Gas sensor technologies for fire detection

Abstract

The physical mechanisms of spreading of smoke and gas during a fire event must not be necessarily the same. Due to the heat smoke particles are more likely transported by convection with a minor contribution of diffusion effects whereas gas is transported by both convection and presumably with a higher fraction of diffusion. In order to investigate these differences we selected a variety of gas sensors and placed them at different positions in a fire test room. Gas sensitive field effect transistor (GasFET)-arrays, metal oxide sensors (MOS) and electrochemical cells (ECs) were used for gas measurements in test fire scenarios. Beside the investigation of the performance of the sensor elements itself, we additionally focused our investigations on the propagation behavior of different aerosol and gas components of standardized (EN54) test fires in time and space. We mounted different gas sensors on PCBs which were setup into different vertical “multi-sensor” chains representing a measurement grid in space. The metal oxide sensors showed the fastest response whereas the GasFET-array was responding slower but shows advantages with respect to low-power consumption and pattern recognition capabilities. The EC carbon monoxide sensor has a good selectivity but a high price comparing to semiconductors. We observed that smoke aerosols mainly stay beneath the ceiling whereas the fire related gases also are transported in regions below the ceiling and near to the floor. As a very surprising and promising result we observed that gases also diffuse through heat layers which may occur during fires right below the ceiling and which smoke particles are not able to pass through and thus are not able to enter into the detector to reach the optical measurement chamber. In our case CO reached the gas sensors over 4 min earlier before any smoke could be detected by optical smoke detectors.