PH3, or phosphine, is a chemical compound made up of one phosphorus atom and three hydrogen atoms. It is a colorless gas with a distinct, unpleasant odor similar to that of rotten fish. PH3 is primarily used in the semiconductor industry and as a fumigant for stored grains and other agricultural products. In terms of safety, phosphine is highly toxic and can be dangerous if inhaled. It is classified as a flammable gas and can form explosive mixtures in the air. Proper handling and storage are essential to prevent accidents and ensure safety when working with PH3.