Today's fire detection products integrate innovations developed in our nuclear and space programmes with computer technology, resulting in a level of protection never before experienced by mankind.
Early fire detection systems were heat activated. Spring-wound mechanisms released and sounded alarm bells when the air temperature rose above the melting point of metallic releasing links. This technology is still in use in limited fire door applications.
Early electrically powered alarm systems received signals from the contact closures of fusible link and bimetallic contact sensors. Manufacturers later developed rate of rise heat detectors to reduce false alarms. Although these sensors are among the earliest electrically operated fire detection products, they are still in use in unoccupied areas or in combination with other detection technologies.
Predictable pattern
Fire detection technology changed drastically in the late 1950s. Investigation of tragic fatal fires revealed that the majority of lives lost in fires are from smoke inhalation, not the actual flames. At the same time, manufacturers applied the emerging semiconductor technology to smoke detection, resulting in low-cost, highly effective sensor products.
Fire develops in a predictable pattern. At ignition, combustion releases tiny invisible particles into the air. They are invisible and often have no odour, but they are measurable. As time elapses, the temperature rises and visible smoke - a combination of gases, vapour and larger airborne particles-appears. Finally, a developing fire reaches the flash point, where visible flames appear and the temperature rises rapidly. Data from fire investigations and full-scale testing led fire protection experts to a unanimous conclusion: Early detection in the development stages of fire saves lives.
Smoke detection
The earliest electronic smoke detectors used a visible light beam and opposed photo-electric receiver to detect smoke obscuration between the transmitter and receiver.
Today's beam detectors use infrared light and solid-state electronics. They analyse received light and process its characteristics before initiating an alarm. For example, a sign or ladder placed in the path of a 'state-of-the-art' beam detector will not initiate a nuisance alarm. The receiver electronics compare known smoke obscuration patterns to the sudden blockage of light.
The enormous processing ability of today's electronics defines the nature of environmental changes before initiating alarms. Flame detectors perform rapid spectrum analysis of received light. They detect the presence of infrared and ultraviolet light and compare the information with pre-programmed flame patterns. Flame detectors protect large interior areas and are particularly effective in detecting fast-developing fires.
Ionisation detector technology have also evolved. By inducing a high voltage on one of a pair of opposing plates, the air between the plates becomes ionised, causing electrons to cross the air space, producing a voltage on the opposing plate. The introduction of smoke interrupts the ion flow, causing a voltage at the opposing plate to drop. The detected voltage change initiates an alarm. This technology required a sizable power supply, and the detectors tended to sense airborne materials other than smoke.
Although ionisation and photo-electronic detectors sense products of combustion very early in fire development, their selection may be based on more than performance characteristics. Some code authorities are reluctant to use radioactive source smoke detectors regardless of their effectiveness in sensing the early stages of a fire. Their concern is the very presence of radioactive components within the detectors.
Today's fire protection professionals make their detection choices based on performance and applicability to conditions. Both photo-electronic and ionisation technologies detect the presence of combustion particles early in the fire development process. Others use multiple technologies, including heat detection, integrated with a smart chip that makes the alarm decision.
Furthermore, digital communication opens the way for total building monitoring. Today's fully integrated systems monitor and control fire, security and energy management systems. Fire will still be with us a hundred years from now, but monitoring and protection technology in the next century are limited only by the imagination.
Published with the kind permission of Security Technology and Design magazine - www.simon-net.com
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