Backdraft and Flashover

[Erik M.]

Regarding a recent post asking for an explanation of the differences between
backdraft and flashover:

The most important differences between a backdraft and a flashover are WHEN
they occur during the course of a fire, and the CONDITIONS THAT EXIST to
lead up to the backdraft or flashover.

As it is, flashover is still rather undefined. The most recent definition
calls it a transitional phase of a compartmentized fire in which the effects
of thermal radiation cause all combustible materials to ignite. The
previous definition defined it as all combustibles simultaneously reaching
there ignition temperature and igniting. This definition was flawed
however, because combustibles have different ignition temperatures and how
could all of them be reached at the same time? Regargless of the definition
though, flashover is a very real thing. It occurs during the FREE BURNING
STAGE of a COMPARTMENTIZED fire. As fuel sources are consumed and HEAT and
smoke accumulate within the room, there comes a point when everything
(including smoke and fire gases) ignites. The room is entirely consumed by
flame for a short period of time.

Like flashover, backdraft is a very real thing. The potential for a
backdraft exists during the SMOLDERING STAGE of a COMPARTMENTIZED fire, when
the oxygen is almost entirely consumed (below 15%), carbon monoxide and
carbon have built up, and the temperature remains high. The key to a
backdraft occuring is the lack of oxygen to the fire. When oxygen is
introduced rapidly, which could be anything from a homeowner opening a door
or a firefighter breaking a window, the fire instantly reignites the gases
and combustibles within the room, creating a powerful explosion.

Flashover is the ignition of all materials with a compartmentized fire
during the free burning stage. Backdraft is an explosion (or the reignition
of all materials) during the smoldering stage of a compartmentized, oxygen
deprived fire, due to the rapid introduction of oxygen.

Hope I kept this simple enough and explained the two terms sufficiently.

-- Erik M.

"My ears were saluted with the agreeable sound of a fall of water . . . " -
Meriwether Lewis

[Hlywud]

I would add that flashover occurs much more often than backdraft...

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