Does Fire Need Oxygen?


You may have seen Co2 written on fire extinguishers around public buildings or workplaces, so know that this gas is important in extinguishing a fire. But is it true that we use it to remove oxygen from a fire? Is it a good idea to reduce oxygen levels when dealing with a fire and just how reliant is fire on oxygen?

Fire needs oxygen to continue burning. Oxygen is an essential part of a fire and part of the “fire triangle” that sustains a fire. With enough oxygen in the atmosphere, the fire is sustained and can continue to burn its fuel supply. Therefore, one of the best ways to extinguish a fire is to get rid of the oxygen supply.

The importance of oxygen in a fire cannot be understated so it is important to appreciate its role in creating fire and how firefighters work to remove oxygen from a situation to keep a fire under control.

So, let’s break fire down its vital components and talk more about how to remove oxygen from a fire. This includes the following.

  • The fire triangle
  • The importance of oxygen alongside other fuels to sustain a fire
  • The need to remove oxygen from the equation in order to extinguish the fire
  • Different ways that firefighters remove the oxygen from the fire
  • How firefighters cope in situations with low oxygen levels.

What is the fire triangle?

Let’s start with the basics of how fire is created. There are three key components to a fire. When the three combine, you end up with a chemical reaction that results in a flame.

That flame will then continue to burn while each of those three necessary components is intact.

Oxygen is a big part of that. While there are forms of thermal decomposition that don’t require oxygen, such as pyrolysis, this doesn’t result in the flames we consider to be fire.

The oxygen reacts with a fuel source and heat to create a flame. That fuel source could be a flammable chemical or dry material of various kinds.

This chemical reaction also explains how fires can seemingly start from nothing. A good example of this is the dust explosion where a spark can ignite in the air and set off a chain reaction.

All it takes is the right concentration of dry dust particles in the air – such as sugar or flour dust – in an enclosed space with the right oxygen levels, and the right temperature.

Maintaining fires with a good amount of oxygen

It shouldn’t be too difficult to maintain a fire with a suitable amount of oxygen in most conditions. A good amount of fresh air and a controlled atmosphere with normal oxygen levels should be fine.

Fire needs air with around 16% oxygen to thrive and the average percentage in the air we breathe is 21%. This is great for maintaining necessary fires in fireplaces, campfires, or controlled burns outside.

However, it can prove to be an issue when it comes to extinguishing the fire. We need to find a way to reduce the air quality and remove at least 6% of the oxygen to help put out the flames.

Breaking the fire triangle

The chemical and physical reactions involved in the creation of fire mean that we can use the formula in our favor to stop fires. If a fire needs all three elements of a fire triangle to survive, all we need to do is break that.

If we remove one element from the triangle then the fire should go out. Firefighters can work in various ways to control the flames.

They may focus on the more efficient way of breaking the triangle for a safer and faster result, or look at trying to break the triangle from all sides.

  • You can try removing the heat by lowering the temperature around the fire. This is a common tactic for battery fires where battery banks overheat and cause fires. The safe use of water can help to bring the temperature down.
  • You can try and remove the fuel source. Physically removing flammable materials and risk factors isn’t always practical and safe, but can help to isolate the fire so it burns out more easily.
  • You can also work to remove the oxygen

How to remove oxygen from a fire

Removing oxygen from the available air may sound like a hard task, but there are actually lots of different ways to do so when dealing with fires.

There are various approaches used by firefighters and within official equipment like fire extinguishers.

However, there are also ways that we can better protect our homes and businesses and simple steps that we can take ourselves to smother small fires.

That is what smothering means.

Smothering a fire is an important step when you have something small that could be easily controlled. For example, you may have a small grease fire contained in one pan or a small electrical fire in an isolated device.

Smothering those flames effectively and quickly should put the fire out before it has a chance to spread. There are different options here from specialist equipment to basic items in the kitchen.

Smothering kitchen fires yourself

Kitchen and appliance fires can be pretty scary when they start up. But, you may soon see that they are contained to a small area because of a limited fuel supply.

This is where you may be able to use simple household products to bring the fire under control. You can learn more about the use of baking soda and salt in other guides. These materials have high melting points and can smother flames in the right circumstances.

You may also find that a damp towel or simply the lid of the pan is enough to seal off the fire and stop the oxygen from getting in.

Using fire extinguishers

During other situations where the fire is a little more out of control, you are probably better off using a fire extinguisher or fire blanket. Fire blankets work with a similar principle as the lids and towels above.

It is all about covering the fire with something with a large surface area so that there is a better chance of stopping the oxygen from getting through. A lot of fire extinguishers also use foams as a dense enough substance to smother the flames.

Always make sure that you use the right extinguisher for the fire at hand and always call the fire department for situations you can’t handle.

Fire safety building regulations to reduce oxygen levels

There are also ways to reduce oxygen levels in rooms to limit the spread of a fire. You may know that one of the common pieces of advice is to not only leave the room in question but to shut all the doors and seal the fire in.

Creating a more enclosed space with a limited supply of fresh air can decrease the oxygen supply. That is also why buildings need to have fire doors with barely any gap underneath.

These are important as front doors for apartments and on stairwells.

Do firefighters carry oxygen?

It can sound a little counterproductive and unsafe for firefighters to want to remove vital oxygen from a dangerous situation – especially when smoke would make it harder to breathe.

However, the sooner they lower the oxygen levels in a room while working on reducing the heat and fuel supplies, the better the result.

This means that not only do they need to use the best possible breathing apparatus to help them handle the conditions, but they need to be careful not to bring in too much oxygen as they could risk fueling the fire.

Firefighters use a system called SCBA – the self-contained breathing apparatus – to get a god supply of breathable air with no restrictions.

There is the assumption that these are oxygen masks because we rely so heavily on oxygen.

However, oxygen tanks would be a safety hazard in a fire. There would be a risk of the tanks exploding and of any leaking oxygen from the containers or masks inhibiting fire suppression. Instead, fire crews work with cylinders of compressed air.

The air is filtrated to make sure it is as clean as possible and mask users can take advantage of a demand valve for a one-way system. Air enters the mask through the valve on the inhale but nothing can escape the other way when exhaling.

In short, a fire isn’t going to start or continue to burn without a good supply of oxygen. You can have a flammable material and high temperature but no fire if oxygen levels are too low.

So, you need to maintain the oxygen levels to keep a controlled fire burning or remove the oxygen to put it out. Luckily there are lots of ways we can do this with fires in the home and fire safety measures that focus on this part of the triangle.

Mike Pertz

I’m Mike, I’m a full time firefighter/paramedic/diver for a department just west of Cleveland, Ohio and the founder of FirefighterNOW. I’m also a columnist for FireRescue1. If you’re reading this blog my guess is you are interested in the fire service. There's information on fitness, gear, interviews, tests and more. I hope you find what you're looking for.

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