Before a fire protection system can be designed, it is necessary to define the main objectives of the system.
This is normally determined by a Fire Risk Assessment and should be provided as part of the fire system specification.
The brief guide below details classifications for commercial systems, we also have more information on domestic fire alarm systems. The categories of fire alarm systems are “L” if they are designed to protect life, “P” to protect buildings and “M” if they are manual systems.
BS 5839 splits fire alarm systems into 3 system design categories:
Manual systems e.g. hand bells, gongs etc, may be purely manual or manual electric, the latter may have call points and sounders. They rely on the occupants of the building discovering the fire and acting to warn others by operating the system. Such systems form the basic requirement for places of employment with no sleeping risk.
The system is installed throughout the building – the objective being to call the fire brigade as early as possible to ensure that any damage caused by fire is minimised. Small low risk areas can be excepted, such as toilets and cupboards less than 1m².
Detection should be provided in parts of the building where the risk of ignition is high and/or the contents are particularly valuable. Category 2 systems provide fire detection in specified parts of the building where there is either high risk or where business disruption must be minimised.
A category L1 system is designed for the protection of life, which has automatic detectors installed throughout all areas of the building (including roof spaces and voids) with the aim of providing the earliest possible warning. A Category L1 system is likely to be appropriate for the majority of residential care premises. In practice, detectors should be placed in nearly all spaces and voids. With category 1 systems, the whole of a building is covered apart from minor exceptions.
A category L2 system designed for the protection of life, which has automatic detectors installed in escape routes, rooms adjoining escape routes and high hazard rooms. In a medium sized premises (sleeping no more than ten residents) a category L2 system is ideal. These fire alarm systems are identical to an L3 system but with additional detection in an area where there is a high chance of ignition (e.g. kitchen) or where the risk to people is particularly increased (e.g. sleeping risk).
This category is designed to give early warning to everyone. Detectors should be placed in all escape routes and all rooms that open onto an escape route. Category 3 systems provide more extensive cover than category 4. The objective is to warn the occupants of the building early enough to ensure that all are able to exit the building before escape routes become impassable.
Category 4 systems cover escape routes and circulation areas only. Therefore, detectors will be placed in escape routes, although this may not be suitable depending on the risk assessment or if the size and complexity of a building is increased. Detectors might be sited in other areas of the building, but the objective is to protect the escape route.
This is the ‘all other situations’ category e.g. computer rooms, which may be protected with an extinguishing system triggered by automatic detection. Category 5 systems are the ‘custom’ category and relate to some special requirement that cannot be covered by any other category.