Smoke is a by product of fire. We all know that. So, it might feel like a silly question to wonder if smoke, itself, can catch fire? After all, it’s come from a fire, that must be it, right? Well, it turns out that it’s not such a silly question and the answer to whether or not smoke burns is likely to surprise you. It surprises most people when they first learn it.
Smoke can be flammable, though it is not always. Smoke is produced by incomplete combustion of the fuel in a fire. This leaves unburnt fuel in the smoke (especially in dark, black smoke) that can ignite when the ideal combination on fuel, heat and oxygen is reached.
So, though it may seem counterintuitive – smoke is a real fire hazard and needs to be approached with care for many reasons, here’s why.
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Also read: What Makes Something Flammable?
Table of Contents
What Is Smoke? What Is It Made Of?
Smoke is a collection of tiny particles that result from a fire. It is possible for smoke to contain hundreds or even thousands of different chemical compounds in tiny quantities.
However, it is mainly made up of carbon (in the form of soot), oil, tar and, of course, ash. These elements give smoke the distinct hazy property that it has visually as well as many of its chemical properties.
If it did burn completely, then there would be very little in the way of byproducts, except for carbon dioxide (CO2) and water (H2O).
The exact chemical composition of smoke is determined by what, exactly, is burning and it is impossible to list all the possible combinations of ingredients that you might find in smoke.
A wood fire might contain:
- Organic compounds
- Any minerals that were in the original tree. (The minerals, when burned off, form the ash component expelled from the fire.)
When you add wood to a fire, the first smoke that you see is the organic compounds bubbling off from the wood as they evaporate at fairly low temperatures.
Then, the next smoke you see is the carbon dioxide, water, and wood particles, once the wood is fully aflame. If the wood is fully burned, there will be no more smoke to see.
Also read: Is Oxygen (O2) Flammable? Actually No…
Is It Ever Flammable?
Smoke can be very flammable but is not always. As a general rule, the darker (blacker) the smoke, the more likely it is to be flammable.
Since smoke is created by incomplete combustion, the leftover fuel that is not completely burned can reignite if introduced to additional oxygen.
When there is too much fuel and not enough oxygen, the term is “too rich to burn”. However, when more oxygen is introduced it can easily and violently ignite.
Take a look at the smoke in this video. It is dark, thick, and “angry”. It won’t ignite initially due to being too rich. But once an ignition source meets with the smoke after more oxygen is added, it catches fire fast:
So, while not all smoke is flammable, it most certainly can be.
What Causes a Fire To Smoke?
A fire smokes when there is not enough oxygen to sustain the complete burning of whatever is on fire.
The particles expelled by the fire rise due to their tiny size (and thus lightweight) and the heat beneath them which causes an updraft.
What State Of Matter Is Smoke? Is It A Gas or Liquid?
Smoke is a mixture of all three states of matter. It can contain tiny solid particles, gas particles, and even minute fluid particles (which are most likely to be water).
Smoke isn’t a gas, though it behaves, mainly, like a gas, but it does contain solids and liquids as well.
What Is A Flashover?
A flashover occurs when all the combustible (or nearly all) material in an enclosed area catches fire at once and the fire spreads from floor to ceiling in a confined space.
Hot smoke isn’t just a fire hazard because it is capable of igniting, but also because it is capable of causing other materials to combust too.
What happens is that during the fire, smoke and other gases are heated and they flood a space, as they are hot, they raise the temperature of that space, and if the temperature hits around 932 degrees Fahrenheit to 1,100 degrees Fahrenheit, it will cause everything else in the room to catch fire.
Check it out here:
This is a very common phenomenon and if you ask any firefighter, it’s one of the reasons that even the smallest of fires can quickly get out of hand.
A single piece of furniture on fire could produce enough hot smoke overtime to set everything else in the room with it on fire and a flashover is particularly dangerous because everything catches fire at once with almost no warning!
Is Smoke Dangerous?
Yes, smoke is very dangerous. Not only is smoke flammable and not only can it cause flashovers, but inhaling smoke is a very bad idea.
In fact, more deaths are caused by smoke inhalation in fires than there are deaths by burning. (50 to 80% of all fire deaths are caused by smoke inhalation).
It can only take a few minutes to die of smoke inhalation, as it effectively suffocates the victim by removing any source of oxygen.
One unfortunate fact about smoke inhalation is that smoky environments can often interfere with your vision and even cause hallucinations or disorientation that prevent you from reaching safety.
You must be careful when moving from room to room, if a room is full of smoke, as opening a door can lead to an influx of oxygen which can cause the smoke to catch fire.
What About Candle Smoke?
Candle smoke is flammable because as you burn the candle it melts and evaporates the paraffin wax. This means that the smoke contains paraffin vapor which is flammable.
This isn’t anything to be worried about, mind you. Though holding a naked flame near candle smoke might cause a very brief flair of light, there’s not enough vapor being released for this to be any kind of fire hazard.