Accident at Gilboa?

[jkaterenchuk]

Remember basic gas laws, the biggest change in pressure occurs in the last 10 feet.

A diver ascending from 100 feet experiences a greater change in pressure from 25 ft to the surface than they do from 100 to 25 feet. It literally is the last 25 feet that kills you.

Really, please show us the math to prove this statement.

John

 

[seaducer]

Really, please show us the math to prove this statement.

John

What most people are referencing when that say things like this is that from the surface to 33 feet the pressure doubles(or halves depending on your direction of travel), but each additional 33 feet the change is only a factor of 1. So theoretically your body goes through the most extreme changes in that first (or last) 33 feet. The size of the gas bubbles would expand to twice their size during that last 33 feet. But would still be 4 times bigger than if you were at 99.

Personally I don't buy it, but then I s**k at math, so reader beware.

 

[crpntr133]

I don't understand what the problem is with going to 100' on an AL80? My roommate did his Deep Cert on AL80 there and with Mike's permission. He has 3 deep dives there on AL80 all with Mike's permission. I regularly dive Lake Huron wrecks (New York is 117') on single AL80 both Nitrox and Air.

Its unfortunate the 3 divers weren't trained properly on how to handle the free flow but, it had nothing to do with the tanks themselves.

Let me first say that I have never dove the deep end at Gilboa. My understanding is that Mike wants a redundant air source. A single AL80 is not redundant.

 

[scubapolly]

Let me first say that I have never dove the deep end at Gilboa. My understanding is that Mike wants a redundant air source. A single AL80 is not redundant.

The tank or tank size is not the issue. I could theoretically dive it on a 40, the issue is the redundancy. Therefore not the tank but rather the valve is the issue. A single 80 with an H valve would be sufficient, or even an 80 with a pony bottle.

 

[tiggrr]

Let me first say that I have never dove the deep end at Gilboa. My understanding is that Mike wants a redundant air source. A single AL80 is not redundant.

Maybe he changed his mind since then. I know a few people who have w/o a redundant air source but, all around 2-3 years ago.

One thing that will never change is the f'n speed limit in Gilboa!!

 

[fisherdvm]

The water temp was 52 degrees and I clearly remember thinking my first experience in OW was really, really cold. I'm not an instructor and don't know if any of the agencies have any standards dealing with water temps for OW checkouts. Any thoughts on when it might be just too cold to put OW students in the water for checkout dives?

I hate to be a stickler on this, but 2 weeks ago we did a refresher course for 2 certified diver. We were talking about free flow regulator as the AOW student from last month was with us who had the incident. The married couple who were certified by SSI asked, "how do you deal with a free flow reg?". Again, this would make it 5 certified divers by SSI who was not taught how to deal with free flow regs... Not a big deal some would say. Don't have to discuss it unless the diving environment required it, other will comment. Of the certified SSI diver's I've met, that would have been 5 out of 7 who were not taught a thing about free flow regs. But seems important to at least discuss in class, especially when all 5 of these divers took their OW course in temperate climate (colorado and MI).

For those who say, it is better for the agency to let the instructor to decide what to teach in class, my comment would be, if there is the slightest chance they will dive in cold water, teach them a little bit about free flow regulator, environmental cold water kits, and how to manage if it did happend (in warm or cold water). Better yet, just simply make it part of the standard for OW training.

 

[fisherdvm]

One thing that will never change is the f'n speed limit in Gilboa!!

He chased me down with his golf cart and chewed me up for doing 10 mph on a 5 mph zone (I was in first gear).

I can not say how concern they are about the deep dive and redundant air source. He told us to be careful about 1 month ago, and sure enough, at 70 ft, we had a free flow brand new reg from one of the AOW student. Fortunately, we had about 4 ponies between the 5 of us, and did a full safety stop.

It made all of us aware of the danger of anxiety, breathing fast, and cold thermocline.

 

[crpntr133]

The tank or tank size is not the issue. I could theoretically dive it on a 40, the issue is the redundancy. Therefore not the tank but rather the valve is the issue. A single 80 with an H valve would be sufficient, or even an 80 with a pony bottle.

And if you read my original post it says "JUST an AL80". My point was that it was JUST a tank and no redundancy. Yes, pony or doubles is redundant. What Mikes policy is now I don't know for sure. I do know that a couple at last years M&G were told they couldn't dive it because they had nothing for redundancy. Of course that was shortly after the accident.

 

[scubapolly]

Remember basic gas laws, the biggest change in pressure occurs in the last 10 feet.

A diver ascending from 100 feet experiences a greater change in pressure from 25 ft to the surface than they do from 100 to 25 feet. It literally is the last 25 feet that kills you.

Really, please show us the math to prove this statement.

John

It was late last night when I posted and I erred in that I should have said 35 feet rather than 25 feet.

It boils down to Boyle's law which is p1 v1= p2 v2

If you go from 100 feet to 35 feet you are starting at a pressure of [1+(100/33)] = 4ATM. If you ascend to 35 feet your pressure is now [1+(35/33)] which is 2.06ATM
If you assume that you start at a volume of 1 liter at 100 feet:
4atm * 1 = 2.06 atm * X
X = 1.94 L Therefore your volume increased by 94%

If you go from 35 feet to the surface you are at a pressure of [1+(35/33)] ATM. which works out to 2.06ATM
2.06atm * 1L= 1atm *X
x= 2.06 L Therefore your volume increased by 106%
When you ascend to the surface your volume would increase from 1 liter to 1.78 liters

At a place like Gilboa where you have a drastic temperature change due to the thermocline, if the thermocline is above 35 feet this change can be even greater.

Similarly the pressure change in the last 10 feet works out to [1+(10/33)] which works out to a 30% change in 10 feet, more so than any other 10 foot depth change.

 

[scubapolly]

And if you read my original post it says "JUST an AL80". My point was that it was JUST a tank and no redundancy. Yes, pony or doubles is redundant. What Mikes policy is now I don't know for sure. I do know that a couple at last years M&G were told they couldn't dive it because they had nothing for redundancy. Of course that was shortly after the accident.

Wally,
My post was meant to clarify your comment not to correct it. I knew what you meant. :10:

So would that be the M&G where I decided to put my foot in my mouth while I was unwittingly talking to the "survivor"? Ooops.