The 4 Stages of Fire (Explained) (2022) - FFG (2023)

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There are four stages of fire. These stages are taught to firefighters to identify a fire’s location and act accordingly.

Once the firefighters have assessed the fire’s stage, they can respond accordingly.

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

• What the fire is likely to do, and how they expect it to progress.
• How much risk does it pose to firefighters and civilians?
• What is the best way to extinguish the fire?

This article explains all four stages of fire and what happens in each step. Including the unique dangers each step poses.

The 4 Stages of Fire

The four stages of fire are:

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

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

1. Incipient

The developing or embryonic stage of fire is immediately after ignition. It means that the fire has just begun. You can identify it by factors such as:

• The fire has not affected anything beyond its immediate vicinity.
• Smoke has not reduced visibility, and people around can still breathe.
• Everyone 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 a developing fire is its liminality or uncertainty. It is at a point where it can either extinguish and avert disaster or establish itself and begin to spread.

Whether you can extinguish the fire in this stage has to do with factors such as:

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

You can usually extinguish an incipient fire using a trained user’s household fire safety equipment, such as a fire extinguisher or fire blanket. However, you should call the fire brigade immediately, and people should leave their houses.

Examples

a) A candle that has just tipped over and flames have just started to trickle onto a table, and 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 smoke, 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.

d) A wildfire ember has drifted ahead of the firefront 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 burns self-sufficiently. We call this ‘established burning.’ Then, the fire generates enough heat to cause a positive heat feedback loop. Here, the fire uses its heat to cause the combustion of surrounding fuel sources.

The fire spreads around the area at this stage, 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 accumulate 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 maybe crack. You can no longer see any condensation on the windows.

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

The growth stage often ends when a ‘flashover‘ occurs. A flashover is a moment in a fire’s life that has generated so much heat that fuels in the vicinity catch fire spontaneously. This scenario usually happens around 1150 degrees Fahrenheit (ca. 621 °C).

During a flashover, you typically 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 their homes.

3. Fully Developed

A fire is “fully developed” when it reaches its hottest point and engulfs all the available fuel sources.

The fire’s intensity will likely decline unless its conditions change. Changing conditions include getting a new fuel source, changes in wind patterns, etc.

This stage is the most dangerous moment in a fire’s life when it’s at its hottest and most ferocious point.

People should steer well clear of the fire during the fully developed stage.

Firefighters often fight the fire from a distance and undertake fire reduction practices. These practices include back burning (for wildfires) to ensure new fuels can’t get to the fire.

4. Decay

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

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

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

Video on Stages of Fire

This video provides an excellent demonstration of the four stages of fire. In the video, a fire department demonstrates how quickly a fire can spread through the first three stages. In this example, the video shows a fire that starts in a trash can in a living room.

The fire starts at the embryonic stage, where you could potentially put it out with a personal fire extinguisher. Within minutes, the couch catches, and the fire is self-sustaining. The growth stage is fast, and the fire spreads across the sofa. Smoke begins to accumulate in the room. But the quickest change is the ‘flash point,’ where the room suddenly catches ablaze. The jump in ferocity is fantastic – jump to the 2:45 – 3:00 mark to see how intense the flash point is.

Lastly, the firefighters put out the fire. Watch their technique to aim the water above the fire and use swirls to ensure it extinguishes sufficiently.

As the fire chief states in this video, it’s best to immediately leave the fire’s vicinity and contact the local fire brigade. They are professionals at controlling fires.

Conclusion

Fires go through four key stages. A firefighter will often assess the stage a fire is at when they arrive at a fire. Hence, they are aware of the likely behavior of the fire. From there, they understand how best to extinguish or contain the fire. However, every stage of the fire is hazardous. Human safety is paramount, so trained firefighters are the best people during a fire.