How would you know if a fire started near you? You might see the flickering flames. Feel the heat. Smell or even taste the smoke in the air. Hear popping or other unusual noises. Modern smoke detection systems work somewhat the same way you do – by using a variety of “senses” to identify a problem.
For example, detectors today use some of these technologies:
Photoelectric cells register changes in light intensity as minute smoke particles enter the detector. As shown in this diagram, the smoke particles “scatter” the light beam, causing rays to hit the receiver which triggers the alarm.
Laser detectors measure the tiniest disruption of a light beam due to smoke particles in the air.
Ionization detectors sense a decrease in ion currents if certain particles or gases such as carbon monoxide enter the test chamber. As shown in this diagram, a small radiation source “ionizes” air in the chamber by removing an electron and thus maximizes electrical flow across the circuit. Smoke particles entering the chamber neutralize the air, which reduces the current flowing across the electrical circuit and triggers the alarm.
Light meters identify wavelengths in a specific spectrum that suggest flames are present (these are often called “flame detectors.”)
Video systems detect visual cues such as flickering flames or rising plumes of smoke. Video systems are particularly effective in very large open buildings where smoke or gases are more difficult to detect.
Integrated systems in use today, such as ultra-sensitive air sampling systems, continuously monitor key factors, then apply a computerized logic to determine if, when and how a response is needed. Multi-criteria detectors can sense danger more quickly, avoid nuisance alarms, and even provide valuable information for emergency responders.
Special detectors installed in air ducts of commercial buildings monitor for smoke particles and then close dampers or shut off fans in a fire to prevent toxic gases from being transferred into other areas.
“Smart building” research currently underway may make future smoke detection systems also responsible for ongoing air quality monitoring that directs heating, air conditioning and ventilation systems for utmost energy efficiency. In a fire, such systems could automatically direct occupants away from danger and toward the best escape routes, rather than simply sounding a general alarm.