Types of Fire Detectors

Smoke Detectors

• Smoke detectors sense smoke by one of two methods. Photoelectric smoke detectors sense smoke in the chamber by means of a light beam shining through it into a light-sensitive photocell. Photoelectric detectors work best in detecting smoldering fires. Ionization smoke detectors ionize air molecules as they enter the chamber. Electrical current flows between two plates inside the chamber. Once products of combustion, or smoke, enter the chamber, they connect to the ions and cause an interruption in the current. Ionizing detectors work better for flaming fires. Use both detectors in conjunction with each other, or purchase a newer, combination detector, which combines the technologies.

Flame Detectors

• Flame detectors, also known as light detectors, come in one of three types — ultraviolet light detectors, infrared light detectors or combination detectors. These detectors, true to their name, detect high levels of light that may indicate a fire. Due to their potential sensitivity to sunlight or activities like welding, flame detectors should only be used in enclosed areas or those not often exposed to the type of light they detect.

Heat Detectors

• Both fixed-temperature and rate-of-rise heat detectors sense heat in excess of what it should be, often a reliable indicator of fire. Fixed-temperature detectors sense heat over a specific set temperature. They are inexpensive, but if the ambient temperature in a room is low, they can take some time to detect the high heat of a fire. Alternatively, rate-of-rise detectors sense when the temperature in a room raises more than a set number of degrees within a specific amount of time. They are reliable, but placement too close to an exterior door may cause false activations due to temperature fluctuations.

Fire-gas Detectors

• Fire-gas detectors sense the presence of gases commonly produced by fire. Although the gases produced depend on the fire's fuel, they may include carbon dioxide, carbon monoxide, hydrogen cyanide, hydrogen sulfide and hydrogen fluoride. General fire-gas detectors monitor only carbon monoxide and carbon dioxide levels, but variations can be set to detect those chemicals likely to be put off in fires in specific environments. Not many fire-gas detectors are used in comparison to the other fire detectors.