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

Federal RegisterApr 15, 2024

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0012]

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:

Notice of proposed rulemaking (NPRM).

SUMMARY:

Consistent with a Global Technical Regulation on electric vehicle safety, NHTSA proposes to establish 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 would apply to light and heavy vehicles and would have performance and risk mitigation requirements for the propulsion battery. Relating to a National Transportation Safety Board recommendation, FMVSS No. 305a would also require manufacturers to submit standardized emergency response information for inclusion on NHTSA's website that would assist first and second responders handling electric vehicles.

DATES:

Comments should be submitted no later than June 14, 2024.

Proposed compliance date:

We propose that the compliance date for the proposed requirements be two years after the date of publication of the final rule in the

Federal Register

. Small-volume manufacturers, final-stage manufacturers, and alterers would be provided an additional year to comply with the rule beyond the date identified above. We propose to permit optional early compliance with the rule. After FMVSS No. 305a is finalized, NHTSA intends to sunset FMVSS No. 305.

ADDRESSES:

You may submit comments identified by the docket number in the heading of this document or by any of the following methods:

•

Federal eRulemaking Portal:

Go to

http://www.regulations.gov.

Follow the instructions for submitting comments on the electronic docket site by clicking on “Help” or “FAQ.”

•

Mail:

Docket Management Facility. M-30, U.S. Department of Transportation, 1200 New Jersey Avenue SE, West Building, Ground Floor, Room W12-140, Washington, DC 20590.

•

Hand Delivery:

U.S. Department of Transportation, 1200 New Jersey Avenue SE, West Building, Ground Floor, Room W12-140, Washington, DC 20590 between 9 a.m. and 5 p.m. Eastern Time, Monday through Friday, except Federal Holidays.

•

Fax:

202-493-2251.

Instructions:

All submissions must include the agency name and docket number. Note that all comments received will be posted without change to

http://www.regulations.gov,

including any personal information provided. Please see the Privacy Act discussion below. We will consider all comments received before the close of business on the comment closing date indicated above. To the extent possible, we will also consider comments filed after the closing date.

Docket:

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

www.regulations.gov

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

Confidential Business Information:

If you claim that any of the information in your comment (including any additional documents or attachments) constitutes confidential business information within the meaning of 5 U.S.C. 552(b)(4) or is protected from disclosure pursuant to 18 U.S.C. 1905, please see the detailed instructions given under the Public Participation heading of the

SUPPLEMENTARY INFORMATION

section of this document.

Privacy Act:

In accordance with 5 U.S.C. 553(c), DOT solicits comments from the public to better inform its decision-making process. DOT posts these comments, without edit, including any personal information the commenter provides, to

www.regulations.gov,

as described in the system of records notice (DOT/ALL-14 FDMS), which can be reviewed at

www.transportation.gov/privacy.

In order to facilitate comment tracking and response, we encourage commenters to provide their name, or the name of their organization; however, submission of names is completely optional. Whether or not commenters identify themselves, all timely comments will be fully considered.

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

1. The GTR Process

2. GTR No. 20

III. Proposals Based on GTR No. 20

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

1. Heavy School Buses

2. Heavy Vehicles Other Than School Buses

i. Request for Comment; Mechanical Integrity Test

ii. Request for Comment; Mechanical Shock Test

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 Spillage Versus Leakage

c. REESS Requirements Applicable to All Vehicles

1. Vehicle Controls for Safe REESS Operation

i. Overcharge Protection

ii. Over-Discharge Protection

iii. Overcurrent Protection

iv. Over-Temperature Protection

v. External Short-Circuit Protection

vi. Low-Temperature Protection

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

i. Safety Need

ii. GTR No. 20 Phase 1 Requirements

iii. NHTSA Proposal

3. Warning Requirements for REESS Operations

i. Thermal Event Warning

ii. Warning in the Event of Operational Failure of REESS Vehicle Controls

4. Protection Against Water Exposure

i. NHTSA Proposal

A. Vehicle Washing Test

B. Driving Through Standing Water Test

ii. NHTSA's Consideration of Submersions

5. Miscellaneous GTR No. 20 Provisions Not Proposed

i. REESS Vibration Requirements

ii. REESS Thermal Shock and Cycling

iii. REESS Fire Resistance

iv. Low State-of-Charge (SOC) Telltale

IV. Request for Comment on Applying FMVSS No. 305a to Low-Speed Vehicles

V. Emergency Response Information To Assist First and Second Responders

VI. Request for Comment on Placing the Emergency Response Information and Documentation Requirements in a Regulation Rather Than in FMVSS No. 305a

VII. Proposed Compliance Dates

VIII. Rulemaking Analyses and Notices

IX. Public Participation

X. Appendices to the Preamble

Appendix A. Table Comparing GTR No. 20, FMVSS No. 305, and FMVSS No. 305a

Appendix B. Request for Comment on Phase 2 GTR No. 20 Approaches Under Consideration by the IWG

I. Executive Summary

NHTSA is issuing this NPRM to achieve two goals. First, NHTSA proposes to establish FMVSS No. 305a, “Electric-powered Vehicles: Electric Powertrain Integrity,” to upgrade and replace existing FMVSS No. 305. Proposed FMVSS No. 305a would have all the requirements of FMVSS No. 305, but the proposed standard would expand its applicability to vehicles with a gross vehicle weight rating (GVWR) greater than 4,536 kilograms (kg) (10,000 pounds (lb)) and add requirements and test procedures covering new aspects of electric vehicle safety, such as the performance and risk mitigation requirements for the propulsion battery, referred to as the Rechargeable Electrical Energy Storage System (REESS). NHTSA is also proposing requirements to ensure 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. After FMVSS No. 305a is finalized, NHTSA intends to sunset FMVSS No. 305.

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 NPRM proposes 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 vehicle in drive mode, and charging. Final rule, 82 FR 44950, September 27, 2017.

High Level Summary of the Proposal

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, proposed 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 proposed FMVSS No. 305a:

• Light vehicles would 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 would also be 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 would 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 would not be subject to post-crash requirements. This proposed 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))

would be subject to the requirements for electrical system safety during normal vehicle operations and to the requirements for the REESS, and would 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 proposed 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 already in FMVSS No. 305, but this NPRM proposes to enhance some provisions consistent with GTR No. 20. For example, current 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, NHTSA is proposing to prohibit fire or explosion for a one-hour post-test period.

FMVSS No. 305 already includes the first three compliance options for electrical shock protection but not the low energy option that is available for capacitors in GTR No. 20. This NPRM would complete the alignment by proposing the low energy option for capacitors in FMVSS No. 305a. NHTSA had considered this option years ago and had decided against it. As explained in detail in sections below, NHTSA has changed its view on the matter after further considering data and analysis from the GTR.

A substantial portion of this NPRM focuses on safety provisions for the propulsion battery, the REESS. For what would be the first time in an FMVSS, proposed FMVSS No. 305a includes comprehensive performance requirements and risk mitigation strategies for the REESS. These REESS requirements would 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 proposed 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.

“Normal vehicle operation” means situations such as driving through a pool of standing water or exposing the vehicle to an automated car wash. This NPRM does not propose requirements to address vehicle fires due to vehicle submersions in floods and storm surges, as GTR No. 20 does not have specific requirements to address this area. NHTSA is researching this latter area.

Proposed FMVSS No. 305a 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 demonstrate that they considered, assessed, and mitigated identified risks for safe operation of the vehicle. These proposed documentation requirements would address: (a) safety risk mitigation associated with charging and discharging during low temperature; (b) the safety risks from thermal propagation in the event of single-cell thermal runaway

(SCTR) due to an internal short-circuit of a single cell; and (c) providing a warning if there is a malfunction of vehicle controls that manage REESS safe operation. The GTR takes a documentation approach on 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.

Thermal runaway means an uncontrolled increase of cell temperature caused by exothermic reactions inside the cell.

NHTSA tentatively 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, proposed FMVSS No. 305a would require manufacturers to submit documentation to NHTSA, at NHTSA's request, that identify all known safety hazards, describe their risk mitigation strategies for the safety hazards, and, if applicable, describe 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 would be a means of assuring 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 assure that manufacturers will identify and address the safety risks of the REESS until such time objective performance standards can be developed that can be applied to all applicable REESS designs. NHTSA would also acquire information from the submissions to learn about the safety of the REESS and potentially develop the future performance standards for FMVSS No. 305a. The proposed documentation requirements are based on the approach of GTR No. 20, but NHTSA proposes to focus 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.

Given the proposed documentation specifications are more akin to disclosure requirements that could be issued under general NHTSA regulation rather than pursuant to an FMVSS with specified test procedures, the agency also requests comment on whether the proposed documentation requirements would be better placed in a general agency regulation than in the proposed FMVSS No. 305a.

As part of NHTSA's battery initiative

and in response to a 2020 NTSB recommendation,

this NPRM proposes to include in FMVSS No. 305a 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 would 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.

“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.

“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.

NHTSA would require standardized formatting of the information. The ERG and rescue sheet requirements would meet 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 would 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.

NHTSA believes there are no notable costs associated with this NPRM. This proposal 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 proposed 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 proposed FMVSS No. 305a they would just have to standardize the format and submit the information to NHTSA.

Similar to the issue discussed above regarding having the proposed documentation requirements in a general regulation rather than in FMVSS No. 305a, the agency also requests comment on whether the proposed ERG and rescue sheet requirements would be better placed in a general agency regulation than in proposed FMVSS No. 305a.

Lastly, current FMVSS No. 305 does not apply to vehicles that travel under 40 km/h (25 mph), such as low-speed vehicles.

Given there are low-speed vehicles that are also electric-powered vehicles, NHTSA requests comments on the possibility of applying aspects of FMVSS No. 305a to low-speed vehicles to ensure a level of protection against shock and fire, particularly during normal vehicle operation, and to assure the safe operation of the REESS.

“Low-speed vehicle” is defined in 49 CFR 571.3. See also FMVSS No. 500, “Low speed vehicles,” 49 CFR 500.

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 this “in-use” testing (unlike “post-crash” testing, discussed below) deals with performance criteria that would be assessed without first exposing the vehicle to a crash test.

Normal vehicle operation includes operating modes and conditions that can reasonably be encountered during typical operation of the vehicle, such as driving, parking, and standing in traffic, as well as charging using chargers that are compatible with the specific charging ports installed on the vehicle. It does not include conditions where the vehicle is damaged, either by a crash or road debris, subjected to fire or water submersion, or in a state where service and/or maintenance is needed or being performed.

Normal Vehicle Operations.

FMVSS No. 305 requires vehicles to provide the following measures to protect against electric shock during normal vehicle operations. Vehicles must prevent direct contact of high voltage sources (those operating with voltage greater than 30 VAC or 60 VDC)

; prevent indirect contact of high voltage sources; electrically isolate high voltage sources from the electric chassis (500 ohms/volt or higher for alternating current (AC) and 100 ohms/volt or higher for direct current (DC) sources); mitigate risk of driver error (indicate to the driver when the vehicle is in possible active driving mode at startup and when the driver is leaving the vehicle, and prevent vehicle movement by its own propulsion system when the vehicle charging system is connected to the external electric power supply).

VAC—volts of alternating current; VDC—volts of direct current.

Post-Crash Protections.

For post-crash protections, FMVSS No. 305 requires vehicles to meet the following provisions during and after the crash tests specified in the standard. FMVSS No. 305 limits electrolyte spillage from propulsion batteries and requires the REESS to remain attached to the vehicle and not enter the passenger compartment. The standard requires that during and after a crash test, high voltage sources in a vehicle must be either electrically isolated from the vehicle's chassis; of a voltage below specified levels considered safe from electric shock hazards; or prevented from direct or indirect contact by occupants or emergency services personnel by use of physical barriers. The standard specifies that the post-crash requirements must be met after crash tests involving: a frontal impact up to and including 48 kilometer per hour (km/h) (30 mile per hour (mph)) into a fixed collision barrier; an impact of a moving barrier at 80 km/h (50 mph) into the rear of the vehicle; an impact of a moving barrier at 53 km/h (33 mph) into the side of the vehicle; and under static rollover conditions after each such impact.

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 “1998 Agreement” (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). 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 who 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. By issuing this NPRM, NHTSA is initiating the process to consider adoption of GTR No. 20. As noted above, under the terms of the 1998 Agreement, 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.”

49 U.S.C. 30111.

2. GTR No. 20

GTR No. 20 establishes performance-orientated requirements that reduce potential safety risks of electric vehicles (EVs) 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 were developed in Phase 1 of the GTR. GTR No. 20 was developed in phases due to the differing stages at which technologies have been developed and evaluated. The informal working group (IWG) that developed the GTR determined that Phase 1 would address issues relating to the safe operation of the rechargeable electrical energy storage system (REESS), and for mitigating risks of fire and other safety risks associated with the REESS. In Phase 2, which is on-going, the IWG is addressing issues involving long-term research and verification.

This NPRM pertains to the adoption of the GTR as developed in Phase 1.

In Appendix B to this preamble, NHTSA requests comments on some issues under development in Phase 2.

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 and applies these to light vehicles. GTR No. 20 also has safety requirements for the REESS beyond those in FMVSS No. 305. These additional requirements in GTR No. 20 for the REESS include:

• 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 this NPRM is not proposing 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 *

This NPRM does not propose to require a warning for low energy in REESS. There is no such warning requirement for conventional fuel vehicles in the event of low-fuel, yet all conventional fuel vehicles have a low fuel indicator because it is a consumer convenience feature. The agency expects that, similarly, a low energy in REESS indicator will be voluntarily provided in all electric-powered vehicles.

