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====Fire detection====
{{see also|Flame detector}}
In general, ultraviolet detectors use either a solid-state device, such as one based on [[silicon carbide]] or [[aluminium nitride]], or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by [[sunlight]] and [[artificial light]]. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the [[Infrared|IR]] region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some [[thermal radiation|radiation]] in the UVC band, whereas the [[Sun]]'s radiation at this band is absorbed by the [[Earth's atmosphere]]. The result is that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.

UV detectors are sensitive to most fires, including [[hydrocarbon]]s, metals, [[sulfur]], [[hydrogen]], [[hydrazine]], and [[ammonia]]. [[Arc welding]], electrical arcs, [[lightning]], [[X-ray]]s used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.