ADVICE & TIPS
When designing a fire protection system, it is important to understand and identify the characteristics and fuel material of a potential fire, the environment in which the detector will be sited and the risk of fire.
For general use, smoke detectors are recommended since they give the highest level of protection, and must be used in escape routes for life safety systems to provide sufficient early warning to allow the evacuation of occupants. Two types of smoke detector are recognised by standards as good, general-purpose fire detectors:
Ionisation smoke detectors have a high sensitivity to fires that produce small smoke particles ie fast-burning, flaming fires that can burn for some time without generating much smoke. These detectors are widely used for applications such as printing workshops, paper mills and paint and solvent stores, as well as for general purposes.
Optical smoke detectors are particularly well suited to detecting slow-burning, smouldering fires which produce smoke with large particles. They are widely used for protection in areas such as bedrooms, escape corridors, electrical switch rooms and lift-motor rooms, as well as for general purposes.
Heat detectors offer protection in areas such as kitchens, saunas and garages where the environment is dirty or smoky under normal conditions or where there is a high presence of airborne particles such as water vapour or exhaust fumes. However, it must be recognised that any heat detector will respond only when a fire is well-established and generating a high heat output.
Two types of heat detectors are available:
- Rate-of-rise heat detectors are designed to sense a rapid increase in the temperature and are good for use in environments where the ambient temperature is normal, such as domestic kitchens, workshops, refuse storage areas and grain stores.
- Fixed temperature heat detectors will signal an alarm once the temperature exceeds a pre-defined level. This type of heat detector is effective in environments with fluctuating temperatures (such as boiler rooms) or where the ambient temperature is unusually high (for example in a foundary or kiln).
Multisensor detectors are a combination of an optical smoke detector and a heat detector which means they are good general purpose detectors that respond well to a range of fires: smouldering fires (the optical element) and fast-burning fires (heat element). The purpose of combining sensors in this way is to enhance the detection performance or its resistance to certain types of phenomena likely to cause a false alarm or both. They are well suited to environments such as hotel bedrooms and warehouse loading bays.
CO fire detectors do not detect smoke particles or heat. Instead they sense the levels of carbon monoxide (CO) given off by all carbon-based materials in the smouldering stages of a fire and may be used for early warning of fire in certain well-defined circumstances. However, they are not universal replacements for smoke or heat detectors, but make excellent supplements to fire detection systems. CO fire detectors are resistant to certain environmental conditions that can result in false alarms, such as dust, steam and cigarette smoke whilst responding to many types of fire faster than heat detectors. CO fire detectors are ideal for protecting small volume sleeping risk areas.
