Detector advances aim to cut false alarm rates
Stuart Ball, of System Sensor Europe, discusses advances in fire detector technology which are helping to reduce false alarms
In a typical year more than 50% of false alarms are attributable to automatic fire systems at an estimated cost of more than £1 billion, making this an issue of major concern.
Many smoke detector manufacturers are looking for ways to improve on these false alarm figures. This requires them to look for ways to improve detection efficiency; to improve false alarm immunity; to improve operational functionality; and to enhance system capability.
Multi-sensor detectors
The most significant advance in detector technology has been the development of multi-sensor devices, primarily designed to overcome the relatively poor performance of the optical detector in responding to fast fires with low particulate generation but significant heat rise.
The photo-thermal detector was developed to address the inevitable balancing act between increasing the sensitivity of a detector so that it responds more quickly to an incipient fire and the consequent increase in the false alarm rate. Signal processing in the detector head itself resulted in the panel being presented with a single composite result from the raw data generated by the two sensors, improving the effectiveness of the device across the fire spectrum.
The multi-sensor detector concept has now been extended with the addition of more sensors, each one aimed at detecting a specific product of combustion. All fires have three characteristics in common - they all produce carbon monoxide, heat, and particulate matter. In cases where the fire is flaming, it will additionally produce a changing light signature as the result of the flame generation. Several manufacturers have introduced tri-sensor devices, in which the smoke and heat detectors are augmented by the addition of a carbon monoxide sensor. Extending this principle further, the latest multi-sensor detector is a quad sensor device that combines optical, thermal, carbon monoxide and infra-red detectors into a single device.
Aspiration detectors
Aspiration detectors work by sucking air through a network of pipes in the protected areas back to remote detectors. Applications range from computer rooms, large open areas such as conference rooms and auditoria, data centres, where a single unit could protect a specific bank of server housings and equipment rooms. Since the air being sucked through the unit is filtered to remove dust and dirt particles, it can also be used in harsh and dirty environments, where a standard point detector might false alarm through contamination.
The latest hybrid aspiration systems use the classical aspiration pipe network, in conjunction with loop communications technology, to integrate an aspiration capability into an addressable fire system, enabling enhanced management and control of the aspiration part of the overall fire system.
Radio communications
Using radio communications instead of hard wiring between detectors and the control panel provides greater flexibility in the design and implementation of the system, offering several advantages over completely wired alternatives. The advantages of this over completely wired alternatives include cost savings, limitation of site disruption, and simple fast installation.
Many applications will benefit from radio. An obvious use for this technology would be a heritage site, where strict building rules, often in direct conflict with Health and Safety and Fire Service requirements, will apply. Installations where running cables into particular areas is difficult, if not impossible, because of the construction methods and materials is another opportunity, as are buildings where continual occupation and use makes it very difficult to have access for the time needed to run cables.
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