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Automatic Fire Detection & Alarm Systems

Fire detection is the ability of a system to detect the possible formation of a fire – preferably in the very early stage.  The earlier the system is able to detect the creation of a fire will minimise the possibility of any resulting damage and how difficult it may be to extinguish a fire depending upon how well established it is before it is detected.

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.

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.

There are many different forms of fire detection available ranging from

  • Conventional Rate of Rise Type Thermal Detection
  • Fixed Temperature Thermal
  • Ionisation Type Smoke Detection
  • Photo-Optical Type Smoke Detection to the Addressable Fire detection equivalents of these forms of fire detection.

There are also

  • Aspirated Fire Detection Systems (as mentioned above)
  • Flame Detection Systems in many forms (Ultra-Violet, Infra- Red, Combination UV / IR, Triple IR etc), Beam Smoke Detection Systems
  • Linear Fire Wire, etc .

Just as important as the ability to detect a fire is the need for a fire alarm system to warn occupants of a building and provide a clearly audible and visible (for noisy work areas or hearing impaired) means of warning – Occupant Warning System (OWS).

Larger and more complex buildings and structures may require the installation of an Emergency Warning & Intercommunication system (EWIS) that incorporate Warden Intercom Points (WIP’s) located at escape doors, stairwells etc.

All of these systems are suited to many varied risks and it is for us to recommend the ideal fire detection system for your risk or a combination of various forms of fire detection systems ideally suited to your risk.  Our ability to do this is gained from many years experience in the fire protection industry.