Whilst the main focus of your fire protection strategy should be to prevent fire, should a fire accidentally break out early automatic fire detection is essential. Every second saved through early warning facilities could make the difference to a site's ability to recover from a fire.
It is the fire alarm control panel's job to detect a fire at the earliest possible point in time and to alarm the action forces. In large installations single fault should not prevent it from functioning properly. For this reason modular fire alarm control panels are constructed redundantly.
There are conventional detectors and so called addressable detectors. Most control panels supports both types. At addressable detector systems device communicates directly with the control panel, so it knows the exact location of any fire or fault reported. Each detector reports the value and the panel then decides whether this is an alarm. This allows some panels to make detectors more or less sensitive according to current conditions or time of day. All devices (detectors, manual call points, sounders & interfaces) are all connected on the same loop of wires. Detectors are assigned to zones by the panel, which allows for easier zone changes if the building layout is altered at a future date. Addressable panels typically have an event history which logs past system events. Good addressable panels allow for complicated cause & effect programming, where outputs are only triggered by certain combination and detectors.
Different sensing technologies allow an optimum of fire detection for various situation.
Optical Smoke Detectors are suitable for slow burning or smouldering fires and should be positioned where these most likely to occur.
Ionisation detectors use a low activity radioactive foil to detect fires by irradiating the air in smoke chambers. It is a good general purpose detector that responds well to fast burning, flaming fires.
Heat detectors use a single thermistor to sense the air temperature around the detector. This type of detector is particular useful where the environment is dirty or smoky under normal conditions.
Carbon monoxide detectors are good at detecting deep-seated fires. They don’t detect smoke particles or heat and are not universal replacements for smoke detectors.
Multisensor detectors comprise optical smoke and thermistor temperature sensors and reports both values separately or weighted.
Sophisticate fire alarm system can use information from the building and security system to detect fire at the earliest time. If the alarm system is armed (so nobody is in the building) already small changes in smoke, heat or carbon dioxide values will trigger a pre-alarm. Video cameras will be activated and send pictures of the detected area to the security staff.