Technological Developments

Conventional Fire Detection Systems

Most conventional detectors can only signal when in an alarm condition (and when they are not). They cannot provide information when they become insensitive: e.g. when they need maintenance, a false alarm is signalled. Such a type of detector would be unsuitable for large buildings, such as hotels with an extensive network of smoke detectors.

Conventional zone-type alarm systems link a range of detectors: smoke, heat, sprinkler switches and manual break-glasses to different areas in a building. When a device in a zone is activated, the fire alarm control panel indicates the zone number, but not the location of the activated device or devices. To deal with such limitations, some large fire alarm companies commissioned research and development programmes; as a result, addressable detectors and break-glasses were introduced and improvements in the degree of ionisation and optical detectors were also made.

Addressable Analogue Systems

Addressable analogue fire alarm systems use microprocessors to identify all the individual devices in the system and process analogue signals from smoke detectors (sensors). Each device has its own “address”, e.g. Foyer/ Office 1, sending specific information on the device’s location and type to the main control panel, regularly informing the operator on its state including (for smoke detectors) sensitivity levels and thresholds. The main control panel can then provide an indication for any detector, i.e. Normal, Fault, Pre-Alarm and Fire.

Such addressable systems benefit from no longer requiring separate wiring to each detection zone. They can also have a number of addressed devices representing a zone of a building, allowing numerous detector zones to form part of the same wiring circuit. By connecting both ends of the circuit to the control panel, the “open circuit” effect of, say, a wiring fault, can be overcome.

Some systems only send limited information to the main control panel whereas others provide information for processing at the main control panel, improving the overall system decision-making. This increases fire detection capability and performance monitoring (see below).

Detection

Conventional smoke detectors can signal a fire within a matter of seconds. By making use of analogue information from sensors, many of the underlying causes of false alarms can be identified and rectified. The sensitivity of fire detectors can also be changed to suit the environment. This can be particularly useful in situations where a range of detector sensitivities is needed: when cooking in a kitchen the sensitivity can be lowered and raised when the kitchen is unoccupied (however it may be that heat detectors are more appropriate in kitchens than smoke detectors).

Detector Performance Monitoring

The sensitivity of fire detection can be compensated by the analogue output monitoring of the detectors and the long term logging in the analogue output. This can be beneficial because the servicing requirements of every detector is identified and indicated at the main control panel, before the detectors become insensitive or begin to cause false alarms.

Addressable Systems

While it is not essential that analogue systems are addressable, other systems are available which do not provide the benefits of analogue systems but which do actually have an addressable capability.