Fixed toxic gas detectors (7/03/2003)... SO2, H2, NH3, CL2, NO, NO2, O3, HF and many other common toxic gasses, while semi-conductor sensors are used for methylene chloride, toluene, xylene, trichloroethylene and a range of refrigerant gasses such as R11, 12, 22, 23 and R143A, etc.A ...