What are the risks, really?

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What are the risks, really?

August 17, 2012 - 17:59
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Experience of life suggests that anything which is fun tends to be either illegal, immoral, fattening or dangerous. Recreational diving partly conforms to this universal law, ranking below hang gliding and parachuting but above most sports in regards to the risk of a fatal accident.

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Statistical evidence

Diving statistics from the United States, United Kingdom, Canada and Japan all show diving death rates of 15–30 per 100,000 divers per year, with the statistical chance of a fatality being about 2-3 per 100,000 dives. These figures tend to contradict the misinformation issuing from some sections of the diving industry (fatalities of < 4 per 100,000 divers) which would have us believe that diving is a very safe recreation. It is not, but then we accept risks every day.

Even driving an automobile to a dive site carries an appreciable (but much less) risk of death—a possibility which we generally regard with equanimity. This article will show that many diving deaths should be preventable and that a diver ought to be able to minimise his or her chances of becoming a statistic by understanding and influencing the factors which are now known to be associated with diving deaths.

Dying with weightbelt on

The information presented here is mainly based on data gathered by valuable studies involving recreational diving fatalities. They have been conducted in different countries, but show strikingly similar results. The U.S. recreational diving deaths, originally compiled by John McAniff of the University of Rhode Island and then NUADC, are now collected and reported on by DAN, which recently analysed 947 open circuit scuba divers. The DAN survey also included technical divers, who dive deeper, longer and with gases other than compressed air. The BSAC do a similar job in the United Kingdom, and DAN-AP Diver Fatality Project is the Australian compiler. Unfortunately, significant data is frequently not available, and so relevant causal factors are often underestimated. Another Australian approach (the ANZ series of diving fatalities) was to select and analyse only the accidents in which sufficient data was available to make the analysis credible, and to determine what factors materially contributed to the fatality. Most of our statistics come from this source and are rounded up, for simplicity.

Diving Fatality Data

• 90% died with their weight belt on
• 86% were alone when they died
• 50% did not inflate their buoyancy vest
• 25% encountered their difficulty first on the surface, 50% actually died on the surface
• 10% were under training when they died
• 10% were advised that they were medically unfit to dive
• 5% were cave diving
• 1% of “rescuers” became a victim

Age

The recorded deaths range from children (pre-teens) to septuagenarians. Some decades ago the average age of the deceased was in the early 20’s. Then there developed a small increase in the middle ages (45-60 years). This bimodal curve has now become distorted on the other side, and the average scuba death age is now 43 years. The reasons for this increasing age of death are:

• The “youngsters” from the 1970-80 scuba diving boom are now older.
• Cardiac disease, the sudden death syndrome, affects the elderly and diving introduces more cardiac hazards than many other sporting activities.
• Diving is becoming a lifestyle option for the increasingly active and affluent elderly, with more older people taking up this sport.

Gender

In the 1990s, one in ten of the fatalities were women. The actual percentage of women in the overall diving population was about one in three, suggesting that women are safer divers than men. Even now females account for only 20 percent of the deaths.

Diving experience

In most series, one-third were inexperienced, one-third had moderate experience and one-third had considerable experience. The most dangerous dives were the first dive and the first open water dive. In half the cases the victim, based on witness statements and previously logged dives, was extending his diving experience (depth, duration, environment, equipment etc.) and thus did not have the experience to undertake the final dive. For this reason, any diver extending any of his dive parameters (depths, durations, environments, equipment) is advised to do this only with more experienced supervisors.

Major causes of death identified at autopsy

According to death certificates, most divers ultimately drowned (over 80%), but a number of factors usually combined to incapacitate the diver before this terminal event. Drowning is really only the final act in a sequence of events that lead up to this. It is a reflection of the medium in which the accident happens, more than the accident itself. Often it obscures the real cause of death.

Unless there are other factors, drowning should never happen to a scuba diver, as the diver carries his/her own personal air supply with him! Drowning develops because of preceding problems, such as cardiac disease, pulmonary barotrauma, the stress disorders, unconsciousness from any cause, salt water aspiration, trauma, equipment difficulties or environmental hazards, etc.

