Chimney Fire Progression

[MacPB]

Does anyone know how a chimney fire starts?

Does it always start from the stove pipe and move upwards?

Can it start in the top of the chimney from a spark?

If you're stovepipe and most of the chimney is very clean, but some creosote has accumulated near the top roof exit or on upper elbows, can it still happen?

Thanks

 

[Peter B.]

I'm far from expert, but I think a chimney fire can be started either by raising the creosote to a given ignition temperature, or by steady contact with flame... both assuming there is enough air to support combustion... but of course, there's usually plenty of O2 available in any given chimney.

The most likely point of ignition would be near the stove itself (I think), though I suppose you could take a propane torch to an elbow full of creo and have some fun.

I don't think a stray spark will set off a chimney fire without sufficient temperature and/or companion flame impingement.

But please note... these are not fully educated statements.

Maybe someone who knows better will chime in.

Peter B.

-----

 

[LeonMSPT]

It will spontaneously ignite if heated hot enough in the presence of enough air... flame can definitely light it.

Started a stovepipe fire last week... angle grinder on a screw I couldn't back out as it was stripped... grinding away... sniff, sniff... had my hand stabilizing the pipe against the grinder... hmmm, hand's getting kind of warm, HOT!

Stopped grinding and heard the snapping and popping, and just went around and shut off the air. It went out...

Sense will tell you that the larger percentage of chimney fires likely begin in the stovepipe.. or closer to the wood burner than the top of the chimney. Lots of paper and kindling, trying to heat the stove up quick... fire extends into the stovepipe, hits creosote accumulation and it lights, spreads into the chimney...

I reverse engineered a "T" today so it would orient the way I want it to. The male and female parts were in the wrong place. Nowhere near as complicated as a sex change procedure.

Drill out two rivets, remove the piece. Drill out two more, remove that piece. Rivet them back into place when you swap them... oh, pop rivets won't fit outside in in the female part... go from inside out. Use stainless rivets...

Now I have five inches of pipe coming off the "thimble", a "T" with a male down to go into another "T" which I cut a 7 inch BDD into, into another "T", with about five inches of straight pipe into the boiler. Remove the plugs, run a six inch brush in and out, vacuum or sweep the mess out, and put the plugs back. A hand wire brush cleans the "T" with the BDD in it from the top and bottom. Used radiused "T"s so flow would be closer to that of elbows...

Want to keep the chimney connector clean in this situation... I suspect with the BDD, the chain of events leading to a chimney fire will begin with a connector fire. Mixed with the air from the BDD, I don't believe the exhaust would be hot enough to light a chimney fire.

Peak temperatures between the boiler and BDD are 425/450 degrees, above runs around 250/275... while the door on the boiler is 500 degrees.

 

[BrotherBart]

If you're stovepipe and most of the chimney is very clean, but some creosote has accumulated near the top roof exit or on upper elbows, can it still happen?

No.

 

[jeff6443]

Here I started one quite easily . See you need wet wood ,( I bought the stove the wood was not important ) and alot of news paper .and wet wood
WET wood . But now no news paper I m splitting my wood small toothpics . and next year look out . this will never happen to me again outta wood newbie

 

[LeonMSPT]

Scary, huh? People with families, homes... that's threatened when these things happen. I miss the fire service, although as a PT I have an opportunity to help people everyday, all day. Still, that look on peoples' faces when you climb off the truck, wearing your gear and ready to do business. Priceless, and an honor and a privilege to do it.

Got to watch wood quality, and monitor the condition of the chimney and connector pipe closely. Watch the fresh fires, loads of paper and kindling extending into the connector from the stove or boiler.

I remember dad, every morning, first fire... big fire... in fifteen years of burning we had one chimney fire. He'd climb up on the roof in January and May, every year. He had a bunch of old tire chains all wired together on the end of a piece of chain, tied to a rope... put that in there and thrash it around, and pull it out. Go down and shovel out the clean out... once in awhile he'd "greet" the stovepipe... both hands, opposite sides... give 'er a few slaps and you'd hear the stuff breaking off and falling back into the elbow at the back of the stove... that baby'd glow a little the next morning when the "All Night"-"Big Mo" got breathing hard.

