Learned Wrong...

[Deep South Divers]

Maaaan... I just typed out this rediculously detailed (can you imagine!) response to everything you said, Akimbo... I clicked the button and... Gone. Ugh!

Look, I'm not gonna retype all of that at like 2am.

Let me just give you this point:

Let's use the same divers that I used in my previous example... One skilled and one unskilled at 100'. Both have an OOA that is catastrophic and non-recoverable in any way, just to make you happy.

What you're suggesting is the following scenario: Both divers drop their weights and begin an EBA instead of keeping their weights and doing a CESA. Your math regarding this is errant. Here's how it really looks:

The skilled diver is immediately 20 pounds bouyant.
The unskilled diver is immediately 35 pounds bouyant.

We know this because, prior to dropping their weights, they were both neutral in the water.

In accordance with Boyle's Law, that 20/35 pounds of bouyancy at 100' becomes 80 and 140 pounds of bouyancy at the surface - with the bouyancy doubling in the last 33' of ascent. This doesn't even account for the expansion in the diver's suits, which can add anywhere from zero to 35 pounds (or more) to that number.

Now, we all know that a BC will only hold up to it's rated capacity of bouyancy, but suffice to say that it's maxxed by the time the diver hits the surface if it's burping. So if your BC or wing holds 60 pounds, for example, then that's how positive you're gonna be... Plus your suit. For many, this would be 100 pounds or more. For some, it could even be 200 or more, depending on a variety of gear choices.

...So in effect, what you're saying is that it's better to be positively bouyant by - up to and including something like 200 pounds while you rocket toward the surface - than be neutral or only slightly bouyant while ascending and in some semblance of control. One guy here even has a method for slowing down the ascent... Rather than avoiding it altogether.

Two other points:

$8,000 SLRs are not 20 pounds negative. They are neutral in the water column, just like the multimillion-dollar Volkswagen-sized 3D IMAX camera that filmed Deep Sea 3D.

It's a misnomer to think that a "regulator uses 135 psi to operate." Sure, that's it's intermmediate pressure, and so anything less than that is gonna feel performance-reduced. That is, the gas supply gets slower. But it's not like the bottom 135 psi is unusable... It still comes out just fine. If you don't believe me, take a near-empty tank and hook up a reg and press the purge button until all of the gas comes out. What's left in the tank? That's right... Zero. Not 135 psi.

Yes, I really was OOA at 130'. I was working, and so I hadn't noticed that the last few breaths had been getting progressively more difficult until I got a half breath and no more. Tried as much as I could, there was no more gas in that tank.

During my ascent from 5 to 1 ATA, The gas in my hoses and regulator had expanded five times over... Quintupled in volume... Which gave me more gas to breathe. Since ambient pressure reduced by about 75 psi as I rose, I was able to access another 75 psi from that tank... Those two things combined gave me several more breaths, and I used them. I understand that you're talking about a valve that breaks off mid-dive or the burst disk that pops at 2,000 psi at depth even though it didn't pop at 3200 psi when it got filled, or the unicorn that swims by and takes your scuba unit, or whatever... But I've never seen it happen. What I do see is divers who recommend to other divers to assume the risk of becoming uncontrollably many tens or even hundreds of pounds bouyant to address the irrational fear of sinking suddenly if they're OOA, as if it's the constant stream of breathing gas that is keeping them "up" off the ocean floor.

Lastly, please do not accuse me of "panic" just because I "swam like hell." You know me better than that from our previous posts. It was a clear and concise decision to do so, not an irrational one. I'd have "swum like hell" regardless of HOW bouyant I was - in other words, whether I had dropped weights or not. If I'd been panicked, then I wouldn't have had the mind to stop my ascent when I got another breath due to the reduction in ambient pressure.

I said "Oh****oh****oh****oh****" because it was really, really stupid that I let myself get into the situation in the first place... And any kind of accelerated ascent - and however you want to call it - was definitely NOT part of the plan.

 

[Thalassamania]

Sorry for your loss, I hate it when that happens.

...
We know this because, prior to dropping their weights, they were both neutral in the water.

In accordance with Boyle's Law, that 20/35 pounds of bouyancy at 100' becomes 80 and 140 pounds of bouyancy at the surface - with the bouyancy doubling in the last 33's of ascent. Thsi doesn't even account for the expansion in the diver's suits, which can add anywhere from zero to 35 pounds (or more) to that number.

