From: dwilkins@orion.polaristel.net (Don Wilkins)
Newsgroups: sci.chem
Subject: Re: H2S - safety
Date: Tue, 27 Aug 1996 10:52:46 GMT

On 26 Aug 1996 12:22:09 GMT, ev890@cleveland.Freenet.Edu (Dr. Hector
L. Casal) wrote:

>I will be working with H2S(g) at a concentration
>of 91% in nitrogen.
>
>I would appreciate any comments regarding safety
>issues.

You have not revealed the quantities you will use but you should keep
in mind the following.

1. H2S is toxic. Excessive exposure will paralyze the breathing
muscles which of course can be fatal.

2. At low levels the characteristic odor announces its presence.

3. At higher levels (10 ppm give or take a few ppm) the sense of smell
is unable to detect H2S. It as this point that H2S becomes extremely
dangerous and treacherous. There is no warning of excessive exposure.
The victim simply collapses into an unconscious state. Unless
appropriate action is taken death is a frequent result.

4. It is possible to revive the victim by artificial respiration but
it is also possible to quickly join the victim in a state of
unconsciousness and death. Cases are known where several "rescuers"
without proper breathing apparatus have participated in cost saving
joint funerals for multiple victims. Collection of the bodies is not
difficult because they are usually in one pile near the source of the
H2S and the first victim.

5. Appropriate breathing apparatus and safety precautions are
essential. 

6. Never ever work alone when the possibility of dangerous exposure
exists.

7. Do have some knowledgeable person review your experimental setup
AND LISTEN to their recommendations. I couldn't emphasize this last
comment more because if you needed to ask this question then it is
obvious that you shouldn't be working with anything more than trivial
amounts of H2S without some assistance and supervision.

8. Since your address suggests an educational institution do keep in
mind that students look to people who like to attach "Dr." to their
name and email address as persons of authority and knowledge. If
students are involved please read item 7 several more times as these
students are not in a position to know if the "Dr." knows what he is
getting them into or if the "Dr." even understands the problems
associated with the experiments.

Our "container" was loaded with 85 tons of H2S. Our safety rules were
strictly enforced with immediate dismissal for violations. Trivial
quantities may require more modest safety precautions but do not treat
H2S exposure lightly.

From: dwilkins@orion.polaristel.net (Don Wilkins)
Newsgroups: sci.chem
Subject: Re: H2S more poisonous than HCN?
Date: Tue, 12 Nov 1996 15:49:10 GMT

On Mon, 11 Nov 96 12:59:05 GMT, tim_blackmore@notes.ipl.ca (Tim
Blackmore) wrote:

>In article <565cen$8bv@dfw-ixnews7.ix.netcom.com>,
>   Alan \"Uncle Al\" Schwartz <uncleal0@ix.netcom.com> wrote:
>>bpc@netcom.com (Benjamin P. Carter) wrote:
>>>A chemistry instructor said that H2S is relatively safe only because it
>>>smells so bad, but that a lethal dose of H2S is actually smaller than
>>>a lethal dose of HCN.  Is that true?

NO see below. 

>>HCN does not have a particularly strong smell, and ii specifically takes 
>>out aerobic respiration - the only energy source of your heart and your 
>>brain. The rest of your body can get by with fermentation (which makes 
>>for a rosy-cheeked corpse and an aesthetically poor death).  LD50 (30 
>>minutes inhalation murine) = 169 ppm;  544 ppm kills in 5 minutes.
>>
>>H2S has a powerful odor in small quantities, though it is reputed to have 
>>a sweet smell in lethal doses.  It is a blood and enzyme poison.  LD50 
>>(60 minutes inhalation murine) = 634  ppm 

I have never heard of a "sweet smell" my info says you can't smell it
at high concentrations.

>It's possible that the documentation that I have read is incorrect.
>However, everything that I have read suggests that at about 1000 ppm,
>death is more or less instantaneous (immediate l.o.c. and stoppage of
>respiration). At 500 ppm , it was said that l.o.c would occur within half
>of an hour with respiratory paralysis immediately thereafter. The main
>reason that people say H2S is more dangerous is that you can smell it
>initially and then the smell will "go away" as you sense of smell is
>desensitized. Even if the concentration goes up by an order of magnitude
>you will not smell it any longer, so you may feel safe because it "went
>away".

I think the main reason that H2S is more dangerous is because there is
no warning that you are in trouble.

At about 10 ppm of H2S most people quickly lose the sense of smell. At
lethal levels H2S simply paralyzes the breathing muscles and the
victim goes unconscious without warning from a lack of oxygen. Death
is caused by the fact that the victim stopped breathing. Artificial
respiration is quite effective in reviving the victim with no apparent
damage providing that brain damage did not occur because the victim
stopped breathing for too long.

At one time the company which I worked for was operating a heavy water
production facility using the H2S exchange to concentrate D2O. The
safety rules were strict. We had many tons of the stuff under high
pressure. Employees and visitors were required to go through an
extensive training session before entering the production area. You
were required to work in pairs and not work side by side. Instructions
were that if your "buddy" showed any sign of trouble you put on your
portable respiration gear immediately and then investigated the
problem. Reminds me of the oxygen mask procedure on airlines for
putting your mask on first then the child. Visitors always were
accompanied by two employees even though the visitor had taken the
training course.

The tragedy of finding a pile consisting of the original victim and a
bunch of "rescuers" where these rules were not followed have been
noted in the literature and is the reason the rules were so strict.
Violations could result in immediate dismissal.	

HCN on the other hand will give you ample warning that you inhaled
something which you shouldn't. It also can cause damage which is not
as easily corrected as an H2S knock down.

Any chemistry instructor who says that H2S is relatively safe
shouldn't be a chemistry instructor.