What If That Burning Car Has a Lithium-Ion Battery?

February 9, 2021

Submitted by the National Transportation Safety Board

Every year, more and more electric cars appear on our roads and highways. As the popularity of these vehicles grows, so do the risks they pose – to emergency responders as well as to the public.

The Chevrolet Volt was one of the first electric vehicles designed with a lithium-ion battery. When a Volt caught fire three weeks after a crash test in 2011, it made headlines. The National Highway Traffic Safety Administration investigated and found no record of any other crash-related fires in electric vehicles. Since then, though, fires in electric vehicles have occurred both here and abroad.

The high-voltage battery in an electric vehicle can catch fire as the result of a crash or because of an internal battery failure. If it does, firefighters, tow operators, and other emergency responders risk electric shock from exposure to the battery’s high-voltage components. A further risk is that damaged battery cells can experience thermal runaway – uncontrolled increases in temperature and pressure – that can cause a battery to ignite and to reignite, sometimes more than once.

The National Transportation Safety Board (NTSB) investigated four recent high-voltage lithium-ion battery fires in electric vehicles. Three of the fires erupted after high-speed, high-severity crashes. The fourth resulted from the internal failure of a battery during normal driving. Each case posed special challenges to emergency responders.

For example, when an SUV crashed into a residential garage and caught fire in Lake Forest, California, firefighters poured more than 20,000 gallons of water onto the car for at least two hours. Not until they elevated the vehicle to direct water onto the battery itself did it cool down enough for the SUV to be moved. The battery then reignited on the tow truck and again at the tow yard.

When another SUV crashed and caught fire on a freeway in Mountain View, CA, firefighters quickly put out the fire. But the battery reignited after the SUV reached the tow yard and caught fire again five days later. Firefighters at the tow yard started and stopped applying water because they were worried about electricity traveling up the water stream – a potential risk the National Fire Protection Association (NFPA) has studied and discounted.

After a high-speed crash in Fort Lauderdale, FL, the car’s electric battery burst into flames and then reignited three times after firefighters first put out the blaze. When the battery in an electric car caught fire while the owner was driving down a street in West Hollywood, CA, firefighters called the car’s maker because they could not stop the vehicle from smoking after the flames died down.

Where can emergency responders turn for information about a high-voltage lithium-ion battery fire?

In the United States, responders can use the emergency field guide the National Fire Protection Association (NFPA) publishes. They can also consult the emergency response guides that electric vehicle manufacturers produce. The guides are available from several sources, including the NFPA web site, smartphone applications, and other commercial platforms.

The NTSB reviewed the manufacturers’ emergency response guides and concluded that they are strong in certain respects but weak in others. For example, they all give instructions for disconnecting (but not removing the energy from) an electric vehicle’s high-voltage system – assuming the high-voltage disconnects are accessible and undamaged by a crash. But the guides contain almost no information about how to handle the energy remaining in a damaged high-voltage battery. That energy, known as stranded energy, creates a risk not only of electric shock but also that the battery will reignite after firefighters extinguish the initial fire.

To make the emergency response guides easier to use, the NTSB has recommended that vehicle manufacturers model them on an international standard, ISO 17840. If all guides followed the ISO format, firefighters and tow truck operators could more readily locate emergency information because it would come in the same order in every guide.

Different electric vehicle models are built differently and use different types of high-voltage batteries. That means firefighters must use different strategies for attacking electric vehicle fires, depending on the vehicle model. The NTSB has recommended that manufacturers publish vehicle-specific information for emergency responders on how to fight a high-voltage lithium-ion battery fire and lessen the risks of thermal runaway and battery reignition.

Emergency responders also need advice from manufacturers on dealing with the risk of stranded energy – both during a first emergency response and before moving an electric vehicle from the scene. To date, responders have no way of removing the energy from a damaged high-voltage battery, aside from letting a battery fire burn itself out. And after an electric vehicle with a damaged high-voltage battery is hauled off the road, tow yard operators need to know how to safely store the wreckage. The current advice is to allow a 50-foot radius around a damaged electric vehicle – impractical if not impossible in most tow yards.

The NTSB has issued a report on its investigations, called Safety Risks to Emergency Responders from Lithium-Ion Battery Fires in Electric Vehicles (NTSB/SR-20/01). The report, complete with findings and recommendations, can be accessed on the NTSB web site.