It heated a 32 x 28 two story house with a furnished basement, mostly. Always wondered, with a little fab work... a baffle and some secondary air... that thing would have driven you out of the house. It frequently would anyway as it was.

I've come to the point where I use one sheet of newspaper, or none at all... a few splinters or hardwood ends from the wood turning mill. Buy it for 6 bucks for a burlap bag full of them. Kiln dried, they nearly light with a match anyway... smaller splits on top, graduating to larger ones as needed for length of burn and heat needed... works well and seems much safer than an armload of kindling and half of the daily fishwrapper.

Here I started one quite easily . See you need wet wood ,( I bought the stove the wood was not important ) and alot of news paper .and wet wood
WET wood . But now no news paper I m splitting my wood small toothpics . and next year look out . this will never happen to me again outta wood newbie

 

[MacPB]

So using too much newspaper can be a bad thing if the conditions are right for a fire?

Regarding the fire extending into the flue collar of the stove: Should nat be avoided as well?

Funny thing is is that I have to run my newspaper and kindling (old dried out cedar shakes) with a half open air intake, otherwise all the heat goes up the flue (it gets to 500-600 degress within minutes) and I have a hard time heating up the soapstone for cat ignition.

Should I use an alternative to newspaper (5-10 sheets) and cedar shakes?

Also, regarding flue temp, I have read that creosote forms under 250 degrees. I would imagine that if you control the temp (on startup) to no more than 500 degrees, it has to be significantly cooler up near the roof. Does anybody know how fast the temp drops as it travels upward? For example, will it drop let's say 50 degrees every few feet?

 

[LeonMSPT]

Would depend on alot of factors, but always wondered about a remote probe type thermometer somewhere up there...

Burning most stoves and inserts at above 600 degrees is going to rid the connector pipe and likely the chimney too of any nasties...

It's why all the guy finds when I have him sweep mine is gray dust and some brown dust... brown stuff would likely burn but the grey stuff doesn't.

Wood boiler? Different critter entirely... needs to be kept clean

 

[Todd]

So using too much newspaper can be a bad thing if the conditions are right for a fire?

Regarding the fire extending into the flue collar of the stove: Should nat be avoided as well?

Funny thing is is that I have to run my newspaper and kindling (old dried out cedar shakes) with a half open air intake, otherwise all the heat goes up the flue (it gets to 500-600 degress within minutes) and I have a hard time heating up the soapstone for cat ignition.

Should I use an alternative to newspaper (5-10 sheets) and cedar shakes?

Also, regarding flue temp, I have read that creosote forms under 250 degrees. I would imagine that if you control the temp (on startup) to no more than 500 degrees, it has to be significantly cooler up near the roof. Does anybody know how fast the temp drops as it travels upward? For example, will it drop let's say 50 degrees every few feet?

You will find on your stove that the flue temps can run below the creosote range on your thermometer. That's ok as long as your burning properly the cat will burn up 90% or more of the creosote producing thingys. I checked my chimney a couple weeks ago after burning 1.5 cords and there is very little build up on the top 10' or so. I won't be sweeping til Spring.

 

[mellow]

The one time I had a chimney fire it was started by burning some cardboard, flames went through the stove damper and hit the creosote that had formed inside the chimney and ignited them.

As far as I know chimney fires originate close to the stove then travel up. In another thread I posted that the ignition point of creosote is 635F so it would have to start very close to the stove.

 

[LLigetfa]

Years ago I had a chimney fire that was quite far from the stove. I had single wall going up with a 90 near the ceiling and a long horizontal run through the wall to a Tee on the other side at the base of the SS chimney. The creosote collected in the Tee where the fire started.

 

[WoodMann]

Good subject, don't mean to hi- jack, but what about EPA stoves? Aren't the flames kept in the box via the firebrick, not saying this exempts keeping a clean chimney..........................

 

[karri0n]

Not sure with all stoves, but I know when starting and having really high flames, on my stove, they definitely curve above the baffle and head back to where the stovepipe fits in. I'm quite certain that under the right conditions flames could be licking the inside of the stovepipe.

