Fire Smoke Detection System

Smoke and toxic gases are the main causes of death in building fires. Experience has shown that deaths have occurred in locations remote from the fire due to the spread of smoke and gases and their ability to cause disorientation, incapacitation and ultimately death, depending on the concentration and length of exposure.

The University is required under the Building Code of Australia and the OHSW Regulations to have safeguards to provide early warning to occupants, so that they may safely evacuate before the conditions in any evacuation route become unsafe

The type of detection installed takes into account a range of factors including the following :

Difficulty of evacuation and/or rescue
The likelihood of the risk of a fire occurring in the building
The time it takes to travel to an exit
The effective height of the building
The contents of the building which may influence the speed and intensity of fire development and spread
If the premises contains sleeping accommodation

Selection of Detectors

Detectors are designed to detect one or more characteristics of a fire eg heat, smoke and flame. No one type of detector is the most suitable for all applications and the final choice will depend on individual circumstances. In some University buildings, different types of detectors are combined to achieve the best results. Smoke Detection will provide earlier warning of fire conditions than heat detectors or sprinklers.

Operation of a Smoke or Heat Detector

When a smoke or heat detector is operated, the small red light on the detector will be illuminated (LED – light emitting diode). The detectors are interfaced with the Fire Indicator Panel and will automatically activate the building’s audible (and visual if installed) fire alarm.

Activation of the detector may also :

alert the Fire Service
alert Security
sound external bells
shut down air-conditioning
activate the Emergency Warning and Intercommunication System (where installed)
automatically close fire/smoke doors (where installed)
automatically release designated exit doors

Types of Detectors

Heat (Thermal) Detectors

Heat detectors are installed where a smoke detector would cause an unacceptable level of nuisance alarms. For example where the atmosphere contains particles, such as steam or other vapours.

There are two main types of heat sensitive detectors:

Rate of rise temperature, designed to operate when their temperature rises abnormally quickly; and
Fixed-temperature elements, which are designed to operate when they reach a preselected temperature.

The standard operation range is 58oC, however there are various temperature types dependant upon application eg where high temperatures already exist due to the nature of the activity in the room/area.

Smoke Detectors

All types of smoke detectors depend on combustion products entering the sensing-chamber or light beam to operate.

Since the detectors are usually mounted on the ceiling, response time depends upon the nature of the fire. A hot fire will drive the combustion products up to the ceiling rapidly. A slow smouldering fire produces little heat, therefore the time for smoke to reach the detector will be increased. Flaming fires can burn more cleanly and the thermal turbulence can cause dilution reducing the response by photoelectric detectors. A smouldering fire can cause a dense plume of smoke to reach the detector causing a more rapid response.

There are two smoke-sensing detectors:

Photoelectric
Operates on the scattering or absorption of light by smoke particles in a light beam
Responds quickly to smoke that is optically dense
Preferred to ionization detectors as they respond to a wide range of fire types.

Ionization

Operate on the change in current flowing through an ionization chamber upon entry of smoke particles
Respond quickly to smoke containing small particles normally produced by clean-burning fires
Respond slowly to optically dense smoke containing large particles, which may be produced by smouldering materials.

Sprinklers

A sprinkler is designed to :

Extinguish the fire before it fully develops
Limit and control the spread of fire
Prevent the fire reaching the stage at which “flashover” occurs (ie total involvement of a room’s contents in a fire)
Allow more time to evacuate to a safe place.

A sprinkler system is connected to activate the fire alarm system and will automatically alert the Fire Service.

Activation may also, depending on the interface with the Fire Indicator Panel :

alert Security
sound external bells
shut down air-conditioning
activate the Emergency Warning and Intercommunication System (where installed
automatically close fire/smoke doors (where installed)
automatically release designated exit doors.

The sprinkler system can only be switched off by the Fire Service.

Please note :
Activation of a sprinkler will possibly generate more smoke/toxic gases.
Evacuate the area as quickly as possible, closing doors behind you.
Follow designated exit signs.