Rule of Thirds & Shallow Rec diving

[victorzamora]

And how many did you find that resulted from running out of air during an emergency ascent of a diver and his buddy while observing the 50 b rule?

Foxfish, to answer your question:

There are two ways of looking at it.

1) (Purely semantics, THIS IS THE WRONG WAY OF LOOKING AT IT!!!!) None of them. If they had followed the rule, they would've been on the boat before they ran out of gas....by definition. Right? However, this doesn't work. The 50b "rule" isn't so much a rule as an absolute brainless guide. If all of your diving is to 9m, you ascend at 60b thinking you can make it to the surface with 50b and be fine. Doesn't work on a deep dive. Using the "50b rule" doesn't allow any forethought, despite its ability to save your life.

2) (Not semantics, but logic) The better way of looking at it is that all of them did. Using RB/MinGas guarantees that at the absolute worst point for it to happen, even the catastrophic loss of one air source allows for safe return to the surface. So, anybody following MinGas would be able to return to the surface safely in ALL conditions....unless they got caught/entangled or trapped in an overhead. In those scenarios, it wouldn't be the gas planning but dive execution. So, I can safely say that nobody has ever died diving MinGas procedures. I can also say, categorically, that all other divers were using the "50b rule" as the guideline to their gas management plans. This, by definiton, ensures that all OOA divers have been caused by the use of the "50b rule".

To answer your question from experience, and not so much from logic (which you've been ignoring).....I know 5 or 6 divers that were taught to use the "50b rule" that misjudged the air needed to get to the surface and have run out and performed a CESA from 50ft. I know at least one of them got mild DCS and was immediately put on O2. A buddy was on a boat where a foreign diver surfaced OOA and immediately ran for the O2.....he surfaced on the wrong boat, but needed O2 so he used it anyway. Once, a buddy and I saved people who were doing an air-sharing ascent and ran out of gas again. We both deployed long hoses and saved their lives. This was on the second long dive of the day diving very aggressive profiles in terms of NDL. I know one of my computers would've put me well into deco on that dive. Had I have followed their plan, there could've been up to 4 dead divers that day.

 

[Foxfish]

Okay, let's talk about your buddies who ran into trouble for a moment. Pick the best example.

How deep were they at the start of the ascent?
What was the tank pressure at the start of the ascent?
What was their breathing rate and why? Normal, heavy or very heavy?
What was thier depth versus time profile?

As an aside, you mentioned before you are an aeronautical engineer. Do you design aeroplanes?

 

[GCullen94]

Maybe you forgot about this calculation you did a little while back for an emergency ascent involving two divers breathing at 30 L/min. You came up with about 88 b as the required pressure.



I used similar numbers and got about 81 b.

Let me say it again. Your argument is with the major recreational diving agencies who teach the 50 b rule. I'm simply taking typical results used for a rock bottom calculation and noting that I get a similar ascent pressure to what I'd need if using the 50 b rule.

Am I being impossible or very patient here?

I came up with 88B in a 12L cylinder. It's 95B in an 11L The problem is foxfish, the numbers we are throwing out has you sucking the tank empty at those numbers. You, using your method, would run out of gas somewhere in your safety stop and have to make a bolt to the surface, causing the biggest pressure change to happen (last 5M) VERY quickly which increases your chance of taking a hit. I'd rather follow min gas laws or use a short cut that actually works (I have outlined it before) rather than your "surface with 50B" rule. Yes you are being rather impossible. You fail to recognize the word minimum.

One plus of this thread, I am much more comfortable working in metric now.

 

[boulderjohn]

BSAC is not the only group that tracks fatalities. DAN tracks fatalities in North America. I read their reports every year, and I read every single incident description. If there were any fatalities over the past few years related to dry suit mismanagement, I can't recall them. On the other hand, in every single year, the triggering event most associated with fatalities (other than cardiac events) is OOA.

That was also the conclusion of a joint PADI and DAN study a couple of years ago. As a result of that study, PADI has greatly improved its gas management information and practice in the OW class in the new standards being implemented next year.

That study made no mention of dry suit issues.

 

[victorzamora]

Okay, let's talk about your buddies who ran into trouble for a moment. Pick the best example.

How deep were they at the start of the ascent?
What was the tank pressure at the start of the ascent?
What was their breathing rate and why? Normal, heavy or very heavy?
What was thier depth versus time profile?

