161 Re: Dust Collection, Heating
Description
This article is from the Woodworking FAQ Collection 5, by multiple authors.
161 Re: Dust Collection, Heating
From: rbl@nitrex.UUCP ( Dr. Robin Lake )
Date: 5 Nov 87 14:06:44 GMT
I JUST returned from the AIChE Int'l Conference on Vapor Cloud
Modeling, where a day of papers covered fire and explosion modeling.
Basically, there is a Lower Flammability Limit and an Upper
Flammability Limit, between which a dust or chemical mixture will
burn. Whether or not it burns explosively depends (in a large part)
whether the air flow is turbulent or laminar. Bet with a wood-burner
(and in a grain elevator) the flow is predominated by eddy currents
and is turbulent --- which is the worst case. Field tests of
Liquified Natural Gas burns in England showed that partial confinement
(ala barn) greatly increases the probability of explosive burning,
because there are vapor velocity gradients present.
The grain elevator situation IS related to closed conditions in that
the closed conditions lead to heat build-up from decomposition of the
grain, thus leading to spontaneous combustion. In the barn, you'll
already have an open flame and not need spontaneous combustion to set
off an explosion.
I am NOT an expert in fire/explosion safety! I do NOT know the
LFL/UFL for wood dust in air, but I'd gladly copy the governing
equations (hairy) from the Proceedings if anyone has a burning desire
to model the problem.
Meanwhile, if you DO put the fire and dust together in a barn, please
leave your camcorder running --- it's would be a valuable experiment
should the barn blow!
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