○ 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 separate 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.

This NPRM proposes to complete the alignment of FMVSS No. 305 with GTR No. 20 by extending the standard's electrical safety requirements to heavy vehicles. This NPRM also proposes to adopt the above requirements 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.” To avoid redundancy, NHTSA is not proposing adding these requirements into FMVSS No. 305a. NHTSA explains the bases for the proposals and, for provisions not proposed, the reasons the agency has not proposed them in this NPRM.

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 mechanical integrity test uses a quasi-static load of 100 kN on the REESS to evaluate the safety performance of the REESS under contact loads that may occur during vehicle crash. The mechanical shock test accelerates the REESS on a sled system to evaluate the safety performance of the REESS and the integrity of the REESS mounting structures to the vehicle under inertial loads that may occur. NHTSA discusses its assessment of the component level mechanical integrity and mechanical shock test procedures and requests comment on these issues later in this NPRM.

III. Proposals Based on GTR No. 20

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

NHTSA proposes to harmonize the application of FMVSS No. 305a with GTR No. 20. Currently, FMVSS No. 305 applies to electric-powered vehicles with a GVWR less than or equal to 4,536 kg (10,000 lb); it does not apply to electric vehicles with a GVWR greater than 4,536 kg (10,000 lb). GTR No. 20 applies to both light and heavy electric vehicles. NHTSA proposes to apply FMVSS No. 305a to both light and heavy electric vehicles. The fundamentals for protecting against an electrical shock for light vehicles are the same as for heavy vehicles. A failure of a high voltage system may cause injurious electric shock to the human body.

Specifically, NHTSA proposes to apply FMVSS No. 305a to all passenger cars, multipurpose passenger vehicles, trucks, and buses, regardless of their GVWR, that use electrical propulsion components with working voltages greater than or equal to 60 VDC or 30 VAC, and whose speed attainable over a distance of 1.6 kilometers (km) (1 mile) on a paved level surface is more than 40 km/h (25 miles per hour (mph)).

The NPRM proposes to carry over the current requirements for light vehicles in FMVSS No. 305 to FMVSS No. 305a, except some provisions as enhanced by this NPRM if adopted by a final rule. To sum, light vehicles would have to meet the requirements for normal vehicle operations and the requirements proposed in this NPRM for the REESS. Further, they would have to meet requirements for post-crash protections following a crash test. Under proposed FMVSS No. 305a, heavy school buses would have to meet the requirements for normal vehicle operations and for the REESS, and, following a specific crash test, requirements for post-crash protections. The agency is not adopting the provision in GTR No. 20 that conducts mechanical integrity and mechanical shock tests (component-level) for light vehicles and for heavy school buses. NHTSA believes that post-crash safety is better evaluated at a system level in a crash test than in component-level tests. Currently there are crash tests for light vehicles and school buses, thus, NHTSA proposes to conduct post-crash safety after the specified crash tests.

Current FMVSS No. 305 does not apply to these vehicles that travel under 40 km/h (25 mph).

Heavy vehicles other than heavy school buses would be subject to the requirements for normal vehicle operations described above and the requirements for the REESS. They would not be subject to crash testing requirements because the agency does not know of a crash test that would be appropriate for the vehicles at this time. However, while NHTSA does not have a sufficient basis to proceed currently with dynamic or quasi-static requirements for heavy vehicles other than school buses, this NPRM requests comment on this issue. NHTSA is interested in the merits of component-level tests that are representative of impact loads in heavy vehicle crashes and the appropriateness of applying the tests to different weight classes of heavy vehicles. Even in the absence of post-crash testing requirements, NHTSA tentatively concludes that meeting requirements for normal vehicle operations and for the REESS, as a starting point, will enhance the safety of these heavy electric vehicles.

1. Heavy School Buses

NHTSA proposes to distinguish heavy school buses from other types of heavy vehicles and subject them to crash testing because the school vehicles will be carrying children. This NPRM proposes to assess the post-crash safety of heavy school buses (school buses with a GVWR greater than 4,536 kg (10,000 lb)) in a dynamic moving contoured barrier test. This proposal would be consistent with current school bus safety standards. FMVSS No. 301, “Fuel system integrity,” and FMVSS No. 303, “Fuel system integrity of compressed natural gas vehicles,” require heavy school buses using

conventional fuel or compressed natural gas for propulsion, respectively, to maintain fuel system integrity in a crash test where a moving contoured barrier traveling at any speed up to 48 km/h (30 mph) impacts the school bus at any point and angle. These standards set this high level of safety for heavy school buses even though FMVSS Nos. 301 and 303 do not apply to other types of heavy vehicles.

NHTSA recognizes that FMVSS No. 305 currently does not apply to nor has a crash test requirement for heavy school buses. When FMVSS No. 305 was first promulgated in September 2000, NHTSA decided not to apply proposed FMVSS No. 305 to heavy school buses. NHTSA made this decision after agreeing with commenters that applying the standard to the vehicles at that time could have substantial effect, in terms of cost and weight, on heavy school buses and potentially restrict further development.

The prevailing technology at that time was a series of conventional lead-acid batteries as the energy source for propulsion. Since the 1990s and early 2000s, battery technology and electric powertrains have evolved to include nickel metal hydride and lithium-ion batteries for electric vehicles. The weight and cost concerns raised for electric school buses in 2000 are no longer obstacles with current lithium-ion battery technologies because of their high energy density and their widespread use. Several school bus manufacturers are currently manufacturing and offering for sale heavy school buses with high voltage electric propulsion systems. Given the development of the technology and practicability of designing and producing heavy electric school buses, NHTSA tentatively concludes it is appropriate to adopt requirements to ensure post-crash safety of heavy electric school buses and maintain the current high level of safety of heavy school buses.

Final rule, 65 FR 57980, September 27, 2000.

NHTSA is proposing to include in FMVSS No. 305a a requirement that heavy school buses with high voltage electric propulsion systems meet the requirements for normal vehicle operations (assessed prior to a crash test) and the proposed post-crash electrical safety requirements when impacted by the moving contoured barrier specified in FMVSS No. 301. The crash test requirement would align FMVSS No. 305a's requirements for heavy school buses with those of FMVSS Nos. 301 and 303. Due to the number of electric school bus manufacturers and sales since 2000, NHTSA tentatively concludes that meeting the proposed standard would have no substantial effect on cost and weight due to widespread use of lithium-ion battery and conformance to the proposed post-crash safety requirements.

Currently, all major school bus manufacturers (Blue Bird, IC Bus, Thomas Built) are offering large and small electric school buses (see AFDC-electric school bus) and many school districts have introduced electric powered school buses in their fleets. As of June 2023, there are 2,277 electric school buses that are either on order, delivered or operating in the U.S. In total, there are now 5,982 committed electric school buses in the U.S.

https://www.wri.org/insights/where-electric-school-buses-us#:~:text=As%20of%20June%202023%2C%20there,more%20buses%20since%20June%202022.

2. Heavy Vehicles Other Than School Buses

There are currently no heavy vehicle crash tests in FMVSS. Heavy vehicles are typically made to order with different configurations

based on the operational needs of the purchaser and are produced in low volume. Conducting crash tests of various design configurations from a small volume of representative vehicles would be cost prohibitive. There could also be practicability constraints for conducting crash tests on higher weight classes of heavy vehicles.

These differences include the number of fuel containers and battery packs and the location and attachment of fuel lines and fuel containers.

In this NPRM, NHTSA has proposed requirements to ensure post-crash safety using full vehicle crash tests for light vehicles and heavy school buses. Such full vehicle crash tests evaluate post-crash safety at a system level, so NHTSA is not considering component-level tests of the REESS for those vehicles. However, since there are no full vehicle crash tests currently in FMVSSs for heavy vehicles (other than heavy school buses), NHTSA seeks comment on considerations for component-level tests (other than the mechanical integrity and mechanical shock tests in GTR No. 20) that are representative of impact loads in heavy vehicle crashes and that can be applied to different weight classes of heavy vehicles.

i. Request for Comment; Mechanical Integrity Test

There are currently no crash tests specified in the FMVSSs

for evaluating the integrity of the fuel system or propulsion system of heavy vehicles other than heavy school buses. GTR No. 20 provides an option for evaluating post-crash safety of light vehicles by way of a mechanical integrity test (crush test) of the REESS as an item of vehicle equipment, instead of a full vehicle crash test as in FMVSS No. 305. The loads in the mechanical integrity requirements in the GTR No. 20 were derived from REESS contact loads measured in light passenger vehicle crash tests per UN Regulations ECE R. No. 12, “Uniform provisions concerning the approval of vehicles with regard to the protection of the driver against the steering mechanism in the event of impact,” ECE R.94, “Uniform provisions concerning the approval of vehicles with regard to the protection of the occupants in the event of a frontal collision,” and ECE R.95, “Uniform provisions concerning the approval of vehicles with regard to the protection of occupants in the event of a lateral collision,” using electric and hybrid-electric vehicles available on the market.

FMVSS No. 301, “Fuel system integrity,” and FMVSS No. 303, “Fuel system integrity of compressed natural gas vehicles,” only applies to light vehicles and to heavy school buses.

In the mechanical integrity test, a quasi-static load is applied to the charged REESS

along with any subsystem components (including crush protection systems specified by the manufacturer) along the longitudinal axis of the vehicle (along the direction of vehicle travel) or the lateral axis (perpendicular to the longitudinal axis). A peak load of 100 kN is applied within 3 minutes and maintained for at least 100 milliseconds. During the integrity test, the REESS is required to have no evidence of electrolyte leakage, fire, or explosion. The REESS is required to have electric isolation of at least 100 ohms/volt or provide protection level IPXXB against direct contact of high voltage sources.

The REESS is charged to 95 percent state-of-charge for REESS designed to be externally charged and charged to no less than 90 percent of state-of-charge for REESS designed to be charged only by an energy source on the vehicle.

IPXXB and IPXXD “protection levels” refer to the ability of the physical barriers to prevent entrance of a probe into the enclosure, to ensure no direct contact with high voltage sources. “IPXXB” is a probe representing a small human finger. “IPXXD” is a slender wire probe. Protection degrees IPXXD and IPXXB are International Electrotechnical Commission specifications for protection from direct contact of high voltage sources.

Because there are no full vehicle crash tests currently in FMVSSs for heavy vehicles (other than heavy school buses), NHTSA seeks comment on a mechanical integrity test for REESS on heavy vehicles to evaluate post-crash safety at a component-level. As noted above, the current quasi-static loads of the integrity test specified in GTR No. 20 are specific to light vehicles. NHTSA seeks comment on the parameters for a

possible quasi-static crush test for the REESS on heavy vehicles.

The agency requests feedback on the merits of the integrity test in assessing post-crash safety for heavy vehicle REESS. NHTSA seeks comment on the practicability of such a test and on the specifics of subsystem components that should be included with the REESS while conducting the crush test. NHTSA requests that commenters provide data to substantiate their assertions.

NHTSA's research evaluated the crush resistance of REESS using a displacement-based loading method. See Ford Safety Performance of Rechargeable Energy Storage Systems, Appendix A, DOT HS 812 756, July 2019.

https://rosap.ntl.bts.gov/view/dot/41840

ii. Request for Comment; Mechanical Shock Test

NHTSA seeks comment to inform our research on a mechanical shock test for REESS on heavy vehicles to evaluate post-crash safety at a component level. The aim of the mechanical shock requirement in GTR No. 20 is to verify the safety performance of the REESS under inertial loads which may occur during an impact. The requirement evaluates specifically the performance of the REESS mountings and fixtures to the vehicle.

The mechanical shock test is conducted with the REESS along with any subsystem components installed on a sled system using the mounting structures that are used for installing the REESS to the vehicle. The REESS is decelerated or accelerated with an acceleration profile within the acceleration corridor in Figure 1 and in accordance with acceleration magnitudes in Table 1 through Table 3 for different vehicle GVWRs. The test concludes with an observation period of one hour at the ambient temperature conditions of the test environment.

EP15AP24.044

Figure 1—Generic Description of Test Pulses—Mechanical Shock Test

Table 1—Mechanical Shock Test—Acceleration Values for Vehicles With a GVWR Less Than or Equal to 3,500

(7,716

lbs

)

Point

Time

(ms)

Acceleration (g)

Longitudinal

Transverse

100

4.5

120

Table 2—Mechanical Shock Test—Acceleration Values for Vehicles With a GVWR Greater Than 3,500

(7,716

lbs

) and Less Than or Equal to 12,000

(26,455

lbs

)

Point

Time

(ms)

Acceleration (g)

Longitudinal

Transverse

100

2.5

120

Table 3—Mechanical Shock Test—Acceleration Values for Vehicles With a GVWR Greater Than 12,000

(26,455

lbs

)

Point

Time

(ms)

Acceleration (g)

Longitudinal

Transverse

6.6

100

2.5

120

During the mechanical shock test, the REESS is required to have no evidence of electrolyte leakage, fire, or explosion. The REESS is required to have electric isolation of at least 100 ohms/volt or have protection degree IPXXB.

Since there are no full vehicle crash tests currently in FMVSSs for heavy vehicles (other than heavy school buses) to evaluate post-crash safety at a system level, NHTSA seeks comment to inform possible future research on a mechanical shock test for REESS on heavy vehicles to evaluate post-crash safety at a component level. Among other matters, NHTSA requests comment on the following apparent limitations of the GTR test. The mechanical shock test in GTR No. 20 aims primarily at evaluating the safety performance of the REESS mounting fixture, which does not appear to address a safety need presently observed in the field.