As an aside, you mentioned before you are an aeronautical engineer. Do you design aeroplanes?

All of these numbers were gotten post-incident, as I wasn't watching their air or profile....but it's what I remember being told. I think they were at 90ft when they started the ascent. I think they were at 1100psi when they started their ascent. Neither of them had any reason to be breathing heavy as it was a good dive. Their depth/time profile was fairly square, descending to the sand and then working their way up from 100ft-90ft along the wreck. It was the second dive of a two-tank dip, all running PDCs with no added conservancy and relatively aggressive algorithms. We were all running a really hot nitrox mix.

The point is: They were diving exactly as you prescribed. 80b is 1176psi, which you said you'd use to ascend from 100ft (30m). They ascended slightly later from slightly shallower. It would've been fine, but right at ascent one of the yoke o-rings blew out and emptied the tank with surprising speed. They ascended together like a textbook (we had been practicing for our DM course, so they had just done like 30 air-sharing ascents in a pool) and ran out of gas right before they reached their safety stop. Both were pretty comfortable in the water. Literally everything you were saying you'd do almost got them killed.

Aside: Yes, Aerospace Engineering is what my degree is in. And yes, I do (and have) designed airplanes. My count so far is that I've contributed heavily to over a dozen different aircraft models that were built and flew successfully, and was Chief Engineer over 3 of them.

Edit: The only reason I chose that example was because it's the one I remember the most of. It also had the most dire consequences. That event really sticks out in my mind. It just so happens that it was fantastically similar to what your described profile would be.

 

[nimoh]

Near the start of this thread Foxfish had no minimum gas plan, just the 50 bar rule. A few pages later minimum gas was 70 bar on a 30m dive to arrive on the surface at 50 bar, and now it is 81 bar.

My guess is that 50 more pages in this thread, and Foxfish will have a minimum gas plan of 110 bar for a 30m dive.

 

[MXGratefulDiver]

I'm only on page 10 ... and most of the adults have already left the room ...

... Bob (Grateful Diver)

 

[Drin]

I'm only on page 10 ... and most of the adults have already left the room ...

... Bob (Grateful Diver)

Or are sitting back with popcorn watching Foxfish trying to defend an indefensible position.

-Adrian

 

[victorzamora]

Am I being impossible or very patient here?

I just saw this, but I've got to say:

I think you're being both. You're being absolutely impossible because what you're saying is absolutely wrong, factually, period. The way you dive works, but it puts you and your buddy at MUCH higher risk than a properly planned dive. Your way will work unless things go wrong. That's what we've been trying to get across. An in that sense, you've been absolutely impossible.

On the other hand, I know some people (myself included) have been grumpier than necessary to get the point across....and I apologize for my part in that. It's frustration from me that's coming across as grumpy. You've handled it really well, and for that you should be commended. This could've turned a lot worse than it has if you had a shorter temper.

Long story short, thanks for reading and not being completely angry about things.....but please realize that your way of diving is not sufficient for the worst-case scenario. If you dive the way you do long enough, you'll end up either badly bent or dead. Maybe not tomorrow, or this month, or next year....but eventually, your gas "planning" will end with you being hurt. It's just a matter of time. I hate to think a little stubborn-ness on an internet forum can keep you from being safe. That's why I keep insisting, and that's why I haven't just unsubscribed from the thread.

 

[tattooedjeeper]

I'm an extremely novice diver, 11 dives in fact, and I've gained a lot from this thread. I clearly see the benefit of Rock Bottom/minimum gas planning over the "back on the boat with 50b" theory....

The back on the boat with 50b thing is like asking you to drive around town for a few hours then show up at my house with exactly an 1/16th of a tank of gas in your car...all the while making sure your buddy's vehicle (possibly a gas guzzling s.u.v) makes it as well by donating your fuel to him should he need it. The way I see it you're gonna do one of two things, show up with either too much gas or not enough. Thus cutting your sight seeing short or ending it either dangerously low or running out. I'd rather know exactly what fuel level I needed to head for home safely (R.B.) than to know how much fuel to show up with. (50b 500psi)

Rock bottom or minimum gas gives you the tools to get you back with enough gas, for you and your buddy, without having to GUESS. I've watched the entirety of this thread and even with the stubbornness of some and frustrations of others, one thing has been clear the whole time, DOING THE MATH IS BETTER THAN GUESSING. I thank all of you who participated in this and helped teach me something along the way.