PADI Deep Diver course- gas management

[Blackcrusader]

Last month I was diving with a young man who had completed the PADI deep certificate.
He was asking me if I had done one and I replied I had not. I did not tell him about my bsac sports diver deco training.
He was concerned I was diving deeper than my certificate allows. I told him OW by PADI can dive to recreational depth limit 40m.
He was shocked. He thought certs had a depth limit after training.
I asked did he have DAN dive insurance. He didn't have any dive insurance. He thought his travel insurance would cover him.


I showed him some posts on scuba board back at the dive shop later that day

Anyway I asked him how many liters of air in an AL80 with 210 bar. He didn't know.
I asked him did he know what his sac rate or RMV was. He didn't know what that was.
I asked him what is the emergency ascent rate, he didn't know. He said he did not recall being taught these things in his Deep Cert.
I asked have you been taught a CBA controlled buoyancy ascent using his BCD to bring another diver to to the surface. Nope.
I didn't see him with an SMB or dive computer. He did not own them.
Basically he went diving to deeper depths with an instructor for several dives and passed the written test. He really didn't seem to remember what was in his course.

He did one dive to maybe 32m depth with me but the others were less than 25m. After one dive he asked me why the guide did not check my air very often. The guide and I laugh. I asked why didn't you check yourself you are my buddy we both laughed but he understood the point. I said if you are my buddy you don't wait for the guide to ask you can check yourself. On the next dives he would check.

He asked me how I knew so much about gas management and consumption etc. I told him about BSAC Sports diving courses deco training, and then also by reading Scubaboard forums. Gradient factors and surf GF a lot of good advice on SB.

He saw I have a Perdix and asked what DC he should get. I recommended a Peregrine. I showed him the dive logs and he was like dang, graphs and lots of information on the DC. Told him just upload them so you can study them on your PC.

He was also asking what would be a good course to do. I recommended the TDI ANDP.

 

[MarkA]

Anyway I asked him how many liters of air in an AL80 with 210 bar. He didn't know.

That’s a bit of a trick question. Using metric and American in the same question, instead of 11.1 litre for the size of the cylinder.

 

[grantmac]

GUE use an estimate of 20L/min (0.7cuft), and a conservative ascent rate of 3m/min (10ft) - both because it's hard to control a quick ascent while gas sharing and to account for an actual higher stressed SAC rate in an emergency.

So from 36m:
Consumption - 2 diver x 20L/min = 40L/min
ATA - 36m / 2 / 10 + 1 = 2.8ATA
Time - 1 minute for gas sharing + 12 minute ascent = 13 minutes
Mingas = 40 x 2.8 x 13 = 1456L (51.42cuft)
in pressure of AL80 = 1456 / 11.1L = 131.17 bar rounded up to 140 bar (2000 PSI)

EDIT:
I would challenge anyone with a less conservative gas plan to try practicing gas sharing ascents with your equipment configuration from 36m and time it. Let me know how it goes.

I used 9m/min and a 3 minute stop which I find quite reasonable. If anything people are likely to blow past the stop under stress.

 

[steinbil]

I used 9m/min and a 3 minute stop which I find quite reasonable. If anything people are likely to blow past the stop under stress.

I don't think that's unreasonable. I think the most important thing is that people are taught how to calculate gas reserves, and that they use reasonable parameters that they (and their buddies) understand annd are comfortable with.

I do think it's better to err on the conservative side especially with newer divers, and it's very reassuring knowing that I have an ample gas reserve to handle emergencies.

However, my main gripe is with agencies and instructors that don't even teach or require any proper gas planning at all. I don't consider "be back on the boat with" to be sufficient planning, as the divers should understand and calculate themselves.

 

[Blackcrusader]

That’s a bit of a trick question. Using metric and American in the same question, instead of 11.1 litre for the size of the cylinder.

Not really. Anyone who has been taught should knows this anyway. People should understand both.

 

[Centrals]

Not really. Anyone who has been taught should knows this anyway. People should understand both.

LOL.
What system did they teach you in school?
Imperial(UK/US) or metric or chinese?

 

[Centrals]

That’s a bit of a trick question. Using metric and American in the same question, instead of 11.1 litre for the size of the cylinder.

It was NOT a trick question, it was silly.
A simple conversion and nothing to be proud of. Kid stuff.
I grew up with Imperial(UK) system and then have to adapt to the metric system.

 

[jadairiii]

I suspect he does not,

I'm still trying to understand this seemingly irrational fear of expanding the definition of "decompression diving"? At last check NDL's didn't come down from Mount Sinai.

If you have been diving for any length of time you know for a fact that mild symptoms of DCS goes unreported. So quoting DCS statics is problematic.

But, if you want a good start of actually understanding this premise, read The Physiology and Medicine of Diving, by Bennett. Or just continue to believe that diving within NDL is 100% "safe".

 

[boulderjohn]

At last check NDL's didn't come down from Mount Sinai.....

Or just continue to believe that diving within NDL is 100% "safe".

The straw man argument occurs when someone attempts to make a point by misrepresenting the opposing argument to make it easier to attack. It often does this by holding that misrepresentation up to ridicule. You are pretty good at it here.

No one implied that NDLs are sacred. No one implied that they are 100% effective. In fact, I specifically pointed out that some people do indeed get DCS when diving within limits. When I explained that studies indicate that most people who get DCS were diving within limits, that obviously means that I do not believe those limits are 100% safe.

I am sorry you feel your only recourse in discussion is to make an intentional misrepresentation of what others have said and then hold that misrepresentation up to ridicule.

 

[inquis]

And then of course you have plenty of data on divers getting bent on "no decompression" dives.

So quoting DCS statics is problematic.

Please forgive me, I'm confused by these seemingly contradictory statements. Is there "plenty of data" or isn't there?