Water and waste-water processing facilities use physical, chemical and biological processes to produce healty drinking water and create a clean waste stream that can safely return to the environment. Typically chlorine or chlorine dioxide is used for pre-treatment, and hydrogen sulfide, methane and a host of other toxic and combustible gases are present during effluent post-treatment. Safegas detector is highly reliable, easy to use and cost-effective solution for any combination of target gases.