Now, we all know that a BC will only hold up to it's rated capacity of bouyancy, but suffice to say that it's maxxed by the time the diver hits the surface if it's burping. So if your BC or wing holds 60 pounds, for example, then that's how positive you're gonna be... Plus your suit. For many, this would be 100 pounds or more. For some, it could even be 200 or more, depending on a variety of gear choices.

...So in effect, what you're saying is that it's better to be positively bouyant by - up to and including something like 200 pounds while you rocket toward the surface - than be neutral or only slightly bouyant while ascending and in some semblance of control. One guy here even has a method for slowing down the ascent... Rather than avoiding it altogether.

As for the diver who is over weighted and under trained, we can come up with examples of stupid human tricks 'till the cows come home, that's really not what we are here to do, we are here to examine what should be best practices.

If the diver is diving wet then he might have six pints, or so, of air in his BC, (his gas weighs 4 lbs and he's likely to have about 10 lbs of suit compression). If he is diving dry he has no more than 4 pints of air in his BC (compensating for his gas). So let's go worst case: 6 pints, that's 24 lbs when it gets to the the surface, but that's not 24 lbs. instantly. It's 6 pints on the bottom, 8 pints at 66 ft., 12 pints at 33 ft, etc. There's plenty of time to dump before that air has much of an effect. So realistically his buoyancy gain is from the loss of lead (20 lbs), plus the expansion of his wet suit (add about 10 more). If he's diving dry, he gains no buoyancy from suit expansion because his shoulder valve vents the excess air off. So your calculations are way off, worst possible case is on the order of 34 lbs. regardless of the size of the BC. To put that in perspective, I've done a surface dive and made it down to the bottom of a 13 ft. pool against a little over 90 lbs of positive buoyancy (no weights, full suit and full FENZY).

So he dumps his belt, flares and vents his BC. What is the big deal? Is he wearing hand cuffs?

 

[Akimbo]

Maaaan... I just typed out this rediculously detailed (can you imagine!) response to everything you said, Akimbo... I clicked the button and... Gone. Ugh!...

That is a bummer. Maybe this will help in the future. As hard as this is to imagine; my spelling, grammar, and typing suck even worse than any of you get to see. My habit of writing in Microsoft Word and copying & pasting into the Scubaboard editor helps a lot. That also dramatically decreases my chance of losing work.

If you want to quote all or part of a message, click “Reply With Quote” as usual, highlight, cut, and paste into your word processor. Setting the Scubaboard editor to Basic/Source Mode actually keeps formatting from getting hosed-up more than the WYSIWYG (What You See Is What You Get) mode.

If you get the time and patience, I really would like to see that lost response. We probably aren’t really that far apart, but the devil is always in the details.

 

[Akimbo]

… $8,000 SLRs are not 20 pounds negative…

You’re right, -20 Lbs would be a beast… but I wrote 3 Lbs negative

…You start to vent your BC when the corrugated hose pulls off in your hands. You start to sink during your night dive and the option is drop your 3 Lb negative $8,000 dollar camera or your 20 Lb $50 weight belt.….

You mentioned in a later post that you would be about 10 Lbs negative if your BC failed. That would probably be -13 Lbs with that camera in your hand… which I’d still like to have.

… It's a misnomer to think that a "regulator uses 135 psi to operate." Sure, that's it's intermmediate pressure, and so anything less than that is gonna feel performance-reduced. That is, the gas supply gets slower. But it's not like the bottom 135 psi is unusable... It still comes out just fine. …

That depends on the regulator but that isn’t consistent with any I have tested. On the better regulators with balanced first and second stage regulators the performance dropped dramatically below the IP OBP at high demand rates. I never had a reason to test at low flow rates. The pressure sensor picked up increased resistance with supply pressures about 225 PSI OBP, but not enough that divers were likely to sense. Below IP, the flow-through piston first stages performed a lot better than the diaphragms, but not that long. You could actually see the pressure drop measured at the IP hose on each demand cycle.

In any case, we both agree that you should try to suck gas off the bottle as long as you can, which is a low gas condition. The point of the calculation was more to indicate that all 300 PSIG is not breathable at 100’ — as in there isn’t much time left. Change the supply pressure to 100 PSI from 300 if that helps.

… You try to swim against the current and negative buoyancy and notice the needle approaching [-]300[/-] 100 PSI as the debate continues. You are tired, concerned, and not sure what to do if anything else goes south. Your computer shows green in the deco box.….

The issue in this scenario isn’t whether to dump your cylinder, it whether to dump weight or not… I’d hang onto the camera though.

 

[Bombay High]

......, but I never trusted a SPG again...

This is why we used manifolded (inverted) doubles on black water dives when you could not see (or trust) an SPG. Finish one tank and you now have half your supply available.

