Checklists in Rebreather Diving

[Germie]

That’s why the DIR rake is always there. Or should be there if somebody doesn’t steal it. First time I dove truffe was about 11 years ago before sm was very common in France. A guy watched us zip right into truffle and had to stick around till the end of our dive to talk our ear off about how he raked for 3 minutes and still struggled to get in.
Now you see sm everywhere I’m the Lot.

I also dive sidemount. I already did in a time that DIR was still believing in backmount as only way. But I have done it backount also.
We also have digged it out after heavy rains. Then even with sidemount it was too narrow till you took out a lot of stones.
But the Bial only can be done sidemount (sometimes no mount entrance). But sidemount was always quite common in France, but a different way of sidemount you see in other countries in the world. Steel tanks with floats, steel tanks that have different sizes left and right, etc. But you also see normal bcd's with really independent doubles (2 single tanks), etc. But this is seen less than 12 years ago. But the sunday morning club dives on single tank in the caves with not a lot of penetration distance are still done by clubs there.

 

[rjack321]

If you are smashing and banging your way into caves... Right now would be a good time to stop doing that. That damage and scrapes are forever (well more than a human lifetime).

 

[Germie]

If you are smashing and banging your way into caves... Right now would be a good time to stop doing that. That damage and scrapes are forever (well more than a human lifetime).

I agree. But I answered to an example were it has nothing to do with smashing and banging. Just 1 narrow entrance where people go in with backmount. And yes, maybe there is sidemount better. But nobody worries there if people go in with backmount there. You can agree or disagree, but this is just a fact.

 

[Seameadow]

The presentation by Dr. Pollock on Rebreather Hazards during the latest Rebreather Forum 4.0 might be of interest when it comes to the discussion of pre-breathing.

He quotes a study where 20 divers did a pre-breath (5 minutes) on three different sets of machines / scrubbers, one with a fully working, properly packed scrubber, one partially working scrubber and one absent scrubber.

On the fully working scrubbers 20 (100%) of the divers stayed on the loop.

On the partially failed scrubbers, 18 (90%) stayed on the loop and 2 got off the loop.

On the absent scrubbers, 5 or 25% stayed on the circuit whereas 15 got off the machine.

The major findings of this was that there were no false positives, most failure events on partially working scrubbers were missed, but then most on absent scrubbers caught.

The key takeaway that pre-breathing could actually be useful but certainly not completely adequate for testing scrubber function. (Please note maintaining SP etc is a different matter).

Make of it what you will, but the point was tempsticks, CO2 sensors technology would be useful to aid. On that Dr. Rachel Lance gave an interesting presentation on technologies that may be not too far off in the future that would help detect divers in distress, before it is too late, including sensors that analyze breath sound with algorithms and eye tracking.

 

[Wibble]

Do you run into stuff with your doubles valves? It’s no different. The fathom has 1000s of cave dives on them because that’s what they were built for. Fathoms come valves up for onboard tanks. The unit was built by the guy with world record cave dives. If bashing valves into a ceiling is a concern he wouldn’t have built it the way he did. If you’re bashing ccr tanks in he ceiling you would in doubles too and that’s a skills issue.

Do you stand your cylinders up on the valves or on the cylinder base? Which end is stronger?

When you're aiming to get in a hole and bash the top of the rebreather on the wreck/cave, do you mind that it's hitting the exposed valves? Do you have a "halo" protector above them?

Why is it that the vast majority (99%?) of backmounted rebreathers have a standardised cylinder layout with valves down and bases up? Only a tiny esoteric minority insist on having rebreathers cylinders with the valves exposed on top. That it is easier to reach an inverted cylinder's valves behind your back is another bonus.


Doubles: that's open circuit, not CCR. Different thing and 10 times heavier than a CCR cylinder where it's being dragged across the floor.

BTW, have never seen a Fathom in the flesh.

 

[Germie]

CO2 sensor have sadly too often valse warnings, but it can be a usefull tool. And a tempstick can sign no problems, but there still is an problem. If a scrubber works not for 100%, you will not find problems in the first minutes of a dive. The tempstick can work flawless, but you still can have a CO2 problem.
So also rms can make mistakes.

 

[davehicks]

The presentation by Dr. Pollock on Rebreather Hazards during the latest Rebreather Forum 4.0 might be of interest when it comes to the discussion of pre-breathing.

He quotes a study where 20 divers did a pre-breath (5 minutes) on three different sets of machines / scrubbers, one with a fully working, properly packed scrubber, one partially working scrubber and one absent scrubber.

On the fully working scrubbers 20 (100%) of the divers stayed on the loop.

On the partially failed scrubbers, 18 (90%) stayed on the loop and 2 got off the loop.

On the absent scrubbers, 5 or 25% stayed on the circuit whereas 15 got off the machine.

The major findings of this was that there were no false positives, most failure events on partially working scrubbers were missed, but then most on absent scrubbers caught.

The key takeaway that pre-breathing could actually be useful but certainly not completely adequate for testing scrubber function. (Please note maintaining SP etc is a different matter).

