Posted July 4, 2017

Fire alarm systems – in general it is appropriate to install some sort of fire detection and fire alarm system in virtually all non-domestic buildings. British Standard 5839 Part 1:2013 details the code of practice for the design, installation and maintenance of systems in non-domestic premises. In this article we will talk you through the main types of fire detection/fire alarm systems as contained in the British Standard documentation.

The need to install a fire alarm system is to enable a fire to be quickly detected by occupants and as a mechanism to let all occupants know that there is a fire.

The British Standard states that “manual fire detection and fire alarm systems are often sufficient to satisfy legislation in which no one sleeps”. A manual fire detection/alarm system would include call points (the “break glass in case of fire” boxes) and sounders.

An automatic detection system would include things such as smoke detectors and CO2 detectors. The standard then goes on to discuss particular situations where automatic fire detection would be necessary, including:

1. Buildings where people sleep.
2. Buildings with low occupancy levels, where the potential for a fire to break out and go undetected for long enough may prejudice the means of escape for those occupants.
3. Situations where fire protection systems, such as automatic door closing facilities or smoke control systems are to be operated in the event of fire.
4. Buildings where occupants cannot be readily evacuated, such as a hospital or care home. Where accurate knowledge of the location of the fire is critical to life safety, it is sometimes necessary to use only an addressable system (an automatic fire alarm system which identifies the location of the fire).
5. Situations where the insurance company deem an automatic fire detection system to be necessary in order to limit property damage caused by a fire.

In addition to the choice between manual and automatic systems, there are various categories of system as defined by the British Standard.

Category M Systems. These are manual fire alarm systems and incorporate no automatic fire detectors. They consist of manual call points (those which require human interaction) and sounders. This type of system may be suitable if you are able to rely on people to alert and evacuate personnel quickly.

Category L Systems. Automatic fire detection and fire alarm systems intended to protect life. This is then further broken down into categories:

• 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 places such as hospices, care homes and hotels where people sleep. 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.
• Category L2 system is 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 10 residents) a category L2 system is ideal. These fire alarms are identical to an L3 system but with additional detection in an area where there is a high chance of ignition (eg kitchen) or where the risk to people is particularly increased (eg sleeping areas).
• Category L3 fire alarm – 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 L4 fire alarm systems cover escape routes, circulation areas and circulation spaces such as stairways and corridors. The objective is to provide a warning of smoke within escape routes, thereby enhancing the safety of the occupants. It does not preclude installing detectors in other areas.
• Category L5 fire alarms are designed to satisfy a particular fire safety objective, for example a computer room. It could consist of a single detector in one room (where a fire in that area would create undue risk to the occupants) or a larger systems covering a larger area. The design will be custom and relate to some special requirement that cannot be covered by any other category.

Category P systems are those systems designed to protect property.

• Category P1 are fire alarm systems installed throughout all areas of the building, the objective of which is to offer the earliest warning of fire to minimise the time between ignition of the fire to the arrival of fire fighters.
• Category P2 fire alarms are installed only in defined areas of a building to provide early warning of a fire in a high fire hazard area or where risk to property/business continuity would be high.
So how do the experts decide which type of fire alarm you should have?

The British Standard that covers fire safety & detection (BS5839) does not dictate which category of fire alarm should be installed in any given premises, although there is what is known as Annex A, which provides information on the categorisation of systems that are typically installed in various types of premises.

It may be that your insurance company, local council and/or enforcing authorities let you know what type of system you should install. When you receive a specification it should always state which category of fire alarm you need to install, and where there has been a choice of system it should include a description based on the specific objectives of the category.

The standard does say, though, that the fire detection system should be designed to support your existing fire evacuation procedure, rather than trying to fit an evacuation procedure around a fire detection system. The fire alarm is there to support your fire safety strategy and should be designed around the actions required after the alarm has sounded.

In summary

The legislation regarding fire alarm design is extensive – the British Standard itself is some 180 pages in length. One of the final pieces of advice in the standard is that organisations installing fire alarm systems should consider “consultation between the user or purchaser, the enforcing authority, the system designer and, possibly, specialist consultants” especially for more complex requirements.

At SS Systems Limited we provide free surveys and design services to all our prospective clients. If you are in any doubt whatsoever, please don’t hesitate to contact our technical sales team. They have many years’ experience in this industry and will be glad to take your call.