 

[Corey]

Creosote autoignition temperature is listed as around 640F - when it gets to this temperature, it can simply 'light off' - no spark or flame is needed. Of course if you do have flame, or even a single spark up the flue, that could light it off if the temp is high enough. I would wager that most if not all chimney fires start at the bottom and work up. It would be extremely hard to get enough heat to the very top of the flue (unless you burn like AP's kiln) then it would be hard for the burning creosote to work back down the flue - both against the uprushing draft and the rising heat of the fire.

 

[searay220]

OK With all that said what happens when you have a chimney fire? How do you know you have one? What do you do to stop it?

 

[LeonMSPT]

I've heard it described as sounding like a 747 is landing in the front yard, or a 100 car train is chugging up a 10% grade past your house... or they can be small and you'll miss it entirely, and anything between.

The answer is, "You'll know if you have one that's big enough to worry about."

What to do? Consensus is, shut the air off to it, control and smother it... likely be able to limit it with cutting the air supply. Then call the fire department and at least have them come check it out. Might even be out when they arrive. Don't open the door until everything is cool, as it can easily reignite, hotter and harder.

Have the chimney and flu checked, or if you're comfortable, clean it and check it yourself. But, whatever you decide to do, don't just go on, "Business as usual.", and light another fire until the thing is known to be clean and okay.

 

[LLigetfa]

In my case the roaring sound, the smell of burning paint, and the orange and cherry red colours were a dead giveaway. I grabbed a ladder, went up on the roof, and poured some water down the chimney.

 

[markleyh]

We have had two chimney fires, and both occurred with creosote accumulation at the peak of the roof, where the insulated outside chimney poked up into unrestricted air space. The Fire Chief told us that the creosote condenses at the top of the chimney, which is cooled by prevailing wind and stack cooling. A hot exhaust into this obstruction then ignites at the ignition temp. We had flames shooting out the top of the stack like an afterburner, but no flames in the stove. The firemen threw all the logs out into the snow and the thing still burned.

For both times, the Chief trained his volunteers. One time they climbed on the third story roof and dropped the afore-mentioned chain down, the second time they took the cap off the clean-out tee (the afterburner on top really went crazy then!) and blasted high pressure water from a two-inch line up the flue. Instant extinction and also a good job of sweeping by hydraulics.

We are so paranoid of another one that we are trying to find ways to prevent them--currently worried about the overdrafting masonry chimney in the new house.


herbster

 

[WoodMann]

We have had two chimney fires, and both occurred with creosote accumulation at the peak of the roof, where the insulated outside chimney poked up into unrestricted air space. The Fire Chief told us that the creosote condenses at the top of the chimney, which is cooled by prevailing wind and stack cooling. A hot exhaust into this obstruction then ignites at the ignition temp.

THat's what I always thought it happened, at the end of the stack everything cooled and accumulated there and the next hot fire would set everything off whereas in contrast buildup at the bottom- just above the stove if that were to light up it would be suffocated during the run up the pipe. While I've not had a chimney fore I've been freaked enough times I've gone outside and looked at the top of the chimney for flames, being a noob................

 

[LeonMSPT]

That's truly another avenue for the development of a chimney fire. Likely as prevalent as a connector pipe fire spreading into the chimney. Watching stack temperatures seems to be the key, if your chimney is dirty...

Just cleaned the connector pipe and the BDD I installed last week. Just a layer of dust, but wanted to check and see how things looked at a week with the BDD connected and working at the proper draft. Seems to be less junk than without it.

Certainly maintaining a lower stack temperature under extended high fire. Highest I've seen was 450 degrees, at idle it drops back to 200... to maintain a higher idle temp I'd have to give it go much air it would certainly go to 600 or more under high fire. Don't want that.

We have had two chimney fires, and both occurred with creosote accumulation at the peak of the roof, where the insulated outside chimney poked up into unrestricted air space. The Fire Chief told us that the creosote condenses at the top of the chimney, which is cooled by prevailing wind and stack cooling. A hot exhaust into this obstruction then ignites at the ignition temp.

