Wood near fireplace starts a fire (Dan H.)

DanHolohan

Be careful this winter.

<a href="http://www.beloitdailynews.com/articles/2007/11/16/news/news04.txt"target="_blank">Wood near fireplace starts a fire</a>

ScottMP

pyrolysis

I've never heard of that. Theres another thing I learned on The Wall. One more pieceof information I can use when talking to my customers.

Thanks Dan.

Scott

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Gordy

Prefab

Probably one of those prefab fireplaces in a box. Nothing like good old masonary fireplace material. You can't get carried away with the fire size in those prefab units.

Interesting that incident is not to far from me.




Gordy

Edward A. (Ed) Carey_3

Pyrolysis

Scott & all,

Pyrolysis can occur in all combustible materials that are exposed to heat. The condition directly affects the HVAC industry daily.

Pyrolysis. The chemical decomposition of a compound into one or more other substances by heat alone; pyrolysis often precedes combustion. (Ref, NFPA 921-12, 3.3.121)

A classic case of this is when a heating unit or chimney connector pipe is too close to combustibles, "but it has always been that way", so the techs put it back the same way, year after year when servicing.

Then suddenly something happens to change the dynamics of the heat transfer, and a fire occurs caused by the rise in heat transferring to the decomposed combustible material.

Products such as wood will reach their Autoignition temperature, and easily ignite under such conditions.

Autoignition Temperature. The lowest temperature at which a combustible material ignited in air without a spark or flame. (Ref, NFPA 921- 9, 3.3.13)

If you scan the internet and put “ MSDS sheet and Autoignition temperature” in the search you will find that virtually all of the manufacturers of wood and wood products list their Autoignition Temperatures of wood products at 400 to 500 F.

Picture a chimney connector pipe that is, let’s say, 10 inches from the ceiling joist. It has been that way for 30 years, so the tech takes it down, cleans the pipe, and puts it back up the same way. When he finishes the stack temp is measured at 500 degrees on the OLD boiler.

That temp is above the AIT of the wood but due to the heat dissipation over the 10" distance, the heat transferred is still not enough to ignite the wood at that time.

Now the LWCO fills with sludge because the HO does not flush it properly. The boiler operates devoid of water. The stack temp rises dramatically.

The pipe is still not touching the wood, but the heat transfer now reaches the AIT of the pyrolized wood that has always been there. A fire is caused by heat transferred from the same pipe, connected to the same boiler, which is close to that same wood, for the last 30 years, but has never been a problem before. (“But it has always been that way”)

I have had occasion to deliberately “dry fire” boilers over the years, (in controlled conditions of course) for the purpose of training of others. During the testing I have measured the stack temperatures as low as 350F when full of water, then drained them and measured the stack temp while devoid of water.

Using thermal-imaging I have seen boiler jacket temps over 1000 degrees F. And chimney connector pipes as high a 1200 degrees F. Any normal combustible material (such as a wood joist) that has previously experienced pyrolysis and is in close proximity to that boiler or chimney connector pipe, is going to ignite.

BTW, if a chimney connector pipe on a boiler is not properly supported or sealed into the chimney and comes loose, the exhaust gases released from that pipe alone can in many cases reach the AIT of the wood if it is too close. The exhaust gases can commonly be high enough to Autoignite wood even if pyrolysis has not occurred in the past.

That is why NFPA 31, 211 & 54 all require an 18” clearance between combustible materials and a chimney connector pipe, or approved clearance reduction methods must be employed. Also, chimney pipes can not be “boxed in or enclosed”, unless special approved vent materials are used in the process.

Well, so much for my Saturday Morning rants.

Back to paperwork now.

Ed Carey

Bob Gagnon plumbing and heating

I worried about fire

with my wood stove,I even caught one of my friends flicking his cigarette ashes into the kindling bucket. I put an automatic fire sprinkler in the ceiling and I feel a lot better now. Bob Gagnon

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Steve Gates_3

once upon a time

way back when I was a volunter, we fought and lost one like that. They had flat papers on top of the wood to boot. It's amazing how good your hearing is with all the associated noise and you can here the roof cracking and are able to jump in time.

Owners never did believe my report.