Training for "Recreational Trimix"?

[danvolker]

If it takes that long to come up when using a little helium, then I am way safer on 31% nitrox at 130 ft.... and a small pony

My tables have me coming up with much less time wasted --not doing stops every ten feet until much closer to 30....but this then gets to tables for everyone, including those with pfo's, or, tables for an individual like mine, which I can't share. I can't even say there is any thing wrong with Kevrumbo's approach to this, as I think most would support this approach....but mine is more statistically valid "for me", as I have had zero DCS with it, and many tech instructors have had hits with their "conservative" ascent and stop protocols...and I have done this over so many years that thinking of this in statistical form is practical. George always talked about the "shape" of your deco, of how you do the ascent, and when the stops begin, how fast you get there, and then where the major offgassing is going to occur. There is a different model in play between his concept, and the current deep stop thinking.... One with very little in common. If I do the Hole in the wall on 25 -35, like I said, I will be up on the surface, pretty close to as fast as an air or nitrox diver will.
For the purposes of this thread, I think GUY could find a set of tables cut from a model that would be much less deep stop oriented, and every bit as valid. The real question would be for "who" it would be most valid for, and there is little if any industry discussion on this.
It would be a great discussion to get Bill Mee into, as he worked with Dr Bill Hamilton and with George on the model and the tables that I like to use.... If the great anonymous Dumpster Diver decided he could actually be known in real life, as opposed to only the internet personna, then this WOULD be possilbe on a dive trip sometime in the next month or so

 

[Hatul]

My deepest was at Redondo Beach between 130-140ft on air. It was a non deco dive so turned right around and swam slowly back to shore. Don't know about helium diving, but for regular air/nitrox I too consider a 19 cu ft bottle adequate to safely make it to surface from 130 ft. It's a good rule to take the 19 pony on dives deeper than 100 ft.

 

[kierentec]

My deepest was at Redondo Beach between 130-140ft on air. It was a non deco dive so turned right around and swam slowly back to shore. Don't know about helium diving, but for regular air/nitrox I too consider a 19 cu ft bottle adequate to safely make it to surface from 130 ft. It's a good rule to take the 19 pony on dives deeper than 100 ft.

not that it has much of anything to do with this thread, but how did you come to the conclusion that 19cu ft is enough gas to make it up from 130'?

 

[ianr33]

130 ft @ EAN31 is 1.53 PO2 !!

Instant death !!!!!!! :shocked2:

 

[danvolker]

And in the spirit of the thread....training should have progressed far enough at 60 foot depth levels, so that a buddy team is essentially in-separable on all dives, prior to them being "ready" for the 130 foot dive....and at this point, instead of a 19cu ft pony, you have a very intelligent full sized tank following your every move, ready to help you if you have a problem....the pony has no brains, and will do nothing to help you

 

[dumpsterDiver]

not that it has much of anything to do with this thread, but how did you come to the conclusion that 19cu ft is enough gas to make it up from 130'?

Ok sac is 1 cu-ft per minute

Ascent rate is 30 feet per minute

Depth is 130 , pressure is 5 atmospheres, air used in one minute ascent is less than 5 cu-ft
time = 1 minute, now at 99 feet, pressure is 4 atm, air used in one minute is less than 4 cu-ft
Another minute later depth is 66 ft, P = 3 atm, in one minute use less than 3 cu-ft
Another minute, depth is 33 ft, p = 2 atm, one minute use less than 2 cu-ft
Arrive at surface at time = t = 4 minutes

Total used is less than 14 cu-ft

Want a 3 min safety stop??? use the extra 5 cu-ft.

 

[rhwestfall]

or, can still even go @ 60'/min up to 60', then slow it to 30'/min, and there is more gas...

 

[Parsons]

One thing not mentioned yet is the shortage of helium. I know in the Great Lakes, late in the summer we had some trips canceled just because we had no Helium. BUMMER! DP

 

[dumpsterDiver]

or, can still even go @ 60'/min up to 60', then slow it to 30'/min, and there is more gas...

Yes that is what I would probably try to do in a true emergency. If I can get to 60-70 feet and still have air to breath, I am pretty sure i can make the surface, even if the pony bottle fails too.

The other thing I would do is inflate my BC....I would NOT be kicking up, I would be venting air and managing my ascent rate by flairing my body etc. Complete relaxation of arms and legs and concentration on slow breaths and deep exhalations, should drop heart rate and drastically lower demand for breathing gas within a minute or so, unless the diver is terribly winded or totally freaked out.

If you are at 50-60 feet within 90 seconds and your breathing is in control and you are not exerting yourself, you will have tons of air in a small pony to finish the ascent.

 

[scubadada]

not that it has much of anything to do with this thread, but how did you come to the conclusion that 19cu ft is enough gas to make it up from 130'?

I use a pretty conservative calculation for my estimate, with a uniform 30 ft/min ascent rate and a 3 min safety stop at twice my average SAC (over the last 240 dives, my SAC mean +/- std dev is 0.37 +/- 0.05 cu ft/min)

4 minutes at an average depth of 72.5 ft = 9.6 cu ft + 3 minutes at 15 ft = 3.3 cu ft + 30 seconds at an average depth of 7.5 ft = 0.5 cu ft for a total of 13.4 cu ft over a total ascent time of 7.5 minutes. That leaves a pretty good leeway of 5.6 cu ft to cover other variables. For instance, an additional minute at 130 ft would require 3.7 cu ft. If my SAC was 1.0, the above ascent would take 17.8 cu ft.

For a no-stop recreational dive, if push came to shove, the ascent could be done faster and/or the safety stop could be truncated or eliminated as needed. I feel reasonably confident using my 19 cu ft pony for recreational dives.

Good diving, Craig