New Dangers of Rebreather Diving

A closed-circuit rebreather might not be something you’re keen to use or to spend money on. It costs thousands of dollars, and then there’s the unit-specific training you’ll need to be certified. The total cost doesn’t encourage anyone to change from one make to another, especially if you need to pay for another training course. However, people do and there is no doubt that the market segment has matured. Surprisingly, there must now be nearly 10,000 individual rebreather units in circulation.

With ordinary open-circuit scuba, you inhale gas from your tank and exhale it out into the water, wasting most of it. With a rebreather, you recycle your gas, replenishing the small amount of oxygen you have actually used, and remove the poisonous carbon dioxide, the waste product of metabolism, chemically. The people who devote so much money to buying the gear and diving closed-circuit naturally tend to be very keen divers, and a large number of them use their rebreathers to do dives that are deeper and for longer than would normally be practical on good oldfashioned open-circuit scuba. That’s because gas usage is very low and decompression requirements are drastically reduced. For example, a no-stop time for a dive on a rebreather to 60 feet approaches three hours, whereas the nostop time on simple open-circuit scuba would be around 50 minutes.

Rebreather divers breathe the gas in a continuous loop. The problem arises only in that your unit must supply you with enough oxygen in the loop to sustain life but not so much that it poisons you, and the carbon dioxide exhaled must be removed. Carbon dioxide is both tasteless and odorless. By the time carbon dioxide has built up to disastrous levels, it is often too late, resulting in mental confusion and the inability to self-rescue. Low levels of oxygen are as effective a killer as a bullet in the brain -- there has been at least one recorded case of a rebreather diver suffering shallow-water-blackout at a depth of 240 feet. Alas, because of the nature of these fatal accidents, coroners usually put the cause of death as either drowning or heart attack, which tells us little.

With open-circuit scuba, you either have gas to breathe or you don’t. It’s that simple. The rebreather diver can always breathe but he must know exactly what he is breathing. He relies on onboard analysis of the oxygen content, perfect carbon dioxide scrubber design and self-maintenance to keep the insidious perils of carbon dioxide at bay. Strangely enough, he needs more oxygen as he gets shallower, so he is more at risk on the way up than on the way down. Many of the fatalities have happened in relatively shallow water.

Of course, the training provided by agencies like TDI and IANTD cover all these subjects, and the manufacturers work closely with the training agencies to ensure no units supplied by them fall into the hands of untrained divers. Rebreather trainers do the same with used units they might trade. However, it cannot be denied that there have been an unacceptable number of fatalities of experienced divers when using this equipment despite these precautions. The use of a rebreather statistically appears to increase the risk in the hobby of scuba diving.

New improved versions of rebreathers are arriving on the market every day and people naturally want to upgrade. The problem arises when they try to recover some of the cost of their previous unit. There is now a vibrant second-hand market of rebreather gear developing, and although there have always been a small number of selftaught rebreather divers, there’s also the specter of a greater number of new rebreather divers venturing into the water breathing from units that they only think they know how to use. It is only natural that people trying to claw back several thousand dollars they spent on their old units will mostly be concerned that the buyer’s payment is good and not that the buyer is a good rebreather-user prospect.

A few would argue that some of the official training delivered is not as good as the training agencies intended it to be. This may be true and it reflects the individual instructor. It also reflects the willingness of the trainee to grasp new ideas and ask pertinent questions. It’s a two-way deal. Training doesn’t work by osmosis.

There are also a few who would argue that being self-taught is the better way to approach rebreather use. Some would say the initial training is only the start of the learning curve. I’d agree with that. Closed-circuit rebreathers are unforgiving in their use. You rarely get second chances. Some very competent divers, much more competent than you, have learned that lesson the hard way and paid the ultimate price.

The additional hazards of rebreather diving are insidious. If you know anyone who is about to or has already purchased a rebreather through unofficial channels, as they might when buying a second-hand unit, please implore them to seek out the appropriate training by an instructor before using it unaided. The same goes for you. You owe it to your family, dependents, spouse, and yourself. Get the proper closed-circuit rebreather training.

John Bantin is the technical editor of DIVER magazine in the United Kingdom. For 20 years, he has used and received virtually every piece of equipment available in the U.K. and the U.S., and makes around 300 dives per year for that purpose. He is also a professional underwater photographer.