Meet new scuba divers, maintain a virtual dive log, participate in our forum, share underwater photos, research dive sites and more. Members login here.

Dutch Springs 10/8/10: Diving with the Sound of Silence
AOW_dude - 10/10/2010 12:19 AM
View Member Articles
Category: Equipment
Comments: 2
Dutch Springs 10/8/10: Diving with the Sound of Silence

How do you know if rebreather diving is for you? Dude, one way to find out is to just go ahead and try it. Having dived with only open-circuit scuba gear I couldn’t help but wonder, what does diving with a closed-circuit rebreather feel like? They say it’s silent, that there are no bubbles when you dive, which sounds kinda cool. But what really blows my mind is the possibility of diving way deeper and way longer. So when I read about a rebreather demo (TSC Scuba) I signed up right away. (Yeah, another one of those “dude, I just gotta do this!”)

It’s no secret that we utilize each breath rather poorly. Exhaling about ¾ of the oxygen we inhale doesn’t sound super efficient to me, yet that’s the way we breathe. I mean, if I found out that my car was using only a quarter of a tank of gas and the other ¾ just flows out of the tail pipe, I’d get rid of it. That’s kind of the way open-circuit scuba works, though. If I could use all the oxygen I breathe in without wasting any, and dive several times as long as regular scuba, being able to go deeper… Sounds like progress to me, why don’t we all dive like that? Rebreathers have been out there for quite some time now, so I was just wondering what’s the deal with the majority of divers not having adopted it yet? So the night before my rebreather diving I looked up some manufacturer’s info.
Well, the theory is simple enough; basically, you got two small tanks (I had one with air and another with oxygen), a scrubber (unit that absorbs the carbon dioxide you exhale) and a counterlung (flexible bag that expands and contracts with your breathing, comparable in size and action to your own lungs). So, I first breathe in from the air tank, then the exhaled air goes through scrubber, the ¾ of oxygen I didn’t use goes right back to me and ¼ that I did use is automatically replenished from the oxygen tank. Obviously, there are a bunch of sensors and valves to keep the rebreather running properly but I didn’t have much time to get into all the nuts and bolts. What did grab my attention though were the safety warnings.

This device is capable of killing you without warning”, that was a note on one of the rebreathers I was gonna try (KISS). Here’s another good one (from the dealer’s page): “This rebreather has NOT been tested by the US Navy, DCIEM or any other organization, it is NOT CE approved and the only guarantee that it comes with is that it is absolutely capable of killing you ”. Sounds almost like they’re trying to scare off more impressionable customers and attract the macho “balls of steel” crowd. Then again, to think of it, there’s nothing wrong with honesty, and the good old open-circuit scuba also has its fair share of risks and warnings. You just gotta learn how stuff works before you dive, pay attention and try not to do stupid things that might kill you. Interestingly, “stupid” is incorporated in the very name of one of the rebreathers, the dreamy sounding KISS stands for “Keep It Simple, Stupid”. I kinda like that principle (hey, good thing they didn’t name the rebreather SNAFU).

My first rebreather dive was with a KISS (wait, or was it a SMOOCH?) The whole thing is mounted on a steel backplate with a harness and a wing BCD, so I didn’t need the gear I normally use (jacket BCD with 20 lb in weights, my computer and reg, didn’t need a snorkel either). The rig was something like 18 lb negatively buoyant because of the backplate so even with a 7mm wetsuit all I needed was only a couple pounds in weights. I thought that rebreathers are lighter than open-circuit scuba, yet that’s not exactly the feeling I got when diving with KISS and rEvo (another rebreather). Mostly because of the weight of the backplate, and also by the time I strapped on the additional bailout tank on the side (a must for emergencies) it didn’t feel any lighter. Besides the bailout cylinder, both rebreathers had a selector knob installed in the mouthpiece that provides an option of switching to on an open circuit if need be (nice feature for dummies like me although this kind of switching is not exactly a standard operating procedure in a CCR).

The mouthpiece was obviously heavier than the usual reg (rEvo even had a strap for it that wraps around the head), so it did not feel as comfortable. The biggest challenge for me was probably getting a hang of breathing with a counterlung. It just has to be kept inflated properly (like your own lungs), otherwise breathing gets more difficult. If it’s under inflated you feel like you don’t get enough air and take shorter breaths; if it’s over inflated you have difficulty fully exhaling. Even when I had it right the ease of breathing still felt different from an open circuit. I could see how some people might get dizzy on a rebreather without much experience. It just didn’t feel as easy to breathe but I realize that I’m spoiled with regular scuba where breathing normally feels pretty much effortless.

Another big difference is maintaining your oxygen content (“partial pressure”) at certain levels at different depths. So I had to be checking my oxygen sensor data much more often than the tank pressures and bottom time. Depending on the changing readout, you can add either air or oxygen (got buttons for both) to the circuit to keep the breathing mix right. You wanna pay close attention to your O2 because not enough of it in your circuit can kill you (hypoxia), and if there’s way too much of it, well, there is a chance to wind up dead that way too (hyperoxia). It was a beautiful day, 70° and sunny, and I didn’t feel like dying, not ready to make DAN statistics just yet. So I was checking my gauges often like a good boy (my log book was signed with a "Nice job!!" comment afterwards).

As far as diving in silence and absence of bubbles, that was true! Compared to open circuit scuba, that is. While there was no air bubble noise, I was still hearing myself breathing and the valves quietly closing and opening inside the circuit. But those were very low sounds, not something that fish around me could hear. And while it’s almost all bubble-less, there still was some bubble action going on during ascent and when the counterlung got over inflated (some air gets dumped).

After diving with KISS I dove with a rEvo rebreather which I think I liked a little better (rEvo set had a larger counterlung and it just felt a bit easier to breathe). There was a tiny traffic light-style oxygen indicator that was mounted on the mouthpiece so that you see it at all times, interesting idea.

Overall, I enjoyed the experience although to truly have lots of fun diving on rebreather you really need to take a complete training course (a quick crash course don’t cut it). I’m not sure if I’ll ever take that course, the cost of it all being the main limiting factor. When you add the price of the rebreather course plus the unit plus maintenance, seems like a whole lot of dough. But I’m glad that at least I got to try it, it’s likely that I would’ve never dived on a closed circuit otherwise. And it’s not like I’m not a dummy anymore as far as rebreathers, it’s just that now I feel like I am an advanced dummy.


SaintsReturn - 10/13/2010 9:24 AM
Great Blog! Very interesting and not dry. Thank you for sharing the experience
rashley - 10/10/2010 9:16 AM
Great Blog. Thanks for taking the time to share your experience with rebreathers.