Furthermore, the accelerations captured in the GTR No. 20 for the mechanical shock requirement may be too low, according to a technical study performed by the Transportation Research Laboratory.

The aim of the technical study was to review the appropriateness of the crash pulses used in current European regulations. This study determined that the crash pulse requirements in a number of the EU regulations (including R67, R100, and R110) are not representative of current vehicles. (These are among the reasons NHTSA is not proposing the mechanical shock test in GTR No. 20 for heavy vehicles in this NPRM.)

Under the Vehicle Safety Act, the FMVSSs must, among other things, be practicable, meet the need for motor vehicle safety, and be stated in objective terms. (49 U.S.C. 30111(a).)

European Commission, Directorate-General for Internal Market, Industry, Entrepreneurship and SMEs, Edwards, M., Hylands, N., Grubor, D., et al.,

Technical study to review the appropriateness of crash pulses used in current EU legislation: final report,

Section 4.4, Publications Office, 2021,

https://data.europa.eu/doi/10.2873/58935.

NHTSA seeks comment on the relevance of the mechanical shock test for heavy vehicles. NHTSA seeks comment on how the mechanical shock test would be performed on heavy vehicle REESSs, the appropriate accelerations levels that would be representative of acceleration levels observed in the field or in crash tests, and appropriate requirements which the REESS would need to meet in a mechanical shock test.

NHTSA seeks comment on the best approach or test method for evaluating post-crash safety for electric vehicles with a GVWR greater than 4,536 kg (10,000 lb). Specifically, NHTSA seeks comment and recommendations on other applicable safety tests and corresponding objective performance criteria to evaluate the propulsion system crash safety performance of vehicles with a GVWR greater than 4,536 kg (10,000 lb). NHTSA seeks comment on whether the moving contoured barrier crash test proposed for heavy school buses in the above section in this preamble can or should be applied to all heavy vehicles.

b. General Specifications Relating To Crash Testing

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

1. Low Energy Option for Capacitors

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. This NPRM proposes a low energy option for capacitors in the electric powertrain in FMVSS No. 305a.

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. 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 has previously considered this issue. In a 2007 NPRM responding to petitions for rulemaking from what were then the Alliance of Automobile Manufacturers (Alliance) and the Association of International Automobile Manufacturers (AIAM),

NHTSA sought comments regarding a request of the petitioners to include 0.2 Joule (J) as an appropriate low energy threshold for electrical safety compliance post-crash for high voltage sources.

The petitioners believed that the low energy option was non-harmful, and argued in their subsequent comments to the NPRM

that the option is necessary due to the presence of x- and y-capacitors in the powertrain of fuel cell vehicles. After evaluating the comments, NHTSA ultimately disagreed with the petitioners and decided against a low energy option for post-crash electrical safety because the agency was not convinced that a low energy option was needed and had concerns about the possible disparity between the level of safety provided by 0.2 J of energy and the electrical isolation requirement.

At that time a safety need for a low energy option was not yet clear and the agency expressed concerns regarding the practicality of measuring the residual energy in a crash test environment.

In January 2020, the two industry associations merged to form the Alliance for Automotive Innovation (generally referred to as the Auto Innovators).

72 FR 57260, October 9, 2007.

NHTSA-2007-28517-0004.

Final rule, 75 FR 33515, 33519; June 14, 2010.

NHTSA is reconsidering this issue in this NPRM. GTR No. 20 contains a detailed analysis of the 0.2 Joules energy limit for the low energy post-crash electrical safety compliance option. While the 2007 NPRM considered a low energy post-crash electrical safety compliance option for any high voltage source in the powertrain, GTR No. 20 only provides this option to capacitors in the powertrain.

NHTSA conducted an analysis using human body resistance charts, long and short duration capacitance discharge pulse profiles, and the graphs of physiological effects of AC and DC body current by duration of exposure from two International Electrotechnical Commission (IEC) technical publications,

to determine safe energy levels for the human body. NHTSA has submitted a technical memorandum to the docket for this NPRM that provides details and results of the agency's analysis.

IEC 60479-1 and 60479-2 Effects of Current on Human Beings and Livestock—Part 1: General Aspects, Part 2: Special Aspects, 2005-07, Reference Nos. CEI/IEC/TS 60479-1:2018 and CEI/IEC/TS 60479-2:2019.

https://webstore.iec.ch/publication/62980; https://webstore.iec.ch/publication/63392

(last accessed September 26, 2023).

Based on the analysis results, NHTSA tentatively concludes that a 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. Providing this post-crash compliance option would allow for practicable powertrain designs for battery electric and fuel cell vehicles without any reduction in safety. Automotive high-voltage systems typically utilize a number of capacitors connected to high voltage buses, and it is not always practical to discharge every capacitor post-crash. NHTSA tentatively believes that by providing this compliance option for a safe energy limit, vehicle manufacturers would have the flexibility to design products that assure safety. NHTSA seeks comments on the parameters (human body resistance, discharge profiles) used in the analysis and the analysis method.

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

After a real-world crash, passengers within the vehicle need time to safely egress from the vehicle or be rescued by first responders. During this time, passengers should not be exposed to hazards such as fire or explosion of the REESS, which may hinder their egress or rescue.

GTR No. 20 requires that for a period of one hour after a crash test, there shall be no evidence of fire or explosion of the REESS. However, such a requirement is not currently in FMVSS No. 305. In accordance with GTR No. 20, NHTSA proposes 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.

3. Assessing Post-Crash Voltage Measurements

This NPRM proposes to clear up a source of ambiguity in FMVSS No. 305. FMVSS No. 305 requires that the post-crash voltage measurements be made at least 5 seconds after the vehicle comes to rest. However, at times it is not entirely clear when the vehicle comes to rest because there is always some vibration and slight vehicle motion post-crash. For consistency with the GTR No. 20 test procedure, NHTSA proposes that the voltage measurements in FMVSS No. 305a would be made between 10 seconds and 60 seconds after the impact. The agency tentatively believes that 10 seconds after impact is sufficient time for voltage measurement and 60 seconds after impact is early enough that any high voltage arcing would be detected. NHTSA seeks comment on this approach.

4. Electrolyte Spillage Versus Leakage

Currently, FMVSS No. 305 S5.1 addresses “electrolyte spillage from propulsion batteries.” The standard specifies that following a crash test, not more than 5.0 liters of electrolyte from propulsion batteries shall spill outside the passenger compartment, and that no visible trace of electrolyte shall spill into the passenger compartment. NHTSA proposes to use terms related to “leakage” instead of spillage. When the electrolyte spillage

requirement was originally adopted in 2000, EV propulsion batteries were envisioned to be a series of lead-acid batteries. Lead-acid batteries at the time had large quantities of liquid electrolyte that could spill out of the battery if the battery structure were compromised in a crash. At that time, it was appropriate to eliminate the term “leakage” due to its synonymity to “spillage,” to avoid questions of whether different meanings were intended by the different words.

Per Section B, “S5.1 Electrolyte Spillage from Propulsion Batteries,” NHTSA stated in 65 FR 57980 that “leakage” is synonymous for “spillage.” Both words indicate the escape of electrolyte from the battery.

Current EV propulsion batteries, however, are lithium-ion batteries. The cells of lithium-ion batteries have small quantity of electrolyte that could leak out of the battery casing rather than spill. Thus, NHTSA proposes to use the term “electrolyte leakage,” which is more relevant than “electrolyte spillage” for these batteries.

NHTSA seeks comment on the inclusion of a post-crash electrolyte leakage requirement in FMVSS No. 305a and the necessity and relevance of such a requirement for current EVs. Specifically, NHTSA seeks comment on whether this requirement is still relevant given today's propulsion battery technologies and if it is still necessary based on the safety incidents observed in the field or in crash tests. NHTSA seeks comment on whether a 5-liter maximum amount of electrolyte permitted to be leaked is still relevant and requests commenters to provide data based on safety incidents observed in the field or in crash tests to

substantiate their assertions.

NHTSA seeks comment on and recommendations regarding electrolyte leakage detection methods and how these detection methods can discern between the presence of electrolyte and the presence of other liquids such as coolant.

GTR No. 20 requires that the electrolyte leaking from the REESS during and after the crash test is no more than 7 percent by volume of the REESS electrolyte. However, there is no practical way of measuring the quantity by volume of the electrolyte in the REESS.

c. REESS Requirements Applicable to All Vehicles

This section of the NPRM addresses REESS safety performance requirements during normal vehicle operation. The REESS requirements would apply to all vehicles subject to FMVSS No. 305a.

Introduction

Currently, FMVSS No. 305 does not have any requirements for the safe operation of the REESS and for mitigating risks of fire and other safety risks associated with it. This NPRM's proposed requirements would protect the REESS against external fault inputs, ensure the REESS operations are within the manufacturer-specified functional range, provide protection from thermal propagation in the event of single-cell thermal runaway (SCTR) due to an internal short-circuit, provide a warning if there is a thermal event within the REESS or a malfunction of vehicle controls that manage REESS safe operation, and ensure safe REESS operation during and after water exposure.

While REESS is a general term to represent any rechargeable electrical energy storage system, currently all electric powered vehicles use REESS with lithium-ion chemistry. Therefore, the current safety hazards associated with REESS identified in literature and in the field are those specific to lithium-ion chemistry REESS. However, the proposed requirements in this NPRM will apply regardless of REESS chemistry.

REESSs are designed and manufactured to operate safely within a range of operating parameters, including temperature ranges, charge levels, and current levels. If the REESS is subjected to fault conditions outside these operating ranges such as overcharge, over-discharge, overcurrent, over-temperature, external short-circuit, or low temperature, these conditions can result in damage to the cells. Cell damage increases the risk of hazardous conditions such as electrolyte leakage, reduced electrical isolation, and fire in the REESS (thermal runaway). Manufacturers include controls in electric vehicles to manage REESS operation to ensure they stay within the specified safe operating range, thereby mitigating damage to the REESS. The system that monitors and controls the REESS is referred to as the battery management system (BMS). NHTSA proposes requirements to assure that the BMS has controls that protect the REESS against these faults by,

e.g.,

stopping the vehicle from charging to prevent overcharge.

Performance Criteria For Normal Vehicle Operations—General

The performance criteria specified in GTR No. 20 for each of the vehicle control performance tests specify no evidence of electrolyte leakage, rupture (applicable to high voltage REESSs only), venting (applicable to REESSs other than open-type traction batteries

), fire, or explosion. For high voltage REESSs, the electrical isolation is required to be greater than or equal to 100 ohms per volt, for a DC high voltage source. This NPRM proposes the same performance criteria to protect the REESS against external faults, such as a fault in an external charger that could result in the charger supplying greater current than requested by the vehicle and/or charging the REESS beyond full state of charge.

Open-type traction batteries are a type of battery which are filled with liquid and generate hydrogen gas that is released into the atmosphere.

The control pilot pin of the charger communicates with the vehicle during charging. Based on the state of charge (SOC), the vehicle requests a certain level of current and the vehicle charger provides that level. Other external faults could arise when attempting to drive the vehicle beyond the lowest safe operating SOC of the REESS (over-discharge of the REESS), driving fast up a steep hill for a long period of time that could cause the REESS to heat beyond its highest safe operating temperature, and charging a REESS at very cold temperatures that could cause lithium plating.

Under proposed FMVSS No. 305a, the evidence of electrolyte leakage, venting,

or rupture 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 overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit test procedures specify that the agency would perform a standard cycle after completing exposure to each of the external faults, provided that the vehicle permits charging and discharging at that time. A standard cycle, as specified in GTR No. 20 and proposed FMVSS No. 305a, consists of a standard discharge and followed by a standard charge. If the vehicle is operable after exposure to the external fault, running the standard cycle after exposure to the external fault condition—while observing the vehicle for one hour for evidence of electrolyte leakage, rupture, venting, fire, or explosion, followed by voltage measurements for determining electrical isolation—would ensure that continuing operating the vehicle would not result in safety hazards.

NHTSA elaborates on the proposed venting requirement at the end of this section.

The vehicle might not permit charging and discharging after detecting a dangerous condition; NHTSA considers this a safety feature and that such a test outcome would not amount to an apparent noncompliance. The inability to perform a standard cycle after exposure to the external fault does not terminate the test. If the vehicle does not permit charging and discharging after exposure to an external fault, then the standard cycle is simply not performed and the test proceeds. Specifically, the test ends 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.

The standard cycle would be conducted with the breakout harness connected to the manufacturer-specified location(s) on the traction side of the REESS

on the vehicle's electric power train. The REESS is charged and discharged using a high voltage battery tester/cycler (with appropriate power and voltage ranges) which is connected to the vehicle through the breakout harness, as shown in Figure 2 below (for illustration purposes only).

The manufacturer is required by proposed FMVSS No. 305a to specify the location for connecting the breakout harness and may also provide appropriate breakout harnesses for testing the vehicle. If the manufacturer does not provide a breakout harness, NHTSA would use a generic breakout harness to connect to the traction side of the REESS.

