Scuba diving risks: Predicting how bad the bends will be

Researchers have created a new model for predicting decompression sickness after deep-sea dives that not only estimates the risk, but how severe the symptoms are likely to be.

The US Navy Diving Manual may incorporate the model into its next update, as will commercial products intended to help recreational divers plan their ascents to avoid “the bends.”

The results appear online on March 15, 2017, in the journal PLOS ONE.

“The current guidelines only give you a probability as to whether or not decompression sickness is likely to happen after a given dive,” said Laurens Howle, professor of mechanical engineering and materials science at Duke, who has been working on these models with the Navy for a decade. “This is the first time we’ve been able to also address the likely severity of the potential sickness, helping divers determine acceptable risk.”

All risks have two components — the likelihood of something bad happening and just how bad that something is likely to be. Having a model that accurately provides both aspects will allow divers to better plan safe depths and ascents to help their bodies adjust — preventing painful and potentially fatal results.

Decompression sickness occurs when dissolved gasses such as nitrogen and helium come out of solution inside the body, forming dangerous, painful bubbles. This happens when divers ascend too quickly, and the pressure of gasses within various tissues exceeds that of the surrounding pressure.

“Getting the bends is not fun,” said Greg Murphy, a doctoral candidate in Howle’s laboratory, who has experienced the full severity spectrum of decompression sickness firsthand. “While I was diving in a salvage zone for the Navy, my anchor broke and I shot to the surface. On the ride to the hospital, I could barely breathe even with pure oxygen.”

No divers had to take such risks to gather data for the new model, as the Navy has a dataset of more than 3,000 simulated dives conducted in a carefully controlled hyperbaric chamber. Using that data, along with models of how gasses are absorbed and released by human tissue, Howle crunched the numbers to sort dives into six levels of potential severity.

Howle then divided the categories into a mild manifestation grouping (pain only) and a serious manifestation grouping (likely neurological or cardiopulmonary symptoms). He then assigned the same levels of acceptable risk currently used by the Navy to each. With a slight tweak to the definition of mild decompression sickness, the resulting model and boundaries of acceptable risk closely matched the practices already in place in the Navy, making it a useful predictive tool moving forward.

“Now that we have this model, we can use it to quickly and accurately predict the likelihood and severity of decompression sickness simultaneously to make decisions,” said Howle. “We’re also working to optimize the algorithm so that it could operate on a diver-worn computer so adjustments and new predictions could be made on the fly.”

Story Source:

Materials provided by Duke University. Original written by Ken Kingery. Note: Content may be edited for style and length.

Can You Really Get Bent After One Dive?


A: The short answer is: Yes, you can get decompression sickness with a single dive that stays within the “ no-decompression limits” on your computer. However, that answer deserves a detailed explanation. There are several standard variations of dive tables, all of which can be traced back to the early work of the British and U.S. navies. Different brands of computers are based on different tables, usually with some built-in proprietary “fudge factors.” Most dive computers are fairly safe when used as directed and under standard conditions.

Dive tables and therefore computers are based on theoretical models that have undergone limited formal testing. Additionally, the actual testing of those early dive tables was accomplished using healthy, young, male military divers. Several important points should be apparent here. Sometimes the body doesn’t entirely obey the theories of 19th- and 20th-century diving-physiology researchers. Recent decompression modelers have refined those original tables and created highly technical modifications, especially for mixed gas diving. It should also be apparent to most divers that we probably do not all have the anatomy and physiology of a 25-year-old military man.

The probability of DCS after a single, conservative dive that is well within no-decompression limits is almost, but not quite, zero. The risk increases if the diver pushes the limits; deep dives or long bottom times at a moderate depth certainly incur a higher risk. The greatest limiting factor for safe diving is the mindset and diving behavior of the diver.


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