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Most anybody.
0.8
Recreational limits.
10 cuft.
I know you are messing with me.
40' 3 min
30' 3 min
20' 5 min
10' 15 min
gas mixes for the pony....
- Thread starter rhwestfall
- Start date
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Most anybody.
0.8
Recreational limits.
10 cuft.
I know you are messing with me.
40' 3 min
30' 3 min
20' 5 min
10' 15 min
Your interpretation of the risk of oxygen toxicity is so inconsistent with my experience in recreational, military, and commercial diving it is difficult for me to understand. I have used and administered more than 150,000 Ft³ of O2 over 40 years, which is a small fraction of several friends. A 1.6 PPO2 is considered safe for short duration emergency exposure in recreational diving by all standards extremely safe IMHO.
Without an underlying medical condition, I have never heard of anyone experiencing even suspected very mild OxTox symptoms at 2.8 PPO2 in the short time you would be at max depth on a pony. It is not unusual for combat swimmers to see 3.5 ATA for short times under high stress situations. I have been on several jobs where surface supplied divers were on 1.8 PPO2 HeO2 for more than an hour bottom time followed by completing decompression in a deck chamber at 2.8 PPO2 daily for weeks at a time.
IMHO, the benefits far outweigh the risks for any competent Nitrox diver (or above) with a potential decompression obligation.
ianr33
Contributor
It's for emergencies only. If you ever switch to it the dive is over and you ascend immediately. N2 loading on a direct ascent to a safety stop is minimal,no practical difference between air or 32%
So: KISS, air in pony. (recreational dives,no deco,no overhead )
So: KISS, air in pony. (recreational dives,no deco,no overhead )
waterpirate
Contributor
I allways used 21% in my pony. Ohh the horror when diving the top of a wreck on nitrox and you have to chase the anchor to the sand to do the tie in. Spit out primary, switch to air to chase the hook, tie off up high, switch back to nitrox. Allways air in the pony. If I used a pony now I would dive 21/20 at a minimum.
Eric
Eric
My pony is filled with air to start with. If I needed to top it off during a dive trip, I top it off with what ever I am diving back gas.
If I need to use the pony, the days diving is most likely done.
Jim Breslin
If I need to use the pony, the days diving is most likely done.
Jim Breslin
I have a couple AL40, but neither have air in them. One has EAN50 and the other 100% O2. For a solo dive, I would take the 50% bottle and plan my dive accordingly as I'm not going to dump one just to have one full of air.
For practice I will sometimes do a gas switch to it and continue my ascent on 50% while practicing 2-3min stops every 10' too - as long as no issues occur. Obviously I don't do the dive below the MOD for EAN50 (70')
For practice I will sometimes do a gas switch to it and continue my ascent on 50% while practicing 2-3min stops every 10' too - as long as no issues occur. Obviously I don't do the dive below the MOD for EAN50 (70')
OP
My 40cft has 100 O2 in it therefore it is out of the equation wrt using it as a pony. However, I also happen to have a 80cft rigged as a stage with EAN 32. Being in the Advanced forum I will venture to say that we are still talking rec dives down to 130 ft without any overhead. In this case, I would be very comfy slinging my 80cft containing EAN 32 which covers the 111 to 132 ft depth range (PPO2 1.4 - 1.6) keeping in mind that the only reason that I am carrying it, in the first place, is to get my sorry rear end (or my buddy's or the two of us) back to the surface should an unforeseen situation dictates and not to be used as a range extender. If the latter was really what I had in mind, then, quite frankly, I would just opt strapping 2 X HP120 on my back for some peace of mind.
OP
What gas in the pony?
That's a pretty valid question. My knee-jerk reaction was to say "Air", because 32% didn't seem to have a significant deco gradient advantage for a just-pushed it NDL dive.
...But I decided to generate some numbers to check it out.
First, a 29 minute dive on air, with an additional minute on air (the switch to the pony):
Then, I looked at the same dive, 29 minutes on air, followed by a 1 minute switch to 32% & an ascent:
So there is a slight advantage to 32%; it's about 60 seconds less deco. When I ran the same scenario with 28%, it had the same slight advantage (1 minutes less).
Quite frankly, though, I feel the "slight deco advantage" to be a red herring. At first, it sounds like a lot, but it isn't, really.
I believe there is far more advantage to quick deployment and an uncluttered mind in the case of an emergency.
The pony isn't really there, I feel, for someone without deco training to get out of a sudden whopping obligation (and where would that come from? It's not like you'll suddenly end up with 30 minutes of deco by surprise). It seems it's there to accommodate a catastrophic loss of breathing gas.
So after talking myself into a circle, I too, would fall under the KISS mantle: clone the bottom gas.
All the best, James
That's a pretty valid question. My knee-jerk reaction was to say "Air", because 32% didn't seem to have a significant deco gradient advantage for a just-pushed it NDL dive.
...But I decided to generate some numbers to check it out.
First, a 29 minute dive on air, with an additional minute on air (the switch to the pony):
Then, I looked at the same dive, 29 minutes on air, followed by a 1 minute switch to 32% & an ascent:
So there is a slight advantage to 32%; it's about 60 seconds less deco. When I ran the same scenario with 28%, it had the same slight advantage (1 minutes less).
Quite frankly, though, I feel the "slight deco advantage" to be a red herring. At first, it sounds like a lot, but it isn't, really.
I believe there is far more advantage to quick deployment and an uncluttered mind in the case of an emergency.
The pony isn't really there, I feel, for someone without deco training to get out of a sudden whopping obligation (and where would that come from? It's not like you'll suddenly end up with 30 minutes of deco by surprise). It seems it's there to accommodate a catastrophic loss of breathing gas.
So after talking myself into a circle, I too, would fall under the KISS mantle: clone the bottom gas.
All the best, James
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