EP15AP24.045

Figure 2—Connection of the Breakout Harness & Laboratory Test Equipment to the Vehicle

NHTSA proposes that the discharge and charge rates for the standard cycle would be provided by the vehicle manufacturer. NHTSA proposes that, if the discharge rate is not specified by the manufacturer, NHTSA would use a discharge rate (C-Rate) of 1C current. A “nC Rate” is the magnitude of constant current that would charge or discharge the REESS in 1/n hour between 0 percent state of charge (SOC) and 100 percent SOC. Discharge would continue until automatically terminated by vehicle controls at the manufacturer-specified minimum operating SOC of the REESS. After discharge, the standard cycle would include a 15-minute rest period before the charging procedure commences. If a charge procedure is not specified, then a charge rate (

i.e.,

C-Rate) of

1/3

C current would be used. Charging is continued until automatically terminated by vehicle controls at the manufacturer-specified maximum operating SOC of the REESS.

REESS Venting

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 be associated with (a) combustion and/or decomposition of electrolyte, or (b) vaporization of the electrolyte. In case of condition (a), the emissions from the cells may increase the risk to vehicle occupants if they are exposed to such substances. In case of condition (b), the amount of the gases released is considered less likely to pose a safety risk to the occupants. Venting in the case of condition (a) may result in the release of gases and particulates from the REESS, thereby potentially exposing vehicle occupants to the emissions (gases and particulate matter).

Hazards associated with toxicity, corrosiveness, and flammability of the gases emitted from the REESS and associated human health exposure limits vary considerably. As noted above, NHTSA proposes to include a provision in FMVSS No. 305a to limit the safety risks to vehicle occupants due to venting during normal vehicle operations. The provision is based on GTR No. 20 requirements described below.

Gases generated in and vented from lithium-ion (Li-ion) batteries typically include carbon dioxide (CO

), carbon monoxide (CO), hydrogen (H

), oxygen (O

), light C

-C

hydrocarbons,

e.g.,

methane and ethane, and fluorine-containing compounds such as hydrogen fluoride (HF) and fluoro-organics,

e.g.,

ethyl-fluoride.

GTR No. 20 specifies that under normal vehicle operation, the vehicle occupants are not exposed to any hazardous environment caused by venting from the REESS. To avoid human harm that may occur due to potential toxic or corrosive emissions, GTR No. 20 specifies that there be no venting from the REESS for the following normal vehicle operations tests: vibration, thermal shock and cycling, external short circuit protection, overcharge protection, over-discharge protection, over-temperature protection and overcurrent protection. GTR No. 20 includes a no-fire requirement in these tests which addresses the issue of vented gas flammability. During the development of GTR No. 20, a robust and repeatable method to verify the occurrence of

venting and the potential exposure of vehicle occupants to various gases from the venting was sought, but no suitable method was found. Visual inspection was found to be the best approach at this time for verifying the occurrence of venting for assessing the influence of vented gases on vehicle occupants. Therefore, GTR No. 20 specifies that evidence of venting in these tests is verified by visual inspection (evidence of soot, electrolyte residues) without disassembling any part of the REESS.

NHTSA proposes to use a similar approach in FMVSS No. 305a to evaluate the safety risks to vehicle occupants resulting from venting from the REESS. The agency acknowledges that research is needed to develop a repeatable, reproducible, and practical method to verify the occurrence of various vented gases and the potential exposure and harm to vehicle occupants. However, NHTSA tentatively concludes that in the absence of such a method, the requirement that there must be no fire, electrolyte leakage or venting during the tests evaluating vehicle controls for safe REESS operation (external short-circuit protection, overcharge protection, over-discharge protection, over-temperature, and overcurrent protection) would reduce some safety risks to vehicle occupants due to venting from the REESS. The evidence of venting in these tests would be verified by visual inspection (evidence of soot, electrolyte residues) without disassembling any part of the REESS.

NHTSA also requests comment in an Appendix to this preamble on the IWG's continuing work on venting in Phase 2 of the GTR.

1. Vehicle Controls for Safe REESS Operation

This NPRM proposes the following performance requirements and associated test procedures for vehicles to ensure they have controls managing safe REESS operations. There are some minor differences between the GTR No. 20 test procedures and those proposed in this NPRM that are based on the lessons learned from NHTSA's test program. Those differences pertain to the ease of conducting the test.

For example, the state of charge of the REESS at the beginning of the test differed in some instances from that in GTR No. 20 to enable completing the test more readily.

NHTSA funded research to validate a collection of test procedures that assess safety hazards to electric vehicles while being charged or when the REESS exceeds its recommended operational limits.

47 48

The research independently evaluated, refined, and validated vehicle-level test procedures that could be robustly applied to a wide range of vehicle technologies and battery configurations. Based on the results of NHTSA's research, the agency proposes to conduct full vehicle-level tests using a breakout harness connected to a battery tester/cycler

to evaluate vehicle controls for safe REESS operation, rather than conducting the tests on the REESS as a separate component. NHTSA is proposing vehicle-level testing because evaluating REESS safe operation at the vehicle level would evaluate the entire vehicle system and the associated vehicle controls, whereas conducting the tests at the equipment level would not evaluate all the relevant vehicle controls or any interaction or interference between vehicle controls.

DC Charging Safety Evaluation Procedure Development, Validation, And Assessment, and Preliminary AC Charging Evaluation Procedure—DOT HS 812 754 and DOT HS 812 778—July 2019.

https://rosap.ntl.bts.gov/view/dot/41933.

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.

A battery tester/cycler is equipment that can be used for charging and discharging REESS and for conducting specialized tests on the REESS. An example of a battery tester with hybrid and battery electric vehicles is the NHR 9300 battery test system (NHR 9300).

NHTSA evaluated the GTR No. 20 test procedures for feasibility, practicability, and objectivity by conducting the test procedures on a 2019 Chevy Bolt, 2020 Tesla Model 3, and 2020 Nissan Leaf S Plus.

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NHTSA's test program demonstrated the ease of conducting tests at a 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. The proposed test procedures for overcharge, over-discharge, overcurrent, over-temperature, and external short-circuit tests are non-destructive tests intended to evaluate vehicle controls to protect the REESS and can be conducted in serial order on the same vehicle.

NHTSA Test Report on the 2020 Tesla Model 3 Standard Range 4-Door Sedan can be accessed here:

https://downloads.regulations.gov/NHTSA-2021-0029-0003/attachment_2.pdf.

NHTSA Test Report on the 2020 Nissan Leaf S Plus (62kWh Battery) 5-Door Hatchback can be accessed here:

https://downloads.regulations.gov/NHTSA-2021-0029-0002/attachment_2.pdf.

NHTSA Test Report on the 2019 Chevy Bolt can be accessed here:

https://downloads.regulations.gov/NHTSA-2021-0029-0001/attachment_2.pdf.

i. Overcharge Protection

A battery pack experiences an overcharge when a charger forces its state of charge (SOC) level to rise above 100 percent. Overcharge of a REESS can occur because of a failure of the charging system, such as a fault in an external charger, a fault in the vehicle's regenerative braking system, a sensor failure, or a voltage reference drift.

Overcharge can lead to swelling of an electrochemical cell, lithium plating, stability degradation, or over-heating, and ultimately can lead to thermal runaway.

Severe events such as fire or explosion may occur. Therefore, vehicle controls to ensure the REESS does not get overcharged are important for long-term safe operation of the REESS.

Voltage can drift based on temperature. Higher temperature can result in lower voltage.

Thermal runaway of a lithium-ion cell in a REESS occurs when the thermal stability limit of the cell chemistry is exceeded, and the cell releases its energy via an exothermic reaction at an uncontrolled rate such that the heat generated is faster than that dissipated.

Vehicle level controls or the BMS typically prevent charging when the manufacturer-specified maximum operating SOC of the REESS is achieved. GTR No. 20 includes a test to evaluate the performance of vehicle controls to prevent overcharge of the REESS. NHTSA tentatively concludes that GTR No. 20's overcharge test is practical and feasible based on the agency's own testing.

NHTSA proposes to include the overcharge protection requirement and test procedure in FMVSS No. 305a.

See Test reports in docket no. NHTSA-2021-0029, available at

www.regulations.gov.

Detailed test procedures are provided in the test reports of the 2021 Chevrolet Bolt (NHTSA-2021-0029-0001), 2020 Nissan Leaf (NHTSA-2021-0029-0002), and the 2020 Tesla Model 3 (NHTSA-2021-0029-0003).

The proposed overcharge test would be performed on a complete vehicle as follows. The test is conducted with the REESS initially set at 90 to 95 percent SOC

and at ambient temperatures between 10 °C and 30 °C. The breakout harness is attached on the traction side of the REESS at the vehicle manufacturer's recommended location(s) and attachment point(s), and the battery tester/cycler is connected to the breakout harnesses to supply the charge current. Temperature probes are connected to the REESS case to monitor changes in the REESS temperature. Temperature measurements may also be

obtained through communication with the REESS control module.

Ranges in temperature and SOC are provided for this and other test procedures for practicability and ease of conducting the tests. In the overcharge test, the REESS is initially set at a high SOC (90 to 95 percent) to enable fully charging the REESS in a shorter period of time.

Commercial diagnostic tools or tools supplied by the manufacturer may be used to read the Temperature measurements within the REESS from the vehicle's Controller Area Network (CAN bus).

The vehicle is turned on and the REESS is charged using the battery tester/cycler in accordance with the manufacturer's recommended maximum charge current

until one of the following has occurred:

If the manufacturer does not provide an appropriate charge current, then a charge rate (

i.e.,

C-Rate) of C/3 current would be used.

(a) the REESS overcharge protection control terminates the charge current;

(b) the REESS temperature is 10 °C above its maximum operating temperature specified by the manufacturer;

or,

The manufacturer would specify the procedure for monitoring the temperature of the REESS during testing. This could be measured by attaching thermocouples to the casing of the REESS or obtained from the CAN bus using appropriate tools.

After the overcharge condition is terminated, a standard cycle is performed if possible. The test concludes with a 1-hour observation period in which the vehicle is observed for any evidence of electrolyte leakage, rupture, venting, fire, or explosion. At the conclusion of the post-test observation period, the electrical isolation is determined in the same manner as currently in FMVSS No. 305 S7.6 using a voltmeter to measure voltages.

ii. Over-Discharge Protection

Over-discharging a REESS, which means discharging it below its lowest state of charge specified by the manufacturer, can lead to undesirable aging, electrolyte leakage, swelling, solid electrolyte interphase (SEI) decomposition, internal short-circuit, and damaged cell stability and safety on subsequent recharges. Even though the initial over-discharge response of lithium-ion cells generally appears benign, it can cause damage to cell electrodes that can compromise cell stability and safety on subsequent recharge. Subsequent charging of an over-discharged REESS may lead to fire or explosion.

Vehicle controls or the BMS typically prevent over-discharging when the manufacturer specified minimum operating SOC of the REESS is achieved. GTR No. 20 includes a test to evaluate the performance of vehicle controls to prevent over-discharge of the REESS. NHTSA tentatively concludes that GTR No. 20's over-discharge test is practical and feasible based on the agency's own testing.

NHTSA proposes to include the over-discharge protection requirement and test procedure in FMVSS No. 305a.

See Test reports in Docket No. NHTSA-2021-0029, available at

www.regulations.gov.

The over-discharge test is performed at ambient temperatures between 10 °C and 30 °C on a complete vehicle. The SOC of the REESS at the beginning of the test is set at 10 to 15 percent.

For a vehicle with on-board energy conversion systems (

e.g.,

internal combustion engine, fuel cell, etc.), the fuel supply is set to the minimum level

where active driving mode is permitted. Similar to the overcharge test, the breakout harness is attached on the traction side of the REESS at the vehicle manufacturer's recommended location(s) and attachment point(s), and the battery tester/cycler is connected to the breakout harness to discharge the REESS.

Temperature probes are connected to the REESS case to monitor changes in the REESS temperature. Temperature measurements may also be obtained through communication with the REESS control module.

Ranges in temperature and SOC are provided for this and other test procedures for practicability and ease of conducting the tests. In this case, the test is initiated with the REESS at a low SOC (10 to 15 percent) to enable discharging the REESS in a shorter period of time.

Minimum level of fuel supply needed would be provided by the manufacturer.

A discharge resistor may also be used for this purpose.

The vehicle is turned on and the REESS is discharged using the battery tester/cycler in accordance with the manufacturer's recommended discharging rate

under normal operating conditions until one of the following has occurred:

If the manufacturer does not specify a discharge rate, a power load of 1kW is used.

(a) vehicle controls terminate the discharge current,

(b) the temperature gradient of the REESS is less than 4 °C

through two hours, or

Temperature variation of 4 °C indicates stable operation of the REESS. As noted earlier, the manufacturer specifies the procedure for monitoring the temperature of the REESS during testing. This could be measured by attaching thermocouples to the casing of the REESS or obtained from the CAN bus using appropriate tools.

At the conclusion of the discharge termination, one standard charge is performed, followed by one standard discharge. The test concludes with a 1-hour observation period in which the vehicle is observed for any evidence of electrolyte leakage, rupture, venting, fire, or explosion. At the conclusion of the observation period, the electrical isolation is determined in a similar manner as that in current FMVSS No. 305 S7.6 using a voltmeter to measure voltages.

iii. Overcurrent Protection

As noted earlier, the vehicle and the charging system communicate the level of current needed to charge the REESS. If there is a problem in the communication or if the charging system malfunctions, higher current may be provided though not requested by the vehicle. During direct current (DC) fast-charging, failure of the external charge equipment could cause over-current conditions in which the REESS receives higher current than it was designed to manage at a given state of charge of the REESS. Overcurrent conditions could result in heating of the REESS, electrochemical damage to the cells, and a risk of thermal runaway.

