A: No training agency sanctions solo diving with a rebreather. All training is done with an emphasis on buddy teams. You are taught to brief open circuit buddies on rescue procedures specific to rebreather divers.
That said, you are responsible for yourself. Accident avoidance is the best strategy. As I said before most accidents can be traced back to events or actions of a rebreather diver on the surface. Buddies should be there for random chance events such as a shark biting your leg not for your failure set your unit up correctly and monitoring during the dive. Units setup properly simply work as designed 99.999% of the time. Paying attention during the dive allows one to recognize problems and take action before an accident occurs.
As a note, to break the chain of events leading to an accident due to unit or diver failure, you simply bailout to open circuit and abort the dive. All rebreather divers carry bailout bottles and are trained to use them.
Q: Why use a rebreather?
A: Rebreathers by there nature do two things very well. First is gas logistics. With a rebreather you can stay down 5 plus hours with two 20cf2 bottles at any depth. The second and much more important to fish people is no bubbles. Your interaction with the critters of the sea is much different. With a rebreather you are one of them now. Not some big noisy thing to be avoided. That is why photographers are beginning to use them. I have sat a cleaning station and had my hand cleaned by little shrimp. Swam in a school of marlin having to push them out of the way. Way cool and at 40 feet of less.
A rebreather is a tool that is used in order to accomplish a result. Just like your regulators. Think of it as such.
Dave Talks About Rebreathers – Part 3
A: The key question that I had to answer before I began using a rebreather was, “Why do divers die on a rebreather.” The short answer is rebreather divers die when they forget or stop believing that the laws of physics apply to them.
Q: But when the above mentioned have failed for one reason or another, the next law implied should be survival. Would not the presence of a partner/buddy in close proximity of you, help?
A: Rebreathers are not complex machines but they do require one to setup them properly. Most accidents can be traced to actions or inactions on the surface. Even that, most times does not kill divers, it then takes ignoring warning signs. Generally a rebreather setup properly just works. Monitor it and you will be fine. From the accidents I have been able to research 99% have been diver error. When I use my rebreather I always tell myself the laws of physics still apply to me and complacency and stupidity kills. The definition of an accident is the lost of control. Typically there is a series of events each of itself not causing a loss of control but together causes an accident. Breaking the chain of events prevents the accident. When using a rebreather this is done by paying attention and following your training.
Q; When I dive with my partner/buddy, I have to be honest, I feel as though I am somewhat responsible for his safety, and he mine.
A: When I dive with someone I tell them that no matter what, I am coming back safely. Implied by that is I will drag their sorry butt back also, but I need to know where they are at.
Dave Talks About Rebreathers – Part 2, CO2
As for a CO2 hit, the symptoms are headaches, rapid breathing then unconsciousness. When in doubt bailout.
Q: On open circuit, I breath very lightly, but it would seem to me that, that style of breathing would not lend itself to rebreather?
All rebreathers have unidirectional gas flow. This is done via flapper valves on either side of the bailout valve (BOV). Breathing type or rate is irrelevant to the movement of gas within the loop. There are some issues related to dwell time in the scubber media in extremely rapid breathing conditions. This would be a CO2 issue.
Q: Is it the outside pressure exerted on the counter lungs that forces your breath through the scrubber, and thus returning it to you?
As your lungs expand the counterlung collapses, as you exhale the counter lung expands, pressure on one cancels out the other. External pressure is not relevant, but gas density is however. Counterlungs are but one part of the loop. Work of breathing (WOB) is the resistance encountered. Commercial rebreather units have to have acceptable WOB else no one would buy them. Some units are better than others.
Technical Diving and Commitment
Now what would possess one to want to strap over 100 pounds of stuff onto their body and jump into water over their head? When you find the answer you have found a technical diver.
