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On Tue, 7 Mar 1995 wei@cs*.fs*.ed* wrote:

> A friend of mine is writing a paper on diving in hydrogen sulfide and he
> asked me if I can tell him any information on the issue.  The only thing I
> know about hydrogen sulfide is it tastes horrible and you need a
> non-leaking drysuit to dive in them.  Can someone supply some more
> information on the subject?  

1. A wetsuit is fine. 
2. A standard regulator may kill you, but with a rebreather you may be 
able to do it safely.

Some other points:

1. H2S is substantially heavier than water and does not mix with water 
unless disturbed by something like a diver's movement through it. 

2. When H2S mixes with oxygenated water, hydrosulfuric acid results.

3. There is generally a substantial layer of deoxygenated water between the 
H2S and oxygenated H2O, and in most cases, the dissolved oxygen (DO) in 
that bottom layer is so small that the acid resulting from the H2S/H2O 
mixture is quite weak.

4. H2S is absorbed readily by the human body, much like carbon monoxide (CO).

5. H2S does not affect the body like CO in that it does not produce fatigue.

6. When the human body reaches its overload point with H2S, the pulmonary 
system shuts down; at that point, it doesn't matter how much air you have 
your tanks or how good your buddy is at rescue.

7. The danger of diving in H2S in a normal regulator is that every time you 
exhale, a small amount of the surrounding fluid (droplets) enter into the 
air chamber of the second stage. Those droplets are "atomized" and 
inhaled at the next draw of breath.

8. H2S is odorless, since the diver has a mask on, closing off the sense of 
smell. The only way a diver will "smell" the H2S is if the diver has a 
faulty second stage that lets in excessive ambient fluid -- that is, too 
much to be atomized, and the diver gets a "taste" of the water. This 
happened to me once while I was in H2S, and I can tell you that the taste 
of sulfur is overwhelming. Unless you routinely exhale through your nose 
while you dive, you won't taste it even under those circumstances.

9. H2S is often, though not always, pitch black. When it is black in that 
uniquely H2S way, it absorbs light; a fully charged UK-1200 penetrates 
only about 18 inches.

10. It is the chemical/mineral nature of the bottom and the bottom's 
uninterrupted stillness that allow H2S to form and stay in solution. 
Distance from the surface is not a constant. I have seen H2S in 30 feet 
of water as well as in 90 feet of water.

11. There is generally a veritable soup of filamentous bacteria in the 
layer of deoxygenated water above the H2S. If the diver has a strong 
light, these bacteria can be easily seen as complex strings of 
transparent material. Get out of there as soon as you see them unless 
you're wearing a rebreather or some other closed circuit regulator.

FWIW

John H-C

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