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TLV and STEL of H2S is 10ppm and 15ppm, for SO2 it is 2ppm and 5ppm! But H2S is considered more toxic than SO2. Why?
09/12/2015 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
Because perceptions can be wrong!
It also depends on how you look at it.
SO2 is at least as toxic as H2S.
Having said this, short and long term exposure are different things.
TLV is the long term acceptable exposure limit, considering toxicity.
200-300 ppmv of H2S will paralyses nerves and as such kill a person in 3 minutes.
TLV and STEL don't tell the entire story.