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Rebreathers - The Next Generation

By Jeffrey Bozanic

Jeffrey Bozanic´s Original Paper for his immersed magazine article:
The State of Rebreathers Today,issue summer 2003 / Vol.8,No2.

Here, on this site, you read the original paper without pictures. If you will see the pictures, please read the immersed magazine article.
If anyone has questions about the article, please contact Jeffrey Bozanic.

Jeff, thanks for this exelent article on rebreather diving.

Published with permission from the author
october 2003 Ekki Schepanski, www.crazy-rb-diver.com

Rebreathers - The Next Generation

By Jeffrey Bozanic

In the Spring 2000 issue of Immersed, I wrote about the state of the art in rebreathers, concluding with the thought that, “Using rebreathers today is analogous to using open-circuit equipment 40 years ago…. If rebreathers develop as rapidly as open-circuit scuba has, rebreather use will likely become easier, safer and more accessible to the average diver.” Three years later, this prophecy is already coming to pass, much sooner than I had expected. So where are we now?

The Diving Equipment and Marketing Association (DEMA) trade show was held in Las Vegas in October 2002. Many manufacturers use the event to announce new products, including many rebreather manufacturers. What is new, and what is on the immediate horizon? Let’s look at the various areas I wrote about in 2000.

Solid State Scrubbers:

There are many reasons that traditional granular carbon dioxide absorbents are not user friendly. First, properly packing some canisters takes 15 to 30 minutes. This is time most divers would rather spend diving. Second, granular absorbents all produce dust, which increases the possibility of a caustic cocktail problem should any water enter the rebreather. Third, many divers (especially new rebreather divers) are nervous about improperly packing a canister, which may lead to early breakthrough and hypercapnia. Fourth, trying to repack canisters on boats or in tight areas is often difficult to impossible. Finally, dealing with granular absorbents is often messy, and requires more time for cleanup.

Micropore has introduced a solid state scrubber that eliminates all of these concerns. ExtendAir is what they term a Reactive Plastic Cartridge. It contains the same soda lime chemicals used in granular absorbents, but embedded in a solid plastic substrate. The canisters come as rolled cylinders of the material, and require specially designed replacement canisters for the rebreather being used. Cartridges come wrapped in plastic bags with a foil seal. To use one, you simply tear open the top, slide the cartridge into the canister, and seal the canister with a 30^o twist turn. It takes all of 30 seconds to load, and when it comes time to dispose of the cartridge, you simply throw them away. No muss, no fuss!

Canisters are currently available for the Drager Atlantis and Dolphin, and the San o Sub Azimuth. Micropore expects to have a scrubber out for the A.P. Valves Inspiration soon, and are working on units for six other rebreathers as well. I have been using these since September 2002. As far as I am concerned, they are the neatest things since sliced bread, and should do much to reduce the work effort associated with using rebreathers. The only problem is the cost per unit hour (about 25% more expensive than traditional absorbent), but that is expected to come down over time.

Robust Rebreathers:

One of the most exasperating (and expensive!) problems with CCRs is flooding of the cabling and electronics. Even a minor o-ring seepage can lead to an inoperable unit. One manufacturer, B & E Manufacturing, has designed a CCR, the Nautilus, which utilizes fiber optic cables for all displays, eliminating all electrical connectors and thru-hole penetrations. This reduces the possibility of a flood, and at the same time increases reliability of the unit. B & E Manufacturing has collaborated with Steam Machines (makers of the PRISM Topaz) in the design and production of the Nautilus. It features a primary display that uses LEDs to show not only the consensus oxygen partial pressure in breathing loop, but simultaneously the readouts from each of the individual sensors. Its scheduled release date is second quarter 2003.

Improved Instrumentation:

Two areas of instrumentation needed immediate improvement: dive computers and carbon dioxide sensors. (More reliable oxygen sensors are also on the wish list, but nothing new was seen in this area.)

Many of the rebreathers on the market provide no indication of inert gas loading. To solve this problem, three manufacturers have introduced wrist mounted dive computers that calculate inert gas loading using constant oxygen partial pressure models. Cochran Undersea Technology has the Commander Constant PO₂, which is capable of using two different nitrogen based constant PO₂ mixes. Delta P Technology is making the VR3, and HydroSpace Engineering has the Explorer. Both of these computers are capable of modeling both nitrogen and helium based inert gas mixes, and both have a model with an optional oxygen sensor that will provide a separate readout of the oxygen partial pressure in the breathing loop. All of these computers are available now.

Several rebreather manufacturers incorporate inert gas modeling computers in their units, including all A.P. Valves models, San o Sub’s Nemesis, Innerspace Systems Corporation’s Megalodon, and Olympic Submarine Technologies’ CCR 2000.

The ability to determine when carbon dioxide absorbents are no longer effective is lacking on all current rebreather models. (While Cochran Technologies has shown a rebreather with this capability at past DEMA shows, they have not released the unit to market.) There are two ways this might be accomplished, either by direct reading of carbon dioxide in the breathing loop (CO₂ sensors), or by monitoring the absorbent. Absorbent monitoring uses thermisters to measure usage. The theory is that since carbon dioxide scrubbing is an exothermic reaction (produces heat), thermisters placed along the canister could monitor which part of the absorbent is “active” at any given time. When the reaction approaches the end of the canister, then the absorbent is ready to be replaced. While this is certainly better than no monitoring at all, channeling may lead to bypass and early breakthrough undetected by thermisters.

