Rebreathers and Ferraris
/Breaking down the merits of Rebreathers in a simplified way.
Fast Cars and Rebreathers? What would motivate me to post an article comparing the two? Well…let’s see. Power, capability, advanced technology, cost to name a few. High performance automobiles have the ability to achieve high speeds in relatively short periods of time, they handle very well at these high speeds and they usually have a very smooth ride. All made possible by a well-built engine controlled by sophisticated electronics and complex suspension system. If you have ever dived a closed-circuit Rebreather you should start to understand the parallel.
The individual elements required to dive deep and long are perhaps as complex as taking a Ferrari onto a highway. They also require some equally sophisticated tools. When one first starts diving mixed gas, it is usually on open circuit. Here is what you may already know:
In the past, planning your dives took hours of comparing computer-generated profiles with hard tables and then copying them onto slates. Then you would spend even more time blending and analyzing all of your gases, gases that in the long run still did not provide optimal mixes from a physiological point of view. As technology advanced, it introduced blending apparatus that facilitated quick, accurate and inexpensive mixes. It also married this technology with SCUBA (Rebreathers) essentially providing an onboard, self-contained gas blending machine capable of providing optimal mixes in real time. Now we can knock off a ninety-minute deep mixed gas dive to 60 MSW (200 FSW) with little planning and minimal decompression obligations.
Now think of it this way:
Think of it as multi-dimensional diving MDX: diving to the exponent of X where X represents a couple of different factors;
The elements we need to consider when planning our dives and
The increase in capability to extend our range of diving.
We can begin with deep air diving on open circuit, or MD1. This is one dimensional diving where we dive with a limited volume of gas with a single fixed fraction of oxygen (FO2) and nitrogen (FN2 ). Not only is our quantity of gas restricted, but so is our ability to do things with it because of its qualities (hyperoxic and narcotic).
Eventually a diver learns how to incorporate nitrox (MD2) or trimix (MD3) into his/her bottom gases. This increases their ability to extend their bottom times and reduce the narcotic and hyperoxic effects of a mix. However, he/she is still diving with a fixed FO2 and FN2 . Ideally, a diver wants to maintain a fixed PO2 and change their gas mixture accordingly, anytime their depth changes. They can do this by carrying a number of different tanks or ‘stage bottles’ (MD4) with different gas mixes (semi-fixed PO2); however, they reach a certain point where they are overloaded with gear. They are still not able to change their mix for every significant change in depth.
In both photos above I am about to start a dive to 90 MSW (300 FFW) for 20 minutes. During dive on open circuit I accumulated a total run time of 110 minutes using three travel/deco gases and today the gas costs on that mix would be over $350. The same dive profile on CCR had me out of the water in 80 minutes and I used about $15 in gases. That is a savings of about $335 per dive. In 30 dives on Rebreather I would save enough money to pay for the Rebreather.
A semi closed-circuit Rebreather helps resolve some of these problems by extending the volume of gas supply, reducing the amount of equipment a diver needs to carry, and by making a rough guess at what might be a good gas mix for that particular depth. A well designed, passive, semi-closed Rebreather would have a multi-dimensional factor of about 4 or 5 (MD4 or MD5). Fully-closed circuit Rebreathers, on the other hand, are very smart machines and not only accurately calculate and deliver a premium gas mix to the diver regardless of what depth he/she is diving, but also provides a nearly endless supply of gas (MD6). Some units on the market today are so well equipped they can measure the levels of other constituents in a gas mix such as helium (MD7) and even carbon dioxide (MD8), and are capable of notifying the diver with audible alarms if concentrations reach dangerous levels.
However, with multi-dimensional equipment comes a necessity to think multi-dimensional. That means adopting a comprehensive understanding of advanced diving physics, physiology and theory. It also means that we incorporate a meticulous, uncompromising approach to dive planning and equipment preparation.
Finally, it requires that we maintain our skills and knowledge because the complexity of this level of diving activity makes it extremely vulnerable to deterioration. These are perishable skills and need to be sustained through on-going training, practice and experience. The rewards however, are incomparable.
With Rebreathers now priced around $10,000, many argue costs are prohibitive and outside of the budget of most technical divers. In previous years I would have defended that open circuit mixed-gas diving was still an option. The price of helium and oxygen have increased significantly to the point that the costs of filling your bottom tanks and travel/deco gases alone make deep mixed gas diving prohibitive. Consider the above dive comparison wherein I saved $335 on the dive in gases. Over a period of 30 dives I saved enough in gas costs to purchase a Rebreather. Another argument is nitrox costs now reaching as much as $20 per fill (usually lasting a diver about 40 minutes). A Rebreather provides about 6-8 hours of diving on a fill of about the same price - that is the equivalent of 12 nitrox fills and a $220 savings. Rebreathers take diving to the next level of exploration, and once you dive one you will quickly realize anything else is restricted to the slow lanes or antique car shows.
~ Safe Diving