Hydrogen selenide is an
inorganic compound with the formula H
2Se. It is the simplest (and virtually the only)
hydride of
selenium. H
2Se is a colorless, flammable gas under standard conditions. It is
the most toxic selenium compound with an exposure limit of 0.05
ppm over an 8 hour period. Even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or 'leaking gas', but smells of rotten eggs at higher concentrations.