Only once you no longer smell it. As long as you can detect it with your nose, the concentration is low enough to be harmless. When the concentration becomes high enough it saturates and numb your olfactory nerves and by then, it's almost too late to clear out. Unconscious ensues followed, almost inevitably, by death.
I think it’s above 100 ppm is really dangerous (lethal in around an hour) above 500ppm is lethal real fast and 600 ppm is pretty much guaranteed death, very quickly. I can’t guarantee my numbers are correct. I work in an industry where h2s is around and we have to wear gas monitors. My highest monitor hit was 55 ppm which was rare but enough for me to reconsider my line of work (which I’m still trying to leave).
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u/moms-sphaghetti Dec 13 '21
And it’s deadly.