Shutting off a single tank diver's air supply in a free-flow?

[capt. dave]

Worth more than two cents...

 

[Web Monkey]

Analyzing the dive we came up with a few items to correct. First was technique, he shouldn't have laid on the inflator to slow his descent in cold water, short bursts work better. Second was equipment, he got rid of his piston first stages and replaced them with sealed diaphragm first stages. Third was configuration, this type of a dive should probably be done in doubles or with two first stages. The one mistake we didn't make: we both had a solid dive buddy we could count on.

The only thing that really needs correcting is that you shouldn't be diving in cold water with a reg that isn't designed for the conditions. Doubles would be nice, but really aren't a requirement for a no-deco dive, and won't fix the freeflow problem, just make it possible to handle underwater. The root of the problem isn't that you used the inflator, it's that the first stage couldn't handle it. What happens if you need to use more air, for example if your buddy was OOA and wanted to share?

When you guys say you wouldn't shut off the valve, what I don't get is why you would just let the tank empty? What good does that do you? Sure as a last resort you can breathe of a freeflowing regulator on your way to the surface, buy why would you if you didn't need to? I wonder how many of you have actually seen the volume of bubbles that are generated when both second stages are dumping gas? How many know how fast that will empty a tank?

I see them all the time, but the impressive bubbles are irrelevant. You leave the tank on because it's a no-deco dive and the diver can usually make a normal ascent to the surface, breathing his own reg before the tank empties. Turning off the (still working) tank on a single reg diver means that an air-share is now mandatory and unless the buddy is really good or the OOA diver remembers oral inflation and/or weight ditching from class, there's a good chance of a drowning once he reaches the surface and can't inflate his BC.

Also, unless the donor has a non-freezable first stage, you'll end up with one tank off (OOA) and two divers breathing a freeflow from a single tank.

There's just no reason to turn an annoyance into a potential double fatality just to stop some bubbles.

Terry

 

[String]

In a free-flowing regulator situation between two single tank divers, is it really a good idea to do as some in the other thread suggested and shut off the free-flowing diver's air supply once he/she is breathing off one of your second stages?

I can't think of any real benefit for doing so unless it's in an attempt to see if the free-flow is solvable at depth.

Don't see any problem trying, if the diver is on an AAS or his own redundant air source then its worth a try and could save a dive. If its a frozen freeflow (most common type) then turning off for 30 seconds is likely to cure it. Provided not too much gas is lost if both divers are happy they can carry on.

One of the reasons mentioned for turning off the free-flowing air source was to prevent a possible auto-inflation of the diver's bcd, but wouldn't it just be safer to disconnect the inflation hose? After all, you and the buddy are ascending so there's no need to add air to the bcd anymore.

Wont happen anyway if the 2nd stages are properly serviced - they are designed as the pressure relief not the LPIs.

Also, just to state the obvious, this question revolves around a scenario well within NDL limits, which obviously means a CESA is possible if buddy separation (with the one diver's air-supply off) occurs on ascent.

CESA should NEVER be needed. In this situation just breathe from the freeflowing reg which every diver is supposed to be comfortable in doing since training. Depending on when it happens you'll have 30 seconds to a few minutes of gas.

 

[Web Monkey]

Don't see any problem trying, if the diver is on an AAS or his own redundant air source then its worth a try and could save a dive. If its a frozen freeflow (most common type) then turning off for 30 seconds is likely to cure it. Provided not too much gas is lost if both divers are happy they can carry on.

AFAIK, the above scenario was two divers each with a single tank, no pony or doubles.

Terry

 

[Doc Harry]

I am a proponent of shutting down the valve in an uncontrollable free-flow situation, in certain situations. There are several benefits to turning off the valve, as I shall explain.

As a novice diver I had a free-flow at 70 feet that resulted in an out-of-air situation. The hose loosened at the second-stage regulator, precipitating a free flow. Hand tightening did not stop the free flow and I went OOA during the ascent. Since then, I have put a lot of thought into emergencies and free flow.

Three things have to happen before I would shut down a valve in a free flow:

First, proper gas planning and execution of the dive plan should mean that your buddy has enough gas remaining ("rock-bottom" gas) to get both of you back to the surface with all of your required stops.

Second, trouble-shooting the free flow is unsuccessful and the free flow continues. Depending on where you live, the most common causes of free-flow are second-stage problems (freezing or stuck diaphragm).

Third, my buddy has to be right there for me and I would have to be breathing easily from my buddy's octo.

Then, and only then, would I shut off the tank valve.

There are several benefits to shutting off the tank valve:

1. The bubbles from a free flow are EXTREMELY distracting. Do not underestimate the distraction. It's bad enough that you're worried about your air supply, but the bubbles make it really difficult to concentrate on the task at hand and add greatly to the anxiety. A more advanced diver might not be as affected as a novice diver.

