Frank,
It is an interesting question. Hollywood movies frequently show villages
going up a blaze as you describe. Would they use an accelerant? Usually
they show them lit by torches. A wind would really get it going.
However, as someone who has tried burning bales of hay or straw I can
attest to how difficult some of these materials are to get going,
burning, when they are packed. Combine that with the fact that a spark
from a small cooking fire has to be low enough in mass to travel up in
the lazy open convection current, it likely has a low specific heat. The
cooking environment will include added moisture to the air. It would be
interesting to know the moisture content of the thatch. Perhaps the
species used are selected through time and tradition for their fire
limiting characteristics. I am not sure about all thatched roofs but
exposed underside looks quite different than the top. The finer, thinner
biomass over lapping on the top, with the coarser stem, less easily
ignited, under lapping on the bottom. Chimneys may make it worse,
rapidly conveying any sparks to the top side.
In my work I occasionally have to do 'hot' metal work surrounded by
flammable biomass, usually dry wood chips and fines and dust. Glowing
metal fragments, sparks from a grinder are generally very small and cool
rapidly in contact with anything, except my clothing:) A welding or
cutting splatter is often larger and will get a spot in a layer of wood
dust smouldering. I understand that in many industrial settings they
post a fire watch for up to 6 hours after, around sites where 'hot' work
was completed. I tend to do those kinda jobs in the morning.
Perhaps the cooks are always on the 'fire watch', both up and down.
And then there is wikipedia
http://en.wikipedia.org/wiki/Thatching
with a section on fires.
Alex
On 20/10/2012 2:22 PM, Frank Shields wrote:
Dear Stovers,
One thing I have been thinking about...
Lets see - we have an open fire on the floor where the smoke goes up
and through a straw roof. Where the soot and tars condense and collect
coating the straw with an oily like highly flammable coating. There
must be roof fires that are very dangerous and fast burning and where
flaming straw comes falling down. Do they happen? And when they do I
would think the sparks would start other roofs on fire and the entire
village would go up in smoke. And then the scarcity of available water
to put them out. I would think this would be a huge problem but no one
ever mentions about the fires.
Thanks
Frank
Frank Shields
Control Laboratories, Inc.
42 Hangar Way
Watsonville, CA 95076
(831) 724-5422 tel
(831) 724-3188 fax
www.biocharlab <http://www.biocharlab>.com
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