Pop quiz: An overweight diver in poor physical condition returns to diving after a hiatus of several years. He pulls his old gear off a shelf in the garage, hops on a dive boat and attempts to dive on a current-swept reef at 80 feet. Anxious and struggling for much of the dive, he burns through his air supply at an alarming rate. Upon discovering his tank is nearly empty, the startled diver makes a rapid, barely controlled ascent to the surface and suffers a fatal air embolism. What caused this accident?
You get an A if you answered "all of the above." As this scenario — a composite of the accidents found in one of the annual report of accidents and fatalities from the Divers Alert Network (DAN) — illustrates, fatal dive accidents often have multiple and complex root causes. Dr. Petar Denoble, DAN's research director, puts it this way: "While each accident may be different and some of them occur in an instant, most accidents can be represented as a chain of multiple events that lead to deadly outcome. Removing any link from that chain may change the outcome."
Based on a general look at dive fatalities around the world, there are four general contributing factors that can lead to fatal dive accidents.
Almost any pre-existing medical condition or health factor can affect a diver's safety. Common examples include obesity, heart disease, high blood pressure, breathing difficulties (temporary or chronic), a general lack of fitness, pre-existing injuries and dehydration. The biggest contributing factor involves divers with a body mass index in the overweight, obese or morbidly obese categories.
Today, diving is open to people with a host of medical conditions that a decade or so ago would have prohibited them from participating in the sport. However, if you have one of these conditions, it is important that you have your health regularly monitored and that you manage your medical situation properly. Treated and controlled high blood pressure, for example, may not create nearly the risk factors as uncontrolled high blood pressure.
Temporary health conditions like colds and severe allergies can also be problematic. Whether permanent or temporary, any health condition that impedes your ability to be alert, to recognize and respond to environmental conditions, and otherwise safely plan and complete a dive should contraindicate diving. Even after you recover from your illness or your chronic condition is back in check, your body needs time to recover from the effects of your medical complication. For example: Your cough may be gone, but it may take time for your chest congestion to clear. Rushing into the water before you're physically able to breathe deeply can leave you starved for air, which may lead to panic. In this situation, trying to breathe deeply when the body just is not able to causes you to feel as though you cannot get any air at all. This leads to stress, which can lead to poor decision-making or worse, full-scale panic.
Procedural errors common to dive accidents include buoyancy control problems, rapid ascents, missed decompression stops, general skill limitations, ear equalization problems, and, most critically, failing to properly monitor the air supply, resulting in low-on-air or out-of-air situations. In some cases, the diver lacked the appropriate training for specialized activities like diving in the overhead environment of caves or wrecks or deep diving. In other cases, the diver stayed within the scope of his training, but his emergency response skills simply weren't up to the challenge.
"Three critical words will help any diver be better prepared for dealing with a demanding diving situation: practice, practice, practice," says Dan Orr, former president of DAN and co-author of the book Scuba Diving Safety. "The lack of diving experience or skills or equipment that is unfamiliar adds to the stress of a demanding diving situation and can lead to a task-loading situation resulting in an inappropriate reaction to a situation."
Open-water environments can change rapidly, and divers who are unprepared, out of practice or physically incapable of adapting to those changes can become victims.
Before you dive, evaluate the air and water temperatures, currents, wave action, depth and visibility, etc. Not all diving is the same. For example, if you are a warm-water diver making your first cold-water dive, the effects of the water temperature can be a shock to you on your first entry. Shallow-water divers are often surprised by how rapidly they use their air supply and by the impact of narcosis on their first dives in the 100-foot range. Fighting an unexpected current while exploring a wreck is no fun, especially if you lack good buoyancy control, the ability to swim in a streamlined and efficient manner or lack the physical endurance to fight that current.
While equipment failures account for fewer fatalities than the reasons above, they are one of the most predictable — and easily preventable — causes of fatal dive accidents.
Equipment issues are often obvious before the dive and the observant diver can effectively make a preemptive self-rescue before he ever enters the water. The best policy is to check your equipment thoroughly before you board the dive boat, maintain your gear carefully and follow all recommended service intervals.
The DAN Annual Diving Report is compiled and published annually by the Divers Alert Network, and is available to the public at no cost as a downloadable PDF.