NC Fatality?

[Steve_C]

Do not know if that was the issue here but I have seen many divers check their regs wrong. They take a couple puffs on the regulator but do not look at the pressure gauge while doing so and thus do now know if they are open far enough.

 

[Dan]

My impression from my own diving is that it varies with the valve.

Depends on the valve, some are a lot less than others.

The reason I ask that question is because I have read somewhere (may be in cave diving forum) where a diver drowned with a relatively full tank but only partially open valve. The pressure drop across the valve was sufficiently high to cause the 1st stage not to open at some depth and therefore not to supply enough air to the 2nd stage, as if the tank was empty.

 

[Steve_C]

Understood why you asked. A partially open valve can enable one to breath the regulator at the surface but not at depth. That is why it is important to look at your pressure gauge when testing the reg. Had it happen to me in Cancun. New crew had only cracked my tank open a bit. When I checked it before a hot drop it breathed fine but the pressure gauge plunged. I fixed the issue and had a conversation with the captain.

 

[Dan]

That’s one reason that I open the tank valve counter-clockwise until it stops turning and recheck its position before water entry.

If the crew mess with my valve position, like doing a 1/4 turn back clockwise, I turn it back to fully open and talk to the crew to not mess with my valve position.

I do practice how to check my valve position underwater by loosening my BCD shoulder straps and turning the BCD closer to my left shoulder far enough so I can reach the valve handle with my right hand or simply ask my buddy to check it if he happens to be there to help.

 

[Dan]

I found the article: The Quarter Turn That Kills - Cave Diver Harry

 

[Shot a man in Reno...]

It was a Vindicator valve handle and it was open 2 full turns. My vindicator only rotates 2.25 turns but is very open once cracked.
It was her first dive of the day, she only went down 20-30ft before surfacing.
Her gear was recovered floating on the surface by another nearby boat.
It is unknown whether the gear was removed by crew in order to facilitate getting her on the boat (possibly unconscious) OR whether she removed it herself, in distress.

 

[Steve_C]

Not sure if this boat is rigged like some other NC boats but for those, you descend at the stern, follow the hang bar to the a line leading to the anchor line and then start down the anchor line. If rigged like that, 20-30 ft would mean she was in the water for a brief period before surfacing. Increases chance it was a medical issue but leaves open a gear issue as a possibility.

 

[Bob DBF]

How many 360-degree turns do you need to completely open a scuba cylinder?

I just walked out my workbench and tried a half dozen or so older valves and they varied from one and a half to three complete rotations to open.

As far as the air check at the beginning of a dive, a 1/4 turn open is usually enough to pass the check. As far as I was trained, the air check only lets you know the valve is not shut, if you have problems with air flow as you get deeper check the valve. And as far as the 1/4 turn goes, I've made my choice and am not trying to start another thread, the valve only needs to be turned back enough to insure it is not back seated. If I make an error it will easily be picked up on the check.


Bob

 

[Bob DBF]

Double post


Bob

 

[BRT]

The reason I ask that question is because I have read somewhere (may be in cave diving forum) where a diver drowned with a relatively full tank but only partially open valve. The pressure drop across the valve was sufficiently high to cause the 1st stage not to open at some depth and therefore not to supply enough air to the 2nd stage, as if the tank was empty.

First stage generally stays open until closed by pressure.