The 4 Stages of a Fire (Explained)

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There are four stages of a fire. These stages are taught to firefighters so they can identify what stage a fire is at.

Once the firefighters have assessed the stage the fire is at, they can respond accordingly.

Depending on the stage that the fire is in, firefighters can assess:

  • What the fire is likely to do and how it is likely to progress.
  • How much risk it poses to firefighters and civilians.
  • What is the best way to extinguish the fire.

This article explains all 4 stages and what happens in each stage – including the unique dangers each stage poses.

The 4 Stages of a Fire

The 4 stages of a fire are:

  1. Incipient
  2. Growth
  3. Fully Developed
  4. Decay

You can see in the image below the intensity of a fire at each stage.

graph of the four stages of a fire

1. Incipient

The incipient stage of a fire is the stage immediately after ignition. The fire has just begun. It can be identified by factors such as:

  • The fire has not affected anything beyond its immediate vicinity.
  • Smoke has not reduced visibility in the vicinity. People in the vicinity can still breathe.
  • People in the area can still escape without too much trouble.
  • The heat of the fire is relatively low.
  • The smoke alarm sounds.

Another important characteristic feature of an incipient fire is its liminality or uncertainty. It is at a point where it can either extinguish and disaster is adverted, or it can establish itself and begin to spread.

Whether the fire in the incipient stage is extinguished has to do with factors such as:

  • The vicinity of other flammable fuels,
  • The fire’s access to oxygen,
  • whether people are nearby who can extinguish the fire.

An incipient fire can usually be extinguished using household fire safety equipment such as a fire extinguisher or fire blanket by a trained user. The fire brigade should be called immediately and people should leave their house.

Examples

a) A candle that has just tipped over and flames have just started to trickle onto a table. Whether or not there are other flammable objects on the table may impact whether this fire takes off and enters the growth stage.

b) A cigarette has dropped onto the couch. The couch is beginning to smolder, but the person who dropped the cigarette still has time to smother the fire to prevent a catastrophe.

c) A stove catches fire due to an electrical fault. The stove’s fail safe is triggered, the fuse blows, and the fire extinguishes on its own.

d) A wild fire ember has drifted ahead of the fire front and landed in a backyard, lighting a few leaves where it landed.

2. Growth

The growth stage occurs when the fire has established itself and is burning self-sufficiently. We call this ‘established burning‘. At this point, the fire is generating enough of its own heat to cause a positive heat feedback loop. Here, the fire is using its own heat to cause combustion of surrounding fuel sources.

At this stage, the fire spreads around the area, engulfing fuels in its path.

Ways to identify that a fire is in its growth stage include:

  • A plume or layer of smoke is visible above the fire. If indoors, smoke may now be accumulating in the top two feet of the room.
  • You can feel the room’s temperature has increased.
  • Windows start to turn brown around the edges and may be cracking. You can no longer see any condensation on windows.

The growth stage is the shortest stage of the fire, where the flames spread exponentially. It is incredibly dangerous and people need to be well and truly evacuated from the building. At this stage, people may be trapped in a building and require a fire escape ladder to get out.

The growth stage often ends when a ‘flashover‘ occurs. A flashover is a moment in a fire’s life where it has generated so much heat (usually around 1150 degrees fahrenheit) that the fuels in the fire’s vicinity catch fire spontaneously.

During a flashover, you will often see a ‘flash’ where the fire spreads extraordinarily quickly, engulfing an entire room almost instantly.

The flashover is incredibly dangerous and can trap and burn people and firefighters in the home.

3. Fully Developed

A fire is considered fully developed when it is at its hottest point and is engulfing all of its available fuel sources. 

While the fire’s intensity is most likely only going to decline from here (unless a new fuel source is added, wind conditions change, etc.), this does remain the most dangerous moment in a fire’s life. It is at its hottest and most ferocious point.

During the fully developed stage, people should steer well clear of the fire.

Firefighters will often fight the fire from a distance and undertake fire reduction practices like backburning (for wild fires) that ensure new fuels are not introduced to the fire.

4. Decay

A fire will enter its decay stage when the fire runs out of oxygen or fuel for it to sustain itself. This is the longest stage and can take weeks for larger fires such as wild fires. A burning tree stump can smolder for many weeks at a time, sustaining a fairly high level of heat.

Another danger of the decay stage is the potential for new oxygen or fuels to be introduced to the fire. A sudden wind updraft or a falling tree branch may cause the fire to reignite.

After a fire has finished, care must be taken to ensure the fire does not reignite. The structural integrity of buildings or trees that have been burnt is compromised which can cause injuries due to collapsing structures. Furthermore, a fire may still have many carcinogens that are dangerous to people and animals in the vicinity.

Video on Fire Stages

This video provides an excellent demonstration of the four stages of a fire. In the video, a fire department demonstrates just how quickly a fire can spread through the first three stages. The fire being demonstrated is a fire that starts in a trash can in a living room.

The fire starts at the incipient stage where it could potentially be put out with a personal fire extinguisher. Within minutes, the couch catches, and the fire is self-sustaining. The growth stage is fast, where the fire beings to spread across the couch. Smoke begins to accumulate in the room. But the fastest change is the ‘flashpoint’, where the whole room suddenly catches ablaze. The jump in ferocity is amazing to see – jump to the 2:45 – 3:00 marks to see just how intense the flashpoint is.

Lastly, the fire fighters put out the fire. Watch their technique as they aim the water above the fire, and use swirls to ensure the fire is put out sufficiently.

As the fire chief states at the end of this video, it’s best to leave the vicinity of the fire immediately and contact the local fire brigade who are professionals at controlling a fire.

Conclusion

Fires go through four key stages. A firefighter will often assess the stage a fire is at when they arrive at a fire so they are aware of the likely behavior of the fire and how best to extinguish or contain the fire. However, every stage of the fire is very dangerous. Human safety is paramount, which is why trained firefighters are the best people to be present during a fire.

Remember, this article provides general informational content only and does not constitute advice, professional or otherwise, to you and your circumstances. Seek professional help immediately if you are in fire danger.