Why Divers Die: Part II

Obesity has long been considered a risk factor for decompression sickness, but the Divers Alert Network (DAN) also considers it a top reason for dive fatalities. In its report of U.S. injuries and fatalities in 2004, DAN found that 45 percent of the dead divers had a body mass index (BMI) of 30 or above, classifying them as obese. That’s a much higher proportion than the one-third of the U.S. population considered obese, suggesting that excess weight and poor physical conditioning are risk factors for many divers, both novices and pros. Out-of-shape divers, even those with BMIs under 30, will have to work harder to do standard tasks, such as handling gear and climbing into Zodiacs, than those with regular fitness routines.

Besides having an increased risk for DCS, obese divers have a larger workload in the water due to additional “drag” through the water, says Gisele Mouret, officer in charge of the submarine and underwater medicine unit on the HMAS Penguin in Balmoral, Australia. In a recent issue of Diving and Hyperbaric Medicine, she notes that poor physical conditioning impairs divers’ abilities to do selfrescues, perform buddy duties, and be rescued by their buddies, who may find it hard to physically pull them out of the water. Therefore, physically unfit buddies can’t always be relied upon to come to the rescue in times of need.

Poor physical conditioning impairs divers’ abilities to do self-rescues, perform buddy duties, and be rescued by their buddies

Consider DAN’s 2004 case of a 56-year-old obese diver who had insulin-dependent diabetes and severe coronary artery disease, which had required stents to be placed in his coronary arteries. Both he and his wife had received their initial open-water certification one month earlier and completed five lifetime dives. The diver and his buddy made a shore entry dive in a lake and he had buoyancy problems while at depth. His buddy attempted to give assistance but could not physically get him to the surface. He lost consciousness and his body was brought up 30 minutes later. He apparently drowned after suffering a heart attack.

Red flags are often ignored

In Australia, dive medicals preclude many obese people from diving, but for U.S. divers, the topic often doesn’t come up during their annual medical exam. Diving buddies and instructors can miss warning signs that occur even before overweight divers enter the water, and divers themselves are either unaware — or ignore — problems.

A 47-year-old certified diver who was obese, a heavy smoker and took medication for hypertension, was on a liveaboard. After the last dive one day, he complained about severe shortness of breath. Still, he decided to dive the next day. He went down to 101 feet for 20 minutes, but then signaled his buddy that he wanted to ascend. His buddy accompanied him to the descent line but decided to stay at the bottom. After surfacing, the diver complained again of severe shortness of breath, was assisted back into the boat and lost consciousness shortly after. He died of a heart attack.

An obese 55-year-old male, who had been certified in a resort course and had completed only four lifetime dives, planned a shore-entry ocean dive with a buddy. He had difficulty putting his fins on in the shallows and seemed fatigued during the surface swim away from shore, but the two kept going. They became separated and the man was found by another swimmer, unconscious and just below the surface. Resuscitation efforts were unsuccessful. Ann Marie McMullen, M.D., of the Cleveland Clinic’s department of Emergency Medicine, says doctors need to assess whether their patients are capable of carrying bulky, heavy diving equipment more than 35 pounds over uneven terrain, excessive distances, up and down boat ladders, and in strong underwater currents.

“Diving is physically demanding, so divers must be fit not only to dive but also to cope with the associated activities, like handling heavy equipment and rescuing people who might be incapable of helping themselves,”says McMullen. “Divers don’t need to be Olympic athletes, but they do need a reasonable degree of aerobic fitness, physical stamina, and mobility.” That doesn’t rule out diving for people who are overweight, diabetic or have heart issues, she says, but they do need to take extra care to ensure they’re properly equipped with enough air and bottom-time knowledge before each dive.

This case, previously cited in Part I of this series (Undercurrent, October 2006) is a good example: A morbidly obese male made a boat dive with four other divers, including the divemaster, and descended to 33 feet. He used nearly his entire tank within 30 minutes, but declined the divemaster’s alternate air source. The divemaster surfaced with him and sent him back to the boat before going back down. The diver lost consciousness and died. The autopsy disclosed intravascular air in the blood vessels of the brain and heart as well as pulmonary barotraumas. His dive computer showed several rapid ascents.

