The sensor most commonly used for detecting firedamp (methane) and measuring its concentradon in mines is the catalytic sensor, which costs less than an infra-red detector. The convendonal catalytic sensor has two component parts - a detecting element and a compensating element - enclosed in a flameproof reaction chamber. The detector is a filament encased in a pellet of composite material, made up of alumina mixed with powdered metal (palladium or platinum) which acts as an oxidadon catalyst.