GTR No. 20 includes a test to evaluate the performance of vehicle controls to protect the REESS from overcurrent conditions. NHTSA tentatively concludes that GTR No. 20's overcurrent test is practical and feasible based on the agency's own testing.

NHTSA proposes to include the overcurrent protection requirement in FMVSS No. 305a. In accordance with GTR No. 20, NHTSA proposes to apply the overcurrent test to vehicles that have capability of charging by DC external electricity supply. The test is unnecessary for vehicles that only charge by alternating current (AC) supply because AC charging is slower and the inverters for AC charging manage any overcurrent. Also, overcurrent issues have not been observed in AC charging.

See Test reports in docket no. NHTSA-2021-0029, available at

www.regulations.gov.

The overcurrent test is performed with a complete vehicle. To avoid the overcharge protection terminating the over-current condition, the SOC of the REESS is set between 40 to 50 percent. The test is conducted at ambient temperatures between 10 °C and 30 °C. The breakout harness is attached on the traction side of the REESS at the vehicle manufacturer's recommended location(s) and attachment point(s), and the battery tester/cycler is connected to the breakout harnesses to supply the charge current. Temperature probes are connected to the REESS case to monitor changes in the REESS temperature.

Temperature measurements may also be obtained through communication with the REESS control module. The vehicle manufacturer specifies the highest normal charge current and the over-current level that is applied. The battery tester/cycler is programmed to supply an over-current during charging at the level specified by the manufacturer.

The vehicle is turned on and the REESS is charged using the battery tester/cycler in accordance with manufacturer's recommended charging procedure with the highest normal charge current specified by the manufacturer.

After charging is initiated, an over-current specified by the manufacturer

is supplied above that requested by the vehicle. The charge current is increased over the course of 5 seconds from the highest normal charge current to the over-current level. The charge current and the overcurrent supply is continued until one of the following has occurred: (a) vehicle over-current protection controls terminate the charging, or (b) the temperature gradient of the REESS is less than or equal to 4 °C for a two-hour period.

The manufacturer supplied information define the constant current level and/or constant voltage level combination to charge the REESS. If a charge procedure is not specified, then a charge rate (

i.e.,

C-Rate) of C/3 current is used.

If the vehicle manufacturer does not supply an appropriate over-current level, the battery test/cycler will be programmed to initially apply a 10 Ampere over-current. If charging is not terminated, the over-current level of 20 amps will be applied. Subsequently, the over-current supply is increased in steps of 10 amperes.

If possible, a standard cycle is performed using the connected breakout harness and battery cycler. The test concludes with an observation period of one hour in which the vehicle is observed for electrolyte leakage, rupture, venting, fire, or explosion. At the conclusion of the observation period, the electrical isolation is determined in a similar manner as that in current FMVSS No. 305 S7.6, using a voltmeter to measure voltages.

iv. Over-Temperature Protection

While the impacts of over-temperature operation vary by chemistry, most battery chemistries can be negatively affected if operation by the driver is attempted at high temperatures (per the limits of a specific chemistry) or if aggressive operation is attempted at high temperatures (high-rate charging or discharging). A temperature imbalance or continued operation at elevated temperatures may even lead to thermal runaway of cells if appropriate countermeasures, such as de-rating,

are not taken.

De-rating is the reduction of a battery's available power and is typically due to a state that indicates an undesirable condition such as rapidly increasing cell temperature, elevated temperatures, or very cold cell temperatures. By temporarily reducing a battery's ability to provide and/or absorb power, de-rating allows the battery to cool down (or at least stop increasing in temperature) in situations with elevated temperatures and reduces operation when the battery is so cold that certain usage levels could cause damage.

Vehicle controls such as thermal management systems or the BMS continuously monitor temperature conditions to prevent REESS operation at elevated temperatures above the upper temperature boundary for safe REESS operations. GTR No. 20 includes a test to evaluate the performance of vehicle controls to prevent REESS temperatures exceeding the upper temperature boundary for safe REESS operations. NHTSA tentatively concludes that GTR No. 20's over-temperature test is practical and feasible based on the agency's own testing.

NHTSA proposes to include the over-temperature protection requirement and test procedure in FMVSS No. 305a, which aligns with GTR No. 20.

See Test reports in Docket No. NHTSA-2021-0029, available at

www.regulations.gov.

In the proposed FMVSS No. 305a, the over-temperature test is performed on a chassis dynamometer

with a complete vehicle. The SOC of the REESS at the beginning of the test is set between 90 to 95 percent. The test is conducted at ambient temperatures between 10 °C and 30 °C. For vehicles with on-board energy conversion systems (

e.g.,

internal combustion engine, fuel cell, etc.), the fuel system must have sufficient supply to allow operation of the energy conversion system for about one hour of driving. The cooling system for the REESS is disabled (or significantly reduced for a REESS that will not operate with the cooling system disabled) per manufacturer-supplied information.

For REESSs that will not operate if the cooling system is disabled, the maximum amount of coolant is removed to minimize the cooling system's operation for the test.

A chassis dynamometer is a mechanical device that uses one or more fixed roller assemblies to simulate different road conditions within a controlled environment and is used for a wide variety of vehicle testing.

Methods for disabling the cooling system may include crimping the liquid cooling hose or in the case of a refrigerant cooled package, removing the refrigerant fluid. For REESS cooled by cabin air, block the cabin air intakes used to provide cooling air flow to the REESS.

Temperature probes are connected to the REESS case to monitor changes in the REESS temperature. Temperature measurements may also be obtained through communication with the REESS control module.

GTR No. 20 specifies that the vehicle be soaked for at least 6 hours in a thermally controlled chamber at 45 °C. However, NHTSA's testing

demonstrated that the presoaking of the vehicle at elevated temperatures does not raise the temperature of the REESS as significantly as by driving the vehicle under high acceleration and deceleration drive modes. Therefore, to reduce the test time and test burden, the agency does not believe it needs to specify presoaking of the vehicle.

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.

The vehicle is installed on the chassis dynamometer and is placed into driving mode. The vehicle is driven on the dynamometer using the vehicle manufacturer-recommended appropriate drive profile for discharge and charge of the REESS that would raise the temperature of the REESS (with cooling system disabled or reduced function) above its safe operating temperature within one hour. If the vehicle manufacturer does not supply an appropriate drive profile, NHTSA will drive the vehicle over back-to-back aggressive acceleration (near 100% pedal application) and decelerations (near or above regenerative braking limits) such as the one shown in Figure 3 below, where the vehicle is accelerated to 80 mph and then decelerated to 15 mph within 40 seconds.

EP15AP24.046

Figure 3—Drive Profile on Dynamometer To Quickly Raise the Temperature of the REESS. (For Illustration Purposes Only)

Vehicle battery designs and controls mitigate overheating of the REESS in different ways: (1) Terminate discharge/charge operations when the REESS temperature reaches its operating bounds; (2) Derate (reduce acceleration/speed of the vehicle) to prevent the REESS reaching its maximum operating temperature; (3) REESS cell chemistries are stable at higher REESS temperature. In order to accommodate different approaches to address hazards associated with overheating of REESS, GTR No. 20 provides three different options for terminating the discharge/charge cycles:

(a) the vehicle terminates the charge-discharge cycle,

(b) the REESS temperature gradient is less than or equal to 4 °C for a two-hour period, or

In accordance with GTR No. 20, the agency proposes to use the same three options listed above to terminate the discharge/charge cycle.

At the conclusion of the over-temperature evaluation, a standard cycle is performed if possible. The test concludes with a 1-hour observation period in which the vehicle is observed for electrolyte leakage, rupture, venting, fire, or explosion. At the conclusion of the observation period, the electrical isolation is determined in a similar manner as that in FMVSS No. 305 S7.6, using a voltmeter to measure voltages.

v. External Short-Circuit Protection

The purpose of the external short-circuit protection test is to verify the performance of the vehicle controls (protection measure) against a short-circuit occurring externally to the REESS. During an external short-circuit event, large amounts of instantaneous current can be readily drawn generating copious amounts of heat. Associated safety risks include over-heating, gas venting, or arcing that can occur under fault conditions which can potentially lead to fire or explosion.

Vehicle controls or the BMS typically protect the REESS from an external short-circuit. GTR No. 20 includes a test to evaluate the performance of vehicle controls to protect the REESS from an external hard short-circuit (shorting resistance less than 5 milliohms). NHTSA tentatively concludes that GTR No. 20's external short-circuit test is practical and feasible based on the agency's own testing.

NHTSA proposes to include the GTR No. 20 external short-circuit protection requirement and test procedure in FMVSS No. 305a.

See Test reports in Docket No. NHTSA-2021-0029, available at

www.regulations.gov.

The external short-circuit test is performed on a complete vehicle. The SOC of the REESS at the beginning of the test is set at 90 to 95 percent SOC. The test is conducted at ambient temperatures between 10 °C and 30 °C. The breakout harness is installed on the vehicle at the manufacturer specified location(s).

Temperature probes are connected to the REESS case to monitor changes in the REESS temperature. Temperature measurements may also be obtained through communication with the REESS control module. The short circuit contactor (with the contactors in open position) is connected to the breakout harnesses. The total resistance of the equipment to create the external short circuit (short circuit contactor and breakout harnesses) is verified to be between 2 to 5 milliohms.

To begin the short-circuit evaluation, the short-circuit contactors are closed. The short-circuit condition is continued until (1) current is no longer present or (2) one hour after the temperature probe on the REESS has stabilized with a temperature change of less than 4 °C for a two-hour period.

If the manufacturer does not provide information on the location to connect the breakout harness for the external short circuit test, the breakout harnesses may be connected on either side of the positive and negative terminals of the pack.

GTR No. 20 specifies the external short circuit resistance not exceeding 5 milliohms. The agency is specifying a range from 2 to 5 milliohms for ease of conducting the tests and to ensure objectivity of the test.

If possible, a standard cycle is performed after termination of the short-circuit. Fuses that opened during the short-circuit are not replaced, and the standard cycle procedure is not performed if it is not possible to charge and discharge the vehicle.

The vehicle is observed for one hour for electrolyte leakage, rupture, venting, fire, or explosion. The external short-circuit test concludes with an electrical isolation determination in a similar manner as that in current FMVSS No. 305a S7.6 using a voltmeter to measure voltages.

vi. Low-Temperature Protection

Uncontrolled repeated operation at low temperatures, especially charging

for lithium-ion battery chemistries, may result in lithium plating or cell damage that could eventually lead to reduced performance or degraded life during subsequent operation. While single time operation of REESS in very cold temperatures would not lead to a severe event, some REESS designs use special chemical reactions which can damage the REESS if it is charged at high rates in very cold temperatures. A subsequent high rate of charging of such a damaged REESS may lead to fire or explosion. Therefore, the rate of charging may need to be terminated or limited in very cold temperatures.

Currently, no practical test procedure is available to evaluate the performance of vehicle controls in low temperature conditions because the effects of repeated charging at very low temperatures occur over a very long period of time. Therefore, GTR No. 20 requires manufacturers to provide documentation that includes a system diagram, a written explanation on the lower boundary temperature for safe REESS operation, the method of detecting REESS temperature, and the action taken when the REESS temperature is at or below the lower boundary for safe REESS operation.

NHTSA proposes to include documentation requirements based on GTR No. 20 into FMVSS No. 305a. NHTSA proposes that the manufacturer provide documentation, upon NHTSA's request, to demonstrate how the vehicle monitors and appropriately controls REESS operations at low temperatures at or below the lower temperature boundary for safe REESS operation. The proposed requirements would indicate how manufacturers identify, verify, and ensure vehicles have low-temperature protections in place. Specifically, the proposal requires the manufacturer-supplied documentation for a specific vehicle make, model, and model year would include the following:

(1) A description of the lower temperature boundary for safe REESS operation in all vehicle operating modes.

(2) A description and explanation of C-rates at the lower temperature boundary for safe REESS operation.

(3) A description of the method used to detect REESS temperature.

(4) A system diagram with key components and subsystems involved in maintaining safe REESS charging and discharging operation for temperatures at or below the lower temperature boundary for safe REESS operation.

(5) A description of how the vehicle controls, ancillary equipment, and design features were validated and verified for maintaining safe REESS operations at or below the lower temperature boundary for safe REESS operation.

(6) A description of the final review/audit process of the manufacturer, and the accompanying results of the manufacturer's final assessment of risk management, and risk mitigation strategies.

NHTSA intends these documentation measures to demonstrate that the manufacturer has considered, assessed, and mitigated identified risks for safe operation of the vehicle. NHTSA tentatively agrees with GTR No. 20 that there is a safety need for low temperature protections for the REESS. Without protections, uncontrolled repeated operation at low temperatures poses an unreasonable risk of fire or explosion. In the absence of information enabling NHTSA to propose a practical test procedure to evaluate the performance of vehicle controls in low temperature conditions, the agency is proposing to require manufacturers to submit documentation to NHTSA about pertinent low temperature safety hazards, describe their risk mitigation strategies for the safety hazards, and how they assessed the effectiveness of their mitigation strategies.

NHTSA would review the documentation to understand the safety hazards associated with the particular REESS in the vehicle, see whether the manufacturer conducted an assessment of the risks, and understand the measures the manufacturer undertook to mitigate those known risks. This approach is intended to evolve over time as battery technologies continue to rapidly evolve. It is an interim measure intended to assure that manufacturers will identify and address the low temperature safety risks of the REESS. In section VI., NHTSA requests comments on whether the proposed document requirement would be better placed in a general agency regulation than in proposed FMVSS No. 305a.

