OK to Bounce Dive to 220 Fsw as...

[116fire]

In my opinion, for an instructor to say anything that could be misconstrued as it being safe or a good idea for anybody to dive to 220 on air is a bad idea.

Hey they used to dive the Doria on air all the time, of course they died a lot too.

If I drank 9 martinis and drove home is that a good idea? Possible yes...

I really like a little helium when I get around 100'.

220', hell its not even worth putting a tank on for anything less that 300'...

 

[carrielsal]

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 don't agree that this is a safe practice. If you're diving AL80's and there is a problem at depth, there is NOT enough air in the tank to share to come up safely.

 

[DCBC]

I don't agree that this is a safe practice. If you're diving AL80's and there is a problem at depth, there is NOT enough air in the tank to share to come up safely.

I agree; several divers with 10 to 20 dives apiece, single cylinders, on a 150' profile, led by one DM. What was he thinking???

 

[Gombessa]

I don't agree that this is a safe practice. If you're diving AL80's and there is a problem at depth, there is NOT enough air in the tank to share to come up safely.

That was my concern too. Back-of-the-envelope calculations suggest that almost 60cuft will be required for a direct ascent, holding all stops, with two stressed divers, from 130ft. Assuming a good resting SAC rate, you'd have a little over 5 min bottom time before needing to start your ascent. I'll rcheck my math when I have some time, but 5ATA+ on a single AL80 is over my personal limits.

 

[BDSC]

I don't agree that this is a safe practice.

I didn't say in my first post it was. I was just saying what we did. But all in all I think the dive was done safely.

If you're diving AL80's and there is a problem at depth, there is NOT enough air in the tank to share to come up safely.

Wouldn't that depend on when the problem occured and what the problem was. For instance, if two divers had decended at the beginning of the dive to say around 130 to 140 ft and at that point something happened where the two divers had to share a remaining tank, would an AL80 hold enough air for them to make it back to the surface if they immediately began to accend? (Assuming they are not total air hogs)

 

[DCBC]

I was just saying what we did. But all in all I think the dive was done safely.

New divers generally speaking have relatively high consumption rates. It could be expected that none of these divers had ever been past 60 or 70 FSW; as per their certification agencies maximum depth restrictions. How can this dive be expected to be done "safely?"

None of them had experienced nitrogen narcosis before. If "it was done safely," it only means that the DM was lucky this time.

It's never wise to double the certification agencies maximum depth with new divers.

 

[Gombessa]

would an AL80 hold enough air for them to make it back to the surface if they immediately began to accend? (Assuming they are not total air hogs)

Two problems here.

The big one is that it sounds like this was never actually calculated or discussed during the dive? Is an AL80 enough? How many knew with a reasonable degree of confidence during the dive? How many have thought about it in hindsight? (Btw, by my calculations, if you immediately descended to 140 and came back up, yes an AL80 should be enough with a couple of hoovers, but what if you stay at the bottom 3 minutes? 6 minutes? The full 8 minutes?).

The other is "assuming they are not total air hogs." If you have a catastrophic gas failure at depth requiring an air share at 140ft, wouldn't it be more reasonable to assume there will be greater stress and higher DCR rates than less? I just think it's wiser to consider emergencies in their worst case rather than best case possibilities, let alone probabilities.

 

[boomx5]

Wouldn't that depend on when the problem occured and what the problem was. For instance, if two divers had decended at the beginning of the dive to say around 130 to 140 ft and at that point something happened where the two divers had to share a remaining tank, would an AL80 hold enough air for them to make it back to the surface if they immediately began to accend? (Assuming they are not total air hogs)

You mean like this?

YouTube - Scuba Diving Accident Intervention Bahamas 12/04/08

 

[DennisS]

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.

The lesson the new divers learned was that diving to 144 ft was no big deal.

 

[M_Bipartitus]

Lets, see. My planner software estimates a 1 minute dive to 220ft on air would require 38cf per person assuming 8 minutes of stops and 1cf/min per person on the surface. So it looks like an AL 80 (77cf) is not really enough, and no where near what you should have. Hope for a overfill and don't put air in your BC (I guess that would help you get down to 220.) Then again, don't do it and wait for a set of doubles, trimix, and deco stages along with appropriate training.