flashover

The near simultaneous ignition of all combustible material in an enclosed area.

The blaze turned into what Swiss officials called an embrasement généralisé, a term for a fire that releases combustible gases that can ignite violently, triggering what English-speaking firefighters call a flashover or backdraft.

An unintended electric discharge or arc over or around an insulator.

The overhead line was energised at 25,000 volts and the height of the contact wire was reduced to 11 in. above the chimney, then to 5 and finally to 2 in.; at this last, short distance the flashover occurred, but all the men were perfectly safe because the current went direct to earth through the locomotive.