All three workers were killed by sulfureted hydrogen while clearing a sewage well.
A weak smell of sulphuretted hydrogen and sometimes chlorine gas is noting at Severo-Kurilsk.
It is known that hydrogen sulphide or sulphuretted hydrogen is a foul-smelling, toxic, inflammable, corrosive and explosive gas.
When the level of the sulfureted hydrogen is low, it smells like rotten eggs; when its level becomes higher, we cannot smell the gas because our sensory nerves will have been numbed.
Allow the precipitate to subside; add to it, with the aid of heat, nitric acid until no sulphuretted hydrogen is given off.