Deep bounce dive in Cozumel leads to missing diver

[Ron Lee]

Taking more than one person to 250 feet on air without redundancy doesn't really do anything other than increase the number of casualties.

That is certainly a viable viewpoint. No doubt the accepted way to do this dive is with multiple gas mixes, suitable redundancy, etc etc. But we are dealing with reality here. While I have been below 100' on air I have not been to 250'. The risk using air alone is much higher than that for typical recreational dives. So new divers reading about this event it does show you that the warnings about scuba diving having risks is true. You can die if you screw up.

So where did this pair screw up? AWAP suggests that an 80 cf tank could be adequate for a bounce dive to 250'. Personally, I adhere to the concept of deep stops even for normal dives on Cozumel. Ascents are slow and typically spent viewing the reef. They are not square profiles. So given a deeper than normal dive, I would want a larger tank. One to allow plenty of deep stops and two for contingency.

From an education viewpoint, I wonder about the risk of nitrogen narcosis and O2 toxicity at that depth. Just for purposes of discussion, my vague recollection of O2 toxicity is that there are time and depth components. If a few minutes at 250' has a very low risk of an O2 hit, we can disregard it for now for simplicity.

Then you have to wonder about a person's risk of debilitating nitrogen narcosis. Like many things, that could vary among people. Looking back at the Scuba Mau event, unverified recollection is that the plan was to 250' or possibly deeper. At least two of the three people on that dive lived in Cozumel so they had the chance to make frequent deep dives. Were they comfortable with the effects of air at that depth that the risk was relatively low or did others factors come into play to make it a lethal dive?

Return to the two visitors who reportedly went to 250'. Did they make frequent dives to that depth and knew how their bodies were affected? Does frequent diving to those depths allow a person to deal with those effects better, recognize onset of narcosis, etc.

Since I do not know the answers to those questions, it seems that the failure of the buddy system may have been the real problem. How can a buddy come up and say that he thought his buddy was already up? On a high risk dive like this, they should have been very close once they got to a depth that made it dangerous. Not having redundant equipment was likely not the problem. The use of 80 cf tanks versus 120 cf might have been an issue if one diver "lost" his air supply and had to use the buddies octo. But we will never know since from the report we have now, the survivor apparently has no idea what happened to the presumed deceased.

If we get factual info that the two had ascended from depth and the survivor decided to go through a swim through and the presumed deceased signaled that he was surfacing...and that is when they were separated, all this conjecture/scenario analysis can be thrown out.

I will note that in two recent fatalities (maybe more), buddy separation appears to be a factor. One was the cruise ship lady who was diving with her husband..possibly Santa Rosa March/April of last year I believe. Another was the woman from Utah diving with her two brothers. In both cases, there should be factual info available but it never seems to see the light of day.

Personally, I am a strong advocate of rescue diver training. Being able to help your buddy, other divers and even yourself might go a long way to reducing diver fatalities.

 

[Dirty-Dog]

That is certainly a viable viewpoint. No doubt the accepted way to do this dive is with multiple gas mixes, suitable redundancy, etc etc.

Yes, that would be the accepted way. And for good reason.

But we are dealing with reality here.

The reality is pretty simple, really. If you do 250' dives on a single AL80, you have a very good chance of not coming back.

So where did this pair screw up? AWAP suggests that an 80 cf tank could be adequate for a bounce dive to 250'.

I would disagree. Rock Bottom calculations (Here is a good example) show quite clearly that an AL80 is not even close to adequate for a 250' dive.

Since I do not know the answers to those questions, it seems that the failure of the buddy system may have been the real problem.

I'd say the failure wasn't of the buddy system. It was of the brain system. You know, the one that says "don't do stupid dives".

 

[redacted]

The reality is pretty simple, really. If you do 250' dives on a single AL80, you have a very good chance of not coming back.



I would disagree. Rock Bottom calculations (Here is a good example) show quite clearly that an AL80 is not even close to adequate for a 250' dive.

I suspect you might be very surprised at the number of folks who get through that dive with no ill effects - 99% would not surprise me.

Lots of divers with a SAC of .5 or less. At 250 feet that is less than 4 cu ft per minute. An AL 80 provides that diver plenty of gas to bounce to 250 feet until something goes very wrong.

It should not be necessary to exaggerate the dangers of such a dive.

 

[Tigerman]

Well, at 250ft even a freeflowing regulator is very wrong..

 

[raftingtigger]

For those that have trouble with these calculations:

250 fsw = 250/33 = 7.6 Add 1 ATA for atmospheric ambient and you have 8.6 ATA absolute.

PO2 at sea level (air) is 0.21. Multiply that by the ATA at depth and you have a PO2 of 1.8 at 250 fsw on air. This is higher than the generally accepted safe level. Will it cause oxygen toxicity with a short exposure? Maybe, maybe not -- depends on the particular diver.

FWIW, I'm not saying that a PO2 of 1.8 is particularly toxic. The point of my post is to come up with the number.

If the rumors of what happened are true, then Ox Tox is a possibility in a very sensitive individual, but probably something else (like narcosis) was the triggering factor.

 

[Tigerman]

1.8 used to be considered safe "back in the day" did it not?
Thats beyond the point though, the way this turned out is pretty clear proof that the way this dive was conducted was anything but safe..

 

[tamas970]

1.8 used to be considered safe "back in the day" did it not?Thats beyond the point though, the way this turned out is pretty clear proof that the way this dive was conducted was anything but safe..

Read somwhere, that rare oxtox cases happened between ppO2 1.4 and 1.6bar. 2bars are definitely toxic, the diver maybe has 90% chance to blackout in a couple of minutes.

