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Dr Zzeus - October 2021


How do I know which category of fire alarm and detection system to install?

It's hard to give a short answer to this. Current UK fire alarm regulations state that all business premises must have ‘an appropriate fire detection system’. This statement doesn't automatically mean that all business premises need a fire alarm system.

Clause 4 of BS5839-1:2017 “Need for a fire detection and fire alarm system and type of system”, states that the need for a fire alarm system in any specific building is usually determined by the fire authority and/or by a fire risk assessment.

The Regulatory Reform Safety Order (RRFSO) requires all commercial businesses to carry out a fire risk assessment. If the fire risk assessment has been carried out competently it should state which category of system or, as a minimum, if the assessor has limited BS5839-1 knowledge, the areas of the building requiring fire detection system coverage.

The fire risk assessment is key here and if it has been carried out by a competent fire risk assessor the fire alarm technician will know exactly what system to install.

What should you do if there is no fire risk assessment? My advice is to always err on the side of caution if you're going to propose a category, unless you're a competent risk assessor.

One system category you can safely specify is a category L1 system that covers all parts of the building. If the client wants anything less in terms of a system, let them specify it.

The BS5839-1:2017 categories are:

Category M systems = Manual This category classifies manual fire alarm systems where the alarm needs to be activated, by a person activating a break glass unit. These basic systems rely on a person discovering the fire and acting upon seeing it. Manual call points must also be installed alongside any of the L categories.

Category L systems = Life protection
L4 – Protection of fire escape routes
Fire detectors should to be installed along escape routes and circulation spaces, such as stairways and corridors. The aim is to ensure escape routes are protected by providing warning of smoke within escape routes.

L3 – Protecting paths to fire escape This covers all the same areas as the L4 category, though L3 also involves installing detectors in rooms that open on to an escape route. The objective of this system is to ensure that all occupants of the building are given enough warning to escape a fire, before their exit is impeded by the presence of smoke.

L2 – Fire detection in specified areas L2 category protection is the same as L3, but also requires fire alarms and detection to be installed in any other specified areas of high risk such as plant rooms, kitchens etc. The high risk or defined areas should be specified by the fire risk assessment or specifier of the category.

L1 – Earliest possible fire detection Alarms and detection should be installed throughout the whole building to provide the earliest possible warning of fire.

L5 – Specified fire protection In some buildings, fire detection systems may be required to fulfil a specific fire safety requirement. In these circumstances, detectors would be necessary in these high risk areas – whether this is one specific room or a certain area of a building. L5 may be required in addition to those mentioned under levels 1, 2, 3 and 4.

Category P systems = Property protection P1 – Complete fire protection for earliest possible warning P1 systems offer the earliest possible fire warning. Detectors and alarms need to be placed in all areas of a building.

P2 – Fire detectors for defined parts of a building Where the threat to property is high in certain areas of a building, more specific detection coverage may be required. Areas with high fire risk will require special warning. This could be a single room or an entire floor of a building.

About the author

Tom Brookes

Tom has a PhD with his dissertation, Creation of pathways for the professional recognition of fire alarm engineers in the UK, gaining maximum credits; he has recently become the first Chartered Engineer in the UK based solely on fire alarm knowledge and skills and is keen to help other fire alarm engineers gain professional recognition.

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