Just out of curiosity, I am assuming that you were using heliox or trimix blends that yielded a partial pressure of oxygen of 1.4AtA or less. My guess is trimix blends due to HPNS. With such mixes, did your firm ever calculate at what equivalent air depth would the breathing gas density be the same? For example, at a depth of 970', you might use a mix of 4/96 heliox or a trimix blend yielding an equivalent narcotic depth of 130' or so. Due to the decreased gas density would it be the same as if you were breathing air at 150' or shallower? I've always wondered if there is a commercial diving software program that can give a gas density/depth equivalent. One ballpark figure that I have heard thrown about is that a reg delivering air at 200' breathes about the same as delivering mix at 600'.Phil wrote:Just to put this all in a little more phyical context, in 1972, we (Oceaneering) used a venturi-modified Scubapro Mk2 fed by a redesigned Scubapro 1st stage - diver doing hard hard work - at 970 feet and got good ventilation. Three years later, we used the same set-up at the U of Pennsylvania at depths approaching 2000 feet with similar results.
The reg was used in our standard 'RatHat' -with mouthpiece inside the helmet (and, most importantly, the 2nd stage diaphragm inside the helmet!) We used these rigs between 1966 and about 1986 and logged many tens of thousands of gas dives deeper than 100 meters. At the high point of that period, we operated in 25 countries and employed more than two thousand commercial divers!
It was a helluva run, but by 1980 we could already hear the whirring of the ROV propellors!
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