OK to Bounce Dive to 220 Fsw as...

[peterbj7]

On deeper dives, keeping your ppO2 at 1.2 is very prudent. When you're cold, working hard and stressed you are way more likely to tox on lower ppO2s than in a chamber.

Yes and no. If you're really diving in cold water then perhaps you're right. In warm water on OC it's unnecessarily conservative. When I'm on CC for a long dive (2 hours +) I do restrict myself to 1.2, or even on occasion 1.1, but my fear then is not an oxygen toxicity hit but the cumulative effect of high pO2 on things like eyesight.

 

[MXGratefulDiver]

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

I'm fairly certain that was said in jest ... but I'd just like to chime in that depth is the wrong reason to be doing any dive. People who chase personal depth records have a higher-than-normal risk of putting themselves in a situation they won't be able to get themselves out of.

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.

Even if a diver has made gas measurement calculations, and has determined that an AL80 is enough gas to do such a dive, what they have most likely not considered is how narcosis changes your breathing pattern ... and thereby your buoyancy control. This raises all kinds of issues with respect to your gas consumption ... and most people will have measurably higher consumption rates when narc'ed than when they're not.

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

... and that is not really a good lesson for new divers to learn. Sure, they might ... under carefully controlled conditions ... be reasonably safe at that depth. But how will they know when they exceed those conditions?

FWIW - for most recreational divers, 144 ft under the wrong conditions ... pretty much any condition that creates stress ... WILL be a big deal.

... Bob (Grateful Diver)

 

[BDSC]

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.

So do you think it's possible for a diver (with all the "proper" training") to safely do a dive to a depth of 140 ft on a single Aluminum 80? Or is this just a lack of proper equipment? In other words, would a person need another air source to do this dive safely?

 

[DCBC]

So do you think it's possible for a diver (with all the "proper" training") to safely do a dive to a depth of 140 ft on a single Aluminum 80? Or is this just a lack of proper equipment? In other words, would a person need another air source to do this dive safely?

We are not talking about if "it's possible for a diver with proper training." If we are, I suggest you post this as another question.

We're talking about newly certified divers with less than 20 dives and no experience with narcosis. The answer to this question is that NO competent Divemaster would plan this dive in the first-place. Air consumption is only one problem that could be foreseen.

 

[peterbj7]

Some mention here of the Blue Hole in Belize. I'm pretty familiar with that as a dive site, having done it many times as a quasi-recreational dive with tourist divers, and as a technical dive with like-minded people. To the bottom on several occasions.

The one thing that most recreational divers don't understand, because it's never taught to them and they don't ask, is about air consumption. This can become significant on that dive, when done by relative novices. Left to my own devices, I do that "recreational" dive on around 800psi. But I've seen new divers who most certainly shouldn't have been there, exhaust their tanks when they're still at 140ft or so. On a few occasions I've bailed out divers by putting them on my octopus and taking them up (when I wasn't working on the dive, just along to watch), and on at least one of those I started to get a bit frightened at the rate at which this passenger was depleting my tank. I've surfaced with barely enough air in my tank to keep the water out, all (minus 800psi) used by my passenger. IMO these people should not do the dive, but commercial considerations reign and I haven't made myself popular with some local operators by saying so. Whenever I've taken inexperienced people there myself, I've always built up to it with several deep dives on the local reef. At any depth there you can follow the bottom, and psychologically that's far less daunting than having nothing under you.

As to the Dahab Blue Hole, there's a lot of nonsense written about it, and a lot of really unprepared people dive it. I was there when one of the more infamous deaths occurred (his own film was released on uTube), and really it was totally avoidable given his pigheadedness. It's not a difficult dive nor intrinsically a particularly hazardous one. The problem is the magnet of the arch, which cannot be traversed by someone on a single tank (nor by many inexperienced people on twin tanks). Yet people persist in trying it. I believe diving there is better controlled than it was when I last dived it eight or nine years ago, so hopefully we won't read about more people stupidly killing themselves in it.

 

[carrielsal]

So do you think it's possible for a diver (with all the "proper" training") to safely do a dive to a depth of 140 ft on a single Aluminum 80? Or is this just a lack of proper equipment? In other words, would a person need another air source to do this dive safely?

I do not dive deeper than 100' with an AL80 with a single valve. Not for any reason. If I felt the need to dive greater than 100' with a single tank, the smallest tank I would use would be a 95 with at least a 30 cuft pony. For me, this is non-negotiable.

Carrie

 

[Jim Lapenta]

Dives below 100 feet I'm in min double 72's pumped to 3000 or so. And slinging a 30 or a 40. If I'm on vacation then I've decided that I will do deeper dives only with ops that offer doubles or big steels 95 or HP 100 min and it better be a 100 cu ft fill. Looking forward to going back to the keys now that I know what shops offer doubles.

 

[peterbj7]

Sadly, the realities of life in a warm-water resort environment mean that people HAVE to do such dives on single tanks. On a purely statistical basis I have to say that it is safe.

Having said that, I don't know that Jimlap's idea that using a big tank is safer than using a regular-sized one. Assuming your consumption is predictable and a smaller tank would normally suffice, the risk you face is of a catastrophic failure of a first stage or hose. Better to have an additional tank/reg, and that you can improvise quite easily even when all that is available is standard tanks - take a spare reg/band/sling. That said, I have always offered manifolded doubles to my customers.

 

[carrielsal]

JimLap +1
These days you will only find me in doubles. I find all that air to be extremely comforting.
But this does not mean that I have or every will be complacent. Safety is always my primary concern when diving.

Carrie

 

[carrielsal]

Sadly, the realities of life in a warm-water resort environment mean that people HAVE to do such dives on single tanks. On a purely statistical basis I have to say that it is safe.

I have forgotten what the maximum payout is on my Dive Master liability insurance, but I have no desire to find out. I think taking a diver down to 144' or greater on an AL80 with no redundancy could be viewed as reckless behavior.