why is there more smoke after the fire goes out than while it’s burning?
In: Chemistry
Fire is when the combustible materials release combustible gasses while combusting, resulting in the combustion of those combustable gasses.
The large visible flames are actually “burning smoke.” When the fire cools to embers, the fumes are being released, but not being further combusted into invisible gasses, thus, a huge cloud of uncombusted soot and smoke.
Surely there is more smoke during a fire than when it has gone out. No?
However, you might be refering to a candle? Because it is true that once the candle is burning, you pretty much see no smoke, and once you kill the fire, there is a clear line of black/grey smoke releasing.
Short answer is a non-complete reaction.
When you have an intensive fire, the fire will yield enough energy for the carbon (originated from the hydrocarbon fuel – Wax in the case of a candle) to combine with the oxygen (O2) in the air.
If you have a complete reaction, the byproduct of a burning candle is CO2 (which is colourless like vapour), while a less complete one has more CO (also colourless and at low densities pretty much invisible to the eye). Also free carbon (soot) will be released during the candle fire. But the ratio of soot to COx is quite low.
Now, when the candle’s fire has been killed, there is only the tiny weak ember on the top of the wick.
This glowing ember doesn’t yield enough energy for a complete reaction – so you have quite a big ratio of pure carbon (soot) released along the COx which you can see as a black smoke.
**TL;DR**
**Dead fires doesn’t have enough energy to completly combust hydrocarbon (fuel) to colourless gases like COx. Just enough energy to release the black-ish nano-particle carbon aka soot.**
I don’t know is this is indeed a cold hard fact, but there is a good explanation for it if it is. When an object burns, it releases a certain volume of smoke. Let’s say that if an entire bedroom burned, it would create 100 cubic metres of smoke. That smoke has to go somewhere, it does not vanish. Smoke will rise and if there is an opening in the house, it will go through there. However, such an opening can only allow a certain amount volume per minute. Let’s say that a cracked window allows one cubic metre of smoke to pass through a minute, that means it would take 100 minutes for all the smoke to evacuate. If the fire burned the room in 10 minutes, it would take another 90 minutes for the smoke to clear.
In addition to smoke, fighting fire with water creates steam. Shooting water on the fire will boil the water and make steam. One litre of water creates 1700 litres of steam. Same like the smoke, that steam has to go somewhere, so it can take a while for the steam to clear. Than being said, a lot of the steam would eventually condense back into water.
Another thing to consider is ventilation. Smoke is unburnt fuel. If a room is full of smoke, it could re-ignite and cause a massive fire. A part of fire fighting is ventilating all the smoke out once the flames are gone. This includes opening many windows, and possibly creating holes in the wall and roof. Instead of a single window cracked during the fire, there are now many opening with smoke coming out of all of them. This makes it appear like there is more smoke, where it actually is only more smoke moving out instead of staying inside.
Latest Answers