Fire Alarm System Design

Fire alarm system design varies considerably, depending on the type of premises to be protected and the level of protection required. The full system design requirements are specified in BS5839: Part 1: 1988, including detector spacing, alarm sounder positioning and location of control and indicating equipment.

It is essential, in the early stages of designing / installing a fire alarm system, to consult all interested parties: system installer, Health & Safety Officer, Local Fire Authority / Fire Protection Officer, Consultant, Insurance Company.

During consultations it must be established whether the purpose of the fire alarm system is to: enhance the safety of the occupants (life protection), or minimise the damage to property (property protection).

Life Protection L Systems.
A fire alarm system for the protection of life must be able to sound an alarm while sufficient time remains for the occupants to escape safely.

Property Protection P Systems.
A fire alarm system for property protection must automatically detect a fire at an early stage, indicating its location and raise an alarm in time to summon the fire brigade by means of an automatic link.

Areas To Be Covered
The areas of the building that should be covered by automatic detection for the various types of system are as follows:

L1 Systems.
The coverage should be the same as that for P1 system.

L2 Systems.
To provide detection to areas where a fire could lead to a high life hazard e.g. sleeping areas without supervision. An L2 system should always include the coverage of an L3 system.

L3 Systems.
Protection of corridors and escape routes, this may also require detectors in rooms opening onto escape routes.

P1 Systems.
All areas of the building with the exception of:
    (i)  Lavatories and water closets
    (ii) Voids less than 800mm in height unless the spread of the fire between rooms or compartments can take place through them

P2 Systems.
The areas of the building having a high fire risk e.g. the presence of ignition sources and easily ignitable materials, the potential for rapid fire spread, the absence of supervision or the serious consequences of loss. The unprotected areas must be separated from the protected areas by good structural fire separation.