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Fire & Fire Protection - The Basics

Fire – The Creation:

For a fire to be created there are three elements required and these have to be present in exact amounts to result in a fire – these are;

  • A fuel source (wood, paper, petrol etc).
  • Heat (radiant heat, direct heat such as a naked flame etc)
  • Oxygen (air).

All of these elements are present in various forms in our everyday lives and it is when they come together in the right combination that a fire results.

Fire comprises 3 very specific stages of creation.

Stage 1 - Incipient:

This is the result of the introduction of a source of heat to a fuel source in air such as a burning log rolling from a hearth onto a rug. The incipient stage of this example fire is likely to be quite short due to a large heat source (a burning log) and a good fuel source (the rug) and plentiful air.

As the burning rug comes into contact with the rug the log will heat the rug (the heat excites the loosely bonded molecules of the rug changing the state from a solid to a gas) where the rug will start to give off vapours and fumes. This is the incipient stage of a fire. These vapours and fumes are usually invisible to the naked eye at this stage but they can be smelt and are detectable.

Stage 2 - Smouldering:

As the rug becomes hotter and hotter, the amount of vapour and fumes increases to such a state that these vapours and fumes become visible – this is the second stage of a fire – the smouldering stage.

Stage 3 – Flame / Heat:

The more the burning log heats the rug which in turn gives off more and more vapours and fumes that become hotter, more dense and richer. These fumes and vapour in the form of smoke (the fuel), heat and air mixture will be such that the vapours will ignite, the third stage of a fire will eventuate which is the flame / heat stage.

This is just one scenario of the possible creation of a fire. Each scenario will have its own characteristics and with this the resulting fire will have varied stages – longer incipient stages, longer smouldering stages etc. An explosive fire will have a very short incipient stage, very little if any smouldering stage and a very rapid and violent heat / fire stage.

Fire – What to Do:

As with the creation of a fire being reliant upon the coming together of the three elements of a fire, fuel / heat and air an effective method of extinguishing a fire is the dramatic reduction or removal of one of these elements.

  • Remove the fuel and the fire will extinguish – shut off the fuel supply.
  • Remove the heat and the fire will extinguish – cool the fire.
  • Remove the oxygen (air) and the fire will extinguish – smother the fire.

There are many forms of fire detection and these all have various advantages and failings in being able to detect a fire for a specific risk.

There are Aspirated Smoke Detection Systems that are able to respond to an Incipient Fire in the very early stage. Aspirated fire detection systems also have excellent ability to respond to smouldering fire but they have almost no ability to respond to a fire in the third stage – the flame or heat stage.

Automatic Fire Sprinkler Systems will not respond to a fire in either the incipient or smouldering stage (they will not provide early warning) but they have excellent ability to respond to a fire in the flame / heat stage and are excellent fire suppression medium. A combined system utilising smoke detection systems to respond to the early stage of a fire which will activate a water deluge system to suppress the fire is just one practical solution to utilise the abilities of each system to complement each other.

Early enough fire detection that will activate a fire alarm and the attendance of fire fighting or trained service personnel to investigate the cause of the alarm will quite often result in a simple repair with no fire at all. It’s all in the design.

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