Detection Devices

Fire alarm systems have input devices connected to them to detect fire or smoke. Below is a list of common detection devices found on a fire alarm system: 

  • Manual Call Points – devices to allow people to manually activate the fire alarm. These are usually located near exits and on exit routes within the premises so that building occupants will be able to locate one within a reasonable travel distance after discovering a fire. Manual call points must be at least 85mm x 85mm, be coloured red, and have operating instructions. New Zealand requires two-stage operation (either “the breaking or displacing of a frangible or resettable element followed by the manual operation of a switch” or “the opening of a transparent cover or flap followed by the breaking or displacing of a frangible or resettable element”). 
  • Heat Detectors – devices which are designed to operate when the temperature or rate-of-rise of temperature exceeds a predetermined value. These are most commonly based around either a simple bi-metal thermostatic switch, or a thermistor-based electronic circuit. Eutectic alloy (low melting point metal) devices were used historically, but are now prohibited for new installations. Specialised heat detection technologies also include thermoplastic cable (shorts when the covering plastic melts) and fibre-optic based time domain reflectometry systems (particularly applicable for tunnels). 
  • Smoke Detectors – devices which detect visible or invisible products of combustion, usually emitted prior to the flaming stage. These are most typically point type devices operating on photoelectric (light-scattering) or ionization chamber principles. Other common smoke detector types include: projected beam (“linear”) smoke detectors and air-sampling (“aspirated”) smoke detectors. Smoke detectors can be very sensitive, so precautions may need to be taken to avoid false activations. 
  • Duct Detectors – smoke detectors installed in special housings are able to sample the air from a ventilation duct. These are generally used to trigger automatic precautions to prevent an air-handling system from spreading smoke around a building.
  • Carbon Monoxide Fire Detectors – devices which detect the poisonous carbon monoxide (CO) gas produced by smouldering fires. CO fire detectors are primarily used in life safety applications (e.g. sleeping occupancies). For the highest level of life safety CO detectors are usually employed in conjunction with heat or other smoke detection (e.g. multi-sensor detectors), or sprinklers. NOTE: These should not be confused with residential Carbon Monoxide alarms used to detect CO produced by faulty gas heating appliances.
  • Flame Detectors – devices which detect the infrared or ultraviolet radiation from a flaming fire. These are most typically used in commercial and industrial applications where a fast flaming fire can be expected (e.g. aircraft hangar, fuel storage depot). Unlike many other detection types, solar-blind flame detectors can also be used outdoors. 
  • Water Flow Switches – devices which detect when water is flowing through the fire sprinkler system. These will typically indicate on the zone index of the fire alarm system to assist fire fighters in locating the source of a fire, but are not generally permitted to initiate alerting (building evacuation) or a brigade call. 
  • Sprinkler System Alarm Valve – the main alarm output from a fire sprinkler system will generally indicate on the zone index of a fire alarm system and initiate alerting (general building evacuation). The sprinkler system will typically be required to have its own remote connection to the fire brigade. 

Multiple Sensor Detectors – recent advances in technology have allowed for multiple detection principles (combinations of: heat, smoke, CO, flame) to be incorporated into one detector. These so-called “multi-sensor detectors” are becoming increasingly common. Their particular attractions are enhanced detection performance combined with better immunity to false activations (nuisance alarms).