Hydrogen sulfide

[Belmont]

I read this about diving in the hydrogen sulfide layer in Palau's Jellyfish Lake:

"The hydrogen sulfide in the anoxic layer is a serious risk to scuba divers entering this layer. The gas can be absorbed through the skin. In 1977, the maximum safe threshold level for hydrogen sulfide was set at 10 ppm.[20] The concentrations exceed that by eightfold at the bottom of the anoxic layer. However, the hydrogen sulfide concentration down to the chemocline at about 15 metres (49 ft) is reported to be zero, and if the anoxic layer is avoided, the hydrogen sulfide in the lake does not pose a risk for snorkelers. "

Now, what about Cenote Angelita in Mexico, there is no mention or warning of any danger there??

 

[Instructor_Tom]

I dive the hydrogen sulfide layer at Hospital Hole from time to time assisting with AOW classes. The only ill effect is the rotten egg smell and the effect it has on my brass clips.

Students love the site in the winter because we have some very friendly manatees that like to hold hands and get there bellies rubbed.


T.

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[TSandM]

I have actually wondered about this, myself. H2S is a fairly potent poison, and CAN be absorbed through the skin, but most exposures on land involve breathing the gas. In those cases, the poison has access to the tremendous surface area for gas exchange which is the lung. My guess is that the reason divers seem to tolerate the H2S in places like Angelita is that, first off, most of them is covered, including the eyes (which are an early site of irritation when in contact with that gas). And secondly, since a regulator is used, the gas is only able to exchange through dry skin, which is a relatively poor absorber of anything. I HAVE heard of people getting nauseated and even vomiting when diving in caves where there is a lot of H2S present -- Claire Pooley wrote a very vivid account of having to be more or less dragged out of a cave in MX because of GI symptoms, and one of the possible causes there was hydrogen sulfide.

 

[kelemvor]

Interesting post! Planning a dive at Hospital Hole in the next few weeks and I had not yet looked up the details on the hydrogen sulfide.

Tom, do you dive wet at hospital hole?

 

[Belmont]

I've felt some tingling on the lips last time at Angelita. The layer there was about six feet deep and I was told not to linger in it, even diving in a dry suit.

Any chemist here who can tell us if the H2S concentration could vary depending on the environment?

 

[Instructor_Tom]

Interesting post! Planning a dive at Hospital Hole in the next few weeks and I had not yet looked up the details on the hydrogen sulfide.

Tom, do you dive wet at hospital hole?

I've been wet and dry in the hole several times and only had issues once when the hydrogen sulfide was really thick and i spent a bunch of time in the cloud looking for a student who fail to follow the dive plan.

I ended up with discomfort and dryness in my sinuses and with redness on my face ( kind of like wind burn).

Lips do tingle if you stay in the cloud too long, but no serious issues. So long as the weather is cold hospital hole is a fun dive to hang out with manatees.


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