Your Fireplace might not be as Safe as you Think: Chimney Fires
- Fire Roots
- Jul 21
- 3 min read
With the summer solstice having passed over a month ago and as we approach colder temperatures in autumn and winter, we might start to think about starting fires in the fireplace as a relaxing night-time activity. However, while it may seem quite relaxing and serene, these fires may prove to be quite dangerous, reaching up to 2000ºF. Each year, there are 25,000 fires caused by these chimney fires, making up almost 10% of all annual fires! One might have thought that chimney fires were extremely rare, but this statistic actually underestimates the actual percentage of chimney fires, as they happen almost exclusively during the winter.
So what causes chimney fires? The answer is actually quite simple: besides the few cases of improper installations, damage or blockage on chimney flue liners are the culprit, as they disrupt the flow of smoke, leading to a higher chance of a fire. Before diving into the details, it would be helpful to familiarize oneself with the structure of chimneys. In short, the flue is the space that allows gases to escape, and the flue liners are the material that enclose the space. So, what exactly causes fires to happen in the flue? The most likely answer is the buildup of creosote, the by-product of the incomplete combustion of wood. This may happen if there is too much wood, as it will suffocate the fire. Another possible reason for the incomplete combustion is that improper wood is used. Creosote is highly flammable and sticks to the flue liners; with sufficient heat, it will easily cause a chimney fire. Besides creosote, random debris may fall into the chimney. This is quite rare and usually won’t cause much trouble, with the exception of nesting materials. Believe it or not, bird nests often appear in chimney flues, and a chimney fire will very likely occur.
Additionally, there are 2 types of fires: fast-burning ones and slow-burning ones. The fast-burning ones are much more perceptible and are often characterized by loud cracking, popping, or even roaring sounds; thick, dense smoke; flames and sparks; and a burning smell coming from the chimney. If this happens, it is best to evacuate and call emergency services immediately, as they may spread and cause more damage. The second type, slow-burning fires, though not as noticeable, are equally as dangerous. These fires does not have enough oxygen; however, they are still very hot, and can cause damage to flue liners. These fires are characterized by gray, fluffy, and honeycomb-like creosote, instead of the normal black and flat creosote.
Luckily, chimney fires can be easily prevented. The most important measure is to have regular annual inspections done by professionals. Even if one does not use the fireplace, debris and nesting material may still end up in the chimney flue, and a future fire in the fireplace may result in a large chimney fire. In order to prevent debris from landing in the chimney, it is also beneficial to have a chimney cap, which blocks most falling objects from reaching the chimney flue but still allows smoke to escape. Furthermore, using the correct type of fuel is imperative to reduce creosote buildup. Specifically, one should burn dry and well-seasoned firewood. The moisture level should be between 15-25%, which can be measured using a moisture meter. Additionally, knocking two pieces of wood against each other can help distinguish between wet and dry wood: wet wood will create a dull sound, while dry wood will create a hollow sound. However, make sure that the firewood is not too dry, as it may burn too fast. To check that a fire will not cause a chimney fire, using a chimney thermometer to confirm the temperature of the fire can be an important indicator. Also, cracks on the exterior masonry of the chimney may indicate damage in chimney and a higher likelihood of a chimney fire occurring. Finally, one should always keep Chimfex in their homes: when a chimney fire occurs, Chimfex can suffocate the fire and take most chimney fires out in less than half a minute.
-Written by Ethan Liang
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