Hydrogen Sulfide Layer

[BioDiver]

I have never thought of this and found the topic quite interesting, so I did a little investigation and inquired with our local experts. I could not find any definite answers but did get some interesting responses. It sounds like H2S gas in water and its affects on divers has not been looked at. Here is what I found:

Hydrogen sulfide can accumulate in lakes if all oxygen is consumed, which can happen in the hypolimnion during the summer, or under ice in the winter, if there is organic matter for bacteria to utilize, and low dissolved iron (which precipitates H2S as it forms, to form insoluble iron sulfide compounds). 

We can’t find any evidence that there is a health hazard, but it is certainly not good for you.

You can also search the web; I found the following:

which recommends that you minimize exposure to H2S when diving.

H2S will bond with some metals, and may discolor some metal parts on your equipment.  The discoloration may be reversible upon exposure to oxygen, when the sulfide becomes sulfate.  That reaction also produces some sulfuric acid, which probably would not be very much, but could conceivably slightly etch metal surfaces. 

Good luck,

Edward Swain, Ph.D.

Research Scientist
Minnesota Pollution Control Agency
520 Lafayette Road
Saint Paul, MN 55155-4194
edward.swain@pca.state.mn.us
voice: 651-296-7800
fax:    651-297-8324 (shared)

and:

I can't come up with much information.  First, I believe the question is about dermal toxicity.  It is unlikely that H2S would have systemic effects (from dermal exposure) before there is noticeable irritation and burning of the skin - but I'm thinking of H2S in air - not in water where the chemical may act totally different.  In anoxic water it may not be as irritating to the skin - - and who knows how easily it can penetrate skin?  From a chemistry perspective I'm not sure if the skin irritation from H2S gas is caused by H2S or by the formation of acid that may occur when it is hydrated...  I don't think there is much information out there... I'd focus on experiences of other divers in waters known to contain high concentrations of H2S.  Would these be lakes in more temperate climates???  I don't think you'll find much tox data - except possibly as anecdotal information in diving literature.  Sorry I'm not much help.

Carl Herbrandson, Ph.D.
Toxicologist, Minnesota Department of Health
625 Robert St N
St. Paul, MN
carl.herbrandson@health.state.mn.us
651-201-4906
Adjunct Assistant Professor
School of Public Health
University of Minnesota

So, I would surmise that spending the little time dropping through these small layers is not going to do much to us or our equipment diving on purely a recreational, even a very active recreational level. Another question I would have is in the Crosby pits, or any other iron ore pit used for diving, is with a high level of dissolved iron is there actually any H2S gas that stays in solution long enough to do us harm? Or does it precipitate as Dr. Swain suggests?