San o Sub announced their new Nemesis CCR in October, which is the first unit to actually provide any type of absorbent monitoring device. It uses the thermister principle, and is exciting not only because it provides this capability, but also because it should help drive market development in this area. The Nemesis is currently in testing, and should be available third quarter 2003.

Smaller and Lighter:

With many rebreathers weighing in at greater than 60 pounds (27 Kg), recreational users are hesitant about diving with them. Several units overcome this barrier. The PRISM Topaz (and their military version, the Invader) CCRs are 47 pounds (21 Kg) when ready to dive. A.P. Valves has announced the Evolution, a CCR both smaller and lighter than the Inspiration, which should be ready in late 2003 or early 2004. At DEMA Innerspace Systems Corporation showed a smaller version of their CCR, and Jetsam Technologies had a 25-pound (11 Kg) KISS “travel” CCR on display.

Another issue is the counterlungs, or breathing bags. Most rebreathers feature “one size fits all” counterlungs. While this exactly how open circuit gear was originally issued, that has progressed to a multitude of sizes and designs to fit different divers. Rebreather manufacturers have not yet followed this lead, with some manufacturers offering at most two sizes in counterlungs. Speaking of counterlungs, Olympic Submarine Technologies’ CCR 2000 has a removable breathing loop, which can be purchased by individual divers. They then pop that in to a shell containing the gas cylinders, electronics, etc., and can dive a unit that is personalized to them. The potential infection transmission issue is thus avoided, a significant benefit in some divers’ minds.

Less Expensive:

One extremely large barrier to entry to rebreather utilization by advanced recreational divers is the associated price tag. With CCR costs averaging $6,000-$10,000 (and ranging to over $20,000!) many are deterred from any consideration of rebreather use. In a much-needed move, three manufacturers have announced CCRs that will cost less than $5,000. These include the Jetsam Technologies’ KISS CCR (available now), B & E Manufacturing’s Nautilus, and San o Sub’s Nemesis.

Another factor that will reduce the costs associated with diving rebreathers is the availability of third party parts. Just as in the automotive market third party manufacturers often provide replacement automotive parts at much less expense than original parts, so too can third party manufacturers in the rebreather market. OxyCheq has taken an aggressive stand in this area, providing replacement oxygen sensors, protective breathing hose covers, SCR interstage pressure adapters, and other rebreather parts and accessories for a wide variety of manufacturers and models. They also act as a distribution channel for products they do not directly produce, in an effort to make them a “one stop shopping” solution for rebreather users. Juergensen Marine is also manufacturing a variety of control electronics, replacement parts, add-on components and display electronics for a wide variety of CCRs.

Another innovative idea to make CCRs affordable was developed by Laguna Sea Sports of California. They have formed The Rebreather Club®, which is essentially a timesharing arrangement for rebreather divers. They have a number of PRISM Topaz rebreathers available in their shop for local users. Instead of individuals buying a unit, they pay an initiation fee, plus an annual renewal fee. For that, they get 30 days of usage every year, with additional days costing $10/day… and the shop sees to all of the maintenance!

Standardized Rebreather Testing:

This is one area in which more needs to be accomplished. While some manufacturers have utilized independent test groups to conduct extensive testing (Steam Machines with their PRISM Topaz/Invader CCRs comes most readily to mind), most manufacturers test their units in house. While this in itself is not a necessarily a bad thing, the larger problem is that each of the test programs are conducted differently, yielding different results. As an example, one manufacturer says that their scrubber canister lasts for six hours, and another claims ten hours. It would appear that the second unit is “better.” However, when test protocols are examined, the first tested their unit in 32^oF (0C) water at a 1.6 liter per minute (LPM) carbon dioxide flow, while the second was in 80^oF (27C) water at 0.8 LPM CO₂ flow. From the information provided to the potential purchaser, it is impossible to tell which will actually last longest in equal conditions.

Rebreather manufacturers and suppliers need to collaborate to set not only testing protocols, but minimum standards as well. There are several places from which they may begin, such as the protocols used by the U.S. Navy Experimental Diving Unit (NEDU) or Canada’s Defense and Civil Institute of Environmental Medicine (DCIEM). Efforts are underway in Europe to institute such standards, and some rumblings have been heard from within the U.S. on a similar project, but at this time no consensus has been reached.

At this time, no single rebreather has all of the desirable features one may want, but the pace of development is both surprising and gratifying. Development is progressing much faster than I expected, and it may not be much longer until we see broad availability of many of these features. Looking at the state of the art, it may not be 2003 yet, but we are certainly beyond the 1950’s spoken of earlier!

Manufacturers Referenced:

A.P. Valves

Water-ma-Trout Industrial Estate

Helston, Cornwall, U.K.

TR13 0LW

44-1326-563-834

www.ambientpressurediving.com

B & E Manufacturing, S.A. de C.V.

P.O. Box 195

Cabo San Lucas, BCS 23401 Mexico

www.divenautilus.com

Cochran Undersea Technology