Hydrogen Sulfide is a toxic, colorless gas that is invisible, explosive, flammable, heavier than air and a leading cause of fatalities in the oil and gas and petrochemical industries. It is formed when organic material decomposes. At low concentrations, it has an offensive odor of rotten eggs. At high concentrations, it deadens your sense of smell. It is corrosive to metals having two active protons making it acidic in nature. It combines with iron to form iron sulfides which are often pyrophoric and can be the cause of fires in processing and storage equipment.