Problem at Gilboa 4/21

[Dan Gibson]

I'm not saying that at all. In my case, my ScubaFlow (I mean ScubaPro) piston first stages are not sealed and are just fine. They are not improper equipment at all. They do have some environmental measures that are supposed to reduce icing, but they get wet regardless. In the wrong hands, they are not good for dives like Gilboa. In the right hands, they are as good as any other reg. I'm not suggesting people use POS equipment or not using the required equipment for the particular dive.

Good technique is a wonderful thing, and would be a great compliment to the proper equipment. Suggesting that good technique allows the use of improper equipment is the wrong message IMHO.

-s

 

[b1gcountry]

Or even worse the wing will auto inflate leading to a ballistic ascent.

The valve on a LP inflator is an upstream valve, which means the orifice is held into the LP seat by the intermediate pressure inside the hose. In order to add air to your wing, you need to press the inflator button, and overcome the hose pressure. A free-flowing first stage will increase the IP, and thus make it HARDER to open the LP inflator. This is why Argon bottles used for drysuit inflation need Over Pressure Valves. Drysuit valves are also upstream.

Most second stages are downstream, which means the orifice is held against the LP seat by pressure from a spring, which opposes the pressure from the LP hose. When the IP rises, the spring is no longer strong enough to keep the valve closed, and a freeflow occurs. Ironically, the more finely tuned your second stage is, the smaller the rise in pressure needs to be before the stage freeflows.

Tom

 

[jon m]

so am i correct in thinking that if your first stage free flows, then both primary and secondary regs will be flowing? also, this would decrease time before the tank ran dry?
and second stage free flow would only involve 1 hose?
thanks!

 

[b1gcountry]

Most probably yes.
If your second stage starts free flowing slightly it probably won't affect anything, but if it really starts going, and the water is cold enough, the extra flow could cause the first stage to also free flow. Once the first stage ices up, both regs will probably start flowing.
Tom

 

[M_Bipartitus]

so am i correct in thinking that if your first stage free flows, then both primary and secondary regs will be flowing? also, this would decrease time before the tank ran dry?
and second stage free flow would only involve 1 hose?
thanks!

If the first stage free flows this will cause the LP hoses to get much higher presure than teh normal 150 psi intermediate presure. Second stages are designed to fail and free floww if there is too much presure behind them. This falure mode ensures that air is available in the event of a problem, and prevents the LP hose from bursting due to overpressure. Since all LP hoses will be ate simmilar pressure it is possible that both teh primary and octo will fail and freeflow. It is also possible that just one will. That is if the free flow from one second stage lowers the pressure enough the other would not fail.

I don't know if it would make a significant differeance as to how long it takes to drain the tank. I would expect this is mostly limited by the volume of air that can pass through the first stage, thus would not significantly change the time to drain dry.

If just the second stage fails (first stage is ok) then the other second stage, such as an octo, should be able to work normally. However,the increased air flow through the LP hose will lower the pressure on the octo reducing it's ability to function as you would expect. Also the increased air demand will make a first stege free flow more likely. Most free flows due to issing involve the first stage.

 

[b1gcountry]

If just the second stage fails (first stage is ok) then the other second stage, such as an octo, should be able to work normally. However,the increased air flow through the LP hose will lower the pressure on the octo reducing it's ability to function as you would expect.

You can test this by breathing off of the octo while holding down the purge of the primary. I can barely tell a difference when doing this with my mk17 (no IP drop). It is noticable a bit on my old Sherwood Blizzard (IP drop 5-10psi). With an older Mares it is pretty obvious.

Tom

 

[slackercruster]

Regs can free flow at any temperature, although it is more rare at warmer temps. They can also free flow because of mechanical problems.

My rule of thumb is that free flows are always a possibility below the thermocline. The 38f temp doesn't sound unusually cold for that depth at this time of year.

As far as learning goes- the fact that this is a double fatality in a group of three seems alarming. It sounds like there were simultaneous free flows. Just to put some perspective- I think Curt Bowen did some tests and found that a free flowing reg will drain an AL80 in about 90 seconds. I've had a 2nd stage free flow at 100' and it emptied the AL80 before I made it back to the surface. In my case, I was already sharing air when it ran out.

