Hydrogen sulfide

Hydrogen Sulfide, chemical symbol H2S, is a colorless, toxic, and flammable gaseous chemical compound responsible for the foul odor of rotten eggs and flatulence.

When the Engineers resort to anaerobic digestion for food, bacteria in its anaerobic sacs convert the organic material to energy. This process gives off trace amounts of hydrogen sulfide.

List of appearances

 * Halo: Contact Harvest
 * Halo 3: ODST