Fire Alarms

There is a huge choice of fire detectors on the market and choosing the correct one is crucial for your safety.

Fire Alarms

A fire alarm system has a number of devices working together to detect and warn people through visual and audio appliances when smoke, fire, carbon monoxide or other emergencies are present. These alarms may be activated automatically from smoke and heat detectors or may also be activated via manual fire alarm activation devices such as manual call points or pull stations. Alarms can be either motorized bells or wall mountable sounders or horns. They can also be speaker strobes which sound an alarm, followed by a voice evacuation.

Fire detectors can detect a range of factors associated with a fire, such as smoke, heat, combustion gas or, ultraviolet and infrared radiation. Even if one of these elements is detected, the fire alarm system will be triggered.

Conventional, four-wire or fire alarm systems have been extensively used in smaller properties such as shops and restaurants for many years.

Less expensive to purchase than other types of alarm system, they work by dividing the building into a number of detection zones, with the detectors and call points within each zone hardwired on dedicated circuits to the control panel. There may be multiple detectors on a single zone. A separate two-core, fire-protected cable for each alarm sounder or bell is needed because they are wired to different loops.

If a detector is activated, the control panel identifies the circuit that contains the triggered device and so indicates the zone from which the fire alarm has originated, but the area then has to be manually searched to pinpoint the individual device.

Designed for smaller operations, two-wire fire alarm systems are based on standard conventional system technology. In a two-wire system, the detectors, call points and alarm devices for each zone are wired on the same set of two-core zone cables back to the control panel, enabling it to use a single circuit per zone both for detection and to power the sounders or sirens.

Although two-wire systems cost more to purchase than four-wire systems, they are quicker, more flexible and less expensive to install. Two-wire systems also provide more flexibility in operation and have additional functionality such as fault conditions, isolation and detector recognition.

Analogue-addressable fire alarm systems give details on individual detectors, whereas conventional systems only give information about specific circuits or zones.

Addressable or “intelligent” fire alarm systems are designed for large commercial premises and more complex networked systems since they are much more expensive and more complicated than conventional two or four-wire systems which have increased flexibility, intelligence, speed of identification and scope of control.

In addressable systems, different types of initiating devices are wired in one or more single loops around the premises. This requires less cabling than conventional systems and each detector or call point can have its own unique address.

The fire control panel receives information and status reports from each device and indicates its exact location if there is a fire, fault, smoke, heat or contamination.

More expensive to buy but more flexible, cheaper and much quicker to install, wireless or battery-powered radio-linked fire alarm systems provide just as much protection as conventional wired systems and are useful when wired installations are not suitable (such as in grade-listed properties where wiring may be prohibited). There are no cables between the detection devices and the control panel, so doing away with the need for long-term cable tests.

Wireless systems need to comply with EN54-25 standard. Increasingly sophisticated, today’s wireless fire alarm systems are much more reliable than the ones that originated in the 1980s and have multi-frequency links to eliminate signal blocking and collision, allowing a high margin of signal strength to be maintained.

Although technically a detection solution, aspirating smoke detection systems are extremely sensitive and can detect very small or smouldering fires far quicker than other systems.

Aspirating systems use a fan to draw in air from around a building via a network of sampling pipes and sampling holes. The air is then passed through a highly sensitive precision detector that analyses it and generates warning signals of potential fire when it detects smoke particles.

Expensive to install and maintain, these systems are highly sensitive and can detect cool smoke that does not rise to the ceiling, as well as smouldering fires and particles given off by overloaded electrical cables. They are therefore especially useful where early warning is required.

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