Hypothetical overexpansion question

[Jake]

Hopefully this is the right place for this, and hopefully I'm not asking a dumb and/or frequently repeated question.

I'm going to be working on my Rescue Diver certification and have been talking to various people about it. In relation to rescuing someone, someone brought up the female free diver who died a few years ago while going for a new depth limit. One of the issues was that even though there was a safety diver to assist, he could not give her air at 150 or more meters because it would cause an instant and fatal overexpansion (explosion might be more appropriate).

The question was ultimately put to me in a different way, however. Suppose someone were removing gear at the surface for whatever reason and was not handling the situation correctly. They lose their gear and it starts heading to the bottom. Would there be any danger to the diver if they dove after it, and at a fairly shallow depth (let's say above 35 feet) decided to take a breath from the rig? In this case they are heading down with surface pressurized air and possibly breathing it at two atmospheres.

It would seem to me that at this depth there is no risk of harm: the demand valve can deliver gas at a safe pressure relative to the compression state of your lungs, which is not the case at a significant depth.

Anyone care to comment? Obviously, this would be a dumb situation and I hope nobody's dumb enough to get into it, but the hypothetical portion of it still stands.

Thanks!

 

[radinator]

The account I read of her death said that she did not go for the safety diver when she encountered the malfunction, but the reason was unknown. That was what she should have done. According to the article that was the plan if there was a problem.

I have swam down on breath hold to my gear on the bottom in 33 feet of water as part of a drill in a class. My scuba unit, mask and weight belt were all on the bottom - all I had were my fins. It's not a problem to grab the reg and breath from it.

Keep in mind that as you are heading down, you are not "heading down with surface pressurized air". As you head down your lungs are contracting, and the pressure of the air in your lungs is the same as the external pressure. That is because your lungs are a flexible container. In other words, your lungs are a balloon, not a tank. So by the time you get to 33 feet, that surface air in your lungs is at 2 atm, your lungs are just compressed in size. Then, when you breath from the reg, you are breathing in air at 2 atm and since there is now more air the lungs can expand in size as you inhale.

 

[DA Aquamaster]

For practical purposes providing air to a concious freediver at depth is not a problem as long as they know enough to vent the air as they ascend like a diver would do in an ESA.