Oceans of Opportunity

a case for oxygen-only rebreathers in our past, present, and future

Some legs of the journey are predictable, and others just aren’t. I first got the deep diving bug almost 20 years ago, and at that time (circa start of the 21st century) deep diving for the masses meant suffering through nitrogen narcosis, and severely limited bottom times given only open-circuit tech being in the mainstream. For the fortunate few who were ahead of the game, helium was accessible, though far from commonplace. Even further from the day to day was the use of mixed-gas rebreathers. Sure, there were a few early adopters, and those more elite individuals and groups just starting to push the limits of this technology, but they were far from commonplace. At that time, those very few out there doing exploration with rebreathers were able to very easily generate a public appeal for the technology given their solving the two aforementioned issues with deep diving – narcosis and gas consumption. Thereafter, rebreather technology’s popularity grew to meet these demands – more and more people wanted to be Mr. Deep Diver or Mr. Cave Diver, and that meant having a rebreather in the toolbox.

Since that time, the community has evolved accordingly, and the time was right. While rebreather tech is far from new – in fact it far pre-dates Cousteau’s Aqualung by a century or more in principle – the more recent advancements in materials science, sensor technology, and the conventional open-circuit regulator itself have all been contributors to rebreathers evolving to meet the current market demand. Fortunately, or perhaps unfortunately, this current market demand is still quite small when considering the global diving community, and merely a peanut when further considering rebreather use among a global population of terrestrial landlubbers. There’s been on and off chatter about ‘day 1’ rebreather training programs, but while training has been grossly simplified, here is a critical juncture at which we must exercise some caution. Frankly, early career training on a mixed-gas rebreather (even with air/normoxic diluent) will prove quite dangerous.

Historically, without citing statistics, I think it is fair to state that many (perhaps the majority) of rebreather diving fatalities have been the result of or at least thought to have been impacted by an adverse physiological response to breathing the wrong gas at the wrong time…i.e. hypoxia (insufficient oxygen) in most cases, though also hyperoxia in some instances. Hypercapnea (elevated carbon dioxide) is also a culprit. I elaborate on these in my book, ‘Closed Circuit | Open Sourced‘ – these ‘triple H’s’ should be considered as the three predominate physiological concerns for all rebreather diving, though perhaps even moreso for mixed-gas rebreathers when there is the very real possibility of inadvertently supplying the diver with an inappropriate gas at an inopportune time. For this reason, the operating logic described in my book emphasizes good practices to restrict the use of hypoxic diluent at or near the surface – indeed these first/last 20 feet or so of depth are the most dangerous transition periods during a mixed-gas rebreather dive. Equipment configuration should be optimized to mitigate these risks, and unfortunately that is still not widely embraced logic…and people have and will continue to die because of it.

Relaying that concern about hypoxia over and over and over again lead me to think long and hard about rebreather training. Sure, at present, most individuals interested in rebreather diving have the deep bug or some semblance thereof, and today’s hardware and training market is engineered to meet this demand.

But what if we’ve got it all wrong?

If rebreather training is viewed as an advanced level skill that comes at some later point in a diving career, then we are stuck having to undo habits from open-circuit training; this is the ‘thinking like an OC diver’ that is often talked about. On the other hand, if we take a mixed-gas unit and introduce it to a new/early career diver, it is perceived as too complex, and is frankly dangerous since the diver hasn’t yet learned to think like a rebreather diver. So, when are we ever truly given the opportunity to think like a rebreather diver? Never at this point…that takes several tens to hundreds of hours. It’s a long road and one that very few have travelled down – but those that have done it, myself included, will speak of fantastic experiences and discoveries that couldn’t have been had in any other way.

So, what to do? Certainly we, as a community, have to recognize that keeping the glory for just a few is no way to chart a course forward…if we give the gift of these experiences and discoveries to a new generation, then the market will expand, and we can then make investments into new and improved capabilities – that’s how this should be working anyway. To expand the rebreather market, early career training, perhaps true ‘day 1’ training will need to be addressed. This allows a diver to learn how to think like a rebreather diver and then progress through a lineage of experience and additional training with a set of tools potentially decades ahead of where they are gathered now. That’s great in principle, but no place for the perceived complexities of a mixed-gas rebreather and risks of hypoxia in particular.

As much as I love the pursuit of deep diving, I’ve been on a three year segue doing very shallow water work (all 30fsw or less). To meet a demonstrated need for more time, less ins and outs to swap tanks, and to be warmer, I designed a purpose-built oxygen rebreather. The unit has gone through a few prototype evolutions and is now in a pre-production state. I dubbed the unit ‘Rebreather Day 1‘ (RD1, spec sheet download here) because its easy enough to learn how to dive in one day, and could be used from day 1 in someone’s diving career. Sales pitch aside, the personal investment into development and subsequently several hundred hours of diving the unit has been a gift presenting a bit of a eureka moment. For the first time in almost 20 years of rebreather diving, I now have a level of confidence that there is a path forward to get people to think like a rebreather diver without subjecting them to unwarranted risks of a mixed-gas unit in shallow water. Of course, there is a hard depth limit to oxygen only units given potential hyperoxic risks, however in practice the diver will quickly recognize that the breathing loop is never truly 100% oxygen, and there is therefore significant buffer towards oxygen toxicity concerns, even for long dives – these topics are addressed in depth on my training program (eh em, you can buy a unit with training here: www.underseatools.com).

The author during an RD1 oxygen rebreather pool demo session.

By using an oxygen-only rebreather, the diver can simply breathe…and get accustomed to breathing on a loop – responding to changes in loop volume, when and how to flush a loop, managing water ingress, when and how to bailout, and similar basic mechanics. These are the things that a new rebreather diver has to reprogram their brain with when transitioning from open-circuit scuba. With enough time spent such that these mechanics are second nature, it becomes much more natural to make some simple plumbing changes and then dive the very same unit deeper as a mixed-gas unit – that equates to simply more careful ppO2 monitoring and gas management since the bulk of the rebreather mechanical skills have been already learned to a degree of proficiency.

This is all great in theory, but only the future will reveal if such a training regimen will be accepted by the community – who knows. The obvious argument against it is that there are inherent depth limitations with oxygen rebreathers, and consequently many practical dive site limitations. I’d counter with the fact that most people learn how to dive in a swimming pool to begin with, so what’s the difference? Dive shallow til you figure stuff out, then march along on your deep diving journey when proficiency is acquired and competence is demonstrated.

Another part of my eureka oxygen rebreather moment has been considering the role of open loop oxygen rebreathers in atmospheric diving (subs, suits, and habitats). All of these platforms use a form of simple oxygen rebreather, and so it would seem logical to emphasize concepts in atmospheric management on an oxygen only rebreather early in one’s career such that future exposure to these highly advanced modes becomes that much more intuitive. That’s a reach for many to consider today, but in the future I believe it’s entirely feasible, and highly likely, that we’ll see lower cost atmospheric diving opportunities, and so why not prepare a wave of new divers that are thinking about things in the right way from the very start?

So, that’s my evening soapbox on oxygen rebreathers. Had I only had one twenty years ago, my world would be vastly different than it is today, but I suppose that’s paying the price of progress.

Who knows what the next twenty years will bring…

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