Till now we have focused on what causes fire, its prevention, timely evacuation and LPG safety in the previous blogs. In this blog, the attention will be on the various stages of Fire and the way it spreads. Only when we know these aspects, it will help us not only to fight the fire but also do timely Evacuation. Normally we all use the words Small Fire or Big Fire. However technically there is no such thing as small fire or large fire it only fire in various stages.

As you all know, by now Fire is the rapid oxidation of material in a process of combustion, releasing heat and light and various reaction products. Basically, there are 4 stages of fire and they are Incipient, Growth, Fully developed, and Decay stage.

The Incipient Stage: This first stage begins when Fuel, Oxygen and Heat combine and have a chemical reaction called Combustion, resulting in a fire.  This is also known as Ignition stage and in this stage there will be a Flame and a little heat but no Fire. Usually in this stage the fire goes out on its own but if there are fuel sources around then it starts to feed on that and increase. In this stage the fire can be easily put out or suppressed and easy to evacuate. Here one needs to just raise the alarm and can fight the fire if trained to do so.

The Growth Stage: The growth stage is where the structures, fire load and oxygen are used to fuel the fire. In this stage there is flame, fire and extensive heat. There are numerous factors affecting the Growth of fire including where the fire started, what combustible materials are near it, ceiling height and the potential for ”Thermal Layering”. It is in this stage which is very short where a deadly phenomenon called “Flashover” happens thereby trapping, injuring or potentially killing people. In this stage one needs to Raise the alarm, evacuate the persons in the area and call the Fire Brigade. You can fight the fire if you are trained and confident to do so.

The Fully Developed Stage: When the growth stage has reached its max and all the combustible materials have been ignited, a fire is considered fully developed. This is the hottest stage of fire and can be deadly for anyone trapped within the fire areas. In this stage one can hardly do anything. It is foolish to go inside and try to rescue anyone trapped. Leave that work to the Professional Fire fighters. Even they cannot do anything but douse the fire. In the previous two stages damage to property is limited but in this stage the damage is very high.

 The Decay stage: Usually this is the longest stage of a fire, the decay stage is characterised by a significant decrease in oxygen or fuel, putting an end to the fire. Two common dangers during this stage are first—the existence of non flaming combustibles, which can potentially start a new fire when not fully extinguished and Second, there is a danger of a back draft when oxygen is reintroduced into a volatile confined space. In this stage one needs to be careful while opening the doors and also make sure the fire is extinguished completely.

While describing the four stages i have used the terms Flashover and Back draft. Let us now understand the definitions.

Flashover:  A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases.

An example of flashover is ignition of a piece of furniture in a domestic room. The fire involving the initial piece of furniture can produce a layer of hot smoke which spreads across the ceiling in the room. The hot buoyant smoke layer grows in depth, as it is bounded by the walls of the room. The radiated heat from this layer heats the surfaces of the directly exposed combustible materials in the room, causing them to give off flammable gases via pyrolysis. When the temperatures of the evolved gases become high enough, these gases will ignite throughout their extent.

Back Draft pronounced as Back Draught: A back draft is a rapid or explosive burning of superheated gases in a fire, caused when oxygen rapidly enters an oxygen-depleted environment; for example, when a window or door to an enclosed space is opened or broken. Back drafts present a serious threat to fire fighters.

As these blogs are written for the benefit of everyone I will not be too technical though the subject of fire and fire fighting is highly technical.

We shall talk about the spread of Fire and how to put fire out in my next blog.

Stay safe, Be Safe and live happily.

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V.Seshadri
SR. Corporate trainer,
Usha Fire Safety Equipments private ltd, Chennai.
9840814353. Email: seshadri3225@gmail.com