My answer was that I wanted to go to places that required that commitment. It all started when I first went to Bikini Atoll. Prior to our trip, I had heard about that Nitrox thing and since I knew we were going deep I decided to take a class. Well back in 1995 Nitrox was still a voodoo gas in many eyes. So after much searching I found someone to teach it. In addition to the Nitrox class we took a Deep Air class, sort of a introduction to decompression stop diving. Didn’t think we needed it, but what the heck. After completing the classes off to Bikini we went. We knew what we were doing now!
Well, all dives in Bikini are decompression stop dives. The average dive depth is 155 feet. After a week of this diving, had a great time, but we realized we did not have a clue and that clearly was not acceptable. So after our return, back to the dive shop we went and said we wanted to finish our training. Finish our training meant hypoxic trimix and cave.
At that point I had made the commitment to become a technical diver. After completion of the trimix and cave classes I was a certified cool tech diver, or was I? In the fullness of time I have realized that to truly be a technical diver you have to do technical dives. In order to do technical dives you have to want to do technical dives. So in the end the Why is because there is something down there you want to see and technical diving is how to see it safely.
Lose Weight When You Go Diving
Today, David Snyder talks about his goal of losing weight for diving.
Is this some “Biggest Losers” program? Ah, no. Lose weight when you go diving refers to you kit (equipment). As we continue to dive, over time we acquire more and more things. Very important things when we acquired them but are they still important?
The second path of my weight loss quest is to change heavier for lighter. Ounces add up to pounds. Do you really need a 12″ knife when a 6″ knife will do just fine. Lights, if your light is more than three years old you should be able to double the capacity or half the weight with a new one. I look at each piece of equipment to see if there is a lighter or more capable substitute.
My goal for this process, is one bag 40 pounds, two weeks of diving, nothing rented (except bottles) or borrowed. I am getting there.
How much do you weigh?
Dave Talks About Rebreathers – The Basics, Part 1
Q: Do you need a specific class for a specific type of rebreather?
A: Yes, the physics and physiology is the same for all units but each rebreather is different, hence specific classes.
Q: How do you know when it is time to change your scrubber material? Is this a problem with divers trying to get more out of the material then they are suppose to?
A: You track the dive time on the scrubber media and change it per the manufacturer’s recommendation.
Q: What I am now curious about is, you said on a CCR, at 60ft your PO2 is 1.3. Wouldn’t that figure limit your depth, or do you have the ability through out the dive to adjust that percentage? And if that is the case, is it that ability that gets divers into trouble?
A: You dial the set point in and that is then constant, independent of depth. You asked, if you descend won’t the PO2 spike? It would except that because of Boyle’s Law the volume in the loop will decrease as the pressure increases and you will need to add diluent to the loop. This has the effect of negating the spike. As you ascend you vent gas from the loop and O2 is added to maintain the set point.
Q: Is it better (more flexible) and safer to be able to manually inject O2 right into the breathing loop, or is it better to have it done automatically?
A: Since you retain the ability to manually add gas in all units, some divers will adjust the set point lower than their target and then “fly the unit manually” and use the eCCR controller as a backup. With some units this is easier than others. All eCCR training covers this procedure.
Q: Okay, how the heck did you come up with .59 PO2 at 60 feet? If pressure at sea level is 14.7, and the air we breath is roughly 80% nitrogen, and 20% O2, if I then multiply 14.7 x .2= 2.94, would that be the PPO2 at the surface,
A: Now let us remember back to our Nitrox class. Dalton’s Law, the sum of the partial pressures equals the total pressure. At the surface PO2 = .21 and PN2 = .79 for a total of 1.0. This is then 1 ATA. Therefor at 33fsw ATA would be 2. Because of Dalton’s Law, PO2 would be .42 and PN2 would be 1.58. At 66fsw the ATA would be 3, there for PO2 would be .63 and PN2 would be 2.37. The formula to convert depth to ATA is (Depth / 33) + 1.
Now for 60ft the ATA would be (60/33)+1 or 2.8. Since the ratio of O2 to N2 is the same no matter the depth PO2 would be (2.8 * .21) or .59. It is easiest to convert depth to ATA then calculate the PO2 and PN2 as needed.
