Sorry to correct you muffin but one of my back grounds is oilfield safety. 8 ppm is ohs standards is 8 hour exposure limit, at 50 ppm you lose senses ie. Smell, taste , and motor functions start to limit. At 100 to 150 if you are unable to have breathing aid scba etc available death or severe brain damage is likely. Im not trying to be a know it all person just rather educate people from my experience as i have witnessed h2s poisoning and i tell you its frieghtning having to save one who thought it was ok to breath in 20 ppm for 10 mins while he fixed his scba pack. But you are right be scared of h2s by the time you realize it its to late.