According to the National Fire Protection Agency, most electric vehicles today are powered by lithium-ion batteries. When damaged by something like saltwater, heat, or force, a chemical reaction known as thermal runaway can start inside the cells of these energy-dense batteries. In this state, the batteries heat up uncontrollably and can be prone to fires and off-gassing, resulting in explosions in confined spaces.
Compounding the risk of thermal runaway is the fact that there’s no easy way of draining the energy out of damaged batteries—a separate concept known as stranded energy. This is true even after a fire has occurred and been initially extinguished. In 2018, for instance, after a fatal crash and fire involving an electric vehicle in California, the car’s batteries reignited at a junkyard six days later.