By Dr. David Sawatzky
Every year approximately 100 people die in North America while diving, and another 100 die while diving in the rest of the world. Diving is a relatively high ‘risk’ activity. By that I mean there are many ways in which you can be injured while diving and many of these situations result in death.
That said, diving is also a very ‘safe’ activity, statistically, with only one fatality for every 200,000 dives made. As an individual diver you can reduce the probability that you will die while diving even further by knowing why divers die and actively making changes so that you are less likely to become one of those statistics. And, to keep diving in perspective, it’s far more likely that you’ll die while driving or riding in a car than that you will die while diving.
In April 2010, Divers Alert Network (DAN) hosted a two-and-a-half-day Diving Fatalities conference. Many of the statistics in this column are from that workshop. It is interesting to note that 40 percent of fatalities occurred during a period of buddy seperation and 14 percent occurred on planned solo dives. What this means depends on what percentage of time divers spend seperated from their buddies or diving solo. Unfortunately, we do not know these numbers.
Approximately half of all diving fatalities were among divers with fewer than 20 dives. Of note, only eight percent of these (four percent of all fatalities) occurred during training dives. This is a phenomenal statistic and clearly supports close supervision of all inexperienced divers. A dive club I have been a member of for many years, one of the few still training most of its own divers, strongly recommends new divers dive only with an experienced buddy for the first year.
Equipment failure and marine life injuries are extremely rare causes of death in divers. In a well trained and experienced diver, equipment failure should virtually never result in death.
In diving fatalities, there are usually three stages. First there is a triggering event, second there is a disabling or harmful event, and finally there is a disabling injury. A simple example will help make this clear. A new diver bumps his or her facemask and it floods (the triggering event). The diver panics and heads for the surface holding their breath (the disabling or harmful event). As a result they rupture their lungs and suffer arterial gas embolism (the disabling injury). As a result they can die as a result of the interruption of blood flow to the brain or they can drown from loss of consciousness.
Two of these stages can be influenced: we can reduce the likelihood of the triggering event and/or we can reduce the likelihood of the disabling or harmful event.
Divers Alert Network studied almost one thousand diving fatalities and they determined that the root cause of the triggering event was usually one of the following five factors:
- Some sort of pre-existing disease pathology in the diver.
- Poor buoyancy control.
- Rapid ascent or violent water movement.
- Gas-supply problems.
- Equipment problems.
The most common cause of a diving fatality is ‘drowning’ because the victim dies in the water. The more important question for divers is “why did he/she drown?” We’re curious, of course, but the answer helps as guard against the same fate!
When it’s possible to determine why a diver drowned, the most common cause is found to be heart attack. Sometimes it’s pure chance but most commonly it results from the exercise of diving, in a diver already compromised by significant coronary artery disease. The shift of blood from arms and legs into the chest, and the relative absence of gravity, that occurs when we enter the water can also be a factor – see my discussion on heart attacks in DIVER December 2005.
Clearly, having a heart attack while diving qualifies as ‘some sort of pre-existing disease pathology in the diver’, the first root cause of the triggering event. There are several simple things we can do to reduce our chances of having a heart attack and these fit in nicely with the recommendations from the DAN workshop.
We should maintain a healthy body weight. Fat people (BMI greater than 30) have a statistically increased risk of dying while diving.
We should never dive with uncontrolled health issues (elevated blood pressure or cholesterol, heart issues, lung issues, etc.). In diving medicine we teach that a person is either a ‘patient’ or a ‘diver’. If the former they need active medical attention for some health issue and they should not dive. Once their health issue is controlled, they should be evaluated to determine if diving is a reasonable activity for them.
Several of the other DAN workshop recommendations speak to this. They suggest to divers: “be honest with yourself, your instructor and your physician about health issues; educate yourself about health-risk factors like smoking and how they can impact your health for diving”.
That’s why you read my column in every issue of DIVER Magazine, right?
The workshop also recommended: “If you have symptoms of potentially impending health problems … do not dive until you have been checked by a physician”. I would add that the physician should know something about diving medicine. They also recommend that you consider the diving implications of any chronic medical conditions you might have.
The final way in which we can reduce our risk of having a heart attack while diving is to attain and maintain a reasonable exercise capacity for diving. As a rough guide, recreational divers should be fit enough to run a mile in less than 10 minutes (6.25 min/km), have a VO2 max of at least 35 ml/kg/min or be able to exercise at 10+ Mets. For technical/commercial divers I recommend being able to run a mile in less than 8 minutes (5 min/km), have a VO2 max of at least 45 ml/kg/min and be able to exercise at 13+ Mets. In addition, a diver needs enough muscle strength to safely carry and handle his/her gear.
There are two reasons this is really good advice. First it ensures that the diver has the required exercise capacity to dive safely and secondly it suggests that he/she does not have significant heart disease. Few people with significant heart disease could attain that level of fitness. That said, anyone over the age of 40 and anyone under 40 with a family history of heart disease should not start a vigorous exercise program until their family doctor gives the go-ahead.
AGE And Buoyancy
Next to heart attacks the most common reason divers die is arterial gas embolism (AGE). See Coughing While Diving DIVER May 2010 and Spontaneous Pneumothorax DIVER November 2007. Sometimes AGE is the result of lung disease (asthma, pneumonia, etc.) but most often the problem derives from a panic induced ascent holding the breath. All of the five root causes of the triggering event can result in arterial gas embolism.
Poor buoyancy control can also result in drowning, without AGE, and other problems. In fact, buoyancy control is the hardest diving skill to learn, and the easiest to forget. Diving occasionally over the last couple of years it always takes me two or three dives to reacquire the excellent buoyancy control I used to have as a cave, drysuit, rebreather diver. Buoyancy control problems nearly killed me once and were a major factor in the diving death of a good friend. It’s such a critical skill that I will devote my next column to the subject.
The DAN diving fatalities workshop also recommended that divers “follow established training guidelines”. Divers should know how to deal with entanglement problems and they should always carry “a sharp and functional cutting tool on every dive”. They should “learn to avoid uncontrolled ascents” and “practice out-of-air drills”. Over 500 divers have died in caves and therefore the following recommendation should be no surprise. “Never go into an overhead environment unless properly trained and equipped – not even a little way and not even with a guide”.
They also recommend that you “complete a skills refresher course at least once per year or more often if you lack confidence in the currency of your skills”. This becomes even more important if you have logged only a few dives or if it has been a long time since you last dived on a regular basis. Finally, “complete only dives that are well within both your fitness and your skill limitations”.
The bottom line is that dive fatalities are relatively uncommon, and the vast majority of them could have been avoided with a few simple precautions. I have been involved in quite a few diving fatality investigations. Lawsuits usually result from a lack of information and a belief that if something bad happens, it must be someone else’s fault. In most accidents almost always it is the victim who is at fault.
Keep fit, keep healthy, and dive within your limits to reduce your risk of dying while diving to an absolute minimum.
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