Related Phrases: Lower Explosive Limit, LEL, Oxygen, O2, Hydrogen Sulfide, Hydrogen Sulphide, H2S, Carbon Monoxide, CO, Hydrogen Cyanide, HCN, Ammonia, NH3, Nitrogen Dioxide, NO2, Phosphine, PH3, Sulfur Dioxide, Sulphur Dioxide, SO2, Carbon Dioxide, CO2