The science of chimney fires

January begins with flurry of chimney fires across Midcoast

Tue, 01/21/2020 - 6:30pm

KNOX COUNTY — January started with heat in the wrong places for a few Knox County residents as a result of chimney fires. In just over two weeks, firefighters in four municipalities hauled their sweep chains and poles roofward to fight flames in Lincolnville (Jan. 2), Union (Jan. 14), Rockland, (Jan. 16), and Camden (Jan.17).

In Rockland, firefighters were able to read words off of unburned pieces of old pizza boxes that fell from the chimney liner with each sweep of the cleaning tools. The homeowner had only occupied the house a year or two before hooking up a woodstove, reportedly without checking the years of buildup within the bricks.

Pizza box cardboard, like magazine paper, doesn’t always burn completely, adding to the unburned products of combustion – creosote – sticking to the walls of the chimney.

“It’s easy to take cardboard for granted,” said Rockland Fire Chief Chris Whytock. “But it hurts the combustion process and limits the heat’s spread.”

In Camden, the chimney fire was likely attributed to the use of unseasoned (green or wet) firewood, according to Camden Fire Chief Chris Farley. The chimney was recently cleaned, yet green and wet wood contains more moisture, a factor lending to more creosote build-up on the chimney liner.
It’s almost like a plaque in an artery, according to Rockland Asst. Fire Chief Adam Miceli.
The smoke going out includes unburned products of combustion, often in the form of sparks. As rising heat cools, the combustion within the smoke gets sticky, slowly coating the inside liner and restricting the amount of air flow.

When it gets to the cold part of the chimney, like when it goes to an unheated attic, or when it leaves the roof – it quickly gets cold.

Sparks here and there are not a problem, according to Miceli. Yet, every little bit that does gets stuck creates an even less smooth surface. The more buildup, the quicker the situation worsens. More stuff sticks to it, creating a fuel that can ignite. When the right amount of sparks or heat gets stuck on the lining and ignites, a fire forms.
From there, time and aggressive fire departments are essential. Chimney fires are usually contained due to the brick and mortar enclosure, forcing a blind recovery. But liners crack, and old chimneys without liners may have small spaces where flames can connect with the rest of the house. 
A certain mental and physical toll for responders can take root, especially on the coldest of nights. As Whytock described, firefighters must climb ladders (if they don’t have a tower truck) carrying equipment. They balance on slippery roof slopes while swinging around extra long poles and chains more than two and a half stories in distance. Add in frigid temperatures, creating the worry of water freezing in the tankers as extra dirty chimneys are slowly cleared, and the fear of a spark’s escape to another section of house remains.
Creosote buildup also causes damage that can lead to smoke or carbon monoxide emitting from very small cracks and into the house. And you can’t see it or smell it unless you have detectors. 

“You now have a continual source of carbon monoxide in the house that goes unnoticed until something happens,” said Miceli.

A chimney fire may seem like a small issue to some, “but there are a hundred things going through our heads,” said Whytock.


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