None of the fires happened while drive or after an accident, but only during and after crash testing the cars and their batteries packs in a controlled situation.Mary Barra explained that the first Volt that caught fire last June, some three weeks after it was used in a crash test, was due to "significant electrical charge or energy, was left in the battery after the test. When electrical energy is left in a battery after a severe crash it can be similar to leaving gasoline in a leaking fuel tank after severe damage," she explained. "It's important to drain the energy from the battery after a crash that compromises the battery's integrity - or you risk potential fire."