Rock Bottom Gas Management - A Hypothetical Accident Study

[Genesis]

IMHO was assuming that the rule of thirds could be applied the way these two were equipped.

The rule of thirds requires that the third you reserve be based on your buddy's gas consumption!

If your partner is a hoover, you're a miser, and you carry a smaller bottle than he does, he needs a double, stage or pony bottle with an independant reg for gas redundancy, because your "third" is more like a SIXTH or less for him!

The only way that you can give HIM a third is if YOUR supply matches his, AND he turns at the third consumed point, because that way you have at least as much supply (in cf - which is all that counts!) as he does, so your "third" is meaningful.

The irony is that Jane had an effective reserve; if the failure had been hers instead of his she would have been fine!

Dick and Jane made a number of mistakes, but the first and most important was in gas management. By diving a smaller cylinder Jane effectively deprived Dick of "his" third in reserve......

The failure to properly manage the ascent once the original OOA occurred was a contributing factor to the hypothetical accident, but the primary failure was one of gas management engendered by the failure to provide an effective reserve for each buddy in the event of equipment failure.

IMHO of course...

 

[MikeS]

Despite the fact that a mere mention of a pony bottle on Scuba Board results in a torrent of illogical suggestions to use doubles or H-valves, Dick had purchased a 30 cubic foot pony and carried it stage rigged on the dive. Additionally, both he and Jane had practiced deploying the pony in the quarry. So when Jane’s tank went dry Dick simply deployed the pony bottle regulator. They buddy breathed off the pony for the remainder of the ascent. Due to the additional task loading associated with buddy breathing off the pony, the ascent wasn’t pretty and they ascended faster than planned, but they did manage well enough to surface uninjured to a warm reception by Spot.

Since they were using Cobra computers despite the ravings of “computers will rot your brain,” they were able to examine the details of the dive in detail. This allowed them to analyze the dive and learn from their mistakes.

The incident was a real eye opener so they immediately signed up for PADI AOW class, followed by Rescue. They went on to become safe skilled divers. They were never able to take the DIRF class because GUE went out of business after losing a lawsuit filed by a pluming supply manufacturer that had trademarked “Doing It Right” for a line of do it yourself pluming for lawn sprinkler systems.

 

[JamesK]

Oh, so we are re-writing the story now?! Cool.

Dick and Jane turned down the PADI AOW class and continued with their <60ft easy diving style until the DIR-F class came about. Before the class, they met a group of experienced DIR cave divers who mentored them in the basic fundamentals of diving. They learned about gas management, and many other things from this group. They ditched their poodle jackets, and other convoluted gear and bought new gear. They took the DIRF class and learned a tremendous amount. They still continued to stay in their recreational limits of diving until they were able to take a Tech 1 class. Finally, they were able to properly do the deep diving they had always wanted to do, and Do It Right. that day they each strapped on a set of dual AL80s. They made a horizontal descent and started exploring the rig. While they are heading back to the ascent line, after their predetermined turn pressure, Dick's regulator goes into freeflow. He reaches back and shuts down his right post. He has lost only 150psi from his tanks. This is no big deal at all, because he had much more than that in reserve, not too mention Janes reserve gas. They continue their horizontal ascent making the stops that were recommended by DecoPlanner.

In the following months, many others start to realize the flaws in the way things are taught by other agencies. PADI files for Chapter 11, and opens up a week later as a plumbing & sewer inspection group, The Professional Association of Drainage Inspectors.


**Note, of course this was all in good natured fun, so before anyone gets mad at me, remember, this was a JOKE!**

 

[O-ring]

I think this is the basic flaw in Dick and Jane's scenario. There is no way the average new diver can manage gas planning and slow ascents, much less stops. Trying to incorporate this type of stuff into their dive plan when their buoyancy control, gas consumption, and situational awareness is still in the development stage is a mistake, IMHO. Without the guidance of other more experienced divers or further instruction to get the basics squared away, D & J shouldn't have been trying a dive to this depth and then task loading themselves with all the crap they tried to do on their dive.

 

[jeffsterinsf]

This being in the "Basic Scuba" section instead of one of the techincal diving forums, the suggestion of another $1000 of equipment to solve the problem might be tough for those that are still reeling from spending their first $1000 on their own equipment...

...but a couple of things come to mind from my training and instruction. In an air-sharing situation I was taught two things (not mentioned in the scenario) that might have made the ascent a little more robust:

a) The air donor is in charge of the situation (would have allowed Jane to speed the ascent without confusion)

b) The team should be in physical contact (would have mitigated the ascent-rate-control issues by "averaging" the bouyancy changes across both members)

Comments?

 

[roakey]

Genesis once bubbled...
If your partner is a hoover, you're a miser, and you carry a smaller bottle than he does, he needs a double, stage or pony bottle with an independant reg for gas redundancy, because your "third" is more like a SIXTH or less for him!