Contributing factors

Deaths usually followed a combination of difficulties, which alone may have been survivable. The factors contributing to deaths are easier to understand when classified, and we have categorised them into the following groups:

In Part One of this series, we have a closer look at:
• Diving techniques (inadequate air supply, buoyancy, buddy system)
• Human factors (medical, physiological, psychological)

In Part Two, we have a closer look at:
• Equipment factors (misuse, faults)
• Environmental factors

Diving Technique —Inadequate Air Supply

In the ANZ survey in half the deaths (56%), critical events developed when the diver was either running low or was out-of-air (LOA, OOA). When equipment was tested following death, few victims had an ample air supply remaining. The DAN survey found 41% in this situation. Most problems arose when the diver became aware of a low-on-air (LOA) situation. Some divers then died while trying to snorkel on the surface, attempting to conserve air (8%). Concern about a shortage of air presumably impairs the diver’s ability to cope with a second problem developing during the dive, or causes the diver to surface prematurely and in a stressed state of mind, where he/she is then unable to cope with surface conditions. In many cases the LOA diver faced these difficulties alone, as his/her buddy who had more air, continued the dive oblivious to the deteriorating situation (see later). LOA situations should be avoidable by adequate dive planning, using a cylinder with ample capacity for the planned dive, and frequent observation of the contents gauge. A particularly dangerous technique was to intentionally use all the available air (breathing the tank dry). Then there is much less opportunity to cope with unexpected eventualities and greater likelihood of emergency ascent and salt water aspiration. The dive should always be completed with at least 50 ATA remaining.

In some cases the diver was using a smaller cylinder than a 2000 litre (72 cu.ft) tank. A 1400 litre (50 cu.ft) cylinder has much less endurance than a conventional cylinder, and allows fewer breaths once a LOA situation develops at a significant depth. Also, a diver using a smaller cylinder will usually run out of air sooner, encouraging separation from his group.

Buoyancy

In the ANZ survey, half the diving victims (52%) encountered buoyancy problems. Most of these were due to inadequate buoyancy, but some (8%) had excessive buoyancy. The DAN survey buoyancy problems were the commonest adverse event leading to death. The buoyancy changes peculiar to wet suits were a significant factor. The considerable buoyancy offered by a wet suit at the surface needs to be compensated by weights. An approximate formula for this is:

• 1kg for each 1mm thickness,
• 1kg for “long john” extensions and a hood,
• 1kg for an aluminium tank,
• ± 1–2kg for individual body variations in buoyancy.

Based on the above formula, 40% of divers who perished were found to be grossly overweighted at the surface. This factor would have been greater at depth. When weighted according to this formula, a diver should be neutrally buoyant at or near the surface. In this state, descent or ascent are equally easy. During descent, the wet suit becomes compressed, making the diver negatively buoyant. This is where the buoyancy compensator (BC) comes in. It is inflated just sufficiently to restore neutral buoyancy. This is why it is called a buoyancy compensator.

Evidently, some divers deliberately overweighted on the surface, using this excess weight to descend more easily and were then using the BC to maintain depth and then later to return to the surface. This places excessive reliance on the BC This dangerous practice is unfortunately promoted by some instructors. It has advantages from a commercial point of view, as it expedites training. Groups of divers can be quickly taught to descend with minimum skill. The technique is less advantageous in terms of longevity of the diver. In another fatality survey on buddied divers who ran into LOA/OOA situations, it was of interest that irrespective of who became OOA first, the overweighted diver was the one who died—at a 6:1 ratio, dealing with weights, buoyancy compensators, etc.

In spite of being heavily reliant on their BC’s, many divers then misused them. Examples of this include accidental inflation or over-inflation causing rocket like ascents (“Polaris missile effect”), confusion between the inflation and dump valves, and inadequate or slow inflation due to being deep or LOA. The drag induced by the inflated BC (needed in many cases to offset the non-discarded weight belt) was a factor contributing to exhaustion in divers attempting to swim to safety on the surface.

There are other unpleasant consequences of buoyancy problems. The American Academy of Underwater Sciences, in a symposium in 1989, reported that half the cases of decompression sickness were related to loss of buoyancy control. After acquiring the initial open-water certificate, possibly the best course to undertake would be on buoyancy control.

Ditching of weights

This was omitted by most victims (90%). Not ditching the weightbelt, compelled them to swim towards safety carrying many kilos of unnecessary weight, and made staying on the surface very difficult in these cases. This critical and avoidable factor should be easily remedied by restoring the traditional weight belt ditching drills.

Earlier diving instructors taught that the weight belt was the last item put on, the first taken off. It was to be removed and held at arm’s length in the event of a potential problem. The diver then had the option of voluntarily dropping the belt if the situation deteriorated,

Originally published

on page 57

X-Ray Mag #40

February 13, 2011 - 20:47
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