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Fire alarm systems

Did you know there are several different types? Let’s take a look.

As we learned in our blog post about The Regulatory Reform (Fire Safety) Order 2005, a suitable and sufficient Fire Risk Assessment must be completed on all non-domestic properties. An important part of this assessment is to determine how a fire alarm should be used within the building.

The design of a fire alarm needs to take several factors into account, such as the building layout, the building occupancy and use and the current legislation at the time.

Guidance exists to help Fire Safety Consultants with this in the form of BS 5839-1:2013, the code of practice for designing, installing, commissioning, and maintaining fire detection and alarm systems in non-domestic buildings. The guidance splits fire alarm into three categories, which are;

Category L Systems, Category M Systems and Category P Systems. Categories L and M systems are designed to protect life and Category P are intended to protect property. It is common for a fire alarm system to incorporate a mixture of Categories.

All Fire Alarm Systems essentially operate on the same principle. If a detector detects smoke or heat or someone operates manual call point, then alarm sounders will operate to warn others there may be a fire and to evacuate.


Category M – Life Protection

Providing the least responsive/automatic level of protection, this category relies on manual break call points to raise an alarm. This Category is usually used for part of a premise rather than the whole and is well suited to environments where the occupiers are likely to detect a fire quickly themselves.  All Category M installations need to have alarm devices – sounders, beacons, bells, voice alarms, etc.


Category L – Life Protection

Category L systems are designed to protect life and so focus on escape routes and areas of the building with a high fire risk. They can be thought of as cumulative, with each increasing the level of protection provided by the previous Category. All Category L installations should have alarm devices – sounders, beacons, bells, voice alarms, etc – throughout the building regardless of their requirements for detection devices.

Category L4

This category is the most basic Category L4 system. It will have manual call points throughout the building as well as automatic fire detection systems installed along escape routes including stairwells but not in the adjoining rooms.

Category L3

This category goes a little further to include automatic detectors in all rooms which lead to escape routes, as well as escape routes themselves. 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 L2

A category L2 system is designed for the protection of life, it has automatic detectors installed in escape routes, rooms adjoining escape routes and high hazard rooms. These fire alarm systems are the same as an L3 system but with additional detection in areas where there is a higher risk of fire (eg kitchen) or where the risk to people is particularly increased (e.g. dense occupancy).

Category L1

L1 systems are the most comprehensive of all and include both manual call points and automatic fire detection throughout the entire premises. 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.

Category L5

Category L5 is used for meeting specialist fire safety objectives, because of unique building circumstances it means that a fire alarm system cannot fall into one of the above categories. For example it could include automatically closing metal shutters on a shopfront to contain the fire away from a multi-use area.


Category P – Property Protection

These categories are designed with protecting property in mind, however bear in mind that most Category P systems will also provide some protection of life cover and will be used in addition to Category L requirements for certain reasons. Category P systems are usually added as a request made by insurance companies.

Category P1

The system is installed throughout the building, in order to protect the whole premises. Automatic detectors are used throughout the building and installed to cover specific risks present.  Alarm devices such as sounders and beacons are only required in certain locations, usually where occupancy is common.

Category P2

Category P2 includes automatic detectors in high risk areas only. 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.

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