THat's what I always thought it happened, at the end of the stack everything cooled and accumulated there and the next hot fire would set everything off whereas in contrast buildup at the bottom- just above the stove if that were to light up it would be suffocated during the run up the pipe. While I've not had a chimney fore I've been freaked enough times I've gone outside and looked at the top of the chimney for flames, being a noob................

 

[LLigetfa]

My father's house burned to the ground from a top-down chimney fire. It likely started at the top of the chimney and spread to the roof. By the time he noticed it, the whole roof and upper floor was a blaze. It took out his phone line and he had to run a half mile to the neighbor to call the VFD. All they could save were the out buildings.

 

[LeonMSPT]

Definitely have to keep an eye on things. There's a reason the majority of the civilized world burns oil, gas, and electricity for heat. Burning wood and coal is far from "automatic", and it has its dangers. Glad nobody was hurt in the fire at least.

My father's house burned to the ground from a top-down chimney fire. It likely started at the top of the chimney and spread to the roof. By the time he noticed it, the whole roof and upper floor was a blaze. It took out his phone line and he had to run a half mile to the neighbor to call the VFD. All they could save were the out buildings.

 

[LLigetfa]

Glad nobody was hurt in the fire at least.

Well... there was emotional scarring. They lost everything but the shirt on their backs. They decided not to rebuild so didn't get replacement value on insurance and took a big loss.

Stubborn old man was doing all the wrong things and getting away with it for years.

 

[markleyh]

That sounds like a true disaster! Those of us who go through this really carry the memory for a long time. I'm glad no one was injured in your Dad's fire.

My wife's home was destroyed by fire started by a three-year-old playing with matches. The smell of burning house still freaks her out like nothing else, even to drive by a day-old house fire.

In one of our chimney fires, the firemen thought the fire had gotten inside the walls, so they hung around for thirty minutes monitoring surface temps inside and outside. It was scary to see them bring a hose line and fire axes right inside the house!

We didn't run the stove for a week after that, and still sleep lightly waiting to hear that nasty crackling noise of creosote igniting.

The fire was 15 years ago.


herbert

 

[Lumber-Jack]

Does anyone know how a chimney fire starts?

Does it always start from the stove pipe and move upwards?

Can it start in the top of the chimney from a spark?

If you're stovepipe and most of the chimney is very clean, but some creosote has accumulated near the top roof exit or on upper elbows, can it still happen?

Thanks

I think chimney fires always start lower down and progress upwards. I don't see how it is possible for the heat and flames to pass by and not ignite the creosote build up on the lower part of the flue and ignite it further up.

This is my understanding of how a chimney fire can start and can progress under the right circumstances. Somebody correct me if I'm wrong.

Creosote accumulation it is likely to form mostly near the top, coolest part, of your chimney, but if you burn cool fires and/or damp wood you will also get accumulations in the stove pipe closer to the stove. (If you have black build up on your glass you are getting it in the lower part of your chimney).
The thicker (most dangerous) accumulation of creosote are generally out of reach of the heat that goes up the flue, but the lower part is not. If you burn hot enough you will not get any significant creosote deposits near the lower end of you chimney (stove pipe), but if you burn cool fires coupled with moist wood you can and will get deposits in the lower parts of your flue. If you get enough deposits and burn a particularly hot fire those deposits in the lower portion can, and will, begin to ignite. Depending how thick the creosote deposits are, how hot your fire is, and how long you let it burn for will determine what happens next.
If you have relatively thin deposits the creosote will likely just burn off and you won't even know it is happening.
A medium deposit may start making a lot of popping and crackling that you may hear, and it will progress up the flue (towards the thicker deposits), this is when it would be a good time to close your damper all the way as it is still basically being sustained by the fire in the stove, and likely this will be enough to starve the progression of the creosote from being burning off.
If the deposits are not that thick the last sort of "chimney fire" will often go out on it's own accord as it progresses up the chimney away from the heat of the stove, however if your creosote deposits are thick enough, and it is able to burn far enough up your chimney, and your stove fire is burning particularly hot, and the damper is wide open allowing plenty of extra oxygen to flow up the chimney it can start to become self sustaining and literally create it's own real fire and draft and you then have a full fledged chimney fire on your hands.