4.3 The methods and systems available to give early warning of fire Assessment criteria: 4.1-4.6: Outline the principles for fire protection, detection, and prevention. Types of automatic fire detection, their limitations and links with other systems and equipment (fire doors and fire extinguishing systems) Fire Detecting Equipment Listed below are different types of fire-detecting equipment which can be used: • Spot detectors. These are static detectors which cover a certain sized floor area. • Line detectors. These linear heat detector cables are laid around an area to give protection. • Beam detectors. These are beams of light (usually infra-red) which cover a large floor space. • Sampling detectors. These incorporate a range of pipework which connects different areas back to the detector head. Air from each area can be sampled in turn. • Scanning detectors. These are moving detectors which can cover a large area.
Smoke Detectors The main types of smoke detection available include:
• Optical Detection is more effective at detecting slow-burning fires, for example, overheated electrical wiring. When smoke enters the detection chamber, infrared light is refracted off the particles setting off the alarm. The main problem with this type of alarm is that it can be set off by dust and steam, causing false alarms. • Beam Detectors. This device works on the premise that the smoke breaks a beam of infrared light which exists between a transmitter and a receiver. • Ionisation Detectors: are sensitive to free-burning fires with flames. These detectors are also prone to false alarms when they detect an aroma of burning. This device works on the principle of a circuit. When a smoke particle passes between two electrodes the circuit becomes complete and the alarm is activated. Heat Detection There are two main types of heat detectors: • Rate of rise heat detectors work when there is a rapid increase in temperature. These can be used in areas where it would be inappropriate for a smoke detector to be present such as in a room designated for smoking. • Fixed temperature heat detectors have a temperature sensor set to a specific level, if this is reached the system engages. These types of detectors are suitable for areas where there are already high temperatures such as boiler rooms. With more and more flame retardant treatments used in building materials and furniture, photoelectric (optical) smoke detectors tend to be the most popular choice in domestic applications.
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