Prebreathing Survey

[doctormike]

I haven't seen this discussed in a few years, and I'm thinking of changing my pre-dive procedures, so I figured I would see what experienced rebreather divers think.

There are two main reasons why people do a prebreathe - to check to make sure that the unit can maintain a life sustaining PO2 and to see if there is a scrubber problem. Research a few years ago suggested that it was very possible to have a scrubber problem (even an absent scrubber) that was not picked up by a prebreathe. However, while the practice may have a low sensitvity for picking up scrubber faults, I suppose that it's possible that some of them may be detected in a 5 minute prebreathe. So perhaps not totally useless, as long as you don't rely on it, and pay attention to scrubber packing and duration.

I'm thinking of switching to a shorter prebreathe. I still think that it's really important for the first reason, but it probably doesn't have to be a full five minutes for that. I still believe that the prebreathe should be done in the unit, with a mask on, since it's possible to disconnect something while donning.

What do you think?

 

[RainPilot]

I do it wearing the unit, since its way less hassle manning the loop hoses etc like that. My unit requires a 5 minute breathe before diving so I won't shorten it but I can see why one might want to.

In my case, the unit ends up at a 0.7 PPO2 after setup and calibration, with a SP of 0.5. In my prebreathe I am checking whether the PPO2 drops as I breathe (checking against frozen sensors) and then whether the solenoid fires once it gets to 0.5 and keeps it there.

 

[Caveeagle]

I was trained to do a 5m at assembly, which I normally do at home. Then I try to do couple minutes Once strapped in, typically sitting on the tailgate of my truck.

 

[stuartv]

I'm not experienced yet, so I wouldn't vote.

But, if I were to vote, the poll would really be better if it had an additional choice.

My rEvo has the rMS system. With rMS working, the pre-breathe procedure is to breathe until the controller shows at least 45 minutes available on the scrubber. It's normally well less than 5 minutes - at least, in the warm weather I've dived it in so far. Without rMS (or with rMS not working), then it's a 5-minute pre-breathe.

Either way, I do it to spec, after gearing up, and just before splashing.

 

[taimen]

IART level 1 manual for JJ states 2-3 minute prebreathe while in the unit. I was instructed to do 3 minutes. I was emphasized that 5 minute prebreathe won't be able to pick up many scrubber problems. Thus the main point in 2-3 min prebreathe is to verify that the unit is otherwise functioning and able to hold setpoint.

 

[mmadiver]

Breath the unit after assembly for a minute (not wearing it incase something is broken) to ensure solenoid functions, battery life, cmf working, etc..

Then, Put loop in mouth as soon as unit is on my back and breath it while I get other things sorted before splashing.

 

[doctormike]

My unit requires a 5 minute breathe before diving so I won't shorten it but I can see why one might want to.

Gotcha! "Requires" by software, by manufacturer standards, or by your training?

 

[doctormike]

I'm not experienced yet, so I wouldn't vote.

But, if I were to vote, the poll would really be better if it had an additional choice.

My rEvo has the rMS system. With rMS working, the pre-breathe procedure is to breathe until the controller shows at least 45 minutes available on the scrubber. It's normally well less than 5 minutes - at least, in the warm weather I've dived it in so far. Without rMS (or with rMS not working), then it's a 5-minute pre-breathe.

Either way, I do it to spec, after gearing up, and just before splashing.

Of course you should vote, you are a very thoughtful diver!

So what do you do, what is "spec" for you?

 

[doctormike]

IART level 1 manual for JJ states 2-3 minute prebreathe while in the unit. I was instructed to do 3 minutes. I was emphasized that 5 minute prebreathe won't be able to pick up many scrubber problems. Thus the main point in 2-3 min prebreathe is to verify that the unit is otherwise functioning and able to hold setpoint.

Gotcha. Not familiar with IART's materials. The TDI materials aren't unit specific, and I was told 5 minutes in JJ training.

 

[broncobowsher]

I will call it a few minutes. But not exactly 5. Get everything ready, be on the loop. If timing is right, get the fins on and jump. May not be the full 5 minutes, but I try to make it so. Usually have a couple minutes hanging out on the surface before descending. When it gets hot out I am much more likely to be waiting on the water then on the boat, just to prevent overheating. I know I have done 10 minutes waiting on the water, on the loop, while waiting for an issue with another diver still on deck. Do you consider surface time part of the prebreath? Or only before actually getting in the water?