Hydrogen sulfide is a colorless gas that is irritating and asphyxiating. Low concentrations only cause local irritation to the respiratory tract and eyes, while high concentrations cause more obvious systemic effects, manifested as central nervous system symptoms and asphyxiation symptoms. Hydrogen sulfide has a "rotten egg-like" odor, but extremely high concentrations quickly cause olfactory fatigue and the smell is no longer noticeable. Hydrogen sulfide is produced in mining, smelting, beet sugar production, the manufacture of carbon disulfide, organophosphorus pesticides, as well as in the leather, sulfur dyes, pigments, and animal glue industries. Large amounts of hydrogen sulfide can escape when working in places where organic matter decays, such as swamps, sewers, septic tanks, and sewage sedimentation tanks, and it is not uncommon for workers to be poisoned.