Why no poor man's rebreather?

[PfcAJ]

I don't know what to say. My cells work every dive. Lol. I live in hot humid Florida. I have over 2000 hours between 5 different units and the only rebreather that almost killed me was a Revo that flooded. Which is why I only dive CCRs that can recover from a flood now. Changing cells is a pain in the butt, but a lot quicker and easier than overhauling a regulator. Yet we do this without fuss.

It just means that I believe in proper maintenance. Have I had cells die for no reason? Yes. Have I had them die while in a cave? Yes. But, certainly not all 4 of them. But even if all four of them died, or even 2 of them died, I'm trained to overcome it. So are my students.

....

 

[Superlyte27]

....

I didn't say all of them work the entire dive. But to this day, I've only bailed out twice. Once for flooded Revo (caustic - my fault) and once for flooded Revo (not my fault)

I've never needed to bailout or was even concerned about the possibility of bailout due to cell failure. That's what I meant.

 

[KevinNM]

It just means that I believe in proper maintenance. Have I had cells die for no reason? Yes. Have I had them die while in a cave? Yes. But, certainly not all 4 of them. But even if all four of them died, or even 2 of them died, I'm trained to overcome it. So are my students.

As far as decreased mental capacity during a CO2 event, what happens first? Increased breathing rate to void CO2 or decreased mental capacity? So, if you are vigilant, and make sure your breathing doesn't increase, no worries.

Now, some people suffer from decreased mental capacity before they even get out of the car. My argument is that CCR's are not for everyone. The stupid need not apply.

I’ve had described to me and seen other people post experiences where a CO2 hit didn’t cause a significant change is breathing. Forrest Wilson posted this one:
Strange Symptoms

 

[Superlyte27]

That sounds more like mushroom valves to me. So computer could be reading a 1. 2 PPO2 but in that 9 inches of hose he's moving back and forth the same gas over and over again not getting any new gas from the head. lack of oxygen will cause confusion a whole lot faster than CO2 will.

 

[DA Aquamaster]

I dive a KISS Sidekick with 'just' three sensors. It's enough, although there is something of a learning curve to getting things to run trouble free.

For example if you are doing 4 to 6 hours per day, for several dats in a row and expecting the head and sensors to dry outside in a Florida simmer night it's not going to happen, at least no well enough. I had sensor issues until I noted that I could blow water out of the connection end of the sensor even after "drying" over night. There are two solutions - bring the head into the AC'd room or if you are roughing it, use a rubber nozzle and blow some dil into that area of the sensor and connection to displace any moisture and blowing it dry it out.

There are other things I've learned such as 3 or 4 hours into a 5 or 6 hour dive, you start getting enough condensation that clearing it from the loop is worthwhile to prevent any excessive accumulation that could become a problem later in the dive. Similarly, I found that mounting the unit on the left, left the exhale tower at the low point so any accumulation of water would announce itself in the form of some gurgling in the hose. A slight (maybe 15 degree) roll to the right puts the OPV at the low point and a dil flush will blow it over board. And if I'm going to be pushing through restrictions I use the lid off a small spray paint can with a few small holes in it to keep sand and small stones from potentially getting stuck on the sealing surface of the OPV. I've also gravitated toward replacing all three sensors at once, ideally with sensors from the same lot, and I acquired a test unit to periodically test them. The end result is that the last several cave diving trips we've made have had rock solid sensor performance, even in a unit that isn't known to be all that kind to sensors in terms of moisture.

But even before then, a failed sensor wasn't an issue and even three sensors that disagreed was not an insurmountable problem that would put me off the loop, as you can still confirm which sensor is correct with a dil flush and comparison with the dil PPO2 at depth. In the extreme, if you have thoroughly dil flushed, are using an appropriate dil for the depth, and are running minimum loop volume, you're still good to go even with no sensors,until you have to change depth. provided you are maintaining depth, you are metabolizing the O2, and that's the only thing causing a reduction in loop volume. If you add just enough O2 to maintain minimum loop volume, you're also still maintaining the dil PPO2 at depth that you started with, and you can delay or prevent having to bailout to SCR mode.

In short, safety increases with experience on the unit, in knowing how it works in great detail and in fully understanding the various failure modes and options that are available to address any failures.

I'm in agreement that the stupid need not consider CCR since they are probably never going to understand how it works, how it potentially fails and how to prevent a failure or address a failure if it occurs.

 

[DA Aquamaster]

That sounds more like mushroom valves to me. So computer could be reading a 1. 2 PPO2 but in that 9 inches of hose he's moving back and forth the same gas over and over again not getting any new gas from the head. lack of oxygen will cause confusion a whole lot faster than CO2 will.

