The National Transportation Safety Board (NTSB) issued on Wednesday four safety recommendations based on its investigation of four electric vehicle (EV) fires involving high-voltage, lithium-ion batteries and hazards posed to emergency responders.

Fires in EVs powered by high-voltage lithium-ion batteries pose the risk of electric shock to emergency responders from exposure to the high-voltage components of a damaged lithium-ion battery, according to a news release from the NTSB. Another risk is that damaged cells in the battery can experience thermal runaway — uncontrolled increases in temperature and pressure — which can lead to battery reignition. The risks of electric shock and battery reignition/fire arise from the “stranded” energy that remains in a damaged battery.

The federal agency’s findings are based on three lithium-ion batteries that ignited and were damaged in high-speed, high-severity crashes, and a fourth lithium-ion battery fire occurred during normal vehicle operations.

All three of the crash-damaged batteries reignited after firefighters extinguished the vehicle fires. The battery in the fourth investigation did not reignite.

Safety issues with the high-voltage, lithium-ion batteries used in EVs first gained widespread attention when a Chevrolet Volt caught fire three weeks after a crash test in May 2011, according to the NTSB.

The federal agency’s first investigation of EV battery fires on U.S. roadways was in 2017, when a high-voltage lithium-ion battery caught fire after an EV left the road and crashed into a residential garage at high speed.

Between 2017 and 2018, the NTSB investigated two other EV high-speed, high-severity crashes that resulted in post-crash fires and one non-crash fire. During its investigations, the NTSB considered the safety risks to first and second responders posed by the vehicles’ high-voltage, lithium-ion batteries. Those risks are addressed in the NTSB’s Safety Report 20/01, “Safety Risks to Emergency Responders from Lithium-Ion Battery Fires in Electric Vehicles.”

The report identified two main safety issues in its investigation:

• The inadequacy of vehicle manufacturers’ emergency response guides.
  

• The gaps in safety standards and research related to high-voltage lithium-ion batteries involved in high-speed, high-severity crashes.

Here’s a summary of the NTSB’s recommendations:

• To the National Highway Traffic Safety Administration (NHTSA): When determining a vehicle’s U.S. New Car Assessment Program score, factor in the availability of a manufacturer’s emergency response guide and its adherence to International Organization for Standardization standard 17840 and SAE International recommended practice J2990. (H-20-30)
  
  Additionally, NHTSA should convene a coalition of stakeholders to continue research on mitigating or de-energizing stranded energy in high-voltage lithium-ion batteries, reducing the hazards associated with thermal runaway resulting from high-severity crashes, and publish the research results. (H-20-31).

• To manufacturers of EVs equipped with high-voltage lithium-ion batteries: Model emergency response guides on International Organization for Standardization standard 17840, as included in SAE International recommended practice J2990, and incorporate vehicle-specific information on fighting high-voltage lithium-ion battery fires; mitigating thermal runaway and the risks of high-voltage lithium-ion battery reignition and stranded energy; and safely storing an EV with a damaged high-voltage lithium-ion battery. (H-20-32)

• To fire protection associations: Inform members about the circumstances of the fire risks described in the report and the guidance available to emergency personnel who respond to high-voltage lithium-ion battery fires in EVs. (H-20-33)

To highlight the lessons learned in the report, the NTSB produced a video that is available on the NTSB’s YouTube Channel.