Hydrogen Sulfide layers in water

[Tamara Thomsen]

Because of several recent posts on this site I felt compelled to share my experiences with hydrogen sulfide layers. I don’t mean to scare anyone but here it goes: 

My first experience with hydrogen sulfide was working on a scientific expedition several years ago to the blue holes of the Bahamas.  The layer was thin- maybe 6 inches- and looked like a whispy cloud that was sandwiched at about 100 feet deep in between distinct layers of water coming from different water sources.  I was told not to dwell too long in or near the layer.  I quickly moved below the layer, conducted my assigned work and returned to the surface.  Upon surfacing, I noticed that all of the chrome was burned off of my regulator, the brass on my equipment clips was tarnished, and my soft gear retained an odor of rotten eggs.

The next site we visited had a thick, red layer of hydrogen sulfide of about a foot thick.  My assignment was to collect animals that lived and hunted near the layer, it was thought that several of these were breath holders and would live below the layer, but hunt above (and vice versa).  Spending more time near the layer dragging a plankton net, I noticed more prevalently the rotten egg smell and my exposed skin tingled quite a bit.  But by the end of the dive I didn’t notice the egg smell anymore.  I learned later that the nearest cousin (chemically speaking) is hydrogen cyanide a neurotoxin that is trans-dermal i.e. soaks in through your skin. 

After conducting these type of dives with varying exposures- some elongated dives on rebreather- for the duration of 2 weeks I noticed other effects.  Because of my prolonged exposure it was as if I had gotten an expensive chemical peel- most of the skin on my face and hands peeled away and my sense of smell was altered and had become very acute.  I would get out of the water and feel dizzy for several hours before recovering.

I found out later after talking to a friend in NEDU (Navy Experimental Diving Unit) that has done trials with this stuff, that over 25 ppt will affect a human nervous system in air, but in water there are little or no studies.  You actually stop smelling the rotten eggs after 10 ppt- but again this is in air- so who knows about in water!  So you can’t always rely on the smell as an indicator….

Hydrogen sulfide is formed not only because of decaying material or in swamps, but can also be the result of mining, and other industries.  Anyway, because of the mention of a possible hydrogen sulfide layer now at Devils Lake and the one that is below 135 feet in Fortune Pond, I thought that my experience would be of interest and help you decide how to plan for it. 

Safe diving....
Tami