What is smoke and why is it dangerous?

By Carlsson Elkins
Tuesday 22nd February, 20225 minute to read

We’ve all seen smoke before and know it’s usually the result of a fire. We also know that it is incredibly dangerous and can even be fatal when inhaled. However, not everybody is familiar with what smoke is made of and why exactly it can do so much harm to those who are exposed to it. Here we fill in the gaps and outline the specific reasons why smoke can be so deadly.

What is smoke?

Smoke is made up of tiny solid, liquid and gas particles which come together to become visible. This is called propagation. Smoke occurs when there is incomplete combustion, which means there wasn’t enough oxygen to burn the fuel so not everything is burned. Smoke is a collection of these tiny particles which are too small to see on an individual level, but when they come together, they can be seen as smoke.

Why is smoke dangerous?

There are four reasons why smoke is so dangerous:

Particulate matter

The first is particulate matter — the sum of all solid and liquid particles suspended in air — many of which are hazardous. This includes dust, pollen, soot, smoke and liquid droplets which are dangerous when combined in propagation and then entering the lungs. There are tubes called bronchioles inside the lungs and these are responsible for transferring the oxygen from the atmosphere to the alveoli, where it is exchanged with carbon dioxide. If 60% of these bronchioles are covered by soot, oxygen starvation will begin to occur and likely result in death.

Toxic gases

Toxic gases are primarily caused by the burning of various things inside a property, such as chairs and other furniture. These are the three most common:

Carbon monoxide (CO)

The first of these toxic gases is carbon monoxide (CO), which is tasteless, scentless and invisible. According to the NHS, there are around 60 deaths every year from carbon monoxide poisoning. When CO is inhaled, it is transferred into your bloodstream and binds with hemoglobin to create carboxyhemoglobin. When this outnumbers oxyhemoglobin (which transports oxygen around the body), this leads to oxygen starvation and death.

Hydrogen cyanide (HCH)

Next up is hydrogen cyanide (HCH). Most of us will have heard of the poison cyanide from TV and films. Hydrogen cyanide is basically a gaseous version of the same thing: it’s poisonous and deadly. This is down to the inhibition of the respiratory enzyme cytochrome oxidase, which in turn prevents our bodies from making use of oxygen. This results in loss of consciousness, respiratory arrest, and eventually, death.

Phosgene gas (COCl₂)

Finally, there is Phosgene gas (COCl₂). For those of you who remember your history lessons, phosgene gas was used to poison ground troops in World War One. Its effects are the same in a domestic fire scenario — it will burn wet organic material. This includes the throat lining and the lungs.


If you are looking at smoke ventilation systems, you may also come across the word SHEV. This stands for Smoke and Heat Exhaust Ventilation. It’s just as important to get the heat out of a building as it is the smoke. Not only will heat lead to structural collapse, but the body’s tolerance to heat is actually very low. 60 degree heat mixed with water vapour is enough to burn the lining of your throat. At 120°, convected heat is enough to start causing skin burns. So, considering a domestic fire starts off at 300° and burns all the way up to 900°, that’s a very dangerous problem.

Psychological effects

This refers to the difficulty of walking out the door, into the corridor and escaping. This seems like such a simple, obvious action, but many people would rather return to a danger zone — like a burning room or apartment — than pass through a smoke-filled area where they don’t know what’s happening. These psychological effects need to be considered when creating a fire plan.

The importance of effective smoke ventilation systems

So, now we’ve established how dangerous smoke can be, let us explain why smoke ventilation systems are so crucial in keeping you safe.

Put simply, smoke ventilation systems are designed so that smoke can escape when a fire breaks out. Whether it's a natural system (involving windows, shafts and vents etc.) or a mechanical system (involving fans, air inlets, extraction pods etc.), having the right smoke ventilation for residential and commercial buildings is critical. Fires can happen at any time so precautions must be taken.

In a fire scenario, it's likely that some people will have to evacuate and rescue services will have to enter. However, this is only possible if there’s a clear passageway the smoke hasn’t reached, allowing occupants to locate the exit safely. A ventilation system helps the smoke dissipate, clearing the exits for people to escape. An adequate smoke ventilation system also allows cooler air from outside to enter the building and diffuse the hot smoke.

If you would like more information on smoke ventilation and fire safety, be sure to check out our blog and YouTube channel.

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