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sjensenpiper
April 29th, 2010, 11:00 AM
I watch was watching myth busters last night and saw how in a old MKIII if you umbilical is severed and you dont have a one way valve you can be sucked up in to the hat. Has any one ever got a squeeze in a modern hat? just wondering if is possible because of the demand reg not free flow. (I know all the modern hats have one way valves) I have got suit squeeze in a dry suit when I was not paying attention.

Akimbo
April 29th, 2010, 12:08 PM
I remember Bev Morgan telling me in the late 1960s that they developed the super wide and soft face seal on the Band Mask because he (or a friend, can't recall which) got a badly bruised face wearing an old mask (Desco/Jack Brown I think) when a hose blew. They found a piece of debris caught in the check valve. The idea was it sucks less to flood the mask (pun intended). That is also why it is prudent to wear the hat's neck seal pointing up, especially on a push-pull closed circuit rig.

Other than this one, I don’t remember hearing of any suit or face squeeze accidents with modern gear since check valves were introduced.

It was interesting to read Sir Robert H. Davis' Deep Diving and Submarine Operations. Hoses were terrible in the earliest days of deep sea gear, but so were the hand pumps so pressure was limited. There was a period when power-driven compressors started being adapted but the hoses were not upgraded. It's not too hard to figure that hose blow-outs near the compressor suddenly became common; at least in hindsight. From the book, it was as though nobody ever considered the possibility before.

BTW, here are clips on YouTube on the Myth Busters helmet squash segment — and I do mean SQUASH. I hope it was a Yokahama hat instead of a Kirby-Morgan.

YouTube - MythBusters - Dumpster Diving - Meat Man's Deep Sea Dive (http://www.youtube.com/watch?v=tsjGy_cU9Og)

YouTube - Mythbusters - Compresed Diver *Gory* (http://www.youtube.com/watch?v=LEY3fN4N3D8&NR=1)

sjensenpiper
April 29th, 2010, 01:16 PM
Akimbo looks like an old Kirby-Morgan What a waste of a piece of history

Akimbo
April 29th, 2010, 01:50 PM
Akimbo looks like an old Kirby-Morgan What a waste of a piece of history

I never could tell the difference between the Yokahama hats that they literally copied and the KMCs without looking at the nameplate. Bev was lamenting that Yokahama got one of their Helium hats someplace and copied it down to a dent that happened when it was either in use or in shipping. The Yokahamas I saw even had the same hammer pattern instead of the spinning marks. Wasn't it a pentagon about 3/8"???

I ran across this old photo you guys might enjoy of the KMC gas hat, Circa 1968:

Akimbo
April 29th, 2010, 02:28 PM
…Has any one ever got a squeeze in a modern hat? just wondering if is possible because of the demand reg not free flow. (I know all the modern hats have one way valves) ...

I partly addressed your question but realized I got off in the weeds with the answer. Regarding the demand regulator question, the only way I can see a squeeze is if your check valve fails AND the regulator seat also fails/leaks (assuming the freeflow/control valve is closed). Debris in the hose can cause both to fail, but you will notice the demand regulator leaking where not many people test their check valves. An upstream demand regulator is basically an in-line check valve forced open by a lever and diaphragm. The risk is further diminished in a BandMask or if your neck seal is pointing up in a hat as already described.

The greatest concern of squeeze in my experience is on closed-circuit, surface-based, mixed gas systems; sometimes called a push-pull. In that case there is a negative biased back pressure regulator that could fail open, usually in the bell. Since any crap that goes out your exhaust (exhaust regulator in this case) could also go through the back pressure regulator, the chance of failure is pretty real. You definitely want to be careful about the direction your neck dam points on one of these. It is also important to keep the water separator filter upstream of the back pressure regulator clean.

In the incredibly improbably event that you did get a hat or mask squeeze, it would be much faster since there is so little gas volume. I am just guessing here, but I would think a catastrophic squeeze in a hat with a neck-dam or rigid seal mask would involve lung tissue heading up the hose PDQ.

So, blow out your hoses before use and keep them capped when not. If nothing else, it can save some maintenance.

sjensenpiper
April 29th, 2010, 04:39 PM
The Yokahamas I have seen I thought had a small front view port. The one in the Vid looked huge. Thank for all the other info I am an inland diver have not done any mixed gas other then in recreational diving. Learned about it just never did it. But I know what you are talking about with the reclaiming systems. I would figure if all the conditions were right water would be pulled pass the neck dam and you would drown. It is not like the heavy gear were every thing is bolted down and completely sealed except for the wrists.

Akimbo
April 29th, 2010, 05:06 PM
The Yokahamas I have seen I thought had a small front view port. The one in the Vid looked huge…

Yokahama made a lot of exact copies of the KMC air and gas hats. I hear their suits were pretty good but didn’t get much exposure to them operationally. Maybe some of the other guys here know.

The KMC hats were the first to turn large ports out of Plexiglas as far as I recall. Small glass ports with bronze guards disappeared off the market pretty fast after that. Even Desco makes one now.


… But I know what you are talking about with the reclaiming systems. I would figure if all the conditions were right water would be pulled pass the neck dam and you would drown...

That was a real concern so the procedure was to first open your freeflow valve and then release the quick-disconnect on the exhaust hose. Also the bellman would close the umbilical exhaust valve if it sounded like the diver was drowning. The freeflow rate "should" have easily exceeded the closed circuit exhaust rate.

Gilldiver
April 29th, 2010, 05:11 PM
I think it is a Kerby Morgan from the large glass windows.

The main thing with a modern helmet is that if you lost the hose and the check valve failed, the helmet would flood past the neck seal. A hard hat rig like a Mark V or the helmet shown can't flood as the suit is sealed to the helmet. So the only thing that can happen is what is in the suit and the suit gets pulled/pushed/squeezed into the helmet.

Akimbo
April 29th, 2010, 05:12 PM
… The main thing with a modern helmet is that if you lost the hose and the check valve failed, the helmet would flood past the neck seal ...

Especially on a new neck dam, you can easily get a pressure seating seal if it points down toward the shoulders. Think of a neck seal on a drysuit pointing up. You can get a pretty hard squeeze without much water flow.

mattiboy
May 25th, 2010, 01:58 PM
I watch was watching myth busters last night and saw how in a old MKIII if you umbilical is severed and you dont have a one way valve you can be sucked up in to the hat. Has any one ever got a squeeze in a modern hat? just wondering if is possible because of the demand reg not free flow. (I know all the modern hats have one way valves) I have got suit squeeze in a dry suit when I was not paying attention.
Its never happend to me yet and after watchng that I don't think I would be here to tell you if it did!

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