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

i. Safety Need

The potential for thermal runaway is a characteristic of the lithium-ion cells currently used in REESSs for electric vehicle propulsion. Thermal runaway of a lithium-ion cell in a REESS occurs when the thermal stability limit of the cell chemistry is exceeded, and the cell releases its energy via an exothermic reaction at an uncontrolled rate such that heat is generated faster than it is dissipated. The thermal runaway in a single cell may propagate to the surrounding cells through conductive, convective, and radiative heat transfer modes, causing reactions which create smoke, fire or, in very rare circumstances, explosion. Lithium-ion cells have flammable electrolyte that upon decomposition provides oxygen to the fire caused by the thermal runaway, which increases the likelihood of its propagation to other cells and even outside the REESS. The self-oxygenating fires involving the cells in a REESS are therefore difficult to extinguish. The smoke, fire, toxic gas emissions, and explosion resulting from the thermal runaway can cause hazardous conditions for vehicle occupants and those near the vehicle.

One root-cause of single-cell thermal runaway (SCTR) and propagation due to an internal short-circuit relates to problems within the cells. While this NPRM contains many performance tests for the safe operation of the REESS, none of these tests would mitigate or prevent thermal runaway due to an internal short-circuit within a cell of the REESS and subsequent fire propagation. The mechanism of an internal short circuit in a cell is complex and requires further study. Currently, the risk of a spontaneous internal short circuit is heavily dependent on battery design, such as use of non-flammable electrolytes, ionic liquids, heat resistant and puncture-proof separators, and anode and cathode materials. However, as discussed below, a performance test that would establish a minimum standard of performance for the materials is not available now.

GTR No. 20 addresses the hazards associated with SCTR due to an internal short circuit through a documentation approach that requires manufacturers to provide (to the testing authority) information on risk mitigation strategies used in vehicle design to counteract the safety risk. GTR No. 20 also requires a warning system to allow vehicle occupants sufficient time to egress the vehicle before hazardous conditions are present in the passenger compartment due to SCTR within the REESS. GTR No. 20 requires documentation of the warning system, and requires operation of the warning system only when the vehicle propulsion system is turned on.

NHTSA tentatively generally agrees that a documentation approach on risk mitigation strategies currently has merit, given there is no suitable performance test to validate mitigation or prevention of SCTR within a REESS. NHTSA is proposing a documentation approach based on GTR No. 20 but has focused the GTR's requirements to better address this safety need pending development of an objective performance test that can

be applied to all REESSs in vehicles. In section VI., NHTSA requests comments on whether the proposed document requirement would be better placed in a general agency regulation than in proposed FMVSS No. 305a.

NHTSA is not proposing to require a warning system, or documentation of the warning system, as specified in GTR No. 20. As explained fully later in this section, NHTSA believes such a requirement would not mitigate the safety hazards observed in the field.

ii. GTR No. 20 Phase 1 Requirements

GTR No. 20 recognizes that, in general, REESS cells are manufactured with manufacturing controls to mitigate safety problems. Based on current manufacturing control processes, the probability of manufacturing problems within a cell is generally considered to be less than one in a million.

Since the likelihood of two cells in a REESS going into spontaneous single-cell thermal runaway (SCTR) simultaneously is significantly lower,

the focus of GTR No. 20 is to mitigate the hazards associated with SCTR due to an internal short-circuit within a single cell.

A REESS consists of a number of cells (n) in the range of 100 to 500. Therefore, the probability of a single-cell thermal runaway and propagation event due to an internal short-circuit is estimated to be the product of the number of cells times one in a million (n × 10

−6

https://batteryuniversity.com/article/bu-304a-safety-concerns-with-li-ion#:~:text=Lithium%2Dion%20batteries%20have%20a,than%20those%20in%20consumer%20products.

The probability of two cells simultaneously undergoing single-cell thermal runaway and propagation due to an internal short-circuit is equal to the product of the probability of a single-cell thermal runaway (n

× 10

−12

GTR No. 20 addresses the SCTR safety hazard through a documentation approach that requires manufacturers to provide (to the testing authority on request) information on risk mitigation strategies used in vehicle design to counteract the safety risk, and documentation on a warning system that warns occupants to egress the vehicle. The documentation requirements for risk mitigation strategies are only generally described, however. This is because during the development of GTR No. 20, there was no significant evidence of electric vehicle fires due to SCTR and propagation due to an internal short-circuit. At that time, the thought was that vehicle occupants would be exposed to hazardous conditions if the SCTR propagates outside of the REESS to other parts of the vehicle. Therefore, GTR No. 20 focuses primarily on the warning and less on mitigating the risk of the SCTR within the cell. The GTR requires that a warning be provided to the driver 5 minutes before hazardous conditions are present in the passenger compartment due to SCTR and subsequent fire propagation. Five minutes was considered sufficient time for vehicle occupants to egress the vehicle before exposure to hazardous conditions. Under the GTR, manufacturers would satisfy the requirement for a warning by providing documentation that the vehicle provides the required warning.

GTR No. 20 uses a documentation approach for both the risk mitigation strategies and the warning because an objective test procedure is not available. Existing methods of initiating thermal runaway simulating an internal short-circuit within a single cell in a REESS are intrusive and dependent on the type of cell chemistry and cell type.

Additionally, different methods of initiation could result in different results.

NHTSA funded research to evaluate different thermal runaway propagation test methods by examining various existing methods of initiating thermal runaway, including heating element method, rapid heater method, nail penetration, and laser method, on batteries with a variety of chemistries, formats, and configurations.

The 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 battery chemistries, formats, and configurations.

One common method of initiating a thermal runaway is to heat a cell externally using a heating element. This would require disassembly of the casing of the REESS, adhering a heating element to the surface of a cell, and adding thermocouples to verify the heating element only provides heat to a single cell and not to adjacent cells. The amount of heat applied to initiate a thermal runaway depends on the cell chemistry (more volatile chemistries requiring less heat input), and the cell design/type (thick wall cells needing more heat input). The disassembly of the REESS, the addition of a heating element, and the heat input is intrusive to the REESS.

Another method of initiating a thermal runaway in a cell is to penetrate a nail into a cell in the REESS. The orientation of the nail penetration depends on the cell design and in some instances, nail penetration may not cause a thermal runaway. While this method may not require the REESS casing to be opened, the penetrating nail compromises the casing and the cell structure. Additionally, the depth of nail penetration may result in differences in heat release that may not be similar in repeat tests and in tests using a heating element.

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.

The repeatability and reproducibility of a potential performance test using existing methods of thermal runaway initiation, and whether such a test could be conducted on all applicable vehicles, are unknown. Due to the rapid development of electric vehicle propulsion technology, it was unclear during development of the GTR if any existing performance test could apply to future vehicle designs without restricting further enhancement of electric vehicle propulsion systems. Therefore, instead of specifying a performance test for thermal runaway and propagation due to an internal short-circuit in a single cell of a REESS, GTR No. 20 requires manufacturers to submit documentation. Such documentation must show risk mitigation strategies in their vehicle designs for reducing hazards to vehicle occupants associated with thermal runaway due to an internal short-circuit in a single cell in the REESS. The documentation must also detail how the vehicle's warning system activates a warning at least 5 minutes before hazardous conditions arise in the passenger compartment.

Specifically, GTR No. 20 specifies the following documentation requirements:

• A description of the warning system.

• Parameters (such as voltage, temperature, or current) that trigger the warning indicator (telltale).

• A risk reduction analysis using appropriate industry standard methodology (for example, IEC 61508,

MIL-STD 882E,

ISO-26262,

fault analysis as in SAE J2929,

or similar), which documents the risk to vehicle occupants caused by a single-cell thermal runaway triggered by an internal short-circuit leading to thermal propagation and the expected risk reduction resulting from implementation of the identified risk mitigation functions or characteristics.

IEC-61508:2010, “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems”.

https://webstore.iec.ch/searchform&q=IEC%2061508.

MIL-STD-882E:2012, “System Safety”.

https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=36027.

ISO-26262 series:2018, “Road vehicles—Functional Safety”.

https://www.iso.org/search.html?q=ISO-26262&hPP=10&idx=all_en&p=0&hFR%5Bcategory%5D%5B0%5D=standard.

SAE J2929:2013, “Safety Standard for Electric and Hybrid Vehicle Propulsion Battery Systems Utilizing Lithium-based Rechargeable Cells”.

https://www.sae.org/standards/content/j2929_201302/.

• A system diagram of all relevant physical systems and components which contribute to the protection of vehicle occupants from hazardous effects caused by thermal propagation triggered by a single-cell thermal runaway event due to an internal short-circuit.

• A diagram showing the functional operation of the relevant systems and components and identifying all relevant risk mitigation functions or characteristics.

• For each identified risk mitigation function or characteristic:

○ A description of its operation strategy,

○ Identification of the physical system(s) or component(s) which implements the function,

○ One or more of the following engineering documents relevant to the manufacturers design which demonstrates the effectiveness of the risk mitigation function:

Tests performed including procedure used and conditions and resulting data,

Analysis or validated simulation methodology and resulting data.

iii. NHTSA Proposal

NHTSA tentatively agrees with GTR No. 20's rationale for the documentation requirements for risk mitigation of thermal propagation events resulting from SCTR due to an internal short-circuit within a cell in the REESS. NHTSA tentatively concludes that due to the rapidly evolving REESS technology and control systems to manage the performance condition and safety of the REESS, a performance test to validate mitigation of thermal propagation resulting from SCTR within the REESS is not currently feasible. A performance test for a warning, when the vehicle propulsion system is turned on, that provides sufficient time for vehicle occupants to egress the vehicle before hazardous conditions arise in the passenger compartment after a thermal runaway is initiated in a cell of the REESS would be unduly design restrictive, not applicable to all vehicle/REESS types, and not relevant to real world incidents.

In most real-world incidents resulting in fire due to thermal runaway of a single cell in the REESS, the vehicle was parked, with propulsion system turned off, and with no occupants in the vehicle. In some cases, the vehicles were parked in garages of homes. Therefore, a requirement for a warning to vehicle occupants in the vehicle with propulsion system turned on would not have helped prevent the fire or mitigated hazards to people in homes or in the vicinity of the burning parked vehicle.

This NPRM proposes a documentation requirement for FMVSS No. 305a to require manufacturers to provide to NHTSA, upon NHTSA's request, information about their efforts to identify and address potential safety problems with SCTR and propagation due to an internal short-circuit. The information would be provided by a manufacturer in accordance with NHTSA's specified structure in four parts. NHTSA's proposed documentation component structure is based on elements from the 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 three vehicle operational modes (

i.e.,

external charging mode,

active driving possible mode,

and parking mode

). NHTSA's proposal goes beyond GTR No. 20's active driving possible mode to ensure manufacturers consider all risks known to it in three vehicle operational modes. The assessment and validation of these strategies may involve a combination of physical testing and simulations at the component level and/or full vehicle level. The reporting requirements would apply to REESSs of all types (including REESS with non-flammable electrolyte).

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 REESS, 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.

External charging mode is the vehicle operational mode in which the charge connector is connected to the vehicle charge inlet for the purpose of charging the REESS.

Active driving possible mode is the vehicle mode when application of pressure to the accelerator pedal (or activation of an equivalent control) or release of the brake system causes the electric powertrain to move the vehicle.

Parking mode is 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.

The objective of the documentation 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 documentation would accomplish the following goals:

• It would identify all risks known to the manufacturer related to single-cell thermal runaway and propagation due to an internal short-circuit;

• It would discuss whether and how each identified risk is managed and/or mitigated by at least one risk mitigation strategy;

• It would explain the reasons the manufacturer believes each risk mitigation strategy is effective (measures taken to verify and/or validate them, including any final review/audit results); and,

• It would identify, describe, and provide any review/audit process and results that accompany the final assessment of risk management and risk mitigation strategies.

Proposed provisions to achieve the above goals are discussed in detail below.

The documentation requirement proposed by NHTSA is divided into four sections with more detailed requirements than GTR No. 20. Under the agency's requirements, in Part I, System Analysis, the vehicle manufacturer would provide information describing which conditions specific to the vehicle could lead to a SCTR event caused by an internal short-circuit. The conditions identified serve as the inputs to identify the functions and failure modes for the risk identification in Part II.

Part I would require the following documentation:

• A system diagram and a description of all relevant physical systems and components of the REESS, including information about the cell type and electrical configuration, cell chemistry, electrical capacity, voltage, current limits during charging and discharging, thermal limits of the components that are critical for thermal propagation safety;

• A system diagram, operational description of sensors, components, functional units relevant to single-cell thermal runaway due to internal short-circuit and thermal propagation, and the interrelationship between the identified sensors, components, and functional units;

• A description of conditions under which a single-cell thermal runaway and propagation event due to an internal short-circuit could occur;

• A description of how the identified conditions are allocated to each identified component, functional unit, and subsystem;

• A description of the process used to review the identified conditions and their allocation to the identified sensors, components, and functional units, for completeness and validity; and

• A description of any system for warning or notification prior to the occurrence of thermal runaway in a cell, including a description of the detection technology and mitigation strategies, if any.

Part II, Safety Risk Assessment and Mitigation Process, provides a description of all identified safety risks and strategies to mitigate and manage

these risks. Part II distinguishes between primary and secondary risk mitigation strategies. Primary risk mitigation strategies mitigate the risk of SCTR due to an internal short-circuit and the occurrence of thermal propagation that may result from SCTR. 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. In contrast, 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). NHTSA anticipates that secondary risk mitigation strategies would be employed as an addition to primary risk mitigation strategies in the overall safety strategy.

