Do the numbers on this dive:fifteen feet for 64 minutes, thenten feet for 31 minutes. That oughtto be as safe as snorkeling, right?Not at all. It was one of severalrecent bends cases discoveredamong Australian divers in a newstudy on shallow water bends.
According to Dive New Zealand magazine, when Australian physicians noticed several shallow dives leading to bends, they decided to study 35 1996-97 cases. The shallow divers studied represented 10 percent of the 350 DCI cases that occurred during that period.
How great is the risk?
About 40 percent of the bent divers made a single dive with only one ascent. The shallowest depth for a single dive producing bends symptoms was ten feet (three meters), with the bottom time unknown.
However, most of the divers made several shallow dives and sometimes multiple ascents. One diver went to sixteen feet for 30 minutes with four ascents, then ten feet for 30 minutes, 26 feet for 20 minutes, and finally 33 feet for 28 minutes. The last three dives had one ascent each with the surface intervals unknown.
Other dives had multiple ascents and descents. For example, one diver dived to twenty-five feet for 50 minutes with four ascents, twenty-three feet for 35 minutes with four ascents, and six feet for 210 minutes with more than ten ascents. The shallowest dive implicated in a multiple series was six feet.
Two scientific divers did 19 dives to 33 feet for a total bottom time of four hours. Two divers had 20 ascents in a 13-foot dive. One diver had 30 dives over three days and noticed symptoms of a fuzzy head and general tingling six minutes after his last dive. He required eight treatments before he could be discharged from care.
Presenting symptoms
Limb pain was the most common symptom, reported by 36 divers. Paraesthesia (pins and needles) was reported by at least ten divers, and headaches, fatigue, lightheadedness, and weakness were the next most common problems. Six divers reported neurological symptoms and five reported general unwellness. Overall the symptoms were milder than those for divers who had been to deeper depths.
Most divers were treated initially using U.S. Navy treatment table 6, a four-hour 45-minute table, and most required three or four follow-up treatments.
Risk Factors
In the multiple dive cases, several risk factors were common. Twenty-nine divers had more than two dives in one day with one ascent per dive, while six divers did only one dive but had multiple ascents. Seven divers did more than one dive and more than one ascent per dive, and four divers had only dived in a swimming pool but had done many ascents. Some divers also undertook their multiple exposures by going progressively deeper, a well-known risk factor.
Who is most at risk?
About a third of the DCI cases were either instructors or students doing multiple training ascents. But photographers, people doing scientific work, treasure hunters or divers working on a boat or dock were also likely to have similar profiles.
It seems that an exposure less than 33 feet is not as trouble-free as once thought. While sometimes there may be predisposing medical factors such as patent foramen ovale, divers must still treat shallow dives with as much care and respect as any other dive. If you're one of those divers who was taught that "you can't get bent shallower than 30 feet," it's time to revise the theory.
