climberjones
ArboristSite Guru
What usually catches on fire first after a chimney fire that burns a house down? Is it the shingles from creasote dripping on it?
Chimney fires
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Dalmatian90
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Nope.
When you have the structure involved, it's normally framing in the wall and/or attic that catches fire.
This can be for one of two reasons.
First is the chimney itself fails -- you get cracks, liquid creosote flows out of them (it's melting to a tar like consistency from the heat), then the fire follows it out like a wick.
Second is the radiant heat over the years has "pyrolized" the wood -- it's similar to making charcoal (though not necessarily with the change to black; discolored probably). It not only dries out the wood but chemically changes it to have a much, much lower ignition temperature. Then the extra radiant heat from the chimney fire is enough to ignite the wood without an actual flame.
With good stops in the wall, it's then usually limited to being a partition fire. That's not terrible usually -- pull the siding on the outside if you can and squirt just enough water to stop the fire; put down salvage covers to minimize damage inside and pull the sheetrock on the inside if you need to check in there. Often -- not always -- you have time to try and do a neat job of putting it out. If it's a bitter cold night, try and remember to drain the water pipes for them if there's no a big gaping hole where a wall used to be
Or if the damage allows, see if there's some plywood handy to tack up, etc. so they can use their backup heating system.
But if there aren't good stops and it travels up to the attic, or originates there, then there's usually a big area with lots of wood exposed and pretty good ventilation from soffits and eaves and it's off to the races. Usually you'll have at least a fair amount of smoke and water damage inside, and if you don't get a quick stop on the attic fire it'll pretty much write off the house as it collapse and wrecks everything below.
Embers on asphalt shingles aren't going to do much of anything. Not enough heat to ignite them.
Embers on wood shingles, sure. But usually if you've got a fire going it's cool and damp out so there much harder to ignite then during summer time brush fires that will get wood shingles going (and those fires usually throw up a hell of lot more embers!).
When you have the structure involved, it's normally framing in the wall and/or attic that catches fire.
This can be for one of two reasons.
First is the chimney itself fails -- you get cracks, liquid creosote flows out of them (it's melting to a tar like consistency from the heat), then the fire follows it out like a wick.
Second is the radiant heat over the years has "pyrolized" the wood -- it's similar to making charcoal (though not necessarily with the change to black; discolored probably). It not only dries out the wood but chemically changes it to have a much, much lower ignition temperature. Then the extra radiant heat from the chimney fire is enough to ignite the wood without an actual flame.
With good stops in the wall, it's then usually limited to being a partition fire. That's not terrible usually -- pull the siding on the outside if you can and squirt just enough water to stop the fire; put down salvage covers to minimize damage inside and pull the sheetrock on the inside if you need to check in there. Often -- not always -- you have time to try and do a neat job of putting it out. If it's a bitter cold night, try and remember to drain the water pipes for them if there's no a big gaping hole where a wall used to be
Or if the damage allows, see if there's some plywood handy to tack up, etc. so they can use their backup heating system.But if there aren't good stops and it travels up to the attic, or originates there, then there's usually a big area with lots of wood exposed and pretty good ventilation from soffits and eaves and it's off to the races. Usually you'll have at least a fair amount of smoke and water damage inside, and if you don't get a quick stop on the attic fire it'll pretty much write off the house as it collapse and wrecks everything below.
Embers on asphalt shingles aren't going to do much of anything. Not enough heat to ignite them.
Embers on wood shingles, sure. But usually if you've got a fire going it's cool and damp out so there much harder to ignite then during summer time brush fires that will get wood shingles going (and those fires usually throw up a hell of lot more embers!).
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