Chlorine

Chlorine (Cl₂) is a yellow-green gas with a strong, suffocating odor detectable at very low concentrations (0.5 ppm). Chlorine is widely used for water and wastewater treatment, swimming pool sanitation, chemical manufacturing, and bleaching processes. While essential for public health through water disinfection, chlorine is highly toxic and was historically used as a chemical weapon. OSHA PEL is 1 ppm ceiling with IDLH at 10 ppm—one of the most stringent exposure limits. Chlorine attacks the respiratory system, causing pulmonary edema even at moderate exposures. Comprehensive detection and emergency response systems are required in water treatment plants, chemical storage areas, and any facility handling chlorine.