How do combustible gas detectors work?

Combustible gas detectors measure flammable gases/vapors relative to their Lower Explosive Limit (LEL). Catalytic bead sensors have matched beads (active with catalyst, reference without) in Wheatstone bridge; combustion on active bead causes resistance change proportional to gas concentration. Infrared sensors measure absorption at hydrocarbon-specific wavelengths. Results expressed as %LEL (0-100% of explosive limit) or ppm for toxic detection. Used for leak detection, area monitoring, and safety interlocks in refineries, chemical plants, and confined spaces.