Equalise and shut manifold again and you have quarter in each tank.

Finish that quarter and head topside.

 

[KSterling79]

I am almost positive I drink coffee before every dive, and I know somewhere along the line, I was told not to consume large quantities of caffeine. I understand this "large" quantity thing, but I do not believe other divers should look at me like I am the devil, if I show up to the dive boat with my bag in one hand and a cup of joe in the other, hell, I might even have a cig hanging out of my mouth. Just saying

 

[dumpsterDiver]

I am almost positive I drink coffee before every dive, and I know somewhere along the line, I was told not to consume large quantities of caffeine. I understand this "large" quantity thing, but I do not believe other divers should look at me like I am the devil, if I show up to the dive boat with my bag in one hand and a cup of joe in the other, hell, I might even have a cig hanging out of my mouth. Just saying

I would be more concerned about you showing with a bag.

Family guy bag of weed - YouTube

 

[Deep South Divers]

Sorry for your loss, I hate it when that happens.

Yeah, it was pathethic. Usually I'll copy it with my mouse before hitting the reply button just in case. I didn't this time. Serves me right.

As for the diver who is over weighted and under trained, we can come up with examples of stupid human tricks 'till the cows come home, that's really not what we are here to do, we are here to examine what should be best practices.

If the diver is diving wet then he might have six pints, or so, of air in his BC, (his gas weighs 4 lbs and he's likely to have about 10 lbs of suit compression).

I "wagged" the gas-in-wing quantity in that example for the sake of easy math and because I didn't feel like figuring it all out. So I'll do the exact math... It looks different than what you have.

Assuming that the skilled diver is correctly weighted, and that they're both diving wet with single AL80's at the beginning of the dive, and that they both have 10 pounds of bouyancy in their suits and lose 80% of their bouyancy at 100'...

The skilled diver should need about 14 pounds of bouyancy in his wing to be neutral at 100'. That's a displacement of 0.22 cuft of seawater, Thus, the bubble in the wing would be about a quarter of a cubic foot... Admittedly, much less than my example showed.

The unskilled diver needs to displace 29 pounds of seawater, so his bubble would be 0.45 cuft... About half a cubic foot.

If they start neutral and then drop 20 and 35 pounds respectively, they are, by definition, immediately 20 and 35 pounds bouyant. At 100'.

At 66', that bubble has gone from being 14 and 29 pounds bouyant to 19 and 39 pounds bouyant respectively. Including the expansion of fat tissues and wetsuit, and the 20 pounds and 35 pounds are now 27 and 47 pounds bouyant. (20 and 35 pounds bouyant at 3 out of 4 ATAs... So 20 and 35 pounds * 4/3rds).

At 33', our divers are now 40 and 70 pounds bouyant (20 and 35 pounds bouyant at 2 out of 4 ATAs... So 20 and 35 pounds * 4/2nds).

At 0 feet, our divers are 80 and 140 pounds bouyant (20 and 35 pounds bouyant at 1 out of 4 ATAs... So 20 and 35 pounds * 4/1sts).

Again, a BC will only hold so much gas... So, for example, if the BC will only hold 60 pounds of bouyancy, it will have vented the rest... But there's still inherent body and lung bouyancy and wetsuit bouyancy. Altogether, this should mean that the diver would max out at, say, 70 pounds bouyant... Somewhere between 33' and the surface for both of them.

Now's a good time to point out that we assumed above that both divers had full tanks. If, during this OOA emergency, these tanks became empty, you're gonna have to add 6 pounds to this bouyancy figure, for the loss of the gas... And that's over and above what their BCs will hold... So each would be around 76 pounds bouyant, according to your example of any catastrophic loss of all breathing gas.

Alternatively, in a CESA, bouyancy would be offset by the weight belt and... All things being equal... Would equate to a maximum bouyancy of 40 and 25 pounds (with the less skilled diver's BC venting). 46 and 31 pounds bouyant if the tanks are catastrophically empty. So as I've said, a CESA IS bouyant... Just not nearly as badly. This, of course, assumes that the diver did not vent his BC on the ascent, which he probably wouldn't if he did a CESA. But it would be controllable... And faster, since swimming.

Again, it can be plainly seen why there is no point in inflating the BC to ascend, as another poster recommended. There's not enough room anyway unless the diver vents.

Dumping weight isn't much better... It only makes the problems that the diver is experiencing worse - and his ascent completely uncontrollable, which is the difference between dropping weight (EBA) and not (CESA) during the ascent.

