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Last edited 21 Oct 2020
Fire detection and alarm system FDAS
Approved document B, Fire Safety, Volume 2, Buildings other than dwellinghouses (2019 edition), defines a fire alarm system as a: '...combination of components for
giving an audible and/or other perceptible warning of fire.'
Live investigations of false fire alarms, published by BRE in December 2015, suggests that a Fire Detection and Fire Alarm System is ‘…control equipment that utilises detectors, warning devices and other components to detect fires and provide warning.’
Most fire detection and alarm systems operate on the same basic principles. If a fire is detected, then an alarm is triggered. This warns building managers and occupants that there may be a fire and that evacuation may be necessary. Some systems include remote signalling equipment which can alert the fire brigade or a remote monitoring centre.
Fire can be detected by; heat detectors, flame detectors, smoke detectors, carbon monoxide detectors and multi sensor detectors, or an alarm can be triggered at manual call points. Alarms may consist of bells, sirens, horns, lights or a combination these. Two power supplies are required, generally a mains supply and batteries providing 24 hours back up.
- L, (L1 to L5): automatic systems intended for the protection of life.
- M: manual systems, fitted with sounders and call points.
- P, (P1 and P2): automatic systems intended for the protection of property.
Fire detection and alarm systems can be divided into a number of general types:
- Conventional systems.
- Addressable systems.
- Analogue addressable systems.
- Wireless systems.
- Self-contained units.
Conventional systems generally consist of a series of detectors and call points wired to a control panel which drives the detectors and a minimum of two sounder circuits, includes LED indicators and allows de-activation and resetting. Typically, separate circuits will be provided for each fire 'zone' (usually a floor of a building or a fire compartment). This separation into zones means that the approximate location of the fire is known and so the appropriate response can be instigated. It also allows for easier diagnosis of faults.
Addressable systems are similar to conventional systems, but the central control panel can identify exactly which detector or call point triggered the alarm (rather than just a zone), or whether communication has been lost with a detector. In this system the circuit is wired in a loop, with a number of detectors or call points on each loop. The loop can be powered from both ends, so that it continues to function even if there is a break in the loop (separate loops may still be provided for each zone).
The control panel can be programmed to show specific information, or trigger specific responses for different detectors within the system. Addressable systems are generally used for larger or more complex installations because of the benefits of more accurate detection, and so fault finding, and the reduced wiring requirement.
Analogue addressable systems, or intelligent systems can include an analytical capability in each detector which can assess local parameters to determine whether there is a fire, a fault or a maintenance requirement. This can be useful in preventing the occurrence of false alarms. A pre-alarm warning may be indicated if a detector is approaching a trigger condition.
NB: The 2014 BRE briefing paper, The causes of false fire alarms in buildings, found that; 'False alarms generated from remotely monitored fire detection and fire alarm systems cost businesses and Fire and Rescue Service (FRS) authorities an estimated £1bn per year in the UK. In the period 2011-2012 a total of 584,500 fire and false alarms were reported in Britain, 53.4% of these were not fires and therefore considered false alarms. This is a considerable drain on FRS authorities as well as causing business disruptions leading to a loss of productivity and reducing the confidence of the general public.'
The paper proposed that education could contribute significantly to reducing false alarms and that the increased use of multi-sensor detectors is a cost effective way of averting false alarms from common causes such as cooking fumes and steam.
 Related articles on Designing Buildings Wiki
- Automatic fire detection and alarm systems, an introductory guide to components and systems BR 510.
- Carbon monoxide detector.
- Domestic smoke alarms DG525.
- Fire blanket.
- Fire detector.
- Fire spread.
- Heat alarm.
- How fire doors can save lives
- How installer competence can help prevent major residential fires.
- Ionisation smoke alarm.
- Leading built environment bodies call for sprinklers in all schools.
- Live investigations of false fire alarms.
- Making the case for sprinklers and dispelling myths.
- Multi-sensor alarm.
- New requirements for fire detection and alarm network systems IP 12 13.
- Optical smoke alarm.
- Over £1 billion lost every year due to false alarms.
- Smoke detector.
- The causes of false fire alarms in buildings.
- Types of alarm.
- Visual alarm devices for fire: An introduction and guide to BS EN 54-23.
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