Flame detectors activate in response to what three products of combustion?

• A. Ultraviolet (UV), Infrared (IR), and Combination UV-IR
• B. Visible light
• C. Water vapor
• D. Carbon monoxide

Answer: (A)

Flame detectors respond to radiant energy emitted by a flame, focusing on specific parts of the spectrum where flame radiation is strongest. The main signals come from ultraviolet light and infrared light. Ultraviolet detectors respond to the brief, intense UV radiation produced by flame chemistry, while infrared detectors pick up the heat radiation from the hot combustion gases. Some detectors are designed to sense both UV and IR, and these combination units verify flame presence by requiring signals in both bands, which helps reduce false alarms from non-fire sources. Visible light isn’t a reliable trigger for these detectors because it can come from many non-fire sources and is often obscured by smoke or glass, and water vapor or carbon monoxide are products of combustion but don’t provide the characteristic spectral signature these sensors rely on. So the three products of combustion a flame detector uses are ultraviolet radiation, infrared radiation, and a combination UV-IR signal.