a post on the old randi forum now called internationalskeptics
Car battery H2S warning if your battery is inside the vehicle. - Page 2 - International Skeptics Forum
by catsmate
''Unlikely, the effects are different; carbon monoxide causes suffocation by bonding with hemoglobin while hydrogen sulphide is broad-spectrum poison that mainly effects the nervous system. It also corrodes metals like copper leaving a noticeable clue for investigators.
Hydrogen sulphide is far more toxic; a few minutes exposure to 500ppm is around 50% lethal (as well as causing severe eye irritation and some permanent damage; it'll also not be noticeable as the olfactory nerve is rapidly paralysed by exposure to concentrations over 100ppm), while a human can breathe 1,200ppm carbon monoxide for more than an hour with little danger of death and even 2,000ppm wouldn't cause 50% fatalities.
1,000ppm hydrogen sulphide will incapacitate in seconds and cause rapid death; it is actually more dangerous than hydrogen cyanide.''