Considering rebreather diving

Re-circulating self­-contained underwater breathing apparatus (rebreathers) are wonderful devices. Once almost exclusively used by the military, since their introduction into sport diving, rebreathers have opened up a new world of possibilities to the sport and scientific diving communities; incredible exploration has resulted and today, dive sites that were once well beyond the capability of the averagely equipped and trained sport diver are now a routine weekend dive for an increasing number of us. However entry into this new world comes at a cost, the penultimate price I believe being your demise. I say penultimate because what I consider to be the ultimate price will be discussed later.

The once ‘cottage industry’ of sport rebreather manufacturing is maturing, the importance and significance of design standards, third party independent testing, production quality assurance and appropriate training is now at the forefront of diving industry discussion and progression. As a result, the ‘bar’ on these issues continues to be raised and long may it continue to, after all, we’re talking about life support equipment. However, despite best practice in engineering design, testing, production and training, rebreathers remain complex systems that given the opportunity, can quietly and unknowingly incapacitate a diver, often resulting in a fatal outcome.Rebreather self preservation is a survival state of mind I adopt and try to instil in all my students. Do not blindly trust your rebreather to sustain your life, it’s not always going to. With over two-decades of rebreather diving now behind me, much of which has been spent in rebreather development, testing, production and training, I offer here for your consideration some personal thoughts and opinions on surviving rebreather diving.

Rebreathers Are Not Suited To All Diving and All Divers

The first and obvious means of surviving rebreather diving is not to use one. Whilst exact statistics are vague, there is credible evidence to suggest you are significantly more likely to loose your life diving whilst using a rebreather compared to open circuit SCUBA. If you are considering rebreather diving, ask yourself do you need a rebreather and if so why. Consider a rebreather a ‘mission specific tool’ ideally suited to particular applications where the various merits of rebreathers can be exploited. However rebreathers are not necessarily the ideal choice for general sport diving where a risk / reward imbalance likely exists.

Buying a rebreather is a significant personal investment, the initial financial outlay is very high and through life costs can be considerable. However the ever increasing costs of gases means that it really does not take long to re-coup the costs of purchasing and using a rebreather.

Make a Considered Choice

Different manufacturers place different priorities on particular design characteristics, i.e. oxygen partial pressure management, counter-lung position, CO2 monitoring, weight, dimensions, etc, therefore research the subject thoroughly. However, if you have no experience or a limited understanding of rebreather technology, researching a subject from a limited knowledge base presents a challenge to the decision making process and encourages the emergence of a certain human weakness and the salesman's best friend: impulse buying. Try and fight off any impulse to buy a particular rebreather and do not blindly trust marketing literature, forum chat room discussion or manufacture representatives.

With a low knowledge base, it is easy to be persuaded that a particular rebreather has superior performance or advantages when compared to another. Therefore consider carefully your options, take opportunities to participate in ‘try dives’ to experience yourself the fit, form and function of as many different rebreathers as possible. When you have down selected, before you place your order, self check your decision, clarify in your own mind the reasons why you are considering this rebreather.

Be a thinking rebreather diver. Don’t just follow popular trends, which by definition are fashions that appeal to groups with similar tastes or to those who wish to conform. A fashion ceases to be so very quickly and the world of rebreathers is no different. You only need look at what has and has not been fashionable in rebreather market over the last decade. Follow a trend only if the reasons for doing so are based upon rational considerations driven principally by your safety. Study the merits of each rebreather design. This can be difficult if you’ve limited rebreather experience, particularly when an increasing number of novel designs are appearing on the market. However, it’s important to look beyond any novelty factor or ‘sophisticated’ feature when assessing a rebreather, instead remain with fundamental life sustaining design considerations, because when it fails, and it will, these fundamental design features will enhance the likelihood of surviving. Key design safety characteristics to look for are:

• Minimum resistive effort and static lung-load under empirical test conditions
• Oxygen sensor moisture management
• Water ingress management in event of a partial flood (where is the water retained within the loop and/or what means of water blockage is employed to limit water migration within the electrical system)
• PO2 control and a redundant means of independent PO2 monitoring
• Canister performance under empirical test conditions
• Software third party validation
• Environmental testing under empirical test conditions
• Electro magnetic shielding from external radio frequency influences - validated under empirical test conditions
• Build quality and material selection
• Robust O ring seal design, in particular on components that are frequently disassembled, i.e. canister and breathing loop components.

Also consider that the most technically sophisticated option need not necessarily be the safest option; the more complex the engineering the greater the potential number of failure modes that may be inherent within the design. There is a strong case for ‘less is best’ and it is not uncommon to be sat next to persons on a dive boat who cannot, or should not dive because their ‘sophisticated’ rebreather has developed a fault.

Would you like to see more? Go to the page Information.