A forgotten drysuit hose vacuum-packed a rebreather diver
The diver is an experienced open and closed-circuit diver with hundreds of hours underwater in diverse types of diving conditions. He boarded the dive boat with five other experienced divers. His dive partner also was using a rebreather, but the two divers had planned to separate once they entered the water. The diver told his partner he did not want to spend much time at the surface before he descended, so the only equipment check conducted was a quick bubble check on the initial descent. After the bubble check, both divers continued to descend but on their own. The dive partner said he last saw the diver below him at 90 to 100 fsw (~30 msw). He said this occurred at the beginning of the dive. The dive partner said it appeared that the diver was lying on the bottom and looking at something. The dive partner stated he had no idea the diver was probably already unconscious on the bottom.
None of the other divers that entered after the first diver saw him during any portion of the dive. When the diver did not surface as planned, the group became worried and began sending their divers to look for him. The captain of the boat also notified the U.S. Coast Guard and lifeguard divers were dispatched to assist in the search. After a six-hour search, the diver was located at a depth of 92 fsw (~27 msw) at the same location he had descended. The diver was brought to the surface and pronounced dead.
The lifeguards that found the diver said he was lying on his back with the rebreather mouthpiece not in his mouth. The mouthpiece was closed. They also noted that the diver did not have a low-pressure hose connected to the drysuit inflation valve or the BCD inflation valve. They said the diver appeared vacuum packed in the drysuit.
The diver’s bailout regulator was no longer attached to his BCD harness, and it appeared he had removed the regulator to use it. The regulator however had an inline on/off valve that was still in the off position. The investigation revealed that the diver placed the on/off valve above the second stage to prevent the second stage from free flowing. When tested, the on/off valve was very hard to open, especially with gloves on. The diver had plenty of bailout gas left in his cylinder, but none of the gas appeared to have been used.
Equipment testing revealed that the diver was using twenty-seven pounds of added weight on his rebreather rig. This was in addition to the negative buoyancy created by his bailout system and underwater camera equipment. The combined weight would have acted like an anchor if the diver entered the water without low pressure hoses attached to his drysuit or BCD inflator.
The examination and testing of the rebreather showed that the unit worked as intended, but did not provide direct answers as to why the diver went off his working rebreather loop and closed the loop mouthpiece. This decision could have been made because the volume of gas contained in the loop felt insufficient, the diver had some other equipment issue (tight drysuit), or had some type of medical emergency.
Once closed however, the diver would have quickly needed an alternate air source to survive underwater. The diver had two separate choices: The regulator attached to his bailout bottle and the regulator integrated into his BCD inflator. The problem was that no low-pressure hose was attached to the BCD inflator-regulator and the on/off valve would have been hard to open in an emergency.
The autopsy showed the diver had water in both his lungs and stomach consistent with a drowning. If the diver took a breath off either regulator during the emergency, the diver would have only gotten cold saltwater. When combined with the added weight and no way of adding air to his BCD or drysuit, the diver sank directly to the bottom and drowned.
Checklists have saved countless lives in aviation, medicine, and rebreather diving. When diving with rebreathers, skipping the predive check is akin to Russian-roulette.
Peter Buzzacott, MPH, Ph.D.