ABSTRACT
This chapter describes the principles of operation and application of those instruments designed to detect the presence and measure the concentration of combustible gases and vapors on a continuous basis. Many physical and chemical methods have been exploited to detect combustible gases and vapors. The most commonly used combustible detectors are the catalytic filament units, which use a self-heated platinum wire as the catalytic surface that causes combustion. For each combustible gas or vapor, there is a particular mixture with air that contains just enough oxygen to sustain combustion. An important precaution in the operation of combustible detectors is to avoid propagation of flame when sampled air containing an explosive mixture of gas is ignited on the detector filament. In detecting the presence of such vapors or gases, their lower explosive limits are of interest, and in order to maintain safety, flammable gas and vapor concentrations are to be kept below those limits.
