OOA on the Vandenberg

[Rae HalfTheHill]

Good points made by all. To answer a few points:
-both divers were excited to nake this dive, having never been on the Vandy before
-now that I think of it, ge did wear glasses, but I think he had a prescription mask
-The charter I am with dives AL80's, unless otherwise requested. Our policy is to leave the hang tank in the off position, in the event there is a free flow or leak. This is briefed at the site so all divers are aware.

I offered the is to initially at 700 for peace of mind and to get him in a relaxed state. I knew with the amount of air I had we could both safely ascend. I offered it several times during the ascent but he wanted to wait until he was run dry.

Another lesson learned is the safety stop is not the end all be all. None of us had incurred a deco obligation, and aside from the air consumption issue the dive profile was relatively conservative. We could have bypassed the safety stop and just made a safe ascent. Either way, many lessons learned that morning.

 

[Barnaby'sDad]

For me personally, I wouldn't have started a fuss at the ascent line, 90' deep with a diver that had 700psi in their tank and no deco obligation.

I'd be reassuring, signal OK and let's go up, everything is fine - you remain calm and provide comfort, smooth easy ascent, right by their side. Don't fix something that ain't broke - you'd have to be locomotive breathing to kill 700psi in 3 minutes of ascent and 3 minutes at 20' - and if the person actually was - you need to calm them down.

The air checks during the dive are perfect, someone fibbed, misread, equipment issue or was having a personal issue. When there's a possible problem, be right there close at hand, look them in the eyes, signal OK, signal slow down, point to your octo and signal ok - most of all be the calming effect. Taking a perfectly good regulator out of someones mouth and providing an alternate that is supposed to work adds to the tension. 700psi is a lot of air!!!!

What tank are you talking here? For someone with average or above average gas consumption ( I’m in the latter group )...if they’re at 90’ with only 700 psi...they’re most likely going to end up on the hang tank/regulator at their safety stop.

Speaking from personal experience (my gas consumption rate), I think it is VERY likely that the diver in question did not screw up his hand signal for the 1,700 psi point...and that he simply has a high gas consumption rate. Especially with an AL80 (just saw the OP’s update). An AL80 is not enough tank for a ~90’ dive for a big guy with above average gas consumption.

It’s up to someone in that boat to figure out that they need to run HP100+ tanks if they want to be able to spend a reasonable amount of time submerged on a dive profile like this one. That and someone in that boat has to be able to proactively call the dive and ascend prior to their DM calling the dive.

 

[jgttrey]

For someone with average or above average gas consumption ( I’m in the latter group )...if they’re at 90’ with only 700 psi...they’re most likely going to end up on the hang tank/regulator at their safety stop.

I don't agree with that. I'm not advising waiting until you are at 700 psi to start your ascent because you need to have something for a buddy with a problem and, yes, a stressed diver could blow through that quickly.

But, in general, 700 psi is more than enough to get a diver with no deco obligation to the surface, including the safety stop, even with an above average SAC.

I would consider 1.0 cf/min to be a well above average SAC.
700 psi in a AL 80 is more than 18 cf of gas.
An ascent from 90' to the surface should take 6 minutes.
At a 30'/min ascent, it takes 2 minutes to get from 90' to 30', so 2 min at an average of 60', or 3 atm.
Another minute to get to 15', being conservative. And being more conservative, will call that whole minute at 2atm.
A 3 minute safety stop at 15'. Again, being conservative, we'll treat that as 2atm rather than 1.5.

All told, that's 14 ATM-minutes (6 minutes total). Even at a SAC of 1, that's being on the surface with about 200 psi left.

Taking away some of those assumptions, and lowering the SAC rate to what I would think is about average, you'd probably use only half that 700 psi.

I'm only responding to this one issue, not suggesting that waiting to 700 psi to start up is a good practice, or that a panicked diver wouldn't use more, etc.

