How to detect harmful gases? What are the methods?

The gas detector can detect various gases such as hydrogen sulfide, carbon monoxide, oxygen, sulfur dioxide, phosphine, ammonia, nitrogen dioxide, hydrogen cyanide, chlorine, chlorine dioxide, ozone, combustible gas, etc., and is widely used for on-site detection in petrochemical, coal, metallurgical, chemical, municipal gas, environmental monitoring and other places. Can meet the measurement requirements of special occasions; It can detect gas concentration or leakage in tunnels, pipelines, storage tanks and confined spaces.