Poisonous hydrogen Sulfide Gas!!!

Several times I've dove through sulfuric acid layers in deeper sink holes or caves. Some people tell me that they smell and feel this acid as they move through it, but I don't. The only evidence of it is the tarnish I see on all of my brass clips or perhaps I see a cloudy layer suspended that I move through. Yesterday I was reviewing the photos of Wes Skiles in the Abaco, Bahamas National Geo article and they captioned a photo "poisonous hydrogen sulfide gas is present. Divers move through it with all deliberate speed." Yet, the divers appear to me to have bare hands and exposed skin on the face. So my question is, what can it do to you; acid Burn skin, convulsed breathing? What preventive measures can be taken to protect exposed skin tissue: coat with Vaseline, or some other lotion? Certainly if one was to drink this stuff there would be serious problems, but just diving a short while in it, does it cause significant problems?
Has anyone on this board had really bad experiences with hydrogen sulfide in the water column?

funny you should ask. we scootered through hydrogen sulfide for a while this weekend. I didn't feel anything or have any reaction whatsoever. but buddy of mine has skin peeling off now :) kinda funny.

Hydrogen Sulfide (H2S) is a highly toxic gas than can be lethal, even at moderate exposure levels. It is often encountered in the Oil Industry and tends to collect in low areas since it is heavier than air. In the water, it forms a weak acid that is absorbed through the skin. My experience with H2S layers in sinkholes is that it makes my lips numb (and my gear turns black and stinks for a while). In theory, as long as you can still smell it, your exposure level is well below what is considered harmful.

Traversing an H2S layer in a sink hole or a cave usually should not be a significant cause for concern, but I wouldn't spend any more time than is necessary in the actual Hydrogen Sulfide.

Here are the recognized exposure limits (parts per million - gaseous form):

Less than 10 ppm has an exposure limit of 8 hours per day.
10–20 ppm is the borderline concentration for eye irritation.
50–100 ppm leads to eye damage.
At 100–150 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears.
320–530 ppm leads to pulmonary edema with the possibility of death.
530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing.
800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure (LC50).
Concentrations over 1000 ppm generally cause immediate collapse with loss of breathing, even after inhalation of a single breath.

You seem to be confusing two different compounds, hydrogen sulfide (H2S) and sulfuric acid (H2SO4).


edit: boydski beat me to it.

A lot depends on the concentration, and thickness of the layer. I have been through thin layers that were hardly noticeable, except for the smell, and visual distortion. I went through one thicker layer that made me feel a burning sensation on my skin. It rusted "stainless" steel parts on my regs, and rusted out the springs in my bolt snaps.

I've only noticed the annoying smell :(

I know of one case where a diver in one of the Mexican caves became ill with nausea and vomiting, following passing through a significant area of H2S. It was thought the chemical might have played a role in her illness. She had to be towed out from about 3000 feet in.

I will first say you all have an excellent handle on H2S and as far as diving goes you are the experts. I am a Safety Advisor who works in the oil industry and have spent quite a lot of time worrying about H2S gas and on occasion process streams containing liquid H2S, though people who work in paper mills definitely see more H2S than even the sourest oil fields. Best place to pull H2S data is MSDS I can dig one out if you would like to get your hands on one. The action level of h2s is 10 ppm at that level the in gas you need to be leaving immediately. At the level where you can smell it ~80ppm it destroys your ability to smell it and you face a some serious risks / problems. Usually, it doesn't sit at such low concentrations. H2s is usually non existent or pretty darn thick. As for getting it on skin or eyes I am pretty sure it calls for the 10-20 min of soapy water and see the doc immediately, especially if you have a bad reaction. I don't believe it infiltrates through the skin but I would be cautious of open wounds. Avoid at all costs inhalation, I am just thinking flooding your regulator might be a bad idea as a single breath can wipe you out and has caused quite a few confined space deaths. I would take the advice of the guys who have been in it before myself. H2S is highly flammable, even at very low percentages so avoid contact with oxygen rich environments o2 torch, o2 welding and o2 scarfing I don't know if you guys would ever bring an o2 bottle to the depth of H2S? It also has the ability to eat through metal like crazy I work with the chemicals, inspection and corrosion team so the gas and liquid is a real pain in the butt and dangerous for my friends. Hope it helps.

Is it generated from bio reactivity and high pressure in some of the caves?

I hate those layer when I'm on my rebreather.

One of my student try to clean is mask in that layer once... he remember it for long time.

Quote:

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Originally Posted by Attchoum

I hate those layer when I'm on my rebreather.

One of my student try to clean is mask in that layer once... he remember it for long time.

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I made the mistake of flooding my mask a few times in a tunnel with a sulfide layer. I couldn't see anything for a very hairy exit from about 3000'. it was a really bad day