[Stoves] Straw roofs and fires

[Alex English]

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.
>
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