flashover

plural flashovers

1. countableuncountableThe 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.

   2026 January 1, Chris Michael, Rory Carroll, “‘It happened in seconds’: sudden inferno brings horror to Swiss ski resort”, in The Guardian, →ISSN

2. countableuncountableAn unintended electric discharge or arc over or around an insulator.

   1 more example

   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.

   1960 April, “Talking of Trains: Safety with 25kV a.c.”, in Trains Illustrated, page 203

   Synonyms: sparkover