Freeflow at 140'

[jtivat]

I agree with you about hanging the tanks. I learned that lesson the hard way. I started out hanging the O2 at 20' on a line that also had a quick link at 10', so that I could do both 20 & 10' stops, if I so chose to. After diving a 170' wreck in Lake Huron, my buddy and ascended to the the deco tank, that was a brand new Aluminum 80, equipped with a first stage, 2 second stages and an spg. after doing our stops, we got back on the boat and removed our gear. As I started to haul up the line that the deco tank was on, I realized that there wasn't anything on the line. All I got was the first section of line with the steel thimble still intact and nothing else. Apparently, the quick link had worked loose and the chop had caused the tank to jump off the line. Since the wreck we were diving on wasn't buoyed, we had to use grappling hook, which we released when we left the wreck. So, my boat was drifting all the time we were doing our deco and after we got back on board, which means that I couldn't pinpoint with any accuracy where the deco setup might be. A $500.00 lesson that will not be forgotton.

I think you missed the point your deco gas should be with b/c you may not make it to the hang tanks. We always hang back up gas at 20' but do not rely on it, if it is rigged properly you will not have a problem losing it.

 

[JEScholz]

My buddy and I had an 80 hung at 30' for our safety stops. This was a no deco dive but we planned to do safety hangs at 30, 20 & 10.

 

[Soggy]

My buddy and I had an 80 hung at 30' for our safety stops. This was a no deco dive but we planned to do safety hangs at 30, 20 & 10.

A no-deco dive to 140'. That's a hoot...

 

[JEScholz]

Scuba Steve

Thanks for the constructive informative comments. By the way, the tanks were suspended from the boat and attached to the buoy line at 30'. They were there for safety hangs.

 

[JEScholz]

Soggy,

Bottom line is, you dive what your are comfortable with and I will dive what I am comfortable with. This dive was planned for 7 minutes or 1500 PSI on a 100. We had 50+ visibility no current and the surface was so flat we could see the flys landing on the water.

What gas and equipment would you recomend for this dive? Isn't 140 to deep for Nitrox? Just because I haven't been through a NITROX calas does not mean that I don't read, know my air consumption and have some idea of how narcosis effects me. I did some chamber dives under controlled conditions to see how narcosis effects me.

 

[JEScholz]

hehehehe... speak for yourself... =) ... 160 on air in ice cold water on a single with only an Al20... then I get a face-full of bubbles from a free-flow?... yup, I'm a big fat chicken... not gonna do that...

Lamont
And your advice to me was to switch to the pony, shut off my primary, wait five minutes of a seven minute dive for it to melt, go back to the primary and not abort the dive?

 

[rainman_02]

Soggy,

Bottom line is, you dive what your are comfortable with and I will dive what I am comfortable with. This dive was planned for 7 minutes or 1500 PSI on a 100. We had 50+ visibility no current and the surface was so flat we could see the flys landing on the water.

What gas and equipment would you recomend for this dive? Isn't 140 to deep for Nitrox? Just because I haven't been through a NITROX calas does not mean that I don't read, know my air consumption and have some idea of how narcosis effects me. I did some chamber dives under controlled conditions to see how narcosis effects me.

What gas?

21/35, maybe 25/25.
50% for deco.


What equipment?

Minimum: Doubles of appropriate size (LP72s, AL80s, HP100s, HP120s, HP130s) with an isolation manifold. Two cold water regulators (Apeks, ScubaPro, etc) each with a first and second stage.


What training?

Check the course standards for NAUI, PADI, SSI, etc, but I'm pretty sure you'll find that dives greater than ~130' are not recreational dives.

 

[JEScholz]

I couldn't get on the system for a couple of days and now that I am, I see we have lots of comments from arm chair quarterbacks... Well let me respond to a few of the comments.

First of all, thanks to those of you who did offer constructive comments. I posted this message to start discussion so that I and others could learn from your comments and suggestions. To those of you who just want to take potshots :ircqnet::mooner:

Should I do this dive on doubles, sure, it would add a safety margin, but if you were diving it on doubles and had a freeflow, what would you do, continue the dive with one tank turned off or abort and head shallow?

Do I need a larger pony? How about some of you with "Adequate training for this depth" tell me how much air is needed for a straight, safe ascent from 140'. My figures tell me that a 20 would get me to the surface, a 30 would give more time for safety stops, but I knew I had an 80 waiting for me at 30' for my safety stops.

I have not taken any Nitrox classes yet but have taken NAUI Deep, Wreck and other specialty classes and make a habit of safety stops. I don't have anything to prove and get no kick out of above normal risk. If it does't feel right I abort and regroup.

 

[rainman_02]

Should I do this dive on doubles, sure, it would add a safety margin, but if you were diving it on doubles and had a freeflow, what would you do, continue the dive with one tank turned off or abort and head shallow?

Do I need a larger pony? How about some of you with "Adequate training for this depth" tell me how much air is needed for a straight, safe ascent from 140'. My figures tell me that a 20 would get me to the surface, a 30 would give more time for safety stops, but I knew I had an 80 waiting for me at 30' for my safety stops.

I have not taken any Nitrox classes yet but have taken NAUI Deep, Wreck and other specialty classes and make a habit of safety stops. I don't have anything to prove and get no kick out of above normal risk. If it does't feel right I abort and regroup.

Doubles?

Huge margin of safety for a relatively small increase in risk of failure due to the added complexity. With training on how to deal with doubles-specific emergencies.

Personally, I would consider a freeflow one of two situations: fixable or unfixable.

Assume: right post (primary regulator) freeflow.

Procedure: Shut down right post while signalling buddy. Breathe down the reg. Switch to your backup reg. Signal to your buddy "check my right post, bubbles." Buddy checks your gear and signals to you "it's fixed" or "it's broken." Do a flow check. If fixed, switch back to primary, continue dive. If broken, thumb the dive, continuing to breathe on your backup. Either way, with a first or second stage freeflow, you're not losing any more gas due to the way the isolator manifold and dual regulator setup is designed.


How much air?

Assumptions: One minute to figure out if the regulator is good or bad, dissolved gas model dive table (Haldane, Buhlmann, etc), 30'/min ascent, 3 min safety stop at 15', SAC rate 1.0 due to the stress of the situation.

It takes 4.2 minutes to ascend from 140' to 15'. Call it 5 minutes to be conservative. One more minute for 15' to 0'. So, you have 1 minute to "solve" the problem, 3 minutes of stop time, and 6 minutes of ascent time. That's a total of 10 minutes to get to the surface from 140'.

Call it roughly 2 ATA for average pressure over the entire 10 minutes of ascent.

Therefore, the appropriate amount of air to reserve is 10 minutes x 2 ATA x 2 divers x 1.0 SAC, which equals 40 cuft of air. That is roughly 1400 psi in a single HP100.

For your pony, since it is only for one diver (you), 20 cuft is an adequate amount.


You knew you had gas hanging on the line?

It was there when you left it there, but you had no guarantee it was still there. You can't count on it. Therefore it does not factor into your gas planning. It's a bonus if it's still there when you get to it.

 

[rainman_02]

Addendum:

By the design of doubles with an isolation manifold, you can turn off one valve (regulator) and still have access to the air in both tanks with the other regulator. However, shutting down a valve for an unfixable freeflow is a major failure and should drive you to thumb the dive.