 

[boulderjohn]

Some comments:

1. It is very unlikely that a short exposure to 1.8 would cause toxicity. If you read Shadow Divers or the last Dive, you will see that much of the diving on that U-Boat was done at about that depth on air, and they were down for extended periods of time. (Note: I am not advocating this!)

2. Narcosis can be very debilitating at that depth. If you read Shadow Divers or the last Dive, you will see that the key fatal incident was very much related to narcosis. The two very experienced divers did incredibly stupid things that led to their deaths, things they would never have done with clear heads.

3. It is very easy for an attentive diver to lose track of a buddy under those circumstances, especially if narced. We do not look at our buddies constantly, and our ability to stay in touch assumes our buddy is going to be in pretty much the same place relative to us as the last time we checked. I recently did a series of dives with a buddy who for some reason kept changing depth. It felt like I spent half my dive spinning around looking for him. If a diver has something go wrong that leads to that diver dropping or rising rapidly while you are looking away for only a second, even the best of buddies will lose contact.

4. I find it hard to believe that anyone has much experience doing single tank bounce dives to 250 feet. I would imagine that doing it once or twice would pretty much satisfy the curiosity and leave you with the realization that it is a pretty pointless thing to do. There are lots better things to do with your dive time. Even if it were a 100% safe experience, I would not bother with it. When I go that deep, I plan to stay a while and get something out of the experience. If I hear that someone decided to do such a dive, I assume it must be something of a new experience.

---------- Post added May 24th, 2013 at 03:23 PM ----------

Read somwhere, that rare oxtox cases happened between ppO2 1.4 and 1.6bar. 2bars are definitely toxic, the diver maybe has 90% chance to blackout in a couple of minutes.

The diver who toxed in Florida last year was diving at over 150 feet. He thought he was on air, but he was on EAN 36. That's about 2.16 PPO2. It took him about 20 minutes.

 

[Dirty-Dog]

I suspect you might be very surprised at the number of folks who get through that dive with no ill effects - 99% would not surprise me.

And people get away with playing Russian roulette with their skulls intact. I've treated a guy who was shot point blank with a .45 and is fine. All that means is sometimes you get lucky. It doesn't make the behavior any less foolish.

Lots of divers with a SAC of .5 or less. At 250 feet that is less than 4 cu ft per minute. An AL 80 provides that diver plenty of gas to bounce to 250 feet until something goes very wrong.

It should not be necessary to exaggerate the dangers of such a dive.

Call me crazy, but I operate on the assumption that something will go wrong.

 

[dumpsterDiver]

That is certainly a viable viewpoint. No doubt the accepted way to do this dive is with multiple gas mixes, suitable redundancy, etc etc. But we are dealing with reality here. While I have been below 100' on air I have not been to 250'. The risk using air alone is much higher than that for typical recreational dives. So new divers reading about this event it does show you that the warnings about scuba diving having risks is true. You can die if you screw up.

So where did this pair screw up? AWAP suggests that an 80 cf tank could be adequate for a bounce dive to 250'. Personally, I adhere to the concept of deep stops even for normal dives on Cozumel. Ascents are slow and typically spent viewing the reef. They are not square profiles. So given a deeper than normal dive, I would want a larger tank. One to allow plenty of deep stops and two for contingency.

From an education viewpoint, I wonder about the risk of nitrogen narcosis and O2 toxicity at that depth. Just for purposes of discussion, my vague recollection of O2 toxicity is that there are time and depth components. If a few minutes at 250' has a very low risk of an O2 hit, we can disregard it for now for simplicity.

Then you have to wonder about a person's risk of debilitating nitrogen narcosis. Like many things, that could vary among people. Looking back at the Scuba Mau event, unverified recollection is that the plan was to 250' or possibly deeper. At least two of the three people on that dive lived in Cozumel so they had the chance to make frequent deep dives. Were they comfortable with the effects of air at that depth that the risk was relatively low or did others factors come into play to make it a lethal dive?

Return to the two visitors who reportedly went to 250'. Did they make frequent dives to that depth and knew how their bodies were affected? Does frequent diving to those depths allow a person to deal with those effects better, recognize onset of narcosis, etc.

Since I do not know the answers to those questions, it seems that the failure of the buddy system may have been the real problem. How can a buddy come up and say that he thought his buddy was already up? On a high risk dive like this, they should have been very close once they got to a depth that made it dangerous. Not having redundant equipment was likely not the problem. The use of 80 cf tanks versus 120 cf might have been an issue if one diver "lost" his air supply and had to use the buddies octo. But we will never know since from the report we have now, the survivor apparently has no idea what happened to the presumed deceased.

If we get factual info that the two had ascended from depth and the survivor decided to go through a swim through and the presumed deceased signaled that he was surfacing...and that is when they were separated, all this conjecture/scenario analysis can be thrown out.

I will note that in two recent fatalities (maybe more), buddy separation appears to be a factor. One was the cruise ship lady who was diving with her husband..possibly Santa Rosa March/April of last year I believe. Another was the woman from Utah diving with her two brothers. In both cases, there should be factual info available but it never seems to see the light of day.

Personally, I am a strong advocate of rescue diver training. Being able to help your buddy, other divers and even yourself might go a long way to reducing diver fatalities.

You STILL are not getting it...1.8 atm of oxygen is very unlikely to kill you for a few moments if you are not exerting yourself. An 80 IS enough for a bounce dive. You DO NOT do deep stops and slowly work your way up the reef face on ascent.. if you are trying to do a bounce dive with very limited air... But the most important part you are not getting.. is that it is absolutely insane to expect that there "is a buddy system" when 2 guys are doing 250 on air with one little tank. It is not a failure of the buddy system.. there is NO system.,,If you had done many dives below 200 on air,, you would understand how easy it would be to lose a buddy. The narcosis is the most dangerous and uncontrollable factor in a dive like this.