Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

[RyanT]

@Dody, What happens when the current increases unexpectedly and you find yourself swimming harder than expected? It's not hard to double your SAC rate. What happens if your buddy has an OOG emergency at depth near the end of the dive? What happens if the OOG emergency is compounded by working against a current? What happens if you find yourself in this situation and realize that while trying to help your buddy, you've gotten disoriented and now don't know where the anchor line is. So now you have to decide on trying to find the anchor line with a dwindling gas supply or make a free ascent, drifting away in the current from your anchored boat. What happens if you're sharing gas, looking for the anchor line, and then you have to stop and untangle your buddy's fin that got snagged in monofilament?


An inexperienced diver can quickly find themselves in over their head with compounding problems. If you haven't experienced it, you might be astounded at how quickly problems can compound. In those cases, extra gas is always your friend. On deeper dives, there is simply no good reason for not using a larger tank.

 

[Dody]

@Dody, What happens when the current increases unexpectedly and you find yourself swimming harder than expected? It's not hard to double your SAC rate. What happens if your buddy has an OOG emergency at depth near the end of the dive? What happens if the OOG emergency is compounded by working against a current? What happens if you find yourself in this situation and realize that while trying to help your buddy, you've gotten disoriented and now don't know where the anchor line is. So now you have to decide on trying to find the anchor line with a dwindling gas supply or make a free ascent, drifting away in the current from your anchored boat. What happens if you're sharing gas, looking for the anchor line, and then you have to stop and untangle your buddy's fin that got snagged in monofilament?


An inexperienced diver can quickly find themselves in over their head with compounding problems. If you haven't experienced it, you might be astounded at how quickly problems can compound. In those cases, extra gas is always your friend. On deeper dives, there is simply no good reason for not using a larger tank.

I agree with you but what you are saying is standard planning in any matter. Whether it is in the O&G, diving or space industry, it is the same principle. You build your case based on facts and when you can’t know for sure, you use conservative assumptions. This give the operators the big picture. It is not a bible. The operator still needs to monitor his/ her gauges. And it is way better than doing a dive based on mere experience. People need to understand the boundaries of the mathematical (or physical) equation they are into. Then, during the dive, if they are getting out of it, they should safely return to the surface. Basically, if you don’t know what time it is, if you don’t even remember your name, don’t try to do nothing but surface in a controlled way.
Full control is an illusion, a state of mind. It does not exist in real life.

 

[Dody]

I am still a newbie in diving but pretty much very senior in project and emergency management. The question was how safe is a deep dive with a single tank of air with no pony. From my 34 dives experience, I would not do a drift deep dive with strong currents. I would go down and go up in roughly the same azimuth. I would have a spare cylinder for my safety stop. And I would plan for the worst case scenario. What if? I would rely on the boat captain to track my bubbles in case I drift. I would not do it solo or from the shore at my current level of expertise. It is only a matter of covering all angles and not leaving loose ends. And even so, there is no 100% guarantee.

 

[RyanT]

@Dody, I agree, good planning is important. A single AL80 isn't good planning for sub 30m dives, particularly in colder, dark water.

 

[Dody]

I concur. 80 cu.ft is only 5% less than 2400 liters (12 liters with 200 bars) but in cold and dark waters, I would not even try. Anyway, I only dive with water temperatures > 22 degrees C . And I don't understand all those discussions about pony/ not pony. If you fee like it or more importantly, if there is a risk that you might need additional air, just take it and don't listen to the hardliners who would rather lose their life than their pride.

 

[johndiver999]

I concur. 80 cu.ft is only 5% less than 2400 liters (12 liters with 200 bars) but in cold and dark waters, I would not even try. Anyway, I only dive with water temperatures > 22 degrees C . And I don't understand all those discussions about pony/ not pony. If you fee like it or more importantly, if there is a risk that you might need additional air, just take it and don't listen to the hardliners who would rather lose their life than their pride.

