‘Thermal Runaway’: Firefighters explain why lithium-ion battery blazes are so hard to extinguish

So far this year, a number of lengthy road closures in California and Nevada have been caused by crashed trucks carrying lithium-ion batteries.

Why are these battery fires so tough for firefighters to extinguish? Because of a phenomenon called “thermal runaway.”

Crash-Related Lithium-Ion Battery Fires In The News

In the last few months, a number of fiery high-profile truck crashes involving lithium-ion batteries have made national headlines.

On July 26, a semi truck hauling lithium-ion batteries overturned on near I-15 the Nevada/California state line, shutting down the interstate . The batteries burned for days following the crash.

On August 19, a battery-powered Tesla Semi crashed on I-80 near, Emigrant Gap in Placer County, California. The truck caught fire, spewing “toxic fumes,” and triggering a National Transportation Safety Board investigation that determined that it took 50,000 gallons of water to put the fire out .

Another major truck crash involving lithium-ion batteries occurred on September 17 near Indian Springs, Nevada at mile marker 13 on Highway 95 . One of the trucks involved was hauling wood; the other was hauling 31,000 pounds of lithium-ion batteries. This crash also sparked a major fire and lengthy road closure.

The truck crashes and subsequent lithium-ion battery fires have become such a problem that in September, Nevada Rep. Dina Titus introduced the “ Thermal Runaway Reduction Act ” to strengthen federal regulation of the transport of lithium ion batteries.

What Is Thermal Runaway?

Following the July 26 incident, San Bernardino County Fire provided a detailed description of how thermal runway works and why it’s so dangerous:

Thermal runaway is a chain reaction within a lithium-ion battery that can lead to catastrophic failure, resulting in fires or explosions.

Here’s a step-by-step breakdown of what happens during thermal runaway:

1. Initial Trigger: Thermal runaway can be initiated by several factors, such as physical damage (e.g., puncturing or crushing), overcharging, manufacturing defects, or exposure to extreme heat.
2. Internal Heating: Once triggered, a part of the battery starts to overheat. This can be due to an internal short circuit or a chemical reaction within the battery.
3. Chain Reaction: The heat generated from the initial trigger increases the temperature inside the battery. This heat can cause other parts of the battery to react, generating even more heat.
4. Rapid Temperature Rise: As the temperature rises, the electrolyte inside the battery—a flammable liquid—starts to vaporize and decompose, producing gases. This further increases the internal pressure and temperature.
5. Gas Release and Ignition: The increasing pressure can cause the battery casing to rupture, releasing flammable gases. These gases can then ignite, leading to a fire or explosion.
6. Propagation: If the battery is part of a larger battery pack, the heat and flames can spread to adjacent cells, causing them to undergo thermal runaway as well. This can result in a large, intense fire that is difficult to control.

Firefighters also detailed why these thermal runaway incidents are so dangerous:

• Difficult to Extinguish: Thermal runaway fires require massive amounts of water to cool the batteries and stop the chain reaction. Traditional fire extinguishers are often ineffective.
• Toxic Gases: Burning lithium-ion batteries release toxic gases such as hydrogen fluoride, which can be harmful if inhaled.
• Reignition Risk: Even after the fire appears to be extinguished, there is a risk of reignition. The battery cells can remain hot and unstable for hours or even days.

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