I've seen divers with excessively small counter lungs or excessively small scrubbers out breathe their loop and have similar CO2 issues. Working hard in high flow can do that. In a properly packed scrubber the chemistry is very reliable - but the reactions take a certain amount of dwell time in the scrubber to work. If the gas is getting pushed through the scrubber too fast for all the reactions occurring to remove all the CO2, you'll quickly get a buildup of CO2.

 

[DA Aquamaster]

One of the biggest challenges for a CCR diver is really getting a handle on how long the scrubber will actually last. I've never found any solid data on the Sidekick but I've seen 3 hours quoted for a similar scrubber design with the same capacity - based on using 3 liters of O2 per minute (a rate no one can sustain) in 40 degree F water. That just does not generalize well to normal 1.0 liter per minute work loads in 70 degree water.
Consequently, over a number of dives in controlled conditions, I've worked up to 6.5 hours, all of it swimming. I know a diver who has taken his out to 11 hours, but he only recommends a maximum of 8. Personally, after 6.5 hours swimming with an AL 72 bailout along for the ride, 6.0 is as far as I want to go. Experimenting with Increased workload in that last half hour was enough to convince me that the scrubber wasn't as efficient as I'd like it to be if I really needed to exert myself. If the majority of the dive was on a DPV and the rest was on deco than 8+ hours might be just fine, but that's again something I'd have to work up to.

I'm ambivalent about that. On the one had, it's annoying that the certification and testing protocols are so horrendously conservative and worst case that they are effectively useless. On the other hand, there is some value in leaving that responsibility to the individual divers. And on the third hand, some CCR divers are morons who can't be relied upon to feel out those limits and all the qualifiers that go with them in a safe manner.

 

[Superlyte27]

I dive a KISS Sidekick with 'just' three sensors. It's enough, although there is something of a learning curve to getting things to run trouble free.

For example if you are doing 4 to 6 hours per day, for several dats in a row and expecting the head and sensors to dry outside in a Florida simmer night it's not going to happen, at least no well enough. I had sensor issues until I noted that I could blow water out of the connection end of the sensor even after "drying" over night. There are two solutions - bring the head into the AC'd room or if you are roughing it, use a rubber nozzle and blow some dil into that area of the sensor and connection to displace any moisture and blowing it dry it out.

There are other things I've learned such as 3 or 4 hours into a 5 or 6 hour dive, you start getting enough condensation that clearing it from the loop is worthwhile to prevent any excessive accumulation that could become a problem later in the dive. Similarly, I found that mounting the unit on the left, left the exhale tower at the low point so any accumulation of water would announce itself in the form of some gurgling in the hose. A slight (maybe 15 degree) roll to the right puts the OPV at the low point and a dil flush will blow it over board. And if I'm going to be pushing through restrictions I use the lid off a small spray paint can with a few small holes in it to keep sand and small stones from potentially getting stuck on the sealing surface of the OPV. I've also gravitated toward replacing all three sensors at once, ideally with sensors from the same lot, and I acquired a test unit to periodically test them. The end result is that the last several cave diving trips we've made have had rock solid sensor performance, even in a unit that isn't known to be all that kind to sensors in terms of moisture.

But even before then, a failed sensor wasn't an issue and even three sensors that disagreed was not an insurmountable problem that would put me off the loop, as you can still confirm which sensor is correct with a dil flush and comparison with the dil PPO2 at depth. In the extreme, if you have thoroughly dil flushed, are using an appropriate dil for the depth, and are running minimum loop volume, you're still good to go even with no sensors,until you have to change depth. provided you are maintaining depth, you are metabolizing the O2, and that's the only thing causing a reduction in loop volume. If you add just enough O2 to maintain minimum loop volume, you're also still maintaining the dil PPO2 at depth that you started with, and you can delay or prevent having to bailout to SCR mode.

In short, safety increases with experience on the unit, in knowing how it works in great detail and in fully understanding the various failure modes and options that are available to address any failures.

I'm in agreement that the stupid need not consider CCR since they are probably never going to understand how it works, how it potentially fails and how to prevent a failure or address a failure if it occurs.

What he said

 

[PfcAJ]

#nosensors

 

[JohnnyC]

#nosensors

I wouldn't mind getting a cheap PSCR to play around with, something like a Tres Presidentes, Habanero, or GDS AH1. Stupid simple and not much to go wrong. I'd like a cell though, until I get comfy with the concept. Unfortunately all the cheap ones are out of Europe. And while the GUE breather training is well worth the money, the RB80 itself should cost about 75% of what Halcyon charges for one. Hell, you can damn near build one straight out of the McMaster catalog.

You really need to talk to them about getting those things painted that DUI red though. That's a huge oversight in my opinion.