BS5839 currently separates Fire Detection & Alarm Systems into three system design categories:
Category P – Property Protection
These types of systems are purely for the protection of property and fall into two classifications, P1 and P2. The objective of a category P is to provide the earliest warning of a fire to minimise the time taken from ignition of a fire to detection and the subsequent attendance by the fire services, minimising loss to the property.
This type of system is designed to protect the entire building, and thus requires AFD throughout the premises. While not dependent on a thorough fire risk assessment (FRA), a FRA is helpful for designing P1 systems, as appropriate detectors will need to be installed in each room to cover the specific risks present. However, as it is focused on the protection of property, alarm devices (sounders, beacons, bells, voice alarms, etc) are only required where specified – in an on-site security office, for example.
Category P2 requires AFDs in high risk areas, only. Category P2 systems are commonly used when combining with a life protection system other than Category M. For example, a building may have Category L3 protection for escape routes and adjoining rooms, with an additional AFD in the server room that is not directly connected to an escape route.
Category L – Life Protection
Life protection systems can be divided into various categories, L1, L2, L3, L4, L5
L1 systems are the “ultimate” in life protection as they recommend both manual call points (MCPs) and automatic fire detection (AFD) be installed throughout the entire premises. For the AFD installed in addition to L2 requirements care should be taken to choose the detector types according to not only the fire risks in each room, but also the persons at risk. For example, heat detectors should not be the primary detector type in bedrooms as they will not provide quick enough warning to protect the occupant’s life.
While the fire risks in rooms opening onto escape routes should be taken into consideration for L3 systems, this can often be done by common sense or in discussion with the client. L2 systems, however, require that a thorough Fire Risk Assessment (FRA) be carried out by a competent person to identify areas of high fire risk. Appropriate AFD should then be used in the identified locations in addition to the requirements of L3.
In addition to MCPs throughout and optical AFD in escape routes, Category L3 stipulates AFD be installed in all rooms, corridors and compartments that open onto escape routes. These rooms may use any of the common detector types, unlike escape routes, so appropriate detectors should be chosen based on the purpose and fire risks within them. However, the standard does recommend that certain specialist detectors such as flame or video should only be used in these rooms in addition to common detectors.
Building on Category M, L4 has MCPs throughout the building for occupants to manually identify a fire while automatic fire detection (AFD) should be installed along escape routes including stairwells. AFDs used for Category L4 systems should be smoke detectors – specifically, optical point detectors or aspirating smoke detectors (ASD) that rely on optical smoke sensors.
Similar to L2, this Category can only be designed and installed based on the findings of a thorough FRA – except that L5 should not actually be attempted by designers or installers unless specified in the FRA. Category L5 is for meeting specialist fire safety objectives, often in variation to the recommendations where strict adherence would not be possible. Such systems could include automatically closing metal shutters on a shopfront to contain the fire away from a shared concourse, or adding optical point detectors to bedrooms not adjoining the escape route in addition to an L4 system. L5 systems should be designed in conjunction with, and agreed by, relevant authorities before they can be signed off for installation.
A BS5839 Category M Fire Alarm System is a manual operation only system which has call points on all exits as well as corridors where persons are not expected to walk any more than 45m to operate one. All categories of life protection will have a type M system installed.