hydrogen sulphide gas

Refinery Life: "hydrogen sulphide gas"
When inhaled in doses of more than 100 parts-per-million hydrogen sulfide attacks the respiratory system, killing you in a matter of seconds. If you are lucky, the concentration is only half that, and causes what oil and gas workers call a "knockdown," that makes unprotected well operators who stumble into leaks instantly collapse from the toxicity. Routine, lower-level exposure causes neurological damage including memory loss, headaches and dizziness and reproductive disorders like miscarriages and birth defects, and -- depending on whom you ask -- cancer.
http://www.corpwatch.org/article.php?id=10328