Equipment My first out of air situation

[lizardland]

which is far lower than most experienced divers.

That's exactly why it jumped out at me. I've been diving a long time and decent level of fitness and I'm generally around 14-15l/min. A nervous new diver doing 11-12l/min just doesn't seem realistic. I don't use electronic SPG's either so I might be wrong but that flat, steady down trend looks odd. I know my consumption has peaks and troughs (for me usually higher at the start then flattens out then goes up a bit during ascent) throughout the dive. A slow trickle then kaboom looks like a misreading sensor that suddenly caught up to reality. 35min around 20m at 20l/min is going to equate to an empty cylinder so unless the dive profile was a lot different then it doesn't need a mystery disaster to explain it. Again I don't know if this is normal because I don't use it but there are some very big, very erratic spikes in the readings, even after the out-of-air. That's what my money is on. As to what caused it then who knows. The fact that the DM is fobbing the guy off with some rubbish about the reg just needing a service makes me instantly suspicious about the state of their rental equipment.

 

[therookie]

To the OP: Thanks for kicking off an educational thread. Like you I am an inexperienced diver and many of the responses here have been very enlightening.

For what it is worth, at this point, if it were me, I would be digging into my AI setup a bit - starting with comparing my computer's calculation of my average gas consumption (SAC/RMV - seems that sometimes the acronym varies from one computer to another) over the dives prior to that one. At dive 29 my own average consumption was around 18L/min - if it suddenly dropped to 11 or 12 for the first part of dive 30 (as correctly calculated in a previous post) I would be very suspicious of the pressure readings on that dive.

As to why that would be - crud in the tank or other mechanical issues are things that have never occurred to me and thanks to those that posted those thoughts. Since it's rented gear in another country and we can't check the mechanical bits, I would have my AI computer setup checked by a technician. You mentioned the BCD is new and this was your third dive with it - is the AI setup also new? If it's still under warranty an explanation of why I want it checked would hopefully mean it would be covered - but even if not it would be worth the investment of $ in my mind.

And then even if the results of that checkup by a certified tech were "this setup is working as expected", on my next dive I would ask the shop for a loaner of an analog SPG - explaining my reasons for it: I would want it so that I could compare analog readings with my AI setup to increase my confidence in the AI for my own peace of mind. If analog and digital match up pretty closely, I would be pretty confident that the issue on dive 30 that led to an OOO situation was a mechanical/physical one.

For the more experienced who might read this, if what I say would be my next steps here aren't a good approach please smack me down...

 

[rongoodman]

I would expect a transmitter failure to be all or nothing, whether because of a dead battery, loss of synch, or whatever. It continuing to work while providing a plausible but incorrect reading sounds more like the behavior of a mechanical device, such as an SPG. It would certainly be worthwhile for the OP to check it against another gauge, electronic or mechanical, before his next trip.

 

[scubadada]

If you look at a typical dive profile, like the one below, despite variation in the gas consumption rate (purple line), the tank pressure curve is relatively smooth with no acute changes (pink line). The line always slopes downward with ongoing gas consumption.

The tank pressure curve supplied by @ispasov looks very different. There are 2 smaller blips at about 6 and 11 minutes with a decrease in pressure that recovered back to baseline. The 3rd decrease at about 35 min is quite dramatic. At about 40 min the pressure recovers to baseline, or nearly so, but falls again to zero. There is one more increase in pressure at around 50 min. It easily seems most likely that this represents mechanical obstruction of the dip tube and/or first stage filter. Perhaps the OP can inquire with the operator to find out what inspection of the tank, valve, and regulator revealed.

 

[stepfen]

BTW @ispasov welcome to scubaboard. Yes the environment here is occasionally a bit too harsh (as you just discovered), but if you overcome the initial shock and with a bit of persistence you will get invaluable info and help.

Back to topic. Do you remember if the tank was aluminum or steel (steel are generally fatter, shorter and heavier than aluminum)? Steel tanks can get rust debris inside that can easily clog the valve, the filter or both (especially if there is no dip tube). That is more difficult to happen with aluminum tanks.

