DIRF, A Sobering Experience

[WYDT]

Originally posted by JamesK


Now this could be totally off base. Most agaencies teach you to be nuetral with 500psi in your tank. At the end of the dive, if you come up with less than 500, you would in effect be positve, with no way to correct it. Being positive would make it impossible to do a "safety stop" at 15 feet. So, if weighted properly, the 500psi limit to be back on the boat could be to keep you slightly negative when you are on your safety stop. This would allow you to use you wings to be neutral at the stop.

Just a guess though.

Actually James you should be neutral (at 15-20ft) with 0psi in your tank. This is in the even of a catestrophic loss of gas and you're sharing air.

The general rule for buoyancy:

Be able to ascend from depth with full tank(s) and 0 air in BC
Be able to maintain 15-20ft stop with minimum gas in tank and no air in bc.

Now obviously you aren't going to drain a tank to find out what the perfect buoyancy is for 0 air in the tank but if you can be neutral at 15ft with 500psi it's not going to be that different with 0psi. Actually it's going to equal ~1lb if we're talking about an AL80.

DSAO!

 

[JamesK]

Very good points!!!! Like I said, my post could have been totally off base. It simply seemed logical to me when i thought about it.

 

[Rick L]

Hehe I like that!!!
I think it was pizza to slow and french fry to go fast
Gee I couldn't believe I could have more fun! Even after 15 years
I still love going(my wife is getting sick of me scuba diving all the time hehe) Ive done about 15 tanks in the last 10 days.
The freezer is full of lobster and flounder does it get any better?
This dir stuff does look very interesting im going to keep reading
thanks Roakey
Rick L

 

[roakey]

Originally posted by Cave Diver
Roakey. I found your DECO Divers website when I initially started my NetQuest for DIR. I thought it was a very cool site with a lot of good information and many of your posts on here reinforced that opinion

That site is not mine, but done by Jeffrey who was one of my fellow students in Cave I. I only contributed my writeup of the class to it.

Roak

 

[trheeltek]

The current PADI/rec. standard is 60 ft/min ascent rate, and no stops are required except a safety stop on dives within the NDL. That's what their tables are based on, and they seem to work ok. Blowing off the safety stop isn't a great idea and shouldn't be standard practice, but the rest is straight from the book, and you shouldn't take a hit.

So, ok, let's revisit this - assume a 4 cub ft/min SAC for both divers, and they're using their standard RDP table (no stops except 15 ft). Ascending from 90 ft at 60 ft/sec, that's 1.5 minutes to the top, add a minute to get stuff together after OOA, that's 2.5 minutes. 2.5 x 4 = 10 cub. ft. They blow the safety stop, not a good idea, but statistically, so have lots of poor divers without getting bent.

As an intellectual exercise this is fun, but of course turning at 500 PSI at 90 ft is DUMB, so don't do it. I'm simply pointing out that following the current PADI OW training, you'd most likely be ok.

 

[detroit diver]

Originally posted by trheeltek
The current PADI/rec. standard is 60 ft/min ascent rate, and no stops are required except a safety stop on dives within the NDL. That's what their tables are based on, and they seem to work ok. Blowing off the safety stop isn't a great idea and shouldn't be standard practice, but the rest is straight from the book, and you shouldn't take a hit.

So, ok, let's revisit this - assume a 4 cub ft/min SAC for both divers, and they're using their standard RDP table (no stops except 15 ft). Ascending from 90 ft at 60 ft/sec, that's 1.5 minutes to the top, add a minute to get stuff together after OOA, that's 2.5 minutes. 2.5 x 4 = 10 cub. ft. They blow the safety stop, not a good idea, but statistically, so have lots of poor divers without getting bent.

As an intellectual exercise this is fun, but of course turning at 500 PSI at 90 ft is DUMB, so don't do it. I'm simply pointing out that following the current PADI OW training, you'd most likely be ok.

The current PADI standard is garbage. Just about every expert in the field agrees on a max 30 fpm ascent, and slower if possible.

Not only that, but the current thinking is graduated ascent, including deep stops. Going from the bottom to 15 feet is their way of saying: "okay, we'll bend you a little and fix it on the surface". Ever notice how tired some people are after getting back from a dive? They're bent. Not the crippling kind, but bent nonetheless.

DIR's way is to get you out of the water from an emergency OOA without negative consequences. That's why the extra safety margin for gas.

 

[sheck33]

Originally posted by detroit diver


The current PADI standard is garbage. Just about every expert in the field agrees on a max 30 fpm ascent, and slower if possible.

Not only that, but the current thinking is graduated ascent, including deep stops. Going from the bottom to 15 feet is their way of saying: "okay, we'll bend you a little and fix it on the surface". Ever notice how tired some people are after getting back from a dive? They're bent. Not the crippling kind, but bent nonetheless.

DIR's way is to get you out of the water from an emergency OOA without negative consequences. That's why the extra safety margin for gas.

Actually the US Navy tables worked like that, these tables ( i learned to dive with them in the 80's) bring you up quickly, get you bent and then treat you by having you do long stops.
One thing that divers need to realize is the fact that every single table to date is only a very crude model and has little or no connection to what really goes on inside the body.
The body is a lot more complicated than a few theoretical 'tissue' compartments. GUE's decoplanner might be more sophisticated than the navy tables but it is still only a crude approximation, if that, of a body. The body is still far to complicated of a system.
Hence all these extra safety margins ('fudge' factors)

 

[ElectricZombie]

60 FPM is crazy...PADI needs to correct that.

 

[MikeFerrara]

The 60 fpm ascent rate is'nt a PADI standard. It was an assumption used to calculate the tables. The current thinking is that slower is better. Deco models other than Halanian (gas absorbsion) are becomming more main stream. Models like VPM and RGBM are seeing wide use. Some are using softwares like GAP which is Builmen (not sure about the spelling) but uses gradiant factors to generate deep stops. The WKPP doesn't use any of them. They have developed their own rule of thumb method. Others have done the same thing and its nothing new. The stops given here, I think it was 1 min at 40, 30, 20, and 10. Sounds like a rule of thumb thing. Is this what you use for a minimum deco? If you are doing a dive that requires staged deco you should have bailouts in case you end the diver sooner than planned and need to get out of the water as soon as possible. Lets pick a profile and look at when we are terminating the dive then we can run the schedule and see what an excepted model calls for.

 

[JimC]

Worst case sitation following the 'rules' would be a dive to 130fsw for max NDL with the failure right as you start your accent.

So your would have 500psi + whatever you would guess you need to surface. Is the 500 enough to get your buddy up, safely?