Thermal Runaway on the Roads

by Ed Burke and Kelly Burke, Dennis K. Burke Inc.

EV battery Fires Present a New Technical and Safety Challenge for Firefighters

Amid a winter storm on a January night, Wakefield, Mass. fire officials and state police responded to a crash on Interstate 95 where they spotted a Tesla electric vehicle wedged against a guardrail in the right breakdown lane.

As crews attempted to clear the car from the roadway, the guardrail punctured the undercarriage, causing the lithium-ion batteries in the EV to increase in temperature. Bursts of sparks shot out of the car, sending plumes of smoke up into the sky. The vehicle then became “fully involved in fire,” according to a fire department statement.

The car’s 38-year-old driver was not in the vehicle at the time of the fire, according to fire officials.

To extinguish the blaze, firefighters spent two-and-a-half hours spraying “copious amounts of water onto the vehicle,” ultimately totaling more than 20,000 gallons, according to the statement.

Five surrounding mutual aid communities also responded to support firefighting operations and create a water shuttle to continually carry water to the scene.

The car was cleared from the roadway with permission from a responding Fire Services Hazmat Team and the Department of Environmental Protection.

“As sales of electric and hybrid vehicles increase, the fire service is continuing to modify our tactics to properly respond, protect property and firefighters as well as control these types of fires,” said Provisional Fire Chief Tom

Purcell, noting the additional challenges of fighting fires in electric vehicles.Purcell said that controlling EV fires often takes longer and requires a large and continuous water supply. Crews must also maintain heightened situational awareness and prepare for secondary fires.

NFPA Says EV Fires Are Rare

EV crashes have been getting a lot of press and media coverage, but EVs catch fire far less often than gas-powered cars.

While the U.S. government doesn’t track the number of EV fires, Tesla’s reported numbers are far lower than the rate for highway fires overall, according to the National Fire Protection Association (NFPA).

Still, people have started associating electric cars with dramatic fires. Videos of EV fires tend to go viral, promoting the narrative that electric vehicles are far less safe than conventional cars.

Batteries in Thermal Runaway

An electric vehicle battery pack is made up of thousands of smaller lithium-ion cells that hold an anode, a cathode, and a liquid electrolyte to store energy.

The cells are then assembled into a battery pack that’s encased in extremely strong material, like titanium, to protect it during a collision.

When an EV battery is damaged, cells can short-circuit, heating up the battery. The membranes that separate the cathode and the anode melt, exposing the highly flammable liquid electrolyte.

The first moments of an EV battery fire might appear with only smoke coming from underneath the vehicle. Once a fire ignites, heat can spread to even more cells, triggering an event called “thermal runaway.”

As thermal runaway gets going, bright orange flames can quickly engulf the car. When this happens, flames continue igniting throughout the battery, fueling a fire that can last for hours.

Because EV batteries are packed with an incredible amount of stored energy, one of these fires can get as hot as nearly 5,000 degrees Fahrenheit.

Even when the fire appears to be over, latent heat may still be spreading within the cells of the battery, which could re-ignite the vehicle several days later.

New Problems

EV fires are different and present new problems.

Firefighters often try to suppress car fires by, essentially, suffocating them. They might use foam extinguishers filled with substances like carbon dioxide to draw away oxygen or use a fire blanket designed to smother flames.

But because EV fires aren’t fueled by oxygen from the air, this approach doesn’t work. Instead, firefighters must use lots and lots of water to cool down the battery. This is particularly complex when EV fires occur far from a hydrant, or if a local fire department only has a limited number of engines.

Firefighters Need Training

As many as half of the 1.2 million firefighters in the U.S. might not be trained to combat EV fires, according to the NFPA.

There isn’t an established consensus on the best firefighting strategies for EVs. Guidance is shared among fire departments, fire service associations and automakers, but the reality is that fire departments across the country are still learning best practices.

There are new car models released every year, and there is particular guidance on how to disconnect the battery in different cars. While some standards have been released, others are still being developed.

Better Engineering

Engineers are investigating new battery chemistries, like less-flammable electrolytes. Research into solid-state batteries also looks promising. They would replace a liquid electrolyte with a solid that’s far less likely to ignite.

The Department of Energy is working on technology that could incorporate flame retardants directly into the batteries’ design, and General Motors is studying how improving its battery separator could help prevent thermal runaway.

Fire safety officials say that as EVs go mainstream, electric vehicle fires aren’t being studied as much as experts and government officials say they should be.

Ed and Kelly Burke are respectively Chairman of the Board and Senior Marketing Manager at fuel distributor Dennis K. Burke Inc. They can be reached at 617-884-7800 or ed.burke@burkeoil.com and kelly.burke@burkeoil.com.

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