THE CHARACTERIZATION OF SEMICONDUCTOR GAS SENSORS .2. A CRITICAL COMPARISON WITH RESPECT TO PRODUCTS OF COMBUSTION

The early and reliable detection of incipient or developing fires is a n essential aspect of safety in mines. Products of combustion (POC) re sulting from pyrolysis of materials commonly found in mines have long been recognized as an indicator of the onset of a fire. In particular, the gaseous POC are regarded as the most important fire signature bec ause they are produced during the early stages of the combustion proce ss. During the last decade, semiconductor gas sensors have been utiliz ed for detection of gaseous POC in British coal mines. In an earlier p aper the results were presented from the first two phases of a program me which aims to thoroughly characterize a wide variety of semiconduct or gas sensors. These studies produced data concerning the optimum pow er, sensitivity, ambient temperature and humidity dependence, and sele ctivity of these sensors. In the subsequent phase of this programme, t he responses of these sensors to POC of materials commonly encountered in mines, and which may be involved in a fire (e.g., coal, wood and P VC conveyor belts), have been studied in a purpose-built apparatus ove r the temperature range ambient-375-degrees-C.