Fire detection when designing fire alarms

When designing fire alarms and considering fire detection, fire detectors are designed to detect one or more of the four characteristics of fire, namely:
— heat;
— smoke;
— combustion gas (such as carbon monoxide);
— infra-red or ultraviolet radiation.
In some fire detection systems, a fire alarm signal is initiated when the characteristic reaches a pre-determined
threshold. A fire alarm signal may, instead or in addition, be initiated when the rate-of-change of the characteristic is representative of a fire.

In the case of fire systems with smoke or heat detectors, the characteristic is detected at a defined point(s) within the protected area. In contrast “line” detectors are capable of detecting the characteristic along a defined line within the protected space. In a fire alarm “integrating line detector”, the effect of the characteristic on the detector is integrated along the
line. In a “non-integrating line detector”, this is not the case, and the detector behaves, effectively, as though
it comprised an infinite number of point detectors arranged along a line.
In multi-sensor fire detectors, each detector contains more than one sensor and thus monitors more than one
of the characteristic fire phenomena (e.g. heat and smoke). By analysis of the signals received from the
smoke alarm sensors, potential response to phenomena other than fire can be reduced while still providing an adequate
response to fire.