Fire Alarm and Detection Systems

A fire alarm system is a set of electric/electronic devices/equipment working together to detect and alert people through visual and audio appliances when smoke/fire is present. These alarms may be activated from smoke detectors, heat detectors, water flow sensors, which are automatic or from a manual call point.


After the fire protection goals are established – usually by referencing the minimum levels of protection mandated by the appropriate model building code, insurance agencies, and other authorities – the fire alarm designer undertakes to detail specific components, arrangements, and interfaces necessary to accomplish these goals. Equipment specifically manufactured for these purposes are selected and standardized installation methods are anticipated during the design.

EN 54 is mandatory standard in the European Union for Fire detection and fire alarm systems. Every product for fire alarm systems must have a CE mark with an EN 54 standard to be delivered and installed in any country of the EU. It is a standard widely used around the world

UK fire alarm system categories

There are many types of fire alarm systems each suited to different building types and applications. A fire alarm system can vary dramatically in both price and complexity, from a single panel with a detector and sounder in a small commercial property to an addressable fire alarm system in a multi-occupancy building. Systems have to protect both buildings and occupants.

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.

  Manual systems, e.g. hand bells, gongs, etc. These may be purely manual or manual electric; the latter may have call points and audible devices. 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.

P1 The system is installed throughout the building – the objective being to call the fire brigade as early as possible to ensure that any P1 and P2damage caused by fire is minimized. Small low risk areas can be exempt, such as toilets and cupboards less than 1m².

P2 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.

L1  A category L1 system is designed for the protection of life and 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 L1 to L4category L1 systems, the whole of a building is covered apart from minor exceptions.

L2  A category L2 system designed for the protection of life and 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).

L3  This category is designed to give early warning to everyone. Detectors should be placed in all escape routes and all rooms that open onto escape routes. Category L3 systems provide more extensive cover than category L4. 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.

L4  Category L4 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.

L5  This is the “all other situations” category, e.g., computer rooms, which may be protected with an extinguishing system triggered by automatic detection. Category L5 systems are the “custom” category and relate to some special requirement that cannot be covered by any other category.


An important consideration when designing fire alarms is that of individual zones. Specifically:Zones

  • A single zone should not exceed 2,000m² in floor space.
  • Where addressable systems are in place, two faults should not remove protection from an area greater than 10,000m².
  • A building may be viewed as a single zone if the floor space is less than 300m².
  • Where the floor space exceeds 300m² then all zones should be restricted to a single floor level.
  • Stairwells, lift shafts or other vertical shafts (nonstop risers) within a single fire compartment should be considered as one or more separate zones.
  • The maximum distance travelled within a zone to locate the fire should not exceed 60m.