Glossary
L4 fire detection system.
A category of fire detection and alarm system under BS 5839-1. L4 provides automatic detection in escape routes only. The narrowest of the standard L-category coverages, sometimes specified in older or low-rise residential common parts.
L4 coverage scope.
An L4 system has automatic detection in the escape routes (corridors, lobbies, stairwells) only. Rooms opening onto the escape routes are not covered. Manual call points sit at every escape route exit. The system gives warning when a fire has reached the escape route, but does not give earlier warning of a fire in an adjacent room.
When L4 is appropriate.
L4 is sometimes specified for low-rise residential common parts where the design strategy assumes fires will originate in the flats (which have their own domestic detection under BS 5839-6) and the common-parts coverage is targeted at escape-route protection. In taller buildings or buildings with shared facilities opening onto the escape route, L4 is often felt to be too narrow and L2 or L3 is specified instead.
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