This Gastec detector tube is used for detecting the presence of Hydrogen Sulfide (H₂S) gas in air. The tube is specifically labeled No. 4LL and has a detection range from 0.25 to 120 parts per million (ppm). It is designed for quick and accurate gas testing, providing real-time measurements to assess potential H₂S concentrations. The Gastec detector tubes are widely used in environmental monitoring, safety testing, and industrial applications where the presence of hydrogen sulfide gas needs to be detected.