Prognostic technologies predict the health of a system or a component of a system in the future and diagnostic technologies determine a specific problem with a system or component of a system.

Part II would require the following documentation:

• A description of safety risks and safety risk mitigation strategies, and how these were identified (

e.g.,

Failure Mode and Effects Analysis (FMEA), or Failure Modes, Effects, and Criticality Analysis (FMECA));

FMEA and FMECA are established methodologies to identify failure modes and postulate the effects of those failures on the system. Refer to

https://www.dau.edu/acquipedia-article/failure-modes-effects-analysis-fmea-and-failure-modes-effects-criticality.

• A description of how each risk mitigation manages/mitigates the identified safety risks.

In Part III, Verification and Validation of Effective Risk Mitigation Strategies, the manufacturer provides information showing how they verify the effectiveness of the identified mitigation strategies in Part II to mitigate the identified safety risks. The vehicle level assessment examines how the entire vehicle monitors and mitigates safety risks. The vehicle level assessment is the culmination of the verification/validation results of each individual risk mitigation strategy.

Part III would require the following documentation:

• A summary of the process used to verify each identified risk is addressed by at least one risk mitigation strategy;

• A description of how each risk mitigation strategy was verified and validated for effectiveness;

Possible verification/validation methods for Part III include (but are not limited to) fault injection tests, software, and hardware performance tests at component and/or system level, and system level performance evaluation using validated mathematical models.

• A description of the verification and validation results for each risk mitigation strategy; and

• A vehicle level assessment evaluating the system response to safety risks associated with the REESS. Vehicle level assessment and validation could be the use of physical tests and/or validated models/simulations at a component level scaled up to evaluate the system response.

Part IV, Overall Evaluation of Risk Mitigation, shall address:

• Results of any final review/audit responsible for reviewing the technical content, completeness, and verity of the documentation submitted by the manufacturer.

The risk-based methodology outlined above is intended to mitigate the safety hazards associated with SCTR and propagation from an internal short-circuit. The requirement is intended to ensure that manufacturers are aware of the safety risks at issue and have considered safety risk mitigation strategies. The documentation submitted by the manufacturer will inform NHTSA of the safety risk mitigation strategies manufacturers have utilized for the identified safety hazards, enable NHTSA to oversee those safety hazards, and inform future regulatory measures.. This approach is battery technology neutral, not design restricted, and is intended to adapt over time as battery technologies continue to rapidly evolve. NHTSA seeks comment on the documentation requirements described above. In section VI., NHTSA requests comments on whether the proposed document requirement would be better placed in a general agency regulation than in proposed FMVSS No. 305a.

NHTSA's Decision Not To Propose a Warning Requirement

GTR No.20's warning requirement rationale is that the warning would allow vehicle occupants sufficient time to egress the vehicle before hazardous conditions are present in the occupant compartment. NHTSA does not agree with GTR No.20's rationale for a warning requirement related to SCTR due to an internal short-circuit within the cell. NHTSA is not proposing to require such a warning system, or documentation of the warning system, as specified in GTR No. 20 because such a requirement would not mitigate the safety hazards observed in the field, as described in detail below.

Field data and incidents related to SCTR and propagation due to an internal short-circuit in lithium-ion REESSs are sparse and anecdotal. However, when reviewing the limited number of non-crash and non-abuse related electric vehicle fire incidents in the United States,

the following trends emerge:

E.g., Bolt EV Recall Information

https://experience.gm.com/recalls/bolt-ev.

• The vehicle operation mode is in the usual parking mode.

Usual parking mode is the vehicle operational mode in which the main software is “Off”, the gear selector is in “P” (park), the energy supply is disconnected, the REESS power line is disconnected, the cooling system is not operational, the vehicle controls that manage safe operation of the REESS (

e.g.,

Battery Manage System) are not energized, and the vehicle occupants are typically not present.

• The vehicle is parked in a garage attached to a house, a parking garage, or on the street.

• The state of charge (SOC) of the REESS was generally in the upper range.

Fire statistics reports by South Korea identified 35 electric vehicle fires since 2018, among which 20 electric vehicle fires originated in the REESS of the vehicles when the vehicle was parked and the SOC was greater than 90 percent.

In the electric vehicle fire incidents in the United States and South Korea, the vehicle fire propagated to adjacent vehicles and structures with release of copious amounts of smoke, resulting in significant property damage. The GTR No. 20 requirement for a warning to the driver would not have helped mitigate the electric vehicle fires and would not have mitigated property damage.

EVS23-E1TP-0200 [KR] EV Fire Records of Korea.pptx.

https://wiki.unece.org/display/trans/EVS+23rd+session.

Accordingly, this NPRM does not propose to require a warning to occupants or documentation pertaining to a warning, as such requirements would not sufficiently address a safety need. NHTSA believes the documentation requirements in GTR No. 20 for a warning to the driver are not relevant to the field-observed electric vehicle fires likely resulting from SCTR. NHTSA believes that vehicle designs using a risk mitigation strategy to mitigate or prevent the occurrence of SCTR incidents would better address the risks and hazards associated with spontaneous electric

vehicle fires that originate within the REESS than a warning to egress the vehicle. This NPRM proceeds with NHTSA's preferred approach which would require documentation demonstrating that the manufacturer has considered and developed risk mitigation strategies to address SCTR in developing their electric vehicles.

GTR No. 20 Phase 2 Test Procedure Currently Under Consideration

The IWG is continuing work on developing a test-based approach for SCTR due to an internal short-circuit in a single cell within the REESS. The plan is for a future regulation to require that the thermal propagation test procedure fulfill the following conditions:

1. Triggering of thermal runaway at a single-cell level must be repeatable, reproducible, and practicable,

2. Judgment of thermal runaway through common sensors,

e.g.,

voltage and temperature, needs to be practical, repeatable, and reproducible, and

3. Judgment of whether consequent thermal events involve severe thermal propagation hazards, needs to be unequivocal and evidence based.

NHTSA discusses this work in the Appendix B to this preamble. Comments are requested that could assist the agency in future decisions on this matter.

3. Warning Requirements for REESS Operations

As part of a risk-mitigation approach addressing multiple aspects of electrical system safety, NHTSA proposes requiring: (a) a thermal event warning; and (b) a vehicle control malfunction warning for drivers. The thermal event warning would be assessed by a performance requirement, while the vehicle control malfunction warning would be a documentation requirement.

i. Thermal Event Warning

A “thermal event” presents an urgent safety critical situation. The term 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 within REESS could occur due to moisture and dust accumulation within the REESS that cause 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 about a thermal event within the REESS would reduce the likelihood of occupant exposure to smoke, fire, and/or explosion.

GTR No. 20 requires the vehicle to provide a warning to the driver in the case of a “significant thermal event” in the REESS (as specified by the manufacturer) when the vehicle is in active driving possible mode.

The GTR does not contain a performance test for the warning but instead requires manufacturers to provide documentation on the parameters that trigger the warning and a description of the system for triggering the warning. Specifically, the documentation requirements include:

Active driving possible mode means the vehicle mode when application of pressure to the accelerator pedal (or activation of an equivalent control) or release of the brake system causes the electric power train to move the vehicle.

(1) 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.

(2) A system diagram and written explanation describing the sensors and operation of the vehicle controls which manage the REESS in the event of a thermal event.

NHTSA Proposal

NHTSA proposes to include a requirement for an audio and visual warning to the driver if a thermal event occurs in the REESS during the active driving possible mode. Instead of a documentation requirement as in the current GTR No. 20, NHTSA proposes a performance test to evaluate the required warning of a thermal event originating within the REESS.

NHTSA proposes to initiate the thermal event in the REESS by inserting a heater within the REESS that achieves a peak temperature of 600°C within 30 seconds. In the proposed test procedure, the REESS is removed from the vehicle, if possible, and the REESS casing is opened to attach the heater to a cell or cells in the REESS in a manner to put at least one cell in the REESS into thermal runaway. In this test, there is no need to restrict heating to a single cell within the REESS as the test is verifying activation of a warning when a thermal event occurs in the REESS regardless of the cause (

e.g.,

an electric short between electronic components in the REESS, thermal runaway of multiple cells, etc.). Following installation of the heater in the REESS, the REESS casing is closed, the REESS is re-installed in the vehicle, and the vehicle propulsion system is turned on. The heater within the REESS is then activated. NHTSA proposes that the audio-visual warning must be activated within three minutes

of initiating the heater in the REESS. NHTSA has tentatively decided not to specify characteristics of the audio-visual warning to provide flexibility in how manufacturers communicate this safety critical information to vehicle occupants so they quickly egress the vehicle.

3 to 5 minutes is considered to be sufficient time for able body individuals to evacuate light and heavy passenger vehicles before the occurrence of a hazardous event.

https://one.nhtsa.gov/reports/0900006480b01bbc.pdf.

The proposed test is for evaluating appropriate activation of a required warning system when there is a thermal event in the REESS that could be hazardous to vehicle occupants.

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NHTSA tentatively concludes that the proposed performance test to evaluate the warning system would not be design restrictive and can be conducted on all applicable vehicles. Therefore, a performance test is proposed instead of adopting the documentation requirement in GTR No. 20. NHTSA seeks comment on the merits of the proposed performance test to evaluate the thermal event warning system instead of the documentation requirement in GTR No. 20. In addition, NHTSA seeks input on the type of heater, the heater characteristics (power, peak temperature) and possible locations of the heater within the REESS to simulate a thermal event to trigger the warning. While this NPRM does not require specific features of the audio-visual warning itself, comments are requested on what characteristics an effective audio-visual warning should have.

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This is unlike the risk management approach for SCTR where the goal is to mitigate hazards of thermal propagation (fire, smoke, gas emissions). Because risk management strategies for mitigating thermal propagation hazards due to SCTR differ considerably in vehicle designs, an objective performance test that can be conducted on all applicable vehicles is not available and so a documentation requirement is proposed.

ii. Warning in the Event of Operational Failure of REESS Vehicle Controls

NHTSA is proposing to require that drivers be warned if there is a malfunction of vehicle controls that manage the safe operation of the REESS. This NPRM proposes a documentation approach for this type of warning, similar to GTR No. 20.

GTR No. 20 specifies that when the vehicle is in the active driving possible mode, the vehicle shall provide a warning telltale to the driver in the event of a malfunction of the vehicle controls that manage the safe operation of the REESS. GTR No. 20 requires manufacturers to provide

documentation demonstrating that a warning to the driver will be provided in the event of malfunction of one or more aspects of vehicle controls that manage REESS safe operation. Specifically, vehicle manufacturers shall make the following documentation available to the testing authority:

(1) A system diagram that identifies all the vehicle controls that manage REESS operation. The diagram must identify what components are used to generate a warning telltale indicating malfunction of vehicle controls to conduct one or more basic operations.

(2) A written explanation describing the basic operation of the vehicle controls that manage REESS operation. The explanation must identify the components of the vehicle control system, provide description of their functions and capability to manage the REESS, and provide a logic diagram and description of conditions that would lead to triggering the warning telltale.

NHTSA Proposal

Vehicle controls manage several REESS operations, some of which are safety critical. There are multiple external fault scenarios

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that could trigger a vehicle control to take corrective actions to ensure safe REESS operations. This NPRM includes performance requirements to address these external fault scenarios that assume proper functioning of the vehicle controls that manage safe REESS operations. However, if the vehicle controls that manage safe REESS operation are not functioning properly, the REESS may not be adequately protected from fault scenarios, which could lead to REESS degradation and eventually result in thermal propagation and other safety hazards. Therefore, it is important to notify the driver or front row occupants in the event there is malfunction of these vehicle controls that manage safe REESS operations.

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These fault scenarios include overcharge, over-discharge, overcurrent, external short-circuit, and overheating of the REESS.

Due to the complexity and varied designs of vehicle controls that manage REESS safe operation, no single test procedure could be developed that would fully evaluate whether a warning turns on in the event of operational failure of vehicle controls. Therefore, in accordance with GTR No. 20, this NPRM proposes to require manufacturers to provide a visual warning to the driver (

e.g.,

like a check engine light) and documentation demonstrating that the visual warning will be provided in the event of operational failure of one or more aspects of vehicle controls that manage REESS safe operation.

NHTSA proposes the GTR No. 20 requirements for a visual warning to the driver of any malfunction of the REESS vehicle controls, and manufacturer documentation. In addition, NHTSA proposes to include two additional requirements that ensure manufacturers have validated functionality of the warning system:

(1) Any validation test results by the vehicle manufacturer to confirm a visual warning is displayed in the presence of malfunction of the REESS operation vehicle controls.

(2) A description of the final manufacturer review or audit process and results of any final review or audit evaluating the technical content and the completeness and verity of the documentation submitted by the manufacturer.

NHTSA tentatively concludes that a documentation approach is merited to demonstrate that the manufacturer has considered the effectiveness of a visual warning of the malfunction of the REESS operational vehicle controls. In the absence of information enabling NHTSA to propose a practical test procedure to evaluate the performance of a warning, the documentation approach ensures that manufacturers are aware of the safety risks at issue and have considered ways to address the risks. NHTSA would review the documentation to understand the visual warning associated with the particular REESS in the vehicle, see whether the manufacturer conducted an assessment of its effectiveness, and understand the measures the manufacturer undertook to validate such performance.

This approach is an interim measure intended to assure that manufacturers will identify, address, and validate the effectiveness of their visual warnings that help manage safe REESS operation. The approach is intended to evolve over time as battery technologies and NHTSA's information about the REESS safety risk mitigation strategies evolve. In section VI., NHTSA requests comments on whether the proposed document requirement would be better placed in a general agency regulation than in proposed FMVSS No. 305a.