FYI I would have responded to your incident quite similarly to you (I hope). I would have given higher priority to the DM vs to any insta-buddy to seek help. After establishing shared air, I would try to see what was wrong with my reg on the way up - just in case it is something that can be fixed and I would also try to finish the safety stop (assuming this and any previous dives were not trivial). Yes the DM should've been monitoring his gas during all these, but since he also had to take care of the rest of the group, we can't blame him for that.

It can also be quite helpful to see the dive profile (depth vs time) so we can better see how all these unraveled.

About how to overcome such incidents in the future, you can consider the following: Get your own reg set. Learn how to regularly check/maintain it. Use appropriate backups (eg SPG, did you have one? what did it show? ). You need to get to know your normal breathing rate, so you can easily identify any irregularities. Eg these remaining ~100bar after 35mins dive time might be too many (indicating a problem with your AI reading) but we can't know that without knowning your depth profile and your normal breathing rate. Finally, I would add to dive with reputable centers ( yes I'm from Greece and I won't dive with any center that the owner doesn't dive regularly together with the divers/customers YMMV ).

 

[BRT]

BTW @ispasov welcome to scubaboard. Yes the environment here is occasionally a bit too harsh (as you just discovered), but if you overcome the initial shock and with a bit of persistence you will get invaluable info and help.

Back to topic. Do you remember if the tank was aluminum or steel (steel are generally fatter, shorter and heavier than aluminum)? Steel tanks can get rust debris inside that can easily clog the valve, the filter or both (especially if there is no dip tube). That is more difficult to happen with aluminum tanks.

FYI I would have responded to your incident quite similarly to you (I hope). I would have given higher priority to the DM vs to any insta-buddy to seek help. After establishing shared air, I would try to see what was wrong with my reg on the way up - just in case it is something that can be fixed and I would also try to finish the safety stop (assuming this and any previous dives were not trivial). Yes the DM should've been monitoring his gas during all these, but since he also had to take care of the rest of the group, we can't blame him for that.

It can also be quite helpful to see the dive profile (depth vs time) so we can better see how all these unraveled.

About how to overcome such incidents in the future, you can consider the following: Get your own reg set. Learn how to regularly check/maintain it. Use appropriate backups (eg SPG, did you have one? what did it show? ). You need to get to know your normal breathing rate, so you can easily identify any irregularities. Eg these remaining ~100bar after 35mins dive time might be too many (indicating a problem with your AI reading) but we can't know that without knowning your depth profile and your normal breathing rate. Finally, I would add to dive with reputable centers ( yes I'm from Greece and I won't dive with any center that the owner doesn't dive regularly together with the divers/customers YMMV ).

The debris happens with aluminum tanks too if they have no dip tube. I know of two instances of instant gas cutoff when going head down. I watched one of them happen.

 

[CG43]

In the tank pressure graph, there are two noticeable points. At minute 38-40, there is a peak of about 60 bar. Can you remember if you noticed this peak while breathing? After minute 50, there is a rise to at least 25 bar. You must have noticed that while breathing if it occurred, and this is not the time when you switched to the octo of the DM. At 25 bar, almost all modern first stages provide enough air for this shallow depth. Was the breathing from your regs equally heavy the whole time despite these different displayed pressures, it is likely an AI error.

By the way, from my point of view, there is nothing to criticize about your actions and those of the DM.
If you can do it this way do it .

 

[grantmac]

This looks like blockage via either debris or moisture in the tank. Probably no dip tube and happened when the diver trimmed head down to follow the octo.
I'd be questioning any equipment from that operator.

 

[kdlv]

Здрасти,

How did you have the AI on rental regs? Is it your own AI and if yes, on what device, I don't recognize the graph.
Happy to have a dm chat, I am also curious which dive ops in Greece it was (no fingerpointing intended, just curious).
These seizures in pressure are strange. Either blockage as mentioned earlier, or faulty 1st stage... however 1st stages tend to leak, not to block.
What were the regs? Brand / model? No conclusions to draw, just curious.
Did the dive center remove the spg to install the AI (if your device was installed) or did they just use the 2nd HP port?
You have most the gear, now on to the regs

 

[Alurpal]

I’ve seen a novice diver have an ooa emergency exactly like this on a boat once. I always check my own valve right before splashing. I always wondered if a deck hand did a quarter turn from closed by mistake.