 

[johndiver999]

Good points made by all. To answer a few points:
-both divers were excited to nake this dive, having never been on the Vandy before
-now that I think of it, ge did wear glasses, but I think he had a prescription mask
-The charter I am with dives AL80's, unless otherwise requested. Our policy is to leave the hang tank in the off position, in the event there is a free flow or leak. This is briefed at the site so all divers are aware.

I offered the is to initially at 700 for peace of mind and to get him in a relaxed state. I knew with the amount of air I had we could both safely ascend. I offered it several times during the ascent but he wanted to wait until he was run dry.

Another lesson learned is the safety stop is not the end all be all. None of us had incurred a deco obligation, and aside from the air consumption issue the dive profile was relatively conservative. We could have bypassed the safety stop and just made a safe ascent. Either way, many lessons learned that morning.

I don't think that is "the lesson" here. I would have wanted to do the safety stop and also for the "victim" to do one. You had an octopus, there was presumably a hang tank, there was even someone else apparently available to provide air from a pony. With all those resources and without a clear indication that the guy was freaking out - then performing a safety stop would be my choice. Why endanger yourself unnecessarily, just because some guy has no clue how to dive? I think your decision to do the stop was the right one.

Also, I am not a fan of signaling air pressures using hand gestures, I prefer to show my gauge and have the buddy show his. No translation errors possible.

 

[Barnaby'sDad]

I don't agree with that. I'm not advising waiting until you are at 700 psi to start your ascent because you need to have something for a buddy with a problem and, yes, a stressed diver could blow through that quickly.

But, in general, 700 psi is more than enough to get a diver with no deco obligation to the surface, including the safety stop, even with an above average SAC.

I would consider 1.0 cf/min to be a well above average SAC.
700 psi in a AL 80 is more than 18 cf of gas.
An ascent from 90' to the surface should take 6 minutes.
At a 30'/min ascent, it takes 2 minutes to get from 90' to 30', so 2 min at an average of 60', or 3 atm.
Another minute to get to 15', being conservative. And being more conservative, will call that whole minute at 2atm.
A 3 minute safety stop at 15'. Again, being conservative, we'll treat that as 2atm rather than 1.5.

All told, that's 14 ATM-minutes (6 minutes total). Even at a SAC of 1, that's being on the surface with about 200 psi left.

Taking away some of those assumptions, and lowering the SAC rate to what I would think is about average, you'd probably use only half that 700 psi.

I'm only responding to this one issue, not suggesting that waiting to 700 psi to start up is a good practice, or that a panicked diver wouldn't use more, etc.

We’re talking about someone whose situational awareness is such that they allowed their pressure to get to 700 psi at 90’. What are the odds that said person is going to have a calm and collected ascent?

 

[GetDownScuba]

The odds go down if you offer them your alternate at that point is my guess.

 

[rvojr]

The odds go down if you offer them your alternate at that point is my guess.

Are you saying it is less stressful to have them to continue to ascend on their own air or when you offer the octo?

 

[GetDownScuba]

I’m saying it’s probably more stressful if you offer them your octo too soon. Might cause them to think it’s an emergency situation and create panic, when in reality 700 psi on an ascent with a hang tank and a guide with plenty of air is not an emergency. OP handled it fine - no reason to think you did something wrong.

 

[jgttrey]

We’re talking about someone whose situational awareness is such that they allowed their pressure to get to 700 psi at 90’. What are the odds that said person is going to have a calm and collected ascent?

1. I thought I made it clear that I was addressing the assertion that 700 psi was not enough to get an average diver to the surface. That statement is manifestly not accurate. An average SAC diver would use about half that. It's just math.

2.700 psi at 90' is not a crisis. See #1. Is it best practice? No. Is it a catastrophic world ending error? No. It was a problem for this guy only because, if the numbers are accurate, his SAC was 4.5x his buddy's and there was something else going on.

 

[Khrissi]

I think I would prefer to dive with you mate, Normal_life_is_just_SI. Well handled not-quite-an-emergency and us older guys may flake out sometimes. K