fire alarm design considerations

(17) Before a fundamental fire alarm system design can begin, whether it be a wireless fire alarm system or a wired system, it is essential that the category is defined, as this will decide on the areas in which the fire alarm detection are to be installed, along with the other design parameters of the system. The areas that are to be protected by the fire alarm system need to be such at to meet the design objective.

NOTE: Fire System Category is simply a shorthand means of describing whether the fire alarm system is manual or automatic, and in the case of automatic systems, the object of the automatic fire detection system. The appropriate extent of automatic fire detection will normally be determined by a fire risk assessment, rather than a rigid application of system Category to every building of a specific type or occupancy.

If the objective is to protect the occupants of a building in which no one sleeps, and fire is likely to be detected by people before smoke seriously reduces visibility in escape routes, an automatic wireless fire alarm or wired alarm might not be necessary: a Category M system might suffice. Whether there is a need for automatic fire detection and, if so,
the extent to which it needs to be provided, will often be determined by a fire risk assessment carried out on behalf of the user; such a fire risk assessment might be required by legislation, such as the fire safety order.

If there is significant probability that a fire in the building, or part of the building, could threaten escape by occupants before it is detected by people in the building, a Category M system is unlikely to be adequate, and the provision of automatic wireless fire alarm or a wired system will be necessary. This could arise from the likelihood of the presence
of occupants at special risk (including sleeping occupants), inadequate structural fire protection or the probability of very rapid fire development.