Flame Detectors

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UV detectors respond to hydrogen fires, but IR detectors don’t.

Due to their fast detection capabilities, flame detectors are generally used only in high-

hazard areas, such as fuel-loading platforms.

UV Flame Detectors

• A UV flame radiates in the 1850 to 2450 angstrom range. (or 185 to 245 nm)

• Virtually all fire emit radiation in this band, while the sun's radiation at this band is absorbed by the Earth's atmosphere. (remember the ozone layer)

• UV detector is solar blind, so won’t have false alarm due to sun.

• Can be used indoors or outdoors.• UV detectors are sensitive to most fires, including

hydrocarbon, metals, sulfur, hydrogen, hydrazine, and ammonia.

• They detect flames at high speed (3-4 milliseconds) due to the UV high-energy radiation emitted by fires and explosions at the instant of their ignition.

IR Flame Detectors

• An infrared (IR) detector basically is composed of a filter used to screen out unwanted wavelengths and focus only on IR.

• Main problem is false alarm from radiation of the sun. If inside and shielded from the sun, then works well. Good for bank vaults.

• IR detectors are sensitive to most hydrocarbon fires (liquid, gases and solids).

• IR detectors respond in less than 50 msec.• IR detectors are less affected by smoke, oil, and

certain gases and vapors than UV Detectors.

UV/IR Flame Detector

• An ultraviolet/infrared flame detector consists of an UV and single-frequency IF sensor, paired together to form one unit.

• A fire alarm is produced only when both sensors detect a fire.

• Better false alarm rejection• UV and IR spectral band detectors compare the

threshold signal in two spectral ranges and their ratio to each other to confirm the reliability of the fire signal.

IR3 Flame Detectors

• IR3 or triple IR spectral band detectors compare three specific wavelength bands within the IR spectral region.

• Mathematical techniques are used to correlate the three bands to discriminate between fire and false alarm.