4. Protection Against Water Exposure

NHTSA proposes to adopt GTR No. 20's physical water test requirement, 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. However, the agency is not proposing to adopt GTR No. 20's two other water exposure methods: documentation measures and warning requirements.

Environmental effects such as exposure to water and moisture may deteriorate the electrical isolation of high voltage components in the powertrain. This may first lead to an electric system degradation and eventually lead to an unsafe electrical system for vehicle occupants, operators (during charging) or by-standers. Under extreme conditions, fire can originate from compromised electrical components due to water ingress. GTR No. 20 contains water exposure shock protection specifications in which a vehicle shall maintain electrical isolation resistance after the vehicle is exposed to water under normal vehicle operation, such as during a car wash or driving through a pool of standing water.

NHTSA begins by noting that GTR No. 20 does not have specific requirements to address vehicle fires due to vehicle submersion such as floods and storm surges, and this NPRM is not covering that area. Floods are considered as catastrophic events, and as noted above, 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 engine (ICE). NHTSA continues to research the area of REESS performance post-submersions. This issue is discussed in more detail later in this section.

GTR No. 20 Requirements

GTR No. 20 contains water exposure shock protection specifications in which a vehicle shall maintain electrical isolation resistance after the vehicle is exposed to water under normal vehicle operation. GTR No. 20 specifies three compliance options contracting parties may use in their regulations:

• Physical tests—(1) the vehicle is subjected to normal washing using a hose nozzle and conditions in accordance with IPX5, after which (2) the vehicle is driven in a freshwater wade pool (10 cm depth) over a total distance of 500 m at a speed of 20 km/hr for approximately 1.5 minutes (min). The electrical isolation of high voltage sources in the electric powertrain are verified at the conclusion of each test and once again after 24 hours.

• Documentation—The vehicle manufacturers provide documentation

certifying to IPX5

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level waterproofing for protection of high voltage components in the vehicle. IPX5 is a waterproof rating that ensures protection against water ingress under sustained low pressure water jet stream (12.5 liters per minute at a pressure of 30 kilopascals (4.4 psi) from a distance of 3 meters) from any angle. The duration of the jet stream exposure is 1 minute per square meter surface area of the high voltage component.

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IEC 60529:1989/AMD2:2013, “Degrees of protection provided by enclosures (IP Code).”

https://webstore.iec.ch/publication/2446.

• Warning—The vehicle has an electrical isolation loss warning system that warns the driver when electrical isolation falls below 100 ohms per volt for DC electrical components or 500 ohms per volt for AC electrical components. This option is available for individual countries to adopt if they so choose.

i. NHTSA Proposal

NHTSA tentatively concludes that the GTR No. 20's physical test option is a practical and feasible means of evaluating the effects of water exposure under normal vehicle operating conditions. It has advantages of a performance standard in assessing compliance over a documentation approach. Thus, the agency is not proposing the compliance option in GTR No. 20 of providing documentation on high voltage components meeting IPX5 level of protection.

Regarding the electrical isolation loss warning system option in GTR No. 20, NHTSA believes the warning signals alone are not sufficient for addressing loss of electrical isolation concerns. Where objective performance criteria are available and are appropriate for all types of vehicles to which the standard applies, NHTSA believes objective performance criteria should govern when compared to the approach of solely using a warning. The existence of the visual warning cannot necessarily be considered a safety prevention system, as the root cause of the safety hazard remains unaddressed, and the visual warning may be ignored by the driver. 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. Thus, the agency does not propose this alternative as a compliance option in FMVSS No. 305a.

NHTSA Proposed Vehicle-Level Physical Test Procedures

The proposed physical test procedure is comprised of two series of tests, informally referred to as the “vehicle washing” test and the “driving through standing water” test. Electrical isolation is determined at the conclusion of each test, and once again after 24 hours.

A. Vehicle Washing Test

The washing test exposes the vehicle to a stream of water such as when washing a car. The vehicle external surface, including the vehicle sides, front, rear, top, and bottom is exposed to the water stream. GTR No. 20 excludes the vehicle underbody from exposure to the water stream. However, since the vehicle underbody is often exposed to water when the vehicle is washed, NHTSA proposes to also expose the vehicle underbody to the water stream to make this test more representative of vehicle washing. The areas of the vehicle that are exposed to the water stream in any possible direction include border lines,

i.e.,

a seal of two parts such as flaps, glass seals, outline of opening parts (windows, doors, vehicle inlet cover), outline of front grille and seals of lamps.

During the test, the vehicle is sprayed from any practicable directions with a stream of freshwater from a standard test nozzle as shown in Figure 4 below. The standard nozzle, with an internal diameter is 6.3 mm, shall provide a delivery rate of 11.9-13.2 liters/minute (l/min) with water pressure at the nozzle of 30-35 kilopascals (kPa) or 0.30-0.35 bar. These standard nozzle specifications are from IEC 60529 for IPX5 water jet nozzle.

EP15AP24.047

Figure 4—Standard Nozzle (IEC 60529) for IPX5 Water Exposure Test

The vehicle surface is exposed to the water stream from the standard nozzle for a duration of 1 minute per square meter or for 3 minutes, whichever is greater. The distance from the nozzle to the tested vehicle is 3 meters, which may be reduced, if necessary, to ensure the surface is wet when spraying upwards.

After the “vehicle washing” test and with the vehicle surface still wet, electrical isolation is determined for high voltage sources in the same manner as that currently in S7.6 of FMVSS No. 305. The high voltage sources are required to meet the electrical isolation requirements as specified in S5.4.3 of current FMVSS No. 305.

Comments are requested on the merits of including the test in FMVSS No. 305a. NHTSA seeks comment on the representativeness of the washing test, including but not limited to the proposed test conditions (

e.g.,

30-35

kPa versus 80-100 kPa water pressure conditions, water salinity levels, and water exposure durations, etc.).

B. Driving Through Standing Water Test

NHTSA proposes that vehicles should also be subjected to GTR No. 20's “driving through standing water” test. The vehicle is driven through a pool of standing freshwater,

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10 centimeters (cm) (4 inches) deep, for a total range of 500 meters (m), at a vehicle speed of 20 km/hr.

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The pool represents a low-lying portion of a road that can get flooded in excessive rain. Meeting the test is a reasonable indication that the vehicle has safeguards to ensure electrical safety when driven through roads in inclement weather.

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Freshwater means water containing less than 1,000 milligrams per liter of dissolved solids, most often salt.

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NHTSA tentatively concludes that the 10 cm (approximately four-inch) depth is reasonable, as national weather advisories (

https://www.weather.gov/tsa/hydro_tadd

) recommend not driving on flooded roads with more than four inches of water. Six inches of water on the road could reach the bottom of most passenger cars causing loss of control and possible stalling. A foot of water can float many vehicles.

If the wade pool used is less than 500 m in length, then the vehicle is driven through the wade pool several times. The total time, including the periods outside the wade pool, would have to be less than 5 minutes. GTR No. 20 specifies a maximum test time of 10 minutes, but NHTSA believes that 5 minutes is preferable. Traversing 500 m at 20 km/hr takes 90 seconds. A maximum test duration of 10 minutes would allow for an excessive amount of time out of the water and may not be equivalent to a continuous 500 m exposure. NHTSA seeks comment on the maximum duration of this test. NHTSA also seeks comment on the availability and geometric dimensions of different types of wade pools (long rectangular, circular) to accomplish this type of test.

Just after the standing water test is completed and with the vehicle still wet, the vehicle would be required to meet the electrical isolation requirements now specified in FMVSS No. 305 S5.4.3 when tested in the same manner as described in S7.6 of current FMVSS No. 305. The vehicle is also required to meet the electrical isolation requirements that are in S5.4.3 of current FMVSS No. 305, 24 hours after the washing test and the standing water test are completed.

NHTSA seeks comment on the water salinity requirements for the physical tests as described above, including tolerances for the test parameters listed above.

ii. NHTSA's Consideration of Submersions

In the U.S., floods resulting from Hurricane Sandy (2012), Hurricane Harvey (2017) and Hurricane Ian (2022) have led to electric vehicles submerged in flood waters for varying periods of time, with varying reports of vehicle fires in the aftermath. In developing this NPRM, the agency considered whether it could propose requirements to address these types of vehicle submersions and the resulting risk of fire. NHTSA analyzed field data from these hurricanes and made the following key observations of vehicle fires resulting from the vehicle submersions:

(1) Not all electric vehicles submerged in floods catch on fire. The type of water (water salinity), the level of submersion, and duration of submersion are likely factors;

(2) Fire and other hazards are more likely after water exposure (days after flood waters recede) rather than during the exposure;

(3) Fire may not originate in the REESS and may spread to the REESS from another vehicle component; and

(4) While 12V systems may also short circuit and result in vehicle fire, fires involving lithium-ion REESS are more difficult to extinguish and more hazardous because of the self-oxygenating nature of the lithium-ion cells and the energy density of the REESS.

NHTSA evaluated the regulatory approaches taken by other countries to determine if such standards could assist NHTSA in addressing the challenges posed by the submersions and fires resulting from Hurricanes Sandy, Harvey, and Ian. NHTSA analyzed China and Korea's water exposure requirements but determined the focus of those standards do not appear to address the safety matter at issue. Key observations and findings from the field data in the U.S. and the exploratory investigation into the water exposure posed by the hurricanes suggest that the test procedure and parameters and the performance requirements in China GB-38031

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and the Korean Motor Vehicle Safety Standard (KMVSS)

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may not be representative of field events of vehicle fires resulting from Hurricanes Sandy, Harvey, and Ian water exposure. If the standards are not representative of the harm NHTSA wishes to address from the hurricanes, the concern is the countermeasures to meet the performance test requirements of GB-38031 and KMVSS may not be effective at mitigating thermal events resulting from the water exposure at issue.

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GB-38031 water immersion test contains two options. Option 1 is based on ISO-6469-1:2019 where the REESS is submerged in 1 meter of seawater (salinity of 3.5 percent) for two hours. The performance requirement for this test option is for no fire or explosion of the REESS during the submersion. Option 2 is based on ISO-20653, and requires IPX7 level waterproofing. In this test option, the REESS is completely submerged in regular water for 30 minutes such that the lower point of the battery is one meter below the surface or the highest point is 150 mm below the surface (for battery packs with a height greater than 850 mm). The performance requirement in this test option is for no water ingress, fire, or explosion, and the REESS maintains an electrical isolation of 100 ohms per volt after submersion. Option 1 of GB-38031 is intended for most current REESS (open-type or partially sealed) while Option 2 would necessitate a fully sealed REESS.

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KMVSS contains requirements for REESS, including a water immersion test that has been implemented in South Korea since 2009. In the water immersion test, the REESS is fully submerged in seawater (salinity of 3.5 percent) for one hour. The performance requirement in this test is for the REESS to not explode or catch on fire during the immersion. EVS19-E4WI-0300 [KR] Water Immersion Test.pptx.

https://wiki.unece.org/display/trans/EVS+19th+session.

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For instance, NHTSA's understanding is that most of the vehicles involved in Hurricane Ian's post-submersion fires had met China GB-38031.

Specifically, in both standards, the REESS is submerged in 3.5 percent salinity water representing seawater for a long period of time (two hours for GB-38031 and one hour for KMVSS). NHTSA's exploratory investigation of current REESS designs

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suggests submersion in lower salinity water for a shorter duration may result in higher risk of thermal event. Longer immersion times in seawater salinity levels allow the batteries to safely discharge under water without adverse reactions such as arcing, venting, or underwater fires. Additionally, the requirements for no fire and explosion in these two standards are evaluated during the REESS immersion and not after the REESS is pulled out of the water. Such a requirement is not relevant to the electric vehicle fires observed after the flood waters in Hurricane Sandy and Hurricane Ian receded.

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Li-Ion Battery Pack Immersion Exploratory Investigation, DOT HS 813 136, July 2021.

https://rosap.ntl.bts.gov/view/dot/57013.

NHTSA acknowledges that the batteries in conventional vehicles with internal combustion engines (ICE) may also catch fire due to submersion. However, the post-submersion vehicle fires after Hurricane Ian demonstrated that electric vehicle fires are more difficult to put out and therefore more hazardous than ICE vehicle fires. NHTSA believes that a better understanding of the field incidences of electric vehicle fires is needed before a field relevant test and performance requirements can be developed that addresses the observed safety risks

associated with submersion of REESS and high voltage components in events such as floods.

The agency seeks comment on test conditions and test procedures that would address observed safety risks associated with submersion of REESS and high voltage components.

Going Forward

Shortly after Hurricane Ian, NHTSA and other DOT agencies coordinated with emergency personnel in Florida to collect in-depth information on vehicle fire incidences and REESSs involved in the flooding.

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This activity and others like it provided critical information that informed approaches to better protect vehicle owners, responders, and other stakeholders in the future.

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NHTSA has purchased ten electric vehicles damaged during Hurricane Ian and plans to perform a teardown analysis to understand the root cause of the vehicle fires. The teardown analysis will inform the next steps to address the safety risks associated with vehicle submersions.

In the near term, as discussed in sections below, this NPRM proposes to require that electric vehicle manufacturers submit standardized emergency response information to a NHTSA central depository, to assist first and second responders to respond to emergencies as quickly and safely as possible. The agency tentatively concludes that such a requirement would be an important and achievable near-term m

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