Nitrogen, that colorless, odorless gas that makes up 80
percent of our air, is perfectly harmless as it's breathed in
and out on land, but for underwater divers, it's the enemy.
Pressures exerted by water are formidable, each 30 feet in depth is
equal to an added atmosphere of pressure, about 14 pounds per
square inch. At high pressure, nitrogen is dissolved in the blood
and tissues very easily and the deeper a diver goes and the longer
they stay down, the more nitrogen is absorbed. Absorb too much
nitrogen and it actually becomes toxic, causing a very dangerous
condition known as nitrogen narcosis.
But more important is how the nitrogen comes out of solution in
the body as a diver returns to the surface. If there is too much
dissolved nitrogen in the body, or pressure is reduced too quickly,
the gas can begin to form bubbles, causing a host of problems
collectively known as decompression sickness. That's where bubble
science comes into play and where Los Alamos National Laboratory
physicist and master diver Bruce Wienke goes to work.
"I became interested in diving procedures, training and safety during
my time in special warfare in the 1960s," said 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."
How deep a diver can go, and how long they can stay at a given
depth, are the cardinal rules of diving. Recreational sport divers use
standard Self Contained Underwater Breathing Apparatus, or SCUBA
equipment, to generally do what are known as non-decompression
dives, meaning they only go as deep and stay as long is allowed to
keep their nitrogen levels below the danger zone. SCUBA allows a
diver to carry along a supply of compressed air that is delivered
through a regulator system.
Technical, research, commercial and military divers usually go deeper
and stay longer than sport divers, so they must slowly decompress
while returning to the surface and usually do not breathe regular
compressed air but a gas mixture that replaces most of the nitrogen
with helium. All these divers sometimes use systems called
rebreathers, allowing divers to recycle their breathing gases and
regulate the pressures at which the gases are delivered.
Both sport- and technical-diving parameters have long been based on a dive table developed around
1908 and refined through the years by the U.S.Navy. The table, known as the Haldane Table, named
for John S.Haldane, its developer, governs not only how long and deep a diver may go but also how
many decompression stops must be made on the way back up and at what depth they are made. For
instance, a diver who goes to 250 feet and stays there for an hour will have to spend five hours
conducting decompression stops at various depths.
Wienke of Applied Physics Division, Materials Science Group, has developed a new dive algorithm
based on the physics of bubble formation that is setting the diving community, both sport and
technical, on its ear. The table, known as the Reduced Gradient Bubble Model, or RGBM, is already
used in commercial diving and has applications in sport, cave, military and virtually every other
diving situation. Wienke's research is in collaboration with the University of Rochester; the
University of Trondheim, Norway; the National Aeronautics and Space Administration; the
University of Wisconsin; and the University of Hawaii.
The benefits of the RGBM are that divers can go deeper, stay longer and spend less time decompressing than with the Haldane Table. Why? It's all about how bubbles are created.
"Bubbles begin as micronuclei, or tiny seed bubbles," said Wienke. "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.
"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."
Bubbles in the blood, tissue or nervous system cause a host of problems. Growing bubbles in joints,
the spinal column or brain can
cause mechanical pressure, nerve
damage and severe pain. Bubbles
in the blood can grow large
enough to block blood flow,
which in turn causes localized
oxygen starvation and can trigger
an immune system-like response
to attack the blockage.
Keeping nitrogen and helium
bubbles from forming is the goal of
both the Haldane Table and
RGBM. The advantages of RGBM
stem from its use of various diving
gas mixtures, the most common are called trimix, heliox, and nitrox and a different approach to
determining the depth and timing of decompression stops
"Because of the physics of bubble formation and gas transfer, we
determined that the staged decompression would start deeper, and
the stops would not last as long as those called for in Haldane," said
Wienke." Plus we have the diver switching from mixed gas to pure
oxygen on the shallowest decompression stops. These two factors
can literally shave hours off of a typical decompression time."
The impact of RGBM has been huge in the commercial and
technical diving communities and is now having a similar effect
with sport diving, according to Wienke.
"It's a revolution," he said. "The algorithm is being built into dive
computers and tables for the general consumer and has been adopted
as the official model for the National Association of Underwater
Instructors, one of the leading dive-training organizations."
A big part of the reason for RGBM's acceptance is Wienke's diving
experience. Wienke has logged more than 3,000 hours under water as
deep as 400 feet and in locations all over the world, from under the
ice of the arctic to the tropic waters of the South Pacific. Author of
five technical diving books including "Basic Decompression Theory
and Application," and "Basic Diving Physics and Application,"
Wienke credits RGBM's success to a common diving language.
"In the diving community, I'm not just a physicist, I'm a diver, too," he said. "I and many others have been diving using the RGBM table
under a wide variety of conditions, so I have a connection to the
technical divers, we speak the same language. So, it 's not only the
research but the diving experience as well that confirms the value
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