Smoke Detector Technology

Infrared Technology

• An infrared smoke detector projects a constant beam of invisible infrared light across the room or space it monitors, according to Westminster International Limited. Any smoke that rises across the path of the beam causes the alarm to sound. Because of their ability to cover more than 100 meters of space, infrared smoke detectors work especially well in large areas such as warehouses and shopping malls that would otherwise require a large number of individual single-point detectors.

Ionization

• An ionization smoke detector determines the presence and thickness of smoke by measuring its effect on conductivity, according to FireNet. A tiny amount of a radioactive substance inside the detector ionizes the air in the detector. This ionizing effect allows current to flow freely between electrons in the air. When smoke particles enter the detector's sensing chamber they block the free movement of electricity. A microprocessor reads the level of interference compared to reference levels and a sufficient smoke level then triggers an alarm.

Photoelectric Sensing

• Air-sampling smoke detectors that rely on photoelectric principles measure airborne moisture to determine the presence of smoke. These detectors contain a high-humidity chamber that regularly receives pumped-in air samples. The detector then subjects the humidified air to a decrease in pressure, causing any smoke particles suspended in the air sample to form a "cloud." The photoelectric component in the detector measures the density of the cloud against a reference level and sounds the alarm if the density exceeds that level.

Pipe-Based Air Sampling

• Pipe-based air sampling systems also collect air samples from ceiling-mounted pipes that have small air-sampling holes. A fan unit connected to the piping system creates a vacuum that continually feeds air through the system. As the air sample enters the detector unit, an intense light irradiates it to reveal even the tiniest number of smoke particles. The sensitivity of the pipe-based system makes it a good choice for mission-critical sites such as communications centers.

Gas Detection

• Fires cause changes in a location's gas levels. A detector sensitive to these gas changes may use either semiconductor or catalytic technology. A semiconductor-based detector detects changes in conductivity in response to reducing or oxidizing gases. A catalytic-based detector contains a substance that causes combustible gases in the air to oxidize more rapidly, raising the temperature to a degree that alerts the detector.