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Questions and Answers on
Physiology and Medical Aspects of Scuba Diving


Lawrence Martin, M.D. Copyright 1997


Buy the book
Scuba quiz
Myths & Misconceptions
Disclaimer & Invitation

Brief History of Diving
Recreational  Diving
The Respiratory System
Explanation of Pressure

Water & Physical Laws
Unequal Air Pressures
Decompression Sickness
Oxygen Therapy
Gas Pressure at Depth

Dive Tables & Computers
Stress & Diving
Non-air Gas Mixtures
Women & Diving
Medical Fitness for Diving
Asthma & Diving
The Great Debate

All About DAN
Scuba Training Agencies
Magazines & Newsletters
Books & Videos

Diving Odds N' Ends

Internet Links


But Is Recreational Scuba Diving Safe? The Great Debate


Is scuba diving safe? Anyone who has read Scuba Diving Explained to this point would be justified in replying: "What a dumb question!" You, the reader, have reviewed the potential diving complications of DCS and AGE, and examined the controversy surrounding diving with diabetes, asthma and other conditions. It should be clear by now that apart from the bends and gas embolism, divers also risk running out of air or drowning in other ways. You also know that each year there are a small number of diving accidents and deaths among the millions of people who participate in recreational scuba diving. In short, you know the question belies a simple 'yes' or 'no' reply, and that the answer greatly depends on what the question really means, what the questioner is really asking. Safe compared to what? To never diving? To sitting on a couch? To playing golf? To mountain climbing? To jumping out of an airplane? To driving a car on the freeway?

So why do I bother asking the question? My reason is that the question as simplistic as it may be is asked all the time, by many people, and it almost always elicits a heated debate. Simplistic, perhaps, but it is not a dumb question.

Like the debate on many other difficult-to-answer questions, this one seems to be 90% over semantics and personal philosophy (e.g., What do you mean by "safe"?), and only 10% about hard data (e.g., accident rates in scuba vs. other activities). As a result, participants often end up talking at cross purposes. Consider the following portion of an on-line conversation about the safety of scuba diving.

Diver A: Scuba diving is SAFE, and we shouldn't go around teaching otherwise.

Diver B: If you check your dictionary, you'll see that the definition of safe is ". . . without risk." Diving is not without risk.

Diver C: Excuse me, but SAFE and RISK FREE do not have the same meaning. Diving is safe, but it is not risk free.

Diver A: Just what I said, diving is safe. You should not tell students starting a course that diving is unsafe, since that is not true.

Diver B: How can you say it's safe, when there are risks? We are obligated to explain the risks involved.

Diver A: Yes, but there are risks in everything we do in life, including just sitting still or sleeping. Take driving, for example. Diving is certainly safer than driving a car.

Diver B: Where are your data that show diving is safer?

Diver A: I don't have any, but diving must be safer considering all the people killed on the roads each year. Driving is definitely not safe.

Diver C: I don't know, you guys seem to be locked in a semantic struggle not over an activity, but over a word.

This is not idle chit chat, since the debaters are all instructors who teach scuba, and who can be expected to impart their feelings to open water students. Whether or not semantics is a factor, we must acknowledge important differences of opinion, and realize that the opinions and attitudes of the most experienced will affect newcomers to scuba diving.

In the mid 1990s the scuba diving safety debate even extended to concern about long-term, sub-clinical problems, i.e., bubble-related disease that might be found only with magnetic resonance imaging (MRI) of the brain and spinal cord. Researchers in Germany published an article in the respected British journal Lancet, titled "Central nervous system lesions and cervical disc herniations in amateur divers" (Reul 1995). Fifty-two amateur divers (at least 40 dives per year for 4 years) were compared with 55 athletic non-divers.

The divers had more abnormal "bright spots" on their MRI scans than the non-divers. In addition, the divers had much more degenerated intervertebral disc disease than the non-divers. The authors postulated that the abnormalities were due to silent bubble formation occluding small blood vessels (without causing symptoms; only one diver had any history of decompression sickness). Unexplainedly, there was no statistically significant correlation between occurrence of bright spots and years of diving experience, or with the number, mean duration or depth of the dives.

Despite the study's lack of correlation with diving depth or intensity, it was picked up by the lay press and widely publicized, prompting more debate and concern on the safety issue. Unfortunately, the study was far from convincing in its conclusions. While the study raised the question of silent bubble damage, it certainly did not provide a satisfactory answer. Letters to Lancet (Wilmshurst 1995; Hovens 1995; Rogers 1995) pointed out some of the study's major weaknesses (such as the way the two groups were selected). An official response by Divers Alert Network also pointed out the study's faults and sought to assure divers (DAN 1996). To quote from DAN's response:

The supposition of any damage to the brain rests on the occurrence of so called silent bubbles occurring in the blood or brain and spinal cord. That such bubbles do exist has been well demonstrated by Doppler technology in blood and tissue studies of animals' spinal cords. Whether or not, however, these silent bubbles are the cause of changes in the brain is unproved. . . .Divers should not be unduly concerned about [the Lancet study]. More research is needed, but the world is filled with many divers who have been diving for over 40 years who show no unusual deterioration in their abilities which would affect their quality of life. . . .Certainly, [the study's] results should not be discounted. However, in the absence of neurological decompression illness, many other studies in which divers were compared with non-divers, have failed to demonstrate that diving causes long-term neurological impairment or any functional abnormalities.