If you get the time and patience, I really would like to see that lost response. We probably aren’t really that far apart, but the devil is always in the details.

Not gonna happen... I've got to be on the dive site at 8am tomorrow, which means getting up at 5... And it's after midnight now. I don't plan on being done this job until Tuesday evening, and by then I'll have forgotten it all anyway.

You’re right, -20 Lbs would be a beast… but I wrote 3 Lbs negative

Oh, sorry... I must have misremembered. That's right... You said a 20 pound weight belt and a 3 pound camera. Too many numbers flyin' around in here.

You mentioned in a later post that you would be about 10 Lbs negative if your BC failed. That would probably be -13 Lbs with that camera in your hand… which I’d still like to have.

You're welcome to them. I generally don't use them. We have a production company that's been following us around for a while, in an attempt to make a reality TV show like "Billy the Exterminator," only we're diving and finding stuff (so it's a bit like "Pawn Stars" or "Storage Wars" too) instead of killing pests.

Of interest, they're using HD GoPros with the optional waterproof housings and built-in fisheye lenses. They're incredibly rugged, light, neutral in the water, and tiny. We mounted them on Goodman handles for them.

Tomorrow is the editor's deadline for the first show - what they call a "sizzle tape." Here's to hoping that the networks pick this show up. Looks pretty cool to me, but I'm a diver, so I'm biased.

I'll post something on DeepSouthDivers.org to show off and embarrass myself if they let me.

That depends on the regulator but that isn’t consistent with any I have tested. On the better regulators with balanced first and second stage regulators the performance dropped dramatically below the IP OBP at high demand rates.

Oh, I never said that they didn't. Yeah, IP drops dramatically when there's not at least 135 psi powering them. My point is, though, that the gas still comes out just fine. It will give you a few breaths before cutting off completely because of it, and that's exactly what I used to actually perform a "safety stop" during my CESA. (Or at the end of my CESA, since it wasn't really a CESA anymore.)

I never had a reason to test at low flow rates. The pressure sensor picked up increased resistance with supply pressures about 225 PSI OBP, but not enough that divers were likely to sense. Below IP, the flow-through piston first stages performed a lot better than the diaphragms, but not that long. You could actually see the pressure drop measured at the IP hose on each demand cycle.

Yep. Worked well enough for me to do the stop, though, knowing that I had as much as my lungs wanted 10' above.

In any case, we both agree that you should try to suck gas off the bottle as long as you can, which is a low gas condition. The point of the calculation was more to indicate that all 300 PSIG is not breathable at 100’ — as in there isn’t much time left. Change the supply pressure to 100 PSI from 300 if that helps.

Well, that's totally true... Whatever exact number you want to assign to it.

...But because of Boyle's Law, at 0 feet, as compared to 130', I had 75 more psi available to me. In all, it was perhaps a wash, meaning that I still had that quantity of gas available to me.

'Night. Huge job tomorrow... Got a lot riding on this one.

 

[ozzydamo]

1.When I first started diving it was in Cozumel, where the dives required to be led by DMs by law. I brought my newly learned PADI tables with me, and learned immediately that they were of no value on those multi-level dives we were doing. I mentioned it on the boat, and the experienced divers on the boat told me that there was no need for any of that stuff--just follow the DM and don't worry about it. I have since had students tell me that they were given the same advice by experienced friends prior to their classes--no need to remember all that dive planning stuff in the real world--the DM does all that.

2. When I first asked what Nitrox was, an experienced diver (but not a nitrox diver) explained to me that it enable you do dive deeper than you can on air.

3. Experienced divers told me while I was diving in Cozumel in a 0.5 mm suit that a good estimate of my weighting needs would be 10% of my body weight plus 5 pounds. I got that same advice in Florida in a 3mm suit.

4. On ScubaBoard recently a diver intending to dive in a 3mm suit was advised to start with 20% of his body weight for lead.

5. One afternoon after diving in Belize I went to the bar outdoor bar to get a drink. While I was waiting (a long time) for the drink to be made, I listened to a guy going on and on about the physics of scuba diving, decompression, etc., explaining it all to the other patrons who were apparently not divers. He walked away with great satisfaction just as my drink was being handed to me. One of the patrons said, "Would you mind staying a second and telling us the truth? I am a physician and know that at least half of what he said was BS, and I could see from the look of pain on your face while he was talking that you know better." Actually, about 75% of what the guy had said was BS, and it took me most of my drink to straighten it out.

It's funny how drunks legitimize their behavior with "intelligent" conversation...........

 

[ozzydamo]

My favorite "rule" is don't hold your breath!