OOA on the Vandenberg

[jgttrey]

Not running out of gas is part of OW training too, and if we could count on folks to remember their training he wouldn't have been in this situation to begin with. I would not assume he can handle it. Makes sense to leave some for that. Another reason to leave a little in tank. Not a lot, but some.

 

[BlueTrin]

Why? It is a required skill that is a part of most if not all agencies OW certification training.

Because the diver will be stressed. It also means that if he dumps too much air underwater he will be unable to become neutrally buoyant at that depth (unless orally inflate underwater which seems a bit tricky under stress). I guess you should grab his BCD to make sure he does not go away regardless during ascent ?

People do dumb stuff when they are stressed.

How many times have you practiced it, are you sure that in situation of stress you’ll be confident enough to do it without mistake ?

What happens if you need to inflate then for some reason the buddy let go my octo instead of keeping it in your hand and has difficulty finding it ?

Would you trust someone who couldn’t monitor his air consumption with having trained this ? Because, it’s not like I have dived a lot but I got instabuddied more than once with people who had dodgy air consumption monitoring and literally didn’t want to come up before they would hit under 50bar.

Unsurprisingly enough, they were as well the ones who didn’t seem to maintain their equipment well: I had a guy telling me that he was ok to breathe his cylinder under 50bar to almost empty. This same person had an inflator stuck pre-dive. After the dive, he said that he never rinsed his BCD and didn’t want to get his BCD serviced ...

Do you think I can trust this guy to have practiced inflating his BCD orally ?

 

[Steelyeyes]

Why? It is a required skill that is a part of most if not all agencies OW certification training.

While they may have had to prove they could do it once or twice it's never good to add additional complexity to what for some people might be a pretty tense situation already.

 

[Hatul]

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.

I agree with you. A rule of thumb for Rock Bottom is at 90 feet you should have 90*10+500 =1400 psi. That's enough to get two divers up so one diver needs 700 psi.

I can do detailed calculations at the desk but not while diving, which is why I dive with an AI computer that works these things out for me in a reasonably predictive way. If I see my Air Time approaching 0 I know it's time to ascend and I also know that I have enough gas to make a safe ascent as long as I stay calm.

 

[Rae HalfTheHill]

I agree with you. A rule of thumb for Rock Bottom is at 90 feet you should have 90*10+500 =1400 psi. That's enough to get two divers up so one diver needs 700 psi.


Just a quick question, how was that equation thought of and does it apply to most depths?