The toxic gas with the smell of rotten eggs is hydrogen sulfide.

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1. Hydrogen sulfide is a flammable acid gas under standard conditions, colorless, and smells like rotten eggs at low concentrations, and it smells like sulfur at extremely low concentrations and is highly toxic (LC5 = 444 ppm <: 5ppm）。 Its aqueous solution is hydrogen sulfuric acid. According to the genetic mechanism of hydrogen sulfide, hydrogen sulfide in nature can be divided into five genetic types: biodegradation, microbial sulfate reduction, thermochemical decomposition, sulfate thermochemical reduction and magmatic genesis.

2. Hydrogen sulfide is flammable and hazardous. When it is mixed with air, it can form an explosive mixture, which will cause combustion and explosion when it meets open flame and high heat. Hydrogen sulfide is an important chemical raw material. Hydrogen sulfide is not uncommon in daily life. When workers dig sewers or septic tanks, they also produce hydrogen sulfide.

3. Hydrogen sulfide comes from protein and is a weakly acidic water-soluble substance when some chemical reactions decompose. It can be dissolved in water, burned or precipitated. Hydrogen sulfide is easily ignited under normal conditions. When the concentration of hydrogen sulfide is very low, it will give off the smell of rotten eggs. When the concentration is high, because the olfactory system is paralyzed, it has no taste.

4. Hydrogen sulfide is an inorganic compound. Under standard conditions, it is a flammable acid gas, colorless. It smells like rotten eggs at low concentrations and sulfur at extremely low concentrations. The aqueous solution is hydrogen sulfuric acid, which is weak in acidity, weaker than carbonic acid, but stronger than boric acid. Soluble in water, soluble in alcohols, petroleum solvents and crude oil. Explosion limit: it will explode when mixed with air or oxygen in a proper proportion (4.3% ~ 46%).

5. Relative density of hydrogen sulfide: 1.189(15℃, .1133MPa). It exists in low-lying places, such as pits and basements. If you find yourself in a place where you are told that there is hydrogen sulfide, you should take self-protection measures immediately. Whenever possible, work in the upwind and higher ground. The operation site containing hydrogen sulfide gas should be equipped with hydrogen sulfide monitor.