Abstract: The invention relates to combustible gas detectors of the kink in which a heatable wire filament exhibits a change in resistance due to a change in its temperature caused by the oxidation of a combustible gas passing over it. In order to avoid poisoning the heatable wire filament is embedded in a pellet consisting of a homogeneous mixture of an oxidation catalyst material and zeolite material the latter preferbly of type X, Y, L or mordenite of large pore size. Additionally layers of catalytically active material and/or inactive non-catalytic porous material may be provided around the outside of the pellet.

Abstract: The invention provides a combustible gas detector in which a heatable wire filament embedded in a pellet comprising oxidation catalyst material exhibits a change in resistance occasioned by the change in its temperature which occurs due to the oxidation of a combustible gas passing over it.The pellet is provided with an outer layer of inert non-catalytic material which tends to prevent non-volatile residues from reaching catalytically active regions of the detector.