Major free-flow procedures?

jmdiver

Hello all,


Last weekend I was trying out a new dry suit, doing a shallow recreational dive (OC, 8 mts, 11°C). I descended down the line but felt I was under-weighted, so I returned to the surface to add a couple of extra kg to my weight-belt. I was in the process of removing it, when my back-up reg gave me a free-flow.

Being at the surface no harm was done. So I figured out I might practice breathing from a free-flow reg for a couple of breaths before shuting down the first stage. I had only practiced this before while purging the regulator. To my surprise it was very hard: very cold air freezing my teeth and the flow made a small cut in the corner of my lips (I must have sensitive skin). I shutted down. All this lasted less than a min, and the tank pressure droped from 2500 psi to 300 psi (12 Lt tank).

All of this made me wonder:
How do you manage a major free-flow in a rebreather?

I searched the threads for freeflow but other than using an isolator valve / bailing out, I could not find info regarding other procedures like managing buoyancy changes, etc. If someone could point me to the right thread I’ll appreciate it.

Many Thanks,
José Miguel

ScubaDadMiami

For a start, look in the Library for the article about "boom scenarios."

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Howard Packer
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bletso

I have had the problem as well.

Step one KINK the hose to get some control over it. Replace the hose down the road.

If you are not on it then close down the reg. I have a shutdown valve on my OC bail out reg just for this scenario. You can get them from oxycheq and others.

Dale

LukeN

The shut off on the second stage isn't a good idea unless you have a OPV on the first stage. If you blow the first stage seat , then shut it off you would blow the hose next...

How to get better at dealing with a free flow, go buy a guy who teaches OW OC all the time a case of beer... Tune the reg to blow your head off and get them to show you 2-3 different way to do it.

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www.imagedive.com.au

Peter Piemonte

I had a major free flow of my diluent recently due to the failure of a non-rebreather component. (since removed from my gear)

I was at 245fsw of dark cold water, and my onboard diluent supply was exhusted in about 5 seconds.

Good luck identifying the freeflow and shutting down under these conditions with that kind of time constraint.

Much better in my opinion to determine before hand how you will handle the loss of whatever gas, and have a plan in place, or equipment configured in such a manner that any gas lost can be replaced easily from another source.

Regards, Peter

TR300

The lost of the Diluent is normally not a great problem, the Diluent is only for adding and mixing the rebreather loop for descent. If the Diluent is lost or empty then you have to call the dive and ascent normally. All you need the way up is Oxygen for holding the pPO2 constant. Only if you are inside a cave or wreck and have to decent to come out then the Diluent is helpful, but with some exercise it is possible to get gas from your stage tank (take a breath from OC and exhale to the loop) or an in depended BOV. Also a good Idea is to have some in depended buoyancy possibilities (Drysuit, Wing with separate Tank) there are many options on an rebreather to help yourself.

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PCDiver

My procedure is:
When I hear bubbles I close both O2 and diluent at the same time ASAP (muscle reflexes). If I still hear bubbles: close the bailouts.

Then turn them all back on one for one starting with the O2. If too much O2 is lost, abort the dive.

All further decisions are based on my configuration and the type of dive. If I have no diluent left and can't add from the off-board I abort the dive as well.

If I lost my bailout I could be tempted to continue Alpinist depending on depth, type of dive and buddies.

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Ben Field

I'm surprised you where surprised, it is hard!

When we teach basic OC, breathing off a freeflow reg is one of the skills taught- you don't need to put a freeflowing reg "in your mouth" just hold onto the mouthpiece and let it fill your mouth, the excess will vent all around but there is so much gas it doesn't matter. Sometimes just breathing out through it is enough to stop it but most people are cranking the valve wheel shut by then anyway.

Yes its cold and yes it drains the tank fast...

A properly tuned and suitably tested reg shouldn't freeflow so there is normally something to be done if the reg flows more than once- check the IP, make sure no one breathed off it on the surface if its a cold day etc.

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Abbo

I had a nasty moment on OC once, ascending from a deepish wreck at 85m with a significant deco obligation. I opened the travel mix and bang: gas all over the place. Obviously, ascent is not an option, and the gas was not going to last if I just breathed off it, so clearly the only thing to do is to turn off the valve between breaths. Obviously I felt like a chimpanzee: had I really tested the operation before splashing? I was sure I had. It certainly taught me a lesson about double-checking kit before splashing.

On CC, I'll agree that there is a dilemma: do you add isolators or not? With only 3 litre tanks, you really can't afford to lose gas. I chose to add isolators to my BOV, and to the 2nd stage regulator on my bailout. It worries me a little that I will have a hypercapnia hit and the isolator will have been knocked into the closed position. But that is better than the risk of gas loss: I'll just have to keep checking the position of the isolator more often.

I additionally have a Quick Disconnect on the line connecting my bailout tank to my manifold. I don't like it: it won't connect when the line is under pressure, and if it can't be undone under pressure without shooting gas all over the place. I plan on pitching it and going to a swagelock QC6 connector.

jmdiver

Thanks everyone for your input. The boom article is very interesting.

Yes, indeed this skill is practiced at entry level, just the way you've described. I have never had a "real" freeflow before (the reg service is adequate or I don't dive enough, probably both).

In training we simulated freeflow by purging the reg. edit: Thinking back when putting the reg so that half the gas went in the mouth cavity and the rest out to the side of the cheek, I may have put the reg directly in front of my mouth (practice - practice)

I was surprised because even though I was instructed on what to expect, and acted accordingly, the real life experience was very sobering.