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April 2019    Download the Entire Issue (PDF) Available to the Public Vol. 45, No. 4   RSS Feed for Undercurrent Issues
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Technical Diving: Is It For You?

“nobody had any problems using air at 180 feet”

from the April, 2019 issue of Undercurrent   Subscribe Now

As you just read in the previous travel article, our undercover diver writes of the dives on Truk Lagoon wrecks as technical dives; however, all but one of those is totally possible for a recreational diver to do while breathing either air or nitrox from a single tank.

To visit the deepest San Francisco Maru, which sits at 205 feet, may be daunting for some, but others manage it, merely by taking adequate supplies of air with them and being prepared to wait for a bit, depending on how much decompression time they've clocked up, at 20 feet before finally making for the surface. (Or you can simply check out the top deck, at 165 feet, or the tops of the two masts, which stand at the 105 foot-mark, and you'll keep out of deco that way).

Those divers who visited the 180-feet deep wrecks of Bikini Atoll in the Marshall Islands with Bikini Atoll Divers learned to use air for the main part of the dive, then swap to nitrox 80 at 30 feet on the way up to speed up decompression procedures (a procedure devised for Bikini Atoll by Tom Mount, a cave diving pioneer and CEO of the International Association Of Nitrox and Technical Divers). It's not rocket science but it demands that a diver starts off with enough air to do the deep part.

For many basic open water divers, it's a new experience but Fabio Amaral, who ran Bikini Atoll Divers for years, says all his participants seemed to manage it easily. "It was impossible to get supplies of helium in Bikini, so everyone dived on air, speeding up decompression by breathing nitrox 80, supplied by hookah on the decompression trapeze.

With no currents within the lagoon, it was easy for all divers to find their way back to the trapeze hung under the boat."

In Amaral's time there, he only had one suspected case of decompression sickness. "A gentleman from California, who complained of mild shoulder pain. I found out he was not hydrating -- at least not with water, unless you count two bottles of wine a day as hydration. He was not drinking that much in front of us, but privately in his room. I ran the Australian in-water recompression schedule on him with 100 percent oxygen, and he reacted well. As we were still unsure of the DCS, I asked one of his mates to email me if he felt pain on the flight back to Majuro, which was on the unpressurized Dornier 229, and if he did, he should contact DAN and get treated once back in Hawaii."

Then there was another guest who, out of nowhere, had a psychotic episode underwater and put another diver's life at risk. "He had a severe case of bipolar psychosis and had not taken his meds, so he had to be restrained and evacuated from Bikini," says Amaral. "I was not happy with his dive group leader, needless to say."

Otherwise, nobody had any problems using air at 180 feet. "I was a despot as far as safety was concerned, and didn't allow the use of those dive computers I felt were unsafe."

There's nothing really technical about diving with two tanks. If you think making a deco stop on the way up makes the dive technical, then a majority of European divers are technical divers. With so many computers available that easily allow a diver to track what happens when swapping nitrox mixes during a dive, the dive becomes straightforward. It's really just a matter of how you carry that second tank and its regulator, or whether you also have two tanks connected with a manifold so that you can breathe the entire contents of both with the same regulator.

Of course, some people suffer nitrogen narcosis in depths shallower than 100 feet (see our article on that in last month's issue), so training in the use of a breathing gas containing some helium -- a trimix of gases -- might be advantageous. That results in a mix with less oxygen and nitrogen, with helium making up the difference. It's hypoxic in the shallows and should not be breathed.

This means carrying a gas for traveling down to depth, a suitable gas mix to use at that depth, and a third tank of a rich nitrox mix to speed up decompression times. That's three tanks, and often the bottom gas is contained in doubles. A disciplined regime needs to be adopted to avoid tank mix-up accidents, as people have suffered the fatal results of breathing from the wrong tank at the depth they were at.

Helium is often vaunted as a wonderful gas in that it has no adverse effect on a diver's nervous system, which prevents narcosis, but it usually adds to the length of decompression stops. It's also incredibly expensive, thus leading most trimix divers to inevitably move on to closed-circuit rebreathers, which are very frugal with the amount of gas breathed.

My wife (who only has a PADI Rescue Diver certification) and I have made many deco dives using two nitrox mixes and clearly distinguished regulators. She takes a cheap paperback to read during longer deco stops.

Most open water divers are locked into the idea of using a single mix of nitrox or air in a solitary tank. But if you want to go deeper than 100 feet and can't handle the narcosis you might get from a breathing mix with nitrogen in it, then take a technical diving course with any of the dive training agencies, who now do them regularly, and learn about using helium.

-- John Bantin

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