With a partially closed valve, you are rate limited -- you breath the gaz in the hose in fact -- but the pressure come back when you stop breathing. That's not consistent with the graph.
Equipment My first out of air situation
- Thread starter ispasov
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This Thread Prefix is for incidents caused by equipment failures including personal dive gear, compressors, analyzers, or odd things like a ladder.
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johndiver999
Contributor
Look at the graph of air pressure. As mentioned by someone else, this shows immediate drop in pressure to zero (and then a spike). This can not happen from a partially opened tank valve. Also, it can not happen if there was a terrible leak, because the diver would have noticed it and the pressure would not spike up again momentarily.
The description I am reading is entirely consistent with a blockage in the regulator - most likely from crude inside the tank and then clogging the regulator.
If the tank valve was partially open, the pressure would have come back up, particularly when the regulator was not being used on ascent.
The Op made a very serious error in not immediately taking the second stage from the DM. There is no good reason NOT to start accepting air right away.
Some reasons why this was not just a failure to do the smart thing, but was dangerous and short sighted. What if the DM octopus was not working? It is much, much better to know that right away and when your regulator is still giving you some air. Also, if it was a typical low on air emergency, then it would make sense to preserve any air in the victims' tank for operation of the BC - or maybe just a breath or two if the DM tank runs out at 15 feet (which it did) apparently..
Also, it would not be a smart assumption that this was a typical low on air emergency and the diver could have just milked the tank slowly while ascending. If the indicated pressure suddenly went to zero, then the tank may suddenly stop delivering any meaningful air.
I would have taken the regulator off and examined the inlet and also tried to verify that the tank was completely out of air when the regulator was off - after the dive. Then I would have put that regulator on another tank and see how it performed.
The description I am reading is entirely consistent with a blockage in the regulator - most likely from crude inside the tank and then clogging the regulator.
If the tank valve was partially open, the pressure would have come back up, particularly when the regulator was not being used on ascent.
The Op made a very serious error in not immediately taking the second stage from the DM. There is no good reason NOT to start accepting air right away.
Some reasons why this was not just a failure to do the smart thing, but was dangerous and short sighted. What if the DM octopus was not working? It is much, much better to know that right away and when your regulator is still giving you some air. Also, if it was a typical low on air emergency, then it would make sense to preserve any air in the victims' tank for operation of the BC - or maybe just a breath or two if the DM tank runs out at 15 feet (which it did) apparently..
Also, it would not be a smart assumption that this was a typical low on air emergency and the diver could have just milked the tank slowly while ascending. If the indicated pressure suddenly went to zero, then the tank may suddenly stop delivering any meaningful air.
I would have taken the regulator off and examined the inlet and also tried to verify that the tank was completely out of air when the regulator was off - after the dive. Then I would have put that regulator on another tank and see how it performed.
I too would like to see the depth graph.
I don't use AI, but the air consumption graph does not make sense to me: it shows a remarkably constant slope, with ~100 bar used in ~35 min. This is regardless of changes in depth during decent or any changes in diver activity. For folks who do use AI: shouldn't there be greater variation in air consumption rate during decent and during the dive, and not a completely straight slope?
100 bar in say a 12 L tank is 1200 L - so the slope of the graph is 1200L/35 min = 34 L/m at 3 bar/20m. That equates to 11 bar/min on the surface: which is far lower than most experienced divers.
However assuming a more typical breathing rate for an inexperienced diver (say 22 bar/min) would empty a 12l tank in ~35 mins: close to what's seen.
As lizardland points out - I think the issue is with the AI/computer.
Cheers
Rohan.
I don't use AI, but the air consumption graph does not make sense to me: it shows a remarkably constant slope, with ~100 bar used in ~35 min. This is regardless of changes in depth during decent or any changes in diver activity. For folks who do use AI: shouldn't there be greater variation in air consumption rate during decent and during the dive, and not a completely straight slope?
100 bar in say a 12 L tank is 1200 L - so the slope of the graph is 1200L/35 min = 34 L/m at 3 bar/20m. That equates to 11 bar/min on the surface: which is far lower than most experienced divers.
However assuming a more typical breathing rate for an inexperienced diver (say 22 bar/min) would empty a 12l tank in ~35 mins: close to what's seen.
As lizardland points out - I think the issue is with the AI/computer.
Cheers
Rohan.
If I were the diver here I would have my first stage and the Air Integration checked by a service center. A faulty AI can create some extremely funky reading, both if water get through the first stage and if the battery is about to fail. I have logs where the reading jumps in literally impossible ways, and I have seen the battery in a AI explode not once but twice. (Not going to argue in replacing AI with a SPG, but when AI fail it will do so in a different way than a SPG. In doubt use both.)
If the actually air had dropped like the graph said then it should had been noticeable by the diver, buddy, DM, or just divers in the area (and marine life in general). It is possible that a new diver could miss it in the stress/distraction of the wonderful new experience of diving, but people around them is less likely to have missed that much of air exploding.
I would not personally put too much stock in that the DM tanks started to feel empty at the end of the dive. After an out of air experience, stress will makes things unreliable at that point. It could be as mentioned by others that the tanks was low from the start, or a very high breathing rate, or simple the stress making it feel like one can not able to take a full breath. The DM could also have been stressed out. With 30 dives, I would not worry much about this part of the events.
If the actually air had dropped like the graph said then it should had been noticeable by the diver, buddy, DM, or just divers in the area (and marine life in general). It is possible that a new diver could miss it in the stress/distraction of the wonderful new experience of diving, but people around them is less likely to have missed that much of air exploding.
I would not personally put too much stock in that the DM tanks started to feel empty at the end of the dive. After an out of air experience, stress will makes things unreliable at that point. It could be as mentioned by others that the tanks was low from the start, or a very high breathing rate, or simple the stress making it feel like one can not able to take a full breath. The DM could also have been stressed out. With 30 dives, I would not worry much about this part of the events.
lizardland
Registered
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.
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...
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...
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.
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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.
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.
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 ).
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 ).
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