Problem at Gilboa 4/21

[Jchoby]

I've heard singles...

These guys are from our area and frequent the same shop we do... I'm not sure how many dives they had but it appears they had the collect card thing going...they had the master diver rating so that means at least 50. But I don't think they had enough experience nor were they equipped to be on that side. I'm sue the story will flush out here shortly.

 

[crpntr133]

They were diving singles with no redundancy.

http://www.zendiving.com/forums/showthread.php?t=4717

First hand experience at above link.

 

[MikeFerrara]

Did you want to say something?

I thought it was a pretty straight forward question. I've already lost count of the number of divers who have been hurt after a a rapid ascent that began with a free flow at this one quarry alone.

If you can't dive well shallow you aren't doing yourself any favors by going deep. Free flows are common especially in cold deep water and should NOT be a threat to anyone's life.

So, I'll ask again. Is anybody learning anything yet?

 

[MikeFerrara]

I've heard that you don't have to worry about icing unless you take a breath from your reg when it's dry and above water when the temp is less than 32. Any idea how true it is?
Either way, deep condolences to their family and community.

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.

 

[spectrum]

I've heard that you don't have to worry about icing unless you take a breath from your reg when it's dry and above water when the temp is less than 32. Any idea how true it is?

That is a very untrue statement.

I have seen 42F frequently cited as a benchmark to require a cold water capable regulator but it's only a benchmark.

Lots of things enter into the reality of the moment. High air usage from exertion or inflation of the BC or drysuit especially if 2 or more of these draw on the first stage at the same time is a contributor. The deeper the dive the more air the first stage needs to process in order to deliver the volumes. High usage increases adiabatic cooling (Cooling from the expansion of compressed gas) and this is where most of the first stage problems start. This can cause a block of ice to form on a first stage even when the water is obviously above freezing.

Free flow can come from either the first or second stage. The first can stick open causing runaway intermediate pressure that the second stage(s) will release. The second stage can suffer from internal ice build-up from the moisture in exhaled air.

The grain of truth in what you have heard is that compared to being topside and breathing from a regulator that is ice cold when submerged in cold water the water is actually a source of relative warmth when compared to breathing from freezing cold gear and further compounding the risk by exhaling humid breath into the second stage.

Cold water regulators seek to limit these risks however technique is also a big part of staying safe in cold water.

Pete

 

[Aquarianna]

As the gas moves from the high pressure tank to the intermediate pressure in the regulator, the temperature drops due to adiabatic cooling

Gotcha. No explanation needed

 

[MikeFerrara]

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.

I might be wrong but if I remember right Curts test involved testing a tank with an open burst disk which mayempty a tank faster than you can through the valve.

If you open a valve wide open on a full tank, I think it'll take more than 90 seconds to empty it. You won't get more air out than that going through a first and second stage because both add resistance and reduce flow from a wide open valve.

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.

It just shouldn't be a big deal. A diver should be able to breath off a free flowing reg and still be able to control their diving. Real redundancy (dual port valve) makes it real easy...you just shut down the free flowing post. If you lose too much gas in the process, well, that's what your buddy is for.

What usually happens in these cases is that divers panic or just plain lose control of their buoyancy while they are trying to deal with the problem.

A few years ago one of our scubaboard members had a free flow on an AOW deep dive at Gilboa and her, her buddy and her instructor ended up on the surface before they even realized they were going up. As I recall, her computer measured an ascent rate of like 160 ft/minute. A second or two with a closed air way could have killed any one of them. In fact, I printed out her account of the incident and I used to hand it out to students.

 

[fisherdvm]

Interesting, Spectrum, I remembered about not inflating your BC or drysuit while you are inhaling at the same time, but didn't think about the increased flow at deeper depth. Therefore, at 100 ft, the air is flowing through the first stage at 4 times the rate at the surface, compounded by the fact that temp down there is likely below 42 degree or very close to it.

 

[deepstops]

This was posted in issue #17 of Advanced Diver Magazine.

The test was run with an AL80
and Zeagle D50 regulator on the surface, 4atm, and 8atm with
four failure modes: blown burst disk, a severed LP hose, a free
flowing reg, and a severed HP hose. Please note some results
are in seconds and some are in minutes.


Here are the results on the surface:
1. Failed Burst Disk = 72 seconds
2. Failed HP Hose = 22 minutes
3. Failed LP Hose = 83 seconds
4. Free Flow High Performance Regulator = 255 seconds

I then repeated the test at 4 atm’s / 99ft
1. Failed Burst Disk = Same within a second or 2
2. Failed HP Hose = Same within a minute
3. Failed LP Hose = Same within a second or 2
4. Free Flow High Performance Regulator = 155 seconds

I then repeated the test at 8 atm’s / 231ft
1. Failed Burst Disk = Same within a second or 2
2. Failed HP Hose = did not complete due to time restraints but would assume it
would be with a minute difference
3. Failed LP Hose = Same within a second or 2
4. Free Flow High Performance Regulator = 91 seconds

 

[do it easy]

EDIT: Brian has faster fingers!!

I might be wrong but if I remember right Curts test involved testing a tank with an open burst disk which mayempty a tank faster than you can through the valve.

Yes, it does take longer to empty a tank though the reg, but the times are still similar- none of them leave enough time for site seeing or playing around.