While body fat is a great insulator, that advantage is outweighed by the higher demands made on an obese person’s cardiovascular and pulmonary systems while swimming. Fatty tissue absorbs nitrogen at a rate five times faster than muscle does. But blood supply to fatty tissue is poor, causing a slow release of nitrogen and a greater risk of DCS. Combined with the greater effort needed for breathing, an obese diver’s heavy workload underwater increases use of oxygen and production of carbon dioxide.

One size does not fit all

Standard dive equipment and methods are not often suitable for obese divers, says Mouret. Her study notes that dive computers are programmed with dive tables for the average-sized person and do not take obese divers into consideration, which increases their DCS risk. Wetsuits compress the skin and shunt blood to already congested lungs. This, combined with restricted chest-wall movement, makes obese divers increase their work to breathe regularly. Larger-sized wetsuits also increase buoyancy meaning the diver needs to wear a heavier weight belt.

A 51-year-old male who had recently received his openwater certification was making a shore entry dive down to a wreck with a group of divers. He only made it down to 13 feet for a bottom time of 13 minutes, and was then seen swimming away from the group. He was brought to the beach by two surfers who found him unconscious on the surface. The death was drowning due to a heart attack. He was wearing 24 pounds of weights.

All the extra equipment considerations mean that obese divers use more oxygen while diving, meaning they either must have shorter dive durations or need to use larger tanks. Mouret recommends that obese divers use slower ascent rates and reduce their bottom time by 25 to 50 percent.

Affairs of the heart

Some divers are indeed just “big boned,” simply being large and muscular for their size. But those with high BMIs should think twice before diving – they are more prone to coronary heart disease and coronary events underwater. A BMI above 30 is considered excessively risky for diving. Scuba Schools International (SSI) estimates that a large proportion of North American diving deaths are due to coronary artery disease. Divers over age 40 should visit a cardiologist to undergo risk assessment and exercise testing for coronary heart disease. Stressful underwater situations can get the heart beating faster than normal – with fatal results. Cardiac arrhythmias can worsen during dives and cause heart attacks.

In another DAN 2004 case, an obese 39-year-old male was making a wreck dive from a boat in rough seas several miles offshore. Apparently, he spit his regulator out during descent and ascended with his buddy. He would not take an alternate air source from his buddy, subsequently losing consciousness on the surface, and died from a heart attack.

A 55-year-old male in poor physical condition made a shore dive with his son and soon started complaining of difficulty breathing through his regulator. He started back toward shore while his son went underwater for a couple of minutes. When the son came back up, he found his father floating on the surface, unconscious from a massive heart attack. An autopsy found severe coronary artery disease.

Appetite suppressing medications also increase diving risk, because they affect behavior and emotions and can elevate blood pressures. Throw in nitrogen, and you have a risky mix. Already mentioned in Part I of this series, this DAN case involves a 48-year-old female who had received her open-water certification one month before her death, was overweight and used phentermine and fenfluramine for weight loss. She made a solo shore dive to collect shells, but she did not wear a BC. She made numerous excursions to the 15-foot bottom, and then called out for help before losing consciousness. Her body was recovered from the bottom three hours later. She drowned, probably triggered by an air embolism.

Despite the feeling of weightlessness in water, diving is a very physical sport, and divers need to prep themselves physically for it. Aerobic conditioning is needed for leg kicks, and upper-body strength is required to pull oneself out of the water into Zodiacs and inflatables lacking easy stepladders. Poorly conditioned divers should also take a more sensible approach to diving. Slower ascent rates, reduced bottom time and fewer dives in 24 hours can lessen the DCS risk. The best method for better diving is improved cardiovascular fitness and a healthier lifestyle. This will not only help divers lower fatality risks but also let them enjoy this very physical sport even more.

In the next issue, we’ll continue discussing why divers die, focusing on fatal mistakes and poor judgments made on shore and underwater.