Pre-breathe experiment

[Alex]

I assembled my Inspro without the main scrubber o-ring and breathed it for 30 min (in my garage, not in the water ). No ill effects, no strange feeling, nothing (except perhaps a strange taste in the mouth which is probably due to the dinner a couple of minutes before). I am not sure now, what pre-breathing is for actually.

Regards
Alex

[Diving Dude]

Strangely, after l'd cocked up with the o ring a week or so ago, l'd been thinking about doing the same 'Homer Simpson' thing.

So Alex, next go for a jog with it on.

Just remember how long it is before you pass out and that it's in the interest of all the YD inspo divers.

[Okeanos]

Originally Posted by Alex

I assembled my Inspro without the main scrubber o-ring and breathed it for 30 min (in my garage, not in the water ). No ill effects, no strange feeling, nothing (except perhaps a strange taste in the mouth which is probably due to the dinner a couple of minutes before). I am not sure now, what pre-breathing is for actually.

Regards
Alex

I think the check for CO2 is a little over ambitious hoping to find the effect at 1atm. I did 5 minutes without the scrubber canister with no ill effects, so I knew the pre-breathe was going to be useless for me!

It does at least allow you to check your O2 solenoid is working as well as your ADV etc.

[nigelH]

Originally Posted by Alex

I am not sure now, what pre-breathing is for actually.

I thought it was to see that the oxygen control was kicking in and doing things. I would agree that a couple of minutes on the boat being interupted by OCers wondering when you will be ready wouldn't touch the scrubber.

A new scrubber at 1 bar doesn't have much WOB so there isn't much incentive for gas to squeeze round the outside. Get it damp and increase the flow rates 6 times by taking it to 50m and the O-ring starts to earn its living.

[SoggyFox]

Originally Posted by nigelH

I thought it was to see that the oxygen control was kicking in and doing things.
.

thats kind of how i thought it was, a final check to make sure everything is working before you launch yourself into the void.

[Depth-junkie]

Originally Posted by nigelH

I thought it was to see that the oxygen control was kicking in and doing things. I would agree that a couple of minutes on the boat being interupted by OCers wondering when you will be ready wouldn't touch the scrubber.

A new scrubber at 1 bar doesn't have much WOB so there isn't much incentive for gas to squeeze round the outside. Get it damp and increase the flow rates 6 times by taking it to 50m and the O-ring starts to earn its living.

spot on.

as for the pre breath, it will be of no use at 1atm to show serious signs of CO2.

I had to rescue a lad last year who had forgot to place his oring and spacer in his unit

He pre breathed the unit with no ill effects, it was about 10mins into the dive when he had serious problems. CO2 is like nitrogen it effects get worse the deeper you go (a tiny bit of brake through at 50m will be a lot worse efects than the same amount at 2m).

He had probably breathed from the unit for 15-20min before the loop got to a serious stage of CO2 levels As some gas will have gone through the lime bed, but obviuosly he had bypass up the can as well so it was a gradual build up of CO2 over the 15-20min period that created a big problem for him, He was a lucky boy and i am sure he wont make the same mistake again.

ATB
Gareth

[Alan]

I pre breath before every dive, when I got a nip in the O ring, and got under it was too late. I felt terrible for the entire dive and whilst I new something was wrong, i was powerless to rescue myself. At least I had the awareness to keep flushing the loop until I got back on board.

[The Purist]

Yup - pre breathe will show you that your PO2 is stable, that your lung volume is'nt restricted and that your ADV/OPV are working OK (if you bottom/top the lungs). The old argument used to be that it would get the reaction going in the lime too, but it seems that is not quite as essential as some would have it. A pre breath is kak all use for CO2 or for finding leaks if you didn't do a decent +/-ve test... Alpinism, anyone??

[Odin]

It is to stop you having to answer stupid questions to people as you are getting ready to get in the water.

Also, to check handsets working, O2 injector working...

[BJ]

Assemble your unit and wear it in bed. First try breathing off the unit without the O2 turned on. Do not do this while alone or without quick acces to a hospital if need be!

Next day, try the same thing (provided your headache has gone) with the O2 turned on but without the scrubber filled.

I have done both these things. It is very enlightening. You will always be extremely precise about CCR prep afterwards. NEVER do either while underwater.

(I am also known to dive CCR without OC bail-out.)