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David Bradley ISSUE #17
July 2001

Diver down

Diver???
Next time you are sipping on a glass of champagne or a frothy pint of beer, think of the diver physicists who study deep diving...

...but, don't think it is an academic task. The physics underlying bubble formation in the human body during deep, undersea dives has helped Los Alamos National Laboratory physicists devise a new system of dive tables that should make life much safer for divers.

Nitrogen, the colorless, odorless gas seems innocuous, after all it makes up about 80% of the air those of us on dry land breathe. For a diver though it's a deadly gas. At deep-sea pressures, nitrogen readily dissolves in the blood and tissues and the deeper a diver goes and the longer his dive, the more nitrogen is absorbed. A good thing on dry land becomes a poison at depth, due to nitrogen narcosis?

Then there is the "bends." The bends, or decompression sickness, occurs as that dissolved nitrogen comes back out of solution as a diver surfaces. If the diver has absorbed too much nitrogen or surfaces too quickly, bubbles of nitrogen form causing various problems, difficulty breathing, joint pain and even death when bubbles form in the heart or cerebrospinal tissues. "I became interested in diving procedures, training and safety during my time in special warfare in the 1960s," says LANL scientist Bruce Wienke, "and later, as a physicist, I became convinced that a realistic biophysical model that would increase the safety of deep diving could be created based on the physics of bubble formation."

Technical, research, commercial and military divers typically often go far deeper than SCUBA divers and although they use gas mixtures that contain helium to replace most of the nitrogen and prevent nitrogen narcosis, there is a risk of helium bubbles causing decompression sickness. Wienke has now come up with a new dive algorithm, based on the physics of bubble formation that tells divers how they should come back to the surface to reduce the risk of decompression sickness.

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Bruce Wienke
The benefits of the new system, which is already being used technically and commercially, are that divers can go deeper, stay longer and spend less time decompressing than with the original Haldane diver's tables. The answer lies in the way tiny seed bubbles, or micronuclei, lead to bubble formation. "Micronuclei can be stable for up to two hours and can be coaxed into becoming bubbles by a variety of stimuli, like surface friction from muscle tissues rubbing together, called tribonucleation," he explains. "If a newly forming bubble encounters high concentrations of inert gas, such as nitrogen or helium, in solution at high pressure, the lower pressure inside the bubble will cause the gas to diffuse into the bubble and it will grow," he adds. By studying the properties of the various gas mixes used in diving Wienke was able to see that stopping earlier in a diver's ascent would ultimately reduce the overall decompression time needed for a safe return to the surface. He also found that divers switching to pure oxygen on the shallowest decompression stop could shave hours from the decompression time.

"'Statistics gathered over many thousands of deep, deco, and mixed gas exposures in the past three years underscore the efficacy of the dual phase model developed - no reported decompression illness (DCI)," Wienke told Reactive Reports.

Click here to learn more about Wienke's tables.