSA believes that this test is not representative of real-world conditions. In addition, vehicle manufacturers routinely perform vibration testing to ensure customer satisfaction and reliability. At the component level, electric vehicle batteries are currently subject to vibration test requirements for transportation under the United States Hazardous Materials Regulations (HMR), along all three orthogonal axes and for frequencies up to 200 Hz. With these current tests, NHTSA does not believe that the GTR No. 20 vibration test would address an additional safety need.

Similarly, at the component level, REESSs are already subject to thermal cycling test requirements for transportation under the HMR. 49 CFR 173.185 requires lithium-ion cells and batteries to comply with the test requirements in UN 38.3, including Test T2: Thermal test, which is the basis of the GTR No. 20 thermal shock and cycling test and includes a larger temperature range. NHTSA believes that incorporating the GTR No. 20 test would not address an additional safety need.

Comments Received

Comments from Auto Innovators and HATCI stated agreement with the agency's rationale and exclusion of these requirements. Regarding the vibration and thermal shock and cycling requirements of GTR No. 20, HATCI agreed with NHTSA's rationale for not including the tests given the more stringent U.S. regulations. Auto Innovators also agreed that introduction of new vibration profiles is unnecessary, as the test may not be representative of real-world conditions and industry uses other means to assess durability. For thermal shock and cycling, Auto Innovators said the test requirements in UN 38.3 T2 are sufficient. However, Nikola disagreed with the agency's decision not to add the thermal shock and cycling test. Nikola said that the HMR requirements are insufficient because UN 38.3 does not require testing of the assembled battery pack, and that relying on the shipping requirements for the cells or modules is a low bar to set for safety.

Agency Response

After reviewing the comments, the agency is not adopting additional requirements for vibration and thermal shock and cycling. Commenters agreed with the agency's rationale for excluding the vibration test requirements. Nikola said the thermal shock and cycling test requirements in GTR No. 20 should be included because testing of cells or modules is not equivalent to testing of the full battery pack; UN 38.3 does not require pack level testing if the cells and modules were tested. However, Nikola did not provide any data demonstrating that the existing requirements may be insufficient. For the final rule, the agency does not believe there is a safety need for additional thermal shock and cycling test requirements. In the absence of new supporting information, NHTSA maintains that UN 38.3 and the HMR appropriately address resistance to thermal shock and cycling for lithium cells and batteries.

2. Fire Resistance

NPR

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