Make of it what you will, but the point was tempsticks, CO2 sensors technology would be useful to aid. On that Dr. Rachel Lance gave an interesting presentation on technologies that may be not too far off in the future that would help detect divers in distress, before it is too late, including sensors that analyze breath sound with algorithms and eye tracking.

How in the world do you end up with an empty or partially filled scrubber?

This sort of pre-breathing check sounds like driving your car around for 5 minutes to see if the gas tank is empty or not.

There is a much simpler way to verify and prevent this failure mode.

 

[berndo]

How in the world do you end up with an empty or partially filled scrubber?

This sort of pre-breathing check sounds like driving your car around for 5 minutes to see if the gas tank is empty or not.

There is a much simpler way to verify and prevent this failure mode.

That's not the point. They were trying to find out how senitive people are higher CO2 concentration and in what time frame.

 

[rddvet]

Do you stand your cylinders up on the valves or on the cylinder base? Which end is stronger?

When you're aiming to get in a hole and bash the top of the rebreather on the wreck/cave, do you mind that it's hitting the exposed valves? Do you have a "halo" protector above them?

Why is it that the vast majority (99%?) of backmounted rebreathers have a standardised cylinder layout with valves down and bases up? Only a tiny esoteric minority insist on having rebreathers cylinders with the valves exposed on top. That it is easier to reach an inverted cylinder's valves behind your back is another bonus.


Doubles: that's open circuit, not CCR. Different thing and 10 times heavier than a CCR cylinder where it's being dragged across the floor.

BTW, have never seen a Fathom in the flesh.

There is no difference between valves up and back mount. Other than you have a can between them that usually takes the beating not the valves. Valves up is a nonissue and just because it’s been done one way by everybody doesn’t mean valves up is bad. It makes everything stay the same as in bm so you have inherent muscle memory in case you need to do a valve drill. Again, if valves up was a danger I don’t think they would have chose that orientation to do a world record cave dive. It is a nonissue. Give it a try and see for yourself.

 

[Germie]

How in the world do you end up with an empty or partially filled scrubber?

They want to show that a partially failing scrubber does not cause direct problems, but later maybe yes.

With more than 1000 hours on ccr, yesterday I had my first strange feeling what must be a CO2 problem on a really shallow dive with my ccr. I was diving my ccr with new cells, the scubber has a CE limit of 3 hours and only 45-60 minutes were done on this scrubber a week before. Why do I write 45-60 minutes? That has to do with a teaching dive, we practised some skills like bo, descends, etc, so went up for a couple of times, down again, flushes, etc. So I did not feel anything strange during that dive, where the in wate time was 65 minutes, but the time under water some less. So if there was something wrong with this scrubber, I would probably not feel it because of breathing normal air between excersizes. Max depth was 15m.
So yesterday I took my ccr again with the idea of doing 2 shallow dives, or 1 longer one on ccr and the second on oc. This was a fun dive, and after half an hour we split up because I wanted to take some pictures of small snails. I also checked the celles as they were new, if they lookedTo take these pictures, I was diving in strange positions, but really shallow, between 5 and 8m depth. I felt some headache starting, but not that serious. I also had to pee. After about 75minutes I had to decided that I had to go out due to my peeing need. I swam back to the entrance point, a little bit faster than normal because I was not looking anymore for small critters. But it was not a hurry swim. Only at a depth of 4m. I only felt that I was a little bit out of breath, something that is not normal, even not with this a little bit faster swimming. But I still could hold my breath. I tested this because I was thinking that this could be CO2. Yes, I could swim back at surface, yes, I could do a bo, but then was already back to the entrance before I had to take action. When taking off my fins, I was still a little bit out of breath. For sure not normal. Back at the car I had only a slight headache left. Drank some water, and for the second dive I took my oc twinset.
All signs are there for a small CO2 breakthrough, nothing that you will see with a prebreathe, nothing that I felt within the first hour of the dive, it started around 75 minutes, when I was getting a little bit cold also. I checked all at home again, no orings broken, all orings in place, no leaks in the mouthpiece (I also had checked this before assembling), so I know my unit must be ok.
The tempstick still did show 5 out of 6 stripes.
If I was deeper or had been further away from the entance point I had to do a bo or swim back at surface. I don't have a CO2 sensor, but have tempstick, but haven ever seen a breakthrough on the tempstick (have seen this with another diver). On the dive with the twinset, I did not feel anything strange and also no headache appeared again.

So everything is checked, even a prebreathe, but nothing was wrong then. But if you want to test if people feel a partially failing scrubber, the test mentioned above is a good one. You see that most people won't feel it then. If a scrubber only filters out 99% of the CO2, it will take a while before you feel it as a diver. This is what this test shows. If the prebreathe would have taken 30 minutes, more would have gone from the loop with a partially failing scrubber.

So this week I will dive my unit again before going to trimix depths next week.

But I won't say a prebreathe is useless and a waiste of time. There are failures that can be found then. But not all.