A summary of BS5839-1 categories of life fire alarm systems
Category M – Manual fire alarm system
Manual fire alarm systems are the most basic. Employees must physically operate alarms manually on the discovery of fire to alert everyone else in the building to the danger.
Usually, manual fire alarm systems use breakable glass units installed strategically across the building, which then activates the premises-wide alarm system.
(Some manual systems, however, still rely on handbells or gongs if the premises are very small and don’t require more than one sounder to effectively sound the alarm throughout the premises.)
Category L1 – Maximum life protection automated fire alarm system
L1 maximum life protection automated fire alarm systems are the most comprehensive and feature multiple detectors in all parts of the building that a fire could start, including larger cupboards, roof spaces and voids.
The goal is to provide the earliest possible warning for occupants to ensure the preservation of life. The system must cover all areas of a building, with some minor exceptions, including small cupboards and lobbies.
Category L2 – Additional life protection automated fire alarm system
L2 alarm systems provide occupants of a building with advanced warning of the existence of a fire in another room.
Typically, this involves placing fire and smoke alarms in high-risk rooms and opening onto escape routes leading to fire exits. In small and medium-sized premises, L2 systems place fire detectors in areas where the risk of ignition is high, such as kitchens.
Category L3 – Standard life protection automated fire alarm system
Category L3 fire alarm systems – sometimes called standard life protection systems – feature alarms placed along all escape routes leading from the interior of the premises to fire exits.
The goal here is to ensure that all building occupants have sufficient warning to get out of the building before smoke, fire and toxic fumes begin impeding their exit. Unlike L2 systems, L3 systems do not have to place alarms close to high-risk sources of ignition.
Category L4 – Modest life protection automated fire alarm system
L4 systems only place detectors along escape routes such as hallways and stairwells and corresponding circulation areas, not individual rooms.
Businesses that use L4 systems usually operate in a low-risk environment where everyone can exit quickly in the event of a fire.
Ground floor offices, for instance, may only use L4 alarms in their entryways because staff can leave the building quickly.
These systems, however, are not suitable for multi-storey offices where it could take employees longer to escape via stairwells.
Category L5 – Localised life protection automated fire alarm system
L5 category alarms are a specific type of automated fire systems that tackles fire hazards in high-risk areas.
For example, a factory might install additional fire detection equipment in an area dedicated to welding because of the risk of spark ignition.
Conceptually, L5 alarms are different from other types of systems discussed so far. Conceivably, you could have a business operating an L4 system across its premises, but employing L5 in specific, high-risk rooms.
For instance, some companies might install fire detection equipment to L5 standards in a server room while leaving the rest of the building unchanged.