Flame Detectors Watch the Radiation Bands a Fire Uniquely Emits
A flame detector is an optical instrument aimed at a volume, not a device waiting for smoke to reach it, so it responds in milliseconds to seconds and works outdoors and in high-airflow spaces where smoke never accumulates. Ultraviolet detectors watch a band near 185 to 260 nanometres where flames emit and sunlight at ground level does not. Infrared detectors watch the strong carbon dioxide emission near 4.3 micrometres produced by any hydrocarbon flame, and often look for the characteristic flicker of a flame at a few hertz. Neither alone is dependable: welding arcs and lightning trigger ultraviolet, while hot machinery, sun glint off water and moving vehicle exhausts trigger single-band infrared. Triple-infrared designs solve this by measuring three bands and requiring the ratio between them to match a flame rather than a hot object, and multi-spectrum devices add ultraviolet to the same logic. The confusion worth clearing is that a flame detector cannot see a smouldering fire at all, because there is no flame emitting in those bands. After this Concept you can pick a detector band set for a hazard and name the false sources it will still see.
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A flame detector is an optical instrument aimed at a volume, not a device waiting for smoke to reach it, so it responds in milliseconds to seconds and works outdoors and in high-airflow spaces where smoke never accumulates. Ultraviolet detectors watch a band near 185 to 260 nanometres where flames emit and sunlight at ground level does not. Infrared detectors watch the strong carbon dioxide emission near 4.3 micrometres produced by any hydrocarbon flame, and often look for the characteristic flicker of a flame at a few hertz. Neither alone is dependable: welding arcs and lightning trigger ultraviolet, while hot machinery, sun glint off water and moving vehicle exhausts trigger single-band infrared. Triple-infrared designs solve this by measuring three bands and requiring the ratio between them to match a flame rather than a hot object, and multi-spectrum devices add ultraviolet to the same logic. The confusion worth clearing is that a flame detector cannot see a smouldering fire at all, because there is no flame emitting in those bands. After this Concept you can pick a detector band set for a hazard and name the false sources it will still see.
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