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Sure, bubble-free diving allows you to sneak up on fish. But for underwater photographers, closed-circuit rebreathers offer an even greater advantage.
Text and Photography by Stephen Frink
The first time I ever saw a closed-circuit rebreather in use under water was on a Force Recon diver carrying an M-16 and a compass. I was shooting a recruiting poster for the Marines and we were illustrating the romance and adventure of emitting no bubbles en route to placing a limpet mine on an enemy ship. While I was sure I would never embrace rebreather technology for that particular application, I could envision plenty of advantages as an underwater photographer, mostly relating to stealth.
I believe that. Fish know we are there, and in fact a lot of marine life is pretty indifferent to the sound of a diver's exhaust. However, experience does suggest that some animals are better approached with closed-circuit rebreathers. Schooling hammerheads are the obvious example, but there are many more species that can be approached more closely in silence than when accompanied by the alien sound of a scuba exhaust.
Is that enough to justify the hassle and expense of closed-circuit rebreather diving? Probably not. So why go to the trouble? "Bottom time!" says Howard Hall. "My rebreather has the capacity to support me on dives longer than 12 hours! Not only can a diver stay under water almost indefinitely, but decompression is greatly minimized because the system automatically produces the optimum gas mixture for whatever depth the diver descends to."
That, for me, is the "eureka" insight. Having been bent a couple of times on both air and nitrox, the ability to stay longer with a gas mix optimized to my depth at any given point during the dive is an awesome advantage. Stealth would be an appreciated bonus.
I did my rebreather training aboard the Nautilus Explorer in the Socorro Islands with Mike Fowler, Warren Miller and Tom Simonelli of Silent Diving (www.silentdiv ing.com). They are the distributors for the Inspiration and Evolution closed-circuit rebreathers, which is relevant because more Inspiration rebreathers have been sold than any other, and because all rebreather instruction is specific to a particular unit.
The training is not something to be undertaken lightly. In bold letters, the manual states: "If you fail to watch your ppO2 (oxygen partial pressure) and understand the implications--you will die, it is only a question of where and when." Needless to say, I paid close attention for the next five days as we learned the theory of why closed-circuit rebreathers work, the mechanics specific to the Inspiration rebreather, assembly and maintenance, emergency procedures and actual in-water practice dives, without cameras and then finally with them.
I’ll be the first to admit that at times the amount of information was overwhelming, even for an experienced open-circuit diver. The physics and protocols are substantially different from open-circuit, and not necessarily intuitive. But, as I've already suggested, there are good reasons for underwater shooters to investigate rebreather diving.
One widespread belief about rebreather diving is that the gear maintenance is massively time-consuming. I did not find that to be the case. Clearly, you have to be fairly obsessive and ritualistic about maintenance because your life is on the line, but it's not rocket science. If you can maintain the O-rings on a modern SLR housing, you can likely do the required maintenance on a closed-circuit rebreather. However, you do need access to Sofnolime for the scrubber, and pure oxygen to be pumped into one of the two cylinders (air is pumped into the diluent bottle). Not every boat or dive destination will offer these two critical components.
Any of the rebreather companies and certification agencies can provide a database of rebreather-friendly destinations, and you'll find they are far more common than you might have imagined. Plus, as more and more divers embrace the rebreather concept, the service industry will grow exponentially. I think what we are seeing now is the tip of the bubble-free iceberg.
I did find that carrying a camera changes some aspects of rebreather diving. The first and most potentially dangerous aspect is that time spent with your eye to the viewfinder is time not spent looking at computers and gauges. The computers indicate oxygen partial pressure, and the gauges tell the amount of gas in the oxygen and diluent bottles. Being unaware is dangerous. I found that to be a fine line to swim, but if one had to err on one side or the other, less time at the viewfinder is the preferred safety option. For me, that was the hardest part of my education.
Swimming posture is another change from normal open-circuit diving. Zigzag profiles and swimming over objects tend to use gas, and the closed-circuit-rebreather diver seeks to conserve gas. So, the way you get from Point A to Point B will likely change somewhat, but more significantly, your posture once in the shoot zone may need to change.
I noticed when shooting a manta ray circling me in a counterclockwise rotation, I was forced to drop my left shoulder low and kick furiously to keep up. This in turn put the automatic diluent valve (ADV) well below the dump valve on the right counterlung; which in turn constantly dumped air into the loop, which in turn constantly vented out the overrelief valve. I think a cave diver, deep wreck diver, or even a Force Recon marine might not put as many contortionistic demands on the system as a photographer trying to shoot elusive marine life. Therefore, I think, gas dumping from the system as a function of underwater posture is probably a given, making it all the more necessary to force your eye from the viewfinder once in a while to check life-support functions. Maybe even more than once in a while.
I found that on the rebreather I was far more able to approach white-tip reef sharks resting in caves than any of the open-circuit divers were.
Scorpionfish couldn't care less; guineafowl pufferfish were easier on the rebreather. Eels couldn't care less; angelfish were easier on the rebreather. Scalloped hammerheads, predictably, were far easier to approach on the rebreather and remained extremely elusive to all open-circuit divers. The manta rays of Socorro, on the other hand, were just the opposite. They actually like the feel of bubbles apparently, and would often position themselves just above divers.
Clearly the rebreather was no advantage in approaching the manta, but no real disadvantage either. Which is probably the point. Not every fish or marine mammal will be more closely approached while you're diving on a rebreather, but some will. And it is not like the absence of bubbles will keep marine life farther away. So, for stealth, the advantage goes to the rebreather by a large margin.
On the last day of the trip, I was diving an Evolution, which has a constant oxygen partial pressure computer built in. We did a fair bit of time hanging at 100 feet waiting for hammerheads to come near (which they never did, so realize the rebreather is no guarantee of close encounters). This was the fourth dive of the day. On my right wrist I had a nitrox computer set for a 32 percent mix, and by the time we began our ascent it called for a 40-minute decompression stop. My constant ppO2 computer, which monitored the decompression obligation required by the exact gas mix I was breathing at any given time, told me I had more than three hours of no-decompression time left.
Compare: 40 minutes of decompression and the heavy, physically demanding nitrogen load that implies; or three hours of no-decompression time with 100 percent oxygen being delivered during the safety stop for extra safety? No contest. That alone is sufficient justification for rebreather diving for me.
Will I dive rebreathers exclusively, like Howard does now? Probably not, simply because the consumables still do not exist everywhere I want to go. But if given the choice, open-circuit or rebreather, I’ll take the rebreather every time.
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