Principles of Fire Science
For eons, humans have been familiar with fire, and most of us still use it daily, perhaps our familiarity causes us to neglect the danger that it can pose to our lives - but do you really understand what fire is?
In short, fire is uncontrolled combustion.
A definition by Quintiere (2018) stipulates that “combustion is a chemical reaction involving fuel and an oxidizer (typically oxygen – O2) in air, which releases a significant amount of energy to cause damage”.
Stollard and Abrahams (1991) also define combustion as “the rapid chemical reaction between fuel and oxygen (from air) releasing heat and light”.
A fire can be caused or started by natural sources (i.e. lightning, earthquakes, volcanoes, meteors) or unnatural/abnormal sources (i.e. arson, terrorism, plane crashes, accidents, fireworks).
In simple terms, fire is an event (rather than a thing) that naturally occurs when heat, oxygen, and fuel are present and combined in the right mixture. These three elements are commonly represented in the 'fire triangle' an example of which is presented below.
Once ignited, a fire usually keeps burning in a chain reaction while there are fuel, air and heat in the mixture. This chain reaction creates more heat, which further causes the reaction to grow.
This heat energy can generate vapours (gas) from liquid and solid fuels. The fuel vapour will combine with the air forming the perfect mixture that, when exposed to heat or an ignition source, creates a chain reaction that generates heat and light (fire). The cycle will continue with minimal or no outside influence, but if any one of the three components is removed, combustion ceases.
For example: A candle will continue to burn with the melted wax as the fuel (heat causes the was to melt and the liquid to generate flammable vapours) but if you cover the candle, it will not sustain the flame as you have removed the access to further oxygen.
What is Fire Protection?
An optimized Fire Protection design requires a comprehensive approach including three main elements; detection, suppression and compartmentation.
The detection and suppression of fire are called Active Fire Protection Systems. These systems require action (such as automatic detection or manual activation) to work in the event of a fire. Fire or smoke alarms, fire extinguishers and sprinkler systems are all examples of active fire systems.
Compartmentation is also called Passive Fire Protection Systems. These are the group of systems that do not rely on activation from either technology or a human being to help control and prevent the spread of fire and smoke.
How do you suppress or extinguish a fire?
Remembering the fire triangle assists in understanding that the chain reaction (fire) may be interrupted in three primary ways:
Smothering – Eliminating the oxygen (i.e. by using a fire blanket)
Starving – Removing the Fuel (i.e. by closing the gas tap)
Cooling – Decreasing the Temperature (i.e. by using water)
Smothering means eliminating or reducing oxygen in the immediate neighbourhood of the burning material. The method for this action is to prevent or impede the access of fresh air to the fire while allowing the combustion to reduce the oxygen in the confined atmosphere until it extinguishes itself. Examples of smothering are:
If a pan full of oil is on fire, a person may use a fire blanket to cover it.
To cover a burning person with a fire blanket.
Snuffing out Candles
Starving means removing the fuel, where the mixture will become too lean to burn. Examples of Starving are:
topping gas tap to a stove;
not adding more wood (fuel) into a bonfire, causing the fire to extinguish naturally;
removing combustible material from the neighbourhood of fire, e.g. drainage of burning oil tank;
removing fire from the area of combustible material like pulling apart a burning haystack;
breaking up the burning material, e.g. emulsification of surface of the burning oil
Cooling means decreasing temperature, where it will not be hot enough to burn and keep a chain reaction. Examples of Cooling are:
Firefighters using water to fight a house fire;
Sprinklers in a building;
At Nelligan, we have the expertise to help with the specification and detailing of Fire separations on your Fire Safety Design, including Fire Engineering solutions, fire safety systems and Passive Fire Protection systems.
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