Can you describe a situation (on a 100-ft dive) where you think there is NO risk that you might need additional air?

 

[Dody]

Can you describe a situation (on a 100-ft dive) where you think there is NO risk that you might need additional air?

The risk is relative. I have done 4 short dives at below 30 meters while keeping in mind that I should ascend if my gauge reaches 150 bars. And in all cases, I was at the surface with more than 50 bars. The rationale was that at this depth, I still had between 20 and 30 minutes of breathing time in "normal" conditions. Still enough to help a buddy to breath and ascent safely. And much more when I went up to 10 to 15 meters afterwards. Now, of course, if both me and my buddy have a problem at 35 meters, or if if we experience a down current or if everything is against us ( Murphy's law), downcurrent, both out of air or alone, if there is a tsunami at this exact time,... then the odds are not the same. That's why I said that full control is an illusion. I do my best to think and plan for emergencies. And I am not a risk taker. I am risk averse. But if I was to refuse all "risky" activities, I would not have been a racing car driver for 10years, I would not dive or I would arrange for one safety diver to be with me at every 10 meters, for a boat and a chopper to be on stand-by carrying my personal decompression chamber (that's not that expensive. The problem would be the power).

 

[scubadada]

I am at 11l/min but I figured that 15 would speak to more people

Hi @Dody

You recently reported a significant decrease in your RMV from 20 to 11 L/min and you don't have many dives. It is most useful to have an average RMV representing the breadth of dives you do and the conditions you encounter. The variation around the average also helps in choosing what gas consumption to use in planning calculations. Examining your dives with the highest gas consumption helps identify the factors that are most important for you.

I have my RMV for nearly all of my last 1500+ dives and my RMV is 0.36 +/- 0.04 cu ft/min (mean +/- std dev). Sorry for the imperial units, it's what I use. So, 95% of my dives have an RMV between 0.28 and 0.44 cu ft/min. For me, I know that strenuous exertion and thermal stress, due to cold, are the most important determinants of my gas consumption. For routine gas planning, I use an RMV of 0.45-0.5 cu ft/min, the higher value if I expect exertion and/or cold. For emergency planning, I use twice my average RMV. For example I dive a 19 cu ft pony, and know that I would spend a minute at depth, make a normal ascent with a 3 min safety stop, from 130 ft.

Continuing to monitor your RMV will be helpful in your future diving.

 

[Colliam7]

I don't think diving to 108' on a single AL80 is inherently dangerous for the experienced diver. I've also made 100s of solo dives to 130' on a single AL80. For me personally, I no longer think it's a good idea. My level of risk tolerance is lower now than when I was younger.

I suspect that this statement captures the thinking of many of us reading the thread. I have done the same kind of dives. I have made solo dives to 210' quite a number of times (warm water, coral reef, no current, good visibility) on an AL80 without redundancy. Today, I would think twice about doing that. As with RyanT, my risk tolerance has changed over time.

It wasn't 'insane' when I did it, I don't look back on it today as 'insane'. I no longer believe it is a reasonable behavior. Scuba equipment is actually quite safe, the chances of a catastrophic failure are really rather minimal. That doesn't, now, make the behavior any more reasonable. The practice, of engaging in risky behavior and 'getting away with it', is well known, and extensively studied. I did such dives multiple times. Perhaps, that contributed to an increasing sense of confidence and security on each subsequent dive, which might be described by investigators as normalization of deviance, or survival bias. What we call it doesn't matter. For many of us, our feeling of immortality suffers from aging, and gradually begins to show the same signs of deterioration as our physical strength, mental acuity, and integrity of reflex arcs. Sigh.

 

[OTF]

Since this thread has grown and been revived since my first post, I think it's important to reiterate that the Chester Poling wreck (which this discussion was initially about) is NOT a tropical dive. It's a cold low-vis north Atlantic wreck. Different risk profiles demand different dive profiles.