Debate about safety has been going on since the sport of scuba diving began and will likely continue as long as people dive, perhaps because the sport attracts such a diverse group of people. In fact, anyone who attempts to answer the question "Is Scuba Diving Safe?" will probably have a particular bias, whether it is commercial, academic, medical, political or otherwise. For example, a manufacturer of scuba gear (always wishing to sell merchandise) might respond YES to the question, and then qualify the answer with "proper training and high quality equipment are required for safe diving."

A training agency (always seeking to gain new members) might also respond YES but emphasize that one must be in good health to enter their training program.

A physician experienced in treating dive accident victims, and seeking to prevent more, might respond NO, scuba is not safe and that "you dive at your own risk." So might an accident victim or a victim's family respond to this question.

A politician seeking to prevent scuba diving accidents in his district (and the attendant bad publicity) might respond NO, not without further legislation he is currently proposing.

A non-profit agency like DAN might respond with neither YES nor NO, but instead emphasize the importance of continuing research to understand the nature and causes of diving accidents, and on how to make the sport safer.

And I might respond with: "Read my book!" That's not an entirely fair response, however. I may have provided you enough information in the preceding sections to form your own opinion, but I have not really provided any direct, specific answer of my own. So my answer to the question is provided in the following paragraphs.

Is Recreational Scuba Diving Safe?

Lawrence Martin, M.D.

Scuba diving subjects people to altered ambient pressures. These changes in pressure create the risk of developing two important problems, decompression sickness and arterial gas embolism. In addition, being in or under the water presents the possibility of drowning from pressure-related problems or from other causes, such as running out of air or a panic attack. However, in the context of millions of recreational dives a year, the incidence of diving accidents and deaths is considered very small.

The comprehensive data collecting methods of Divers Alert Network assure that most, if not all, scuba diving deaths and serious accidents are reported to it. According to DAN, about 100 North Americans die while scuba diving each year (in 1995, 104 deaths; DAN 1997). A large percentage of these deaths occurred in people who somehow exceeded recreational guidelines, such as: diving deeper or longer than called for by dive tables; entering overhead environments without proper training or equipment; diving with medical illnesses which should have prohibited the dive.

In addition, DAN receives notice of approximately a thousand non-fatal diving injuries each year, and reports on those that contain sufficient information for diagnosing a true scuba diving accident (in 1995, 590 cases; DAN 1997). Most of these are cases in which the diver was ill enough to require referral to a hyperbaric chamber facility.

Based on this information, scuba diving must be considered to present a finite, albeit small, risk to those who participate. Comparing the amount of risk with other outdoor sports (e.g., mountain climbing, snow skiing, bicycle riding) is difficult, if not impossible, for two reasons: 1) the number of people actually participating in any popular sport is unknown, as is the frequency of their activity; and, 2) the nature of accidents varies from sport to sport, and any given injury can affect the victim to a varying (and unpredictable) degree. For example, breaking a leg on the ski slopes or suffering a concussion while bike riding cannot be meaningfully compared with a non-fatal case of the bends.

Similarly, comparing risks of scuba diving with essential but risky activities like driving a car is also difficult, since the number of miles driven, the type of driving, etc., are all unknown variables.

Anyone engaging in scuba diving must accept that the sport presents certain risks that would not otherwise be present (though another sport might present a different set of risks). Accepting this fact, the diver should understand that risks can be significantly minimized by such common sense steps as obtaining proper training, diving in good health, staying physically fit, adhering to established dive tables, and not participating in dives that exceed the limits of the individual's training.

In summary, for the vast majority of participants, recreational scuba diving seems to be a very safe activity. For the vast majority, recreational diving has been, and will continue to be, accident-free. However, as in any sport that carries inherent risks whether it is bicycling, mountain climbing, snow skiing, kayaking, football, or a myriad others accidents will continue to happen to a small number of participants.

It is up to the individual, through proper training and diving common sense, to minimize the risks to himself or herself. Taking everything into consideration, a wholly satisfactory answer to this question can only be provided by the individual diver, based on his or her own expectations and frame of reference.


Annual Report on Diving Accidents & Facilities, Divers Alert Network, Box 3823, Duke University Medical Center, Durham, NC 27710; 1997.

DAN responds to Lancet Article - Long-term consequences of diving. The Journal of Underwater Education, Fall 1996, pages 27-28.

Hovens MMC, Riet G, Visser GH. Long term adverse affects of scuba diving (letter to the editor) The Lancet 1995;346:384.

Reul J, Weis J, Jung A, Willmes K, Thron A. Central system lesions and cervical disc herniations in amateur divers. The Lancet 1995;345:1403-1405.

Rogers G. Long term adverse affects of scuba diving (letter to the editor) The Lancet 1995;346:385.

Wilmshurst P, Edge CJ, Bryson P. Long term adverse affects of scuba diving (letter to the editor) The Lancet 1995;346:384.

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