OK to Bounce Dive to 220 Fsw as...

[BDSC]

When I was a new diver, I would have been the first one in the water to do this dive. I'm sure there were lots of things we did that we just didn't realize how badly things could go wrong. Luckily for me, nothing ever happened. But, you only have to look at the Misshaps and Accidents forums to find out how something that seems to be small can have deadly consequences.
As with anything else in life, the more I dive and the more experience I gain, the more I find I don't know. Knowing what I know now, there is no way in hell I would lead a dive like this with new divers and no redundancy.

I totally understand. Well if those folks are operating on luck, I hope it continues to hold out.

 

[DCBC]

You hit the nail on the head, which is why I made the comment about exposures in my original post.

Based purely on the physiology of an O2 toxicity hit, you would have to be exposed for minutes before any symptoms were felt (based on the lungs reactions to the elevated pO2, and the production of free radicals). Obviously, this all comes down to dosage (amount/time). All this is to say that a pO2 of even something crazy like 4.0 (switching to O2 at 100') would be tolerated if the dosage was low enough (seconds). Just trying to put it into perspective.

Agreed. The problem is not primarily the PPO2, but narcosis, air consumption and inexperience.

I would not hesitate to use a single tank for a bounce dive to 200' on air, but this is based upon the knowledge of my oxygen tolerance, consumption rate and how nitrogen narcosis effects me personally at that depth. This is not however what's being discussed.

Diver's with less than 20 hours, who have never experienced narcosis and who likely are not familiar with either the area that they're diving, or their buddy, have no business diving on a 150' table.

 

[boomx5]

Most folks that I know that have watched this pretty much think it was staged.

Could be...but staging it would be dumber than the dive itself.

 

[BDSC]

Isn't ignorance bliss?

Pretty much.

 

[ucfdiver]

We did the Belize Blue Hole this past August and I went to about 144 ft to be able to swim through the stalactites. We had several new divers (10 to 20 dives) with us and some were a little nervous about the depths but all ended up doing the dive. Folks were given an option to hang out a lot higher if they wanted. No pressure at all to do the dive from anyone. The dive master lead the dive but was constantly looking and checking with the newer divers to make sure they were OK. I think the total dive ended up being maybe 20 minutes or so. After the dive all the new divers were glad they did it and said it helped them overcome some of their fears of diving to some deeper depths.

I think the false sense of security is even scarier than the dive it's self.

 

[carrielsal]

I think the false sense of security is even scarier than the dive it's self.

New divers should have a good healthy fear of deeper dives. It keeps them from doing something stupid. This has all the makings of a TRUST ME dive.

 

[BDSC]

I think the false sense of security is even scarier than the dive it's self.

Could be......assuming that doing that dive gave them a false sense of security. But maybe it will help them become more confident divers.

 

[carrielsal]

Could be......assuming that doing that dive gave them a false sense of security. But maybe it will help them become more confident divers.

Confident that they can dive to 140' on an AL80 with air?
Confident that they can safely make it back to the surface?
I would not want to build this kind of confidence with a student or new diver. It's wrong in so many ways.
Practicing and building skills builds confidence. I teach divers to become proficient at their currently ability level, then get the proper training and necessary equipment for the next step.
IMHO, this is teaching divers risky behavior. New divers just don't have the knowledge on how badly things can go wrong.

 

[Gombessa]

I hear ya and good points. So then what is the answer as to how to dive this dive and others like it "safely"? (New or experienced divers)

To answer your question of how to do this dive safely, I would look at a couple of things.

First, if I recall my facts correctly, this is a dive to >140ft on air with no bottom (400ft depth?) . Is this a recreational dive, let alone a dive to bring newly certified divers with 10-20 dives on? Personally, I don't think so. I believe this general profile is an advanced NDL dive, and requires experience and competence with buoyancy control, blue water skills and ascents, gas planning and management, and demonstrated buddy skills. While I'd personally stick to a hard floor of 100ft END, I'd also not want this dive to be someone's first experience with narcosis at 140ft.

Second, I'd look at equipment. I've given a ballpark calculation of how much gas would be required to effect a worst-case abort. If that's not sufficient for the dive plan, you have to make changes. IMO, an AL80 isn't enough with an 8min bottom time. Is a steel 100 or 120 sufficient for an 8min bottom time? If you provide every diver with pony tanks, how large would they need to be to bring one diver at stressed consumption rate to the surface? Do the divers have experience diving with and deploying a pony?

But this dive is done by probably thousands of divers every year...

Thankfully, catastrophic failures are rare. But if your plan accounts for them, then your plan should also be sufficient to handle all of the numerous lesser failures that are more frequent; besides being in a position to handle the worst case, that's also a huge benefit for conservative planning.

.what if there was a catastrophic failure after 6 or 8 minutes of bottom time. No matter if you are experienced or not, when you're out of air you're out of air!

IMO, if you have a failure after 8 minutes of bottom time, experience matters a great deal. Unprepared, full blown panic at 144ft is not a good thing. But having a plan that accounts for it, knowing a predefined course of action, practicing good buddy skills and generally being as prepared as possible would, to me, be the best way to turn a true emergency into an orderly and successful abort. If I was a betting man, I would put my money on the more experienced diver to be able to accomplish the above over a newly certified diver with 10 dives under his belt.

 

[Web Monkey]

I was sitting at a table of beginner and newly acquired advanced level divers (they were rewarded their advanced cards at dinner) the instructor told one of the divers it would be fine to drop down to 220 and come right back up…

No SSI recreational classes teach emergency procedures that are valid for more than recreational depths (assuming you don't count "mash the inflator and pray" as an valid "emergency procedure"). And in fact, a number of them will kill both you and your buddy. For example:

• If you run out of air @220' and attempt to share with your buddy, chances are excellent that very shortly, you'll both be out of air and now have two divers bolting for the surface instead of one.
• If you run out of air and ditch your weights @220', you could easily end up bent or dead, depending on how long you were down.

While it's certainly possible to dive to these depths (and more) with a reasonable amount of safety, it's not possible to do safely with a single 80 cubic foot tank and the training that comes from any SSI recreational class.

In fact, one of the things I tell my students is that if anybody tells you to do something that sounds dumb or disagrees with what's in your book, don't do it until you've verified it somewhere else. Some of the dumbest/most dangerous things I've ever been told to do have been from instructors and DMs.

While the textbooks aren't always perfect, they do have the benefit of review/editing before publishing and peer review, which means that wing-nuts can't just stuff in any hair-brained thought they happen to come up with.

Terry