2. It is good to have some air remaining in your tank in case you and your buddy have to separate. For instance, if it is rough on the surface, you and your buddy will have to separate so that you can climb up on the ladder. If you can turn on your valve at that time at least you have some air remaining and you can keep your regulator in your mouth. Additionally, you have some air in your tank to operate your BCD.

3. A massive free-flow at depth may be just a little bubble leak at a shallower depth. If you need to separate from your buddy and turn on your valve, the free flow may not be so bad anymore.

4. Leaving the valve open until you are OOA will cause your tank to fill with water. This means the valve will need to be removed and cleaned, and the tank with have to be cleaned and inspected. This is a PITA if you've ever had to do it. There have been several scientific investigations that have proven that tanks drawn down to empty will fill with water if the purge button is depressed at depth.

My reasoning is not all-inclusive for all situations. There may be situations when I would not turn off my valve in a free flow. I just can't think of any now.

Clearly, there are disadvantages to turning off your tank valve, as mentioned above by other people. Having suffered a massive free flow and OOA myself, and having tried to get back aboard a boat in rough seas without any air in my tank, I can say that I would prefer to shut off my tank valve to save some of my air for the surface, rather than let my tank go completely empty at depth.

 

[String]

AFAIK, the above scenario was two divers each with a single tank, no pony or doubles.

Terry

I'd still say the same even if these people are stupid enough to dive without a redundant air source. Get on an alternate, stop the flow, start your abort and retry the valve after 30 seconds or so.

2nd choice would be ascend breathing the freeflowing reg until it stops THEN switch to the buddys gas.

A lot depends when the flow happens, at the start of the dive if its shut off fairly swiftly chances are there's enough gas left to continue a dive if its fixed. If it happens just prior to ascent then obviously there isnt.

And a fully open tank doesnt mean its going to flood or need a test. Most valves will have some residual pressure in them to keep water out and a lot of designs will close anyway.

Only time it happened to me the tank ran empty at 20m on the ascent (was fine as i carry redundancy). Despite that when i got to the surface the hoses were still pressurised and still had enough residual to inflate my wing a bit. Not a drop of water entered the tank or regs.

 

[SparticleBrane]

Feather the valve to breathe...

 

[Doc Harry]

Feather the valve to breathe...

Great idea! Yes!

 

[nereas]

If it's a cold-water freeflow with two equally-equipped divers, shutting off the freeflow and sharing air is almost always a bad move because you would now have one OOA diver (the one you shut off) and another freeflow for the donor due to the increased airflow though the second stage. (edit: should read "first stage")

Terry

That settles it; all the sushi in you avatar tells me what I want for dinner tonight.

On the other issue, I would think that shutting down someone else's valve on a single tank diver qualifies as homicide in most jurisdictions.

The best thing is to get both of you to the surface, without delay, since one of you, if not both, is going to have an empty tank very soon. Imagine not being able to inflate your B/C-vest-BPW, judging from how overweighted many divers are these days?

So, Stop (not a really good idea, in this case).

Breathe (that would be the problem, on a long term basis).

Think (better abort this dive and get to the surface).

Act (if you are properly neutrally buoyant, begin your kick up) and share air (or nitrox whatever) on the way up if need be.

Drop weight belt at the surface (just to be extra safe - I know I know most people won't do this).

Swim back (to shore or boat).

Avoid further diving today, due to omitted safety stop.

 

[TSandM]

Having had a full-blown free-flow, I largely agree with Doc Harry.

First off, the bubbles can destroy your vision (mine were from my bungied backup, so they came up right under my chin) and the noise is tremendously distracting. Stopping the bubbles lowers the degree of arousal to a substantial degree.

Second, there is no reason to permit a tank to empty itself into the water. Gas is gas, and it's always a resource, and in my opinion, shouldn't be wasted.

HOWEVER . . . Sharing gas and turning off the affected diver's valve makes a bunch of assumptions. One is that the two divers sharing gas are comfortable doing so, and can execute an air-sharing ascent with good buoyancy control. Pulling the reg out of the mouth of a diver whose valve is shut is not a good move. Second, the diver with the shut valve MUST be able to reach his valve and turn his own gas back on if he has to. He shouldn't have to. Things happen that shouldn't happen, and he has to be able to turn it back on. If he can't, the air-sharing/valve shutting strategy is invalid. Third, the two divers should be practiced enough in gas sharing that this is NOT a panic situation! Once you have established gas sharing, the "emergency", such as it was, is over. Having someone huffing and puffing off a shared regulator is definitely a setup for a second, and more disastrous, free-flow.

I had a more minor free-flow a couple of months ago. My husband and I initiated gas sharing, I shut my valve, and we began a leisurely swim back to shore. Halfway there, I tried turning my own gas back ON, and the freeflow immediately recurred. I shut it back off, and we went home, and the reg went in for service. The tank, however, didn't have to go for VIP