In fire detection, the number and arrangement of detectors is a function of the type of detector, the geometry of the place to be protected, and the environment that prevails in the supervised room.
The choice of detector is made based on two basic premises:
Some fire protection regulations specify a separation distance between detector centers under ideal installation conditions of 9 m, considering smooth and unobstructed ceilings between the protected area and the detectors. Taking into account that most of the rooms are rectangular or square, placing a detector in the center of a room, it would be ideal for covering a diameter of 13m.
Since problems such as multi-level ceilings, exposed ceiling joists, storage spaces, and partitions that obstruct the passage of smoke to the detectors, air stratification, or sloping ceilings must be addressed in practice, the separation between detectors varies from according to each case.
It must also be considered that for the detector to be 100% effective, the maximum ceiling height must be 3 meters. At a higher height, such as 6 m, the effectiveness is reduced to 64%, so the distance between detectors must be shorter.
In sloped or gabled ceilings, the separation of detectors in the horizontal plane, taking as a reference the vertical plumb line of the top of the roof, must be 1 m from the said vertical line. These must not be less than 0.5 m. Furthermore, the horizontal and vertical distance between the detectors and the stored merchandise must not be less than 0.5 m.
Duct detectors and air conditioning systems are specially designed for this use, differ from those exposed so far, and must meet the standards to work with a certain airspeed within the space for which they are intended.
The manual fire alarms shall be grouped in such a way that the place of origin of the warning can be quickly and unequivocally determined. They will be mounted in a conspicuous manner along escape routes such as exits, corridors, stairs, and sectors especially exposed to dangers. They must keep a distance of not more than 40 m from each other.
The different aspects that must be taken into account for the correct implementation of a fire detection system have been briefly analyzed. But it is considered that the definitive project must take into account all the particularities of the place to be protected and of having been studied in all its details.