Even with redundancy and buddies, free flows can be hard to manage- switching to an independant regulator does not alway remove the conditions that cause the first free flow.

I've practiced with freeflow breathing and did OK.(in warm water and shallow depths)

I never thought an 80' would run out that quick with free flow situation as you mentioned.

Do you think the 2 divers died from air running out before surfacing or had problems breathing with freeflow regs?

 

[slackercruster]

Certified divers need to understand the principles at work here. As "do it easy" points out it's adiabatic cooling. Take a tank out into the back yard on a hot day and crank open the valve and it will ice up.

Depth adds to the problem because the air is more dense and the adiabatic cooling effect is greater (a greater volume of air expanding in the reg). So, the colder the water and the deeper the water, the more likely a free flow due to iceing.

Some regs are dryer than others but if the temp gets below the due point of the air things get wet anyway.

The second stage can also freeze. The adiabatic cooling isn't as great in the second stage but second stages may be much wetter than the inside of a first stage.

Some regs are more prone to free flows than others. On any given weekend at Gilboa you are likely to witness several free flows if you are paying attention but I've never had one of my zeagle or apeks free flow even at depths down to 300 ft in very cold water. I've never had one of our old sherwoods free flow either.

When 1st stage freezes does it cut off air?

Will 2nd stage usually free flow before 1st stage freezes?

 

[spectrum]

When 1st stage freezes does it cut off air?

Will 2nd stage usually free flow before 1st stage freezes?

The failure mode of virtually all moder regulators is to over deliver air.

If the first stage goes into free flow then it will over drive the second stage and that is what you see bubbling. It is venting so you don't rupture a low pressure hose.

If the second stage hangs with frost then it will also bubble. Sustained free flow demand from a stuck second can eventually cause the first stage to freeze open.

Pete

 

[MikeFerrara]

Respectfully, Mike, it only takes a small amount of overpressure and overexpansion to damage the lungs.

Even though you're correct that the 2nd stage exhaust valve could vent some of that free-flowing air, overpressure (overexpansion) of the lungs would still be a major risk with one's mouth wrapped around the mouthpiece.

We could be talking about a significantly greater amount of air and pressure if it's due to a 1st stage failure, than a simple 2nd stage failure.

My guess is that both types of free-flows could overwhelm the exhaust valve's capacity.

Not that my 10-year-old PADI OW manual is the final word, but they state, on p. 155, (with my embolden), "You can breathe from a free-flowing regulator if you follow a couple of procedures. First, don't seal your mouth on the regulator because the continuous flow of high-pressure air may cause lung-expansion injury. Instead, hold the regulator in your hand and press the mouthpiece to the outside of your lips."

Mike, I value your opinions, but surely you know that the lungs can be damaged by relatively small amounts of overpressure.

Besides, a diver, with his mouth wrapped around the free-flowing mouthpiece, even if the overpressurizing from the flow-free didn't cause outright damage by itself, would increase his risk of barotrauma if he momentarily closed his airway during ascent. That's because he may be more likely to have pressurized, full lungs.

A momentary gulp closes his airway and, if he ascends another few feet, pop goes the alveoli! If he's sipping, it would be much less likely, since his lungs would probably not be full or pressurized.

As I think you know, in shallow water, even a 4-foot change in depth has been known to cause lung overexpansion injury when breath-holding on a full breath. That's not much of a pressure change.

The possibility of lung damage, from even small amounts of overpressure, is the precise reason why "sipping" from a free-flowing regulator is recommended, I believe.

Dave C

The thing is this Dave, even if you have a free hand and choose to hold the reg in your hand and sip, by the time you get that done the reg may have already been free flowing for some time.

I can't tell you that a first stage free flow doesn't increase your chances of a lung overexpansion injury but I can tell you that a rapid ascent certainly does and that's what happens to too many diver who suffer free flows.

If you have an extra hand and if your more comfortable "sipping", then sip. But, if you lose control of your diving and the other critical tasks that that involves, you have other problems.

Not to put too fine a point on it and certainly not to insult anyone but if PADI knew anything about teaching free flow managment, we wouldn't have so many injured and dead divers because of free flows.