Photothermal detectors can also be used in buildings, these monitor changes in temperature and density of smoke. The benefit of such an alarm is that the potential for false alarms to occur can be reduced. The limitations of the heat detector may be affected in some situations, such as they do not sense particles of combustion and only alarm when heat on their sensors increases at a predetermined rate. Hazardous levels of toxic gases and smoke can build up before the alarm operates. It may not detect fire if it is slow, smouldering and in a different part of the vicinity and bypasses the detector. Fire Alarm & Detection System Categories and Objectives These systems are designed to protect property or life and are divided into categories P1 and P2 for property protection. The information that follows is based on BS 5839, Part 1. Life protection is divided into categories L1, L2, L3, L4, L5 and M. These categories determine what type of detection equipment is used and where it is placed. Also, sounder positions and quantities within the premises are also a consideration within these categories. Property Risk and Protection Category P systems are automatically activated fire detection systems designed to protect property. These systems are then sub-divided into: • Type P1: Fire system installed throughout the building • Type P2: Fire system only installed in a defined part of the building. (The objective of the above systems is to summon the fire brigade in the early stages of a fire) Life Risk and Protection Category L systems are automatically activated fire detection systems designed to protect life. These systems are then sub-divided into: • L1: Fire system installed throughout the building • L2: Fire system only installed in a defined part of the building where there is a fire hazard or risk of ignition • L3: Fire system only installed for the protection of escape routes and adjacent rooms • L4: A Category L4 system is one in which detectors are only installed within escape routes. A Category L4 system is, therefore, equivalent to a Category L3 system without detectors in rooms opening onto escape routes • L5: A Category L5 system is one in which the protected area or areas and, or the location of detectors is designed to satisfy a specific fire safety objective (other than the objectives of other sub-categories of Category L systems). Thus, a Category L5 system may be used, for example, to address specific requirements emanating from a fire risk assessment
Type M systems encompass all manually activated fire systems.
©SHEilds – All rights reserved FC V 5 JUN 2021
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