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Rebreather diving: ‘Killing Them Softly’

Second in series of reports on Rebreather Forum 3 by Michael Menduno.

Dr. Andrew Fock, head of hyperbaric medicine at The Albert Hospital in Melbourne, Australia, himself an accomplished rebreather diver, took the RF3 stage Saturday morning with an important and sobering presentation on the risks of rebreather diving, titled, ”Killing Them Softly.” One of the problems in the industry is the lack of an accident reporting system that records and details the cause of diver fatalities and near misses in order to inform and improve diver safety. In many cases, information about specific fatalities is sequestered for fear of litigation. As a result, existing accident data is incomplete and in many cases inaccurate.

( RF3 included several discussions of how rebreather incident reporting and analysis could be improved resulting in several Forum recommendations. In addition, DAN announced its new non-fatality online diving incident reporting system for rebreathers, which was endorsed by the Forum. See: The hope is that the DAN system will provide valuable information for the community. Rebreather Forum 3 Consensus Statements: )

Fock analyzed available data from multiple sources from 1998-2010 to answer some basic safety questions such as:

How dangerous is rebreather diving?
What causes fatalities?
Are manual units that depend on the diver to manually add oxygen, and which represent about 15 per cent of the installed base of rebreathers, safer to dive than their electronic counterparts?
Are there any specific brands of rebreathers more dangerous than others, the so-called “box of death”?
And finally, is the risk reduced when diving within the recreational envelope, that is, no stop diving to 130 feet (40m)?

With the caveat that they are “best guess numbers,” Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k.

He found that there was no difference in fatality rates among manual or electronic units, or specific brands of rebreathers; accidents were roughly proportional to market share. Fock also pointed out that while the data suggests that deeper dives carry greater risks, a large number of rebreather fatalities occur in shallow depths within the recreational envelope.

As far as the causes or “triggers” that precipitated accidents, Fock concluded that the source of most problems was the human-machine interface, or so-called “pilot error,” involving assembly and pre-dive preparation, maintenance, training, and high risk behaviours that include ignoring checklists, carrying insufficient bailout and diving beyond one’s limits. “The question,” posed Fock,” is whether the risk can best be mitigated by training (reinforced by dive culture), or engineering out potential problems, or both.”

Writer and technologist Michael Menduno published and edited aquaCorps: The Journal for Technical Diving (1990-1996), which helped usher tech diving into the mainstream of sports diving, and coined the term “technical diving.” He also organized the first Tek, EuroTek and AsiaTek conferences, and Rebreather Forums 1.0 and 2.0. Menduno, who is based in Berkeley, CA remains an avid diver.

More from the forum:
Part 1

Part 3
Part 4
Part 5
Part 6




2 Comments Leave A Reply

2 Responses to “Rebreather diving: ‘Killing Them Softly’”

  1. Frank D.

    So how deep caan one dive with a rebreather? How long can one stay down, at various depths? And is there a need for emergency replenishment of the recirculated air in the rebreather?

    • Charles Stanley

      Hello Frank,

      Different CCRs have different max depths. You’d have to look at each one to determine that one models max depth. As with breathing all gases at depth, a CCR does not eliminate the need to do decompression stops or safety stops, they will make the stops more enjoyable through moist air and warm air.
      Your next question is a little concerning. Emergency replenishment? Do you mean flushing the breathing loop? If your loop gets too high in O2 for a depth, you may be forced to flush and allow the loop to be refilled with diluentent gas. If you actually mean replace all gas in an emergency, the best advise is to bail out! Go to the surface and fix the issue. You’ll be happy you have a bail out bottle or two.


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