It takes 4 times as much cyanide to kill you as it does hydrogen sulfide.
The first thing that happens after you smell H2S, is that it begins to anesthetize your sense of smell for it. That's why they call it "sneaky gas" in the oil fields.
Lethal concentrations will only be detectable by smell for a few seconds.
38 posted on 01/01/2002 8:41:55 AM PST by mfulstone