Prebreathing regs

[TSandM]

It's become obvious from reading threads about the MK25/S600 (of which I just bought two) that prebreathing your regulator on the surface can be a bad idea, especially when it's cold.

On the other hand, prebreathing my regs on the surface does a couple of things for me: ensures that my air is on, and ensures that said regulator appears to be working. It's therefore something I would prefer to continue doing whenever it is safe to do so. I could, of course, always wait until I'm in the water and duck my head under, but it's such a nuisance to have to walk back up to the car without even having a dive to show for it . . .

So the question: At what temperature is it unsafe to prebreathe your regulator? Does it matter how much prebreathing -- in other words, will my usual two breaths be enough to cause trouble? If you prebreathe your regulator on the surface, would you not encounter a free-flow on that basis fairly immediately upon entering the water? Does the temperature of the water you enter have a major impact, and if so, how cold is cold?

 

[captndale]

As long as the air temperature is above freezing I always test breath my regulator.

 

[cerich]

lots of divers make the mistake of doing it with their face in the water but the wet FIRST stages are exposed to the air. When the air temp is close or below freezing the natural cooling that occurs when a reg is used can cause a first stage freeze. If the reg is dry on land then you can breath thru it to test before diving, however once you get in the water my practice is to keep the reg out of my mouth, desend to 3-4 feet put it in then start to breath thru my reg.

AFAIK I'm the only Ice Instructor in Georgia.....

 

[grazie42]

you are obviously reaching...

 

[cerich]

you are obviously reaching...

was that directed at me? I'm in the US but from Canada where I've taught and dove even further north than where you live. That technique has aleways worked for me and my students.

I also detune the IP on a reg for real cold to the 120 psi range (except your swedish regs that don't freeze, just give you icecubes to chomp on with every inhale )

 

[Green_Manelishi]

FWIW ...

Up heeya in (well I won't say where) the air temp drops well below freezing and the water temp will reach low 30s.

I use SP Mk16 1sts on Atomic seconds. I've pre-breathed (inhale only while watching the SPG needle) the regs, with no subsquent problems when the air temp was in the teens and the water temp in upper 30s/low 40s. I also double check the valve just before donning the rig. Most of the problems I've ever encountered have been in that "zone" where all of me is wet but the tank valve/reg is now out of the water because I am talking to the skipper of boat who is hauling the traps I cut free.

 

[TSandM]

cerich, that "reaching" was intended for me. It's a long story (about 16 pages long now).

 

[Mr.X]

lots of divers make the mistake of doing it with their face in the water but the wet second stages are exposed to the air. When the air temp is close or below freezing the natural cooling that occurs when a reg is used can cause a first stage freeze. If the reg is dry on land then you can breath thru it to test before diving, however once you get in the water my practice is to keep the reg out of my mouth, desend to 3-4 feet put it in then start to breath thru my reg.

AFAIK I'm the only Ice Instructor in Georgia.....

Cold wreaks havoc on all sorts of equipment. I think factors like ambient temperature, reg. design, relative humidity and who knows what all play factors in reg. freezes. I pre-breathe only as much as necessary at the surface. With students the reg. is in the mouth going down and breathing as necessary. I have yet to have a reg 1st stage freeze at the surface. I have had them freeze up underwater on a few occasions. Nothing like seeing a huge block of ice surrounding your first stages.

On a side note I once had a first stage freeze and lock up, in addition to the LP inflator of the wing as well as the rear dump. It was truly Murphy's. These days the rebreather is my choice of weapon underwater. X

 

[TSandM]

On a side note I once had a first stage freeze and lock up, in addition to the LP inflator of the wing as well as the rear dump.

Memo to self: Stay out of the water when it's that cold

I guess I want somebody to tell me I'm not going to die because I bought those regulators for use in Puget Sound . . .

 

[do it easy]

Memo to self: Stay out of the water when it's that cold

I guess I want somebody to tell me I'm not going to die because I bought those regulators for use in Puget Sound . . .

You're not going to die, although you might have some short dives. If it starts to freeze, you should have a procedure in place to mitigate the risk.