Many fire detectors are designed to detect a particular kind of fire. The most common are smoke sensors and heat detectors. Both sensors are triggered when smoke is in the room or when temperatures rise quickly. They also both sense the presence of a fire and will send an alarm signal to the alarm control panel.
Smoke Detectors
Smoke detectors are an essential part of a fire alarm system. Most local and state laws require them to be installed in every sleeping area and floor of your home.
Smoke detectors come in two primary categories. One type uses an ionization chamber that monitors “ions” or electrically charged particles.
This type of detector is best for detecting smoky fires. When particles of smoke enter the chamber, they change the electrical balance, triggering the detector’s horn to sound.
Another type of smoke detector is a photoelectric detector that relies on a light beam. When smoke interferes with the beam, it causes light to scatter and be picked up by the photocell.
Motion Detectors
Motion sensors are essential to most home security systems offered by fire alarm system companies. They are designed to detect unauthorized entry and can trigger lights or alarms to alert you to potential threats.
Active motion detectors illuminate a scene with laser light, ultrasound (sound waves pitched too high for the human ear to detect), or microwaves (radar). When these signals reflect from an object, the detector can monitor for rapid changes in wave energy or the Doppler shift. Some motion detectors combine multiple technologies in an attempt to reduce false alarms. Passive infrared sensors, for example, are often paired with microwave detection.
Heat Detectors
Heat detectors sense temperature changes and trigger an alarm if the heat rises to the pre-set value. Like an electrical fuse, a heat detector contains a eutectic alloy that turns from a solid to a liquid when the temperature rises.
The best type of heat detector depends on the type and location of your home or business. While ionization smoke detectors are better at seeing fast-burning flames, optical ones are best at spotting slow-smoldering fires.
Standard, fixed-temperature heat detectors respond to most fires but can suffer from thermal lag when fires build quickly. Rate-of-rise compensated fixed-temperature sensors can help speed up reaction times to fires that are starting to develop. They can also prevent false alarms due to rapid changes in ambient temperature.
Infrared Detectors
An infrared detector identifies the unique signature of a fire as it burns. These devices detect flames in industrial facilities such as refineries, fuel-loading platforms, and mines.
They are highly reliable in harsh environments where other detectors might be subject to spurious activation. They are cooled to low temperatures to increase their sensitivity to infrared radiation.
Infrared detectors use a mixture of metals to create a semiconductor within the sensor. These materials include mercury cadmium telluride (HgCdTe), indium antimonide (InSb) and indium gallium arsenide (InGaAs).
Gas Detectors
Gas detectors work with the fire alarm system by monitoring various gases. These can include oxygen, flammable gases and toxic gases.
These sensors monitor these dangerous gas levels using various sensing technologies, such as infrared point sensors, ultrasonic sensors and electrochemical gas sensors.
The most common type of sensor is the catalytic sensor, which detects combustible gases. This sensor works by detecting a change in the resistance of a wire as it comes into contact with a gas.
These detectors are a great tool for safety managers to keep tabs on hazardous gases in confined spaces and other dangerous environments. They also alert team members to unsafe conditions.
