On Fri, 23 Apr 2004 15:34:27 -0500, Mark Lipton >
wrote:

>James Silverton wrote:
>
>
>> Hydrogen sulfide is actually more poisonous than hydrogen cyanide, I
>> believe. However, H2S poisoning can be reversed by artificial
>> repiration if applied quickly enough unlike cyanide.
>
>My, what a bunch of chem-geeks we are! ;-) You're correct about the
>toxicity of H2S vs. HCN, but HCN is slightly more toxic (LC50 in rats is
>169 ppm for 30 minutes for HCN, whereas is 713 ppm for 1 hr for H2S).
>The big difference is that the smell of hydrogen sulfide is intolerable
>at levels well below lethal (whereas some people can't smell hydrogen
>cyanide at its lethal concentration). Typically, the only way someone
>can be poisoned by H2S is when its concentration is gradually increased
>over a long period of time so that the person's sense of smell is
>desensitized by long exposure to H2S. Was your coworker simply ignoring
>the smell, or was it a sudden exposure that overwhelmed him?

I can recall two incidents where H2S exposure led to death. One was in
a textile mill in Alabama where a worker entered an area where H2S was
present and was overcome. Another worker went in to rescue him and was
also overcome. This sequence of events repeated itself until four or
five men died. The other was in West Texas where a valve on a high
pressure natural gas well failed. The natural gas contained some
concentration of H2S and two nearby residents breathed lethal
concentrations of H2S. I can recall generating H2S in a college
chemistry lab (by adding hydrochoric acid to FeS) and going home with
a headache. I doubt that is done anymore. In any case, H2S is nothing
to fool around with.

Some high pressure (20 Kpsi or so) natural gas deposits contain
significant concentrations of H2S. Because the volume of NG is so
great at STP, they are worth exploiting commercially. Sometimes it it
commercially worthwhile to process the H2S for the sulfur. The
alternative is to burn it off, which generates SO2, which causes
problems of its own.

Vino
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