No, no, no, no, no. Oh, I forgot: No.

You don't start loading up divers with dissimilar gear to “fix” problems. In this case you make dissimilar cylinder calculations so you turn when there’s enough gas to get both divers out.

Your team’s equipment choices should be based on the “worst” (for lack of a better term, anyone got a suggestion?) diver in the team, since the smallest cylinder(s) in the team are the limiting factor, even if they’re not on the back of the “worst” diver.

Roak

Ps. How about “metabolically challenged?” As in "The MC diver's turns the dive."

 

[Genesis]

This was stressed during my training - the donor is the one in charge of the ascent after an OOA.

And in my first cut at what I posted, I had that at the bottom as the "second" cause of the situation - but decided to take it out before I hit the "POST" button....

Why?

Because with the gas situation as posited it would not likely have been material, or if it was, it would have been by pure luck of the draw.

The entire concept of having an octo - so you can donate a reg to your buddy (whether you donate your primary or the octo) is that there must be enough gas behind that reg to support BOTH OF YOU to the surface.

If there is not then donating a reg simply drowns both of you instead of one!

This is why I posited that gas management was the fatal flaw, and that the biggest mistake was for Dick to believe he could rely on Jane for a backup gas support while Jane was diving a smaller - and inadequate to support both of them in an emergency - gas supply.

You cannot calibrate both parties in a buddy team's supply so that you both reach the "turning point" at the same time unless you both consume gas at close to the same rate.

If you do then the hoover of the group is left with NO backup if he has an equipment failure at depth near the end of your planned excursion!

The backup supply, however you arrange it, must be sufficient for the diver with the worst consumption rate of the buddy group, not the best.

The rule of thirds only works if you adhere to this principle.

 

[Genesis]

Please go back and read what I said...

The primary flaw was having Jane dive a SMALLER cylinder.

IF Jane insists on doing so, then Dick's only defense is for HIM to have his own redundancy, because while Dick can provide Jane with redundancy in the situation posited, Jane cannot provide Dick with redundancy.

The better solution is for Dick and Jane to dive EQUAL capacity cylinders, and the hoover of the group is the one who turns the dive when they hit the reserve limit.

This way both divers are assured that the "backup" supply represented by their buddy partnership is sufficient for both of them to reach the surface.

 

[MikeFerrara]

I think some of you have hit the nail on the head. Some of the obvious problems here are the same that I see and hear about all the time. Diving beyond ones skill and training level with the task loading and problems that go along with it. The plan clearly required skills they didn't have.

There is a reason that "recreational diving takes place at modest depths and within the "no deco limits". The reason is so there is direct access to the surface with little risk. In recreational diving safety stops are a precoution that can be done away with in an emergency allowing the troubled diver to go home. As we begin to plan and do more challanging dives there are many skill that must be developed together in a logical order.

I couldn't agree more that many divers lack knowlege and skill and that not enough thought is given to gas planning. IMO, shallow dives are in order for the novice. It does not take much gas to ascend from 30 ft. Does this mean that I approve of divers putting the needle in the red and racing for the surface? No. But, at appropriate depths the risk and the complexity of the planning required is reduced, allowing one to develop skills under conditions forgiving enough to allow mistakes.

I blew run times while I was learning to nail them. Actually, I think this is one of those skills (actually group of skills) that reqiuires ongoing attention.

Maybe divers in trouble should take least risk path to the surface. On a no stop dive when gas supply is the problem should we dally or get the hey out? Certainly if things are under control safety stops are good.

Gas management plans based on a prediction of consumption rate require us to know what it is and be able to "control" it and the speed of our return/ascent. IMO this requires more than a new buz word and some calculations, it takes lots of time in the water and the mastery of specific skills.

I agree with Pug that too many divers not knowing what these skills even are.

What do some of you think is an appropriate gas plan for a novice on a recreational dive? What other skills do you think are required to ensure the effectiveness of the plan?

 

[Genesis]

is a good one, BUT...

1. Both team members must dive equal-capacity cylinder(s).
2. The worst consumption rate diver is the one who turns the dive.
3. During an OOA the priority is to get to the surface consistent with safety. While I do deep stops even on "NDL" dives if I'm out of gas we're going up to 15' on an NDL dive - if there is enough gas to hold for the safety stop then there is; you can make an ESA easily from 15' if you must; from 60' its a whole different game.

One of the themes that I've seen repeated in accident reports is people becoming fixated on returning to the anchor or upline during an OOA event, or becoming fixated on ascent rates to the point that they run out of gas a second time and one or both team members drown. That stuff is nice but being on the surface and bent (or having a long surface swim) is better than being underwater and dead!