Checklists in Rebreather Diving

[berndo]

Wow, pre breathing to check whether the unit is working properly is BS?
A bunch of people would still be around if they had pre breathed their unit.

 

[broncobowsher]

Keep following the checklists. In addition to what is on the revo build checklists, you may want to note MV in air, note MV in 100% O2 (during calibration) and check for linearity (i.e. MV Air x 1/.21 = MVO2). Also if you note the MV during the neg, its easier to see if the neg is working than just relying on a woosh sound at the end of 2 minutes.

...

My method is to pull the negative and set the loop against the harness. Mental note of where two things line up at, mouthpiece to D-ring for example. Come back after doing a couple other things and verify that the alignment is still the same. Open the DSV, get the woosh, and it drops. That is good.

I've had it where there was a little creep over time. Still got the woosh. But the creep was an indication there was something not perfect. Found a nick/pinhole in the loop hose. Not enough to fail the woosh test, not enough to cause issues while diving, just enough that I had a little more water inside than I was expecting after a long dive.

 

[OTF]

Wow, pre breathing to check whether the unit is working properly is BS?
A bunch of people would still be around if they had pre breathed their unit.

The problem with prebreathing is that a meaningful, useful prebreathe has to be extraordinarily long, greater than 10 or maybe even 15 minutes. Simply not feasible. A standard 5 minute prebreathe starts to get the sorb warmed up but isn't actually capable of detecting CO2 breakthrough in most instances.

 

[berndo]

The problem with prebreathing is that a meaningful, useful prebreathe has to be extraordinarily long, greater than 10 or maybe even 15 minutes. Simply not feasible. A standard 5 minute prebreathe starts to get the sorb warmed up but isn't actually capable of detecting CO2 breakthrough in most instances.

But 5 minutes is enough to see if the unit can hold setpoint. Plenty of people have died early into a dive due to hypoxia.
What's the point of skipping a 5 min check?

 

[rddvet]

The problem with prebreathing is that a meaningful, useful prebreathe has to be extraordinarily long, greater than 10 or maybe even 15 minutes. Simply not feasible. A standard 5 minute prebreathe starts to get the sorb warmed up but isn't actually capable of detecting CO2 breakthrough in most instances.

Yep. I find it pointless. I do throw the bov in my mouth and check my p02 moves when I breathe it down and add dil or oxygen, but that's a less than 1 minute check. The 5 minute prebreathe is useless in my opinion.
I don't dive an eccr and never have, so idk if that would make a difference.

 

[rddvet]

But 5 minutes is enough to see if the unit can hold setpoint. Plenty of people have died early into a dive due to hypoxia.
What's the point of skipping a 5 min check?

So a 5 minute prebreathe would solve that issue? IMO if you're dying at shallow depths due to hypoxic mix you're not watching your p02 and a 5 minute prebreathe woudn't fix that. Are these people looking at their computer as they jump or descend? Because hypoxia from the surface down doesn't just suddenly happen.

I'm seriously asking and not trying to argue. I do not see the point. I honestly don't even know my instructors' opinions on it, but it wouldn't change my thoughts.
Maybe it's different on eccr?

 

[rddvet]

My method is to pull the negative and set the loop against the harness. Mental note of where two things line up at, mouthpiece to D-ring for example. Come back after doing a couple other things and verify that the alignment is still the same. Open the DSV, get the woosh, and it drops. That is good.

I've had it where there was a little creep over time. Still got the woosh. But the creep was an indication there was something not perfect. Found a nick/pinhole in the loop hose. Not enough to fail the woosh test, not enough to cause issues while diving, just enough that I had a little more water inside than I was expecting after a long dive.

Same, mental note of position during negative. It can be annoying because I have a bov and sometimes if the bov hose was caught on something and releases you'll get a little movement. But all that means is I do it again and confirm which isn't a bad thing.

 

[billgraham]

Via Ted McCoy, the 2's:

2 tank valves
2 pressure gauges
2 inflators, suit and wing
2 add valves, o-2 and Dil
2 pressure tests, positive and negative
2 ways to check your PPO2

 

[berndo]

So a 5 minute prebreathe would solve that issue?

In the case of the bugge accident, one of the recent accidents in France and a bunch of others it would have helped. They would have noticed that their O2 was closed. They were distracted which is something that can happen to most of not all people under the right circumstances.
I don't see the point in saving 3 or 4 minutes before a dive or using a pre dive checklist. Calling a safety check BS, I don't get either.

 

[bubblemonkey2]

A brief pre-breathe will not necessarily reveal an oxygen supply issue (e.g. tank off etc), unless you are watching the oxygen SPG/pressure during this pre-breathe.

This is normally not watched, just like OC divers fail their OC reg pre-breathe by not watching their SPG.

It can take minutes for the residual pressure in the lines to drop, even though your oxygen valve is closed. Your quick "check" will not catch it. I'm guessing this exactly has killed people. Following an actual checklist item by item can prevent this.

I had this happen underwater once during drills training. A "solenoid stuck open: oxygen freeflow" drill involved turning off the oxygen valve. It was minutes after the drill ended that I finally noticed my ppO2 was abnormally low and remembered to re-open the oxygen valve.

I guarantee this has happened to people, they turn off their oxygen in transit, after the checks, to "save oxygen" or whatever, and hop in the water straightaway. Some drown. Nowhere in the appropriate checklist should it say "turn off your oxygen again before you enter the water," so it's another failure to follow checklists.