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Air breaks...What's everyone doing?
Normally, I take a 5 minute air break every 20 minutes. Lately, I've been doing some dives that are resulting in 21-25 minutes of decompression on O2. My question is what do you do in this situation. Do you take the air break and go back to O2 for 1-5 minutes or do you just finish out the time and do your ascent?
Rob Neto
Chipola Divers - Recreational, Technical, and Cave Diving Instruction & Mentorship
"Survival depends on being able to suppress anxiety and replace it with calm, clear, quick and correct reasoning..." -Sheck Exley
If my oxygen stop were that short, I'd just finish out the stop in one shot and then surface. Of course, I'm assuming that this is your only deco stop for the dive. For longer/deeper dives where I was using multiple deco gasses, I might choose to take the air break. But in that case I'd probably do it more toward the middle of the 20' stop.
Brian
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Assuming 24 minutes, I'd probably go 10-4-10.
John Sampson
Phoenix, AZ
+1 ... though I'd do 10-5-10.Originally Posted by AzTek Diver
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Rob Neto
Chipola Divers - Recreational, Technical, and Cave Diving Instruction & Mentorship
"Survival depends on being able to suppress anxiety and replace it with calm, clear, quick and correct reasoning..." -Sheck Exley
For breaks we do 12 on 6 off
Most of the open ocean diving we are doing results in deco in the 18 to 22 minute range (not including the 6 minute ascent) We usually don't bother doing a backgas break.
I.e. for 18 minutes of deco it doesn't seem worth it (to us) to do 12 on 6 off then a 6 minute ascent on O2 again. Better to just stay on O2 the entire time.
24 minutes and above we do the backgas breaks.
12 on, 6 off, counting the off time as deco time. I don't break unless the 20ft stop is 30mins or longer. I also do the last half of the 30ft stop on backgas.
Commit to Excellence
www.gue.com
Okay, I'm only tech1/cave2 so most of my deco has been on 50% except the cave stuff. The cave stuff hasn't been enough to worry about air breaks yet. That being said, I was taught 12on/6off unless it's < 20mins. If <20mins you can do it all "on."
We do the breaks to reduce the pulm tox issues, but remember that the damage to the lungs isn't instantaneous over some set 20min line and the alveoli are incurring "damage" (or at least freaking out) and losing gas trasfer capacity as you go along. So the air breaks help to give them a break, reset them, and make them efficient again. At least, that's what I was taught.
I think that since all deco theory is just that, theory, and the math that supports it takes into account mostly bubble and gas physics, but not lung efficiency to calculate deco, I'm inclined to be more conservative.
I quit smoking 12 years ago so I know there is damage to my lungs as it is. For me, I'm more inclined to do <15mins as all "on" and anything else I'll add breaks and extend it a bit. it would be 12/6 and then if it was a... say... a 20min deco, I'd probably do another 5 or 6 back on 100%. I tend to extend my shallow stops anyway.
Of course, as time goes on and I get more 100% time under my belt, things may change. But that's my starting point.
Chris
"....But no, it had to be the vibrator that died, dangit." Snowbear
"Everyone gets spanked." Lobstah
yeah it got lost -- here is is
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hi rob
you did not mention whether or not this was at 10 ffw or 20 ffw. What i have done over the years is to let my software (or table maker) generate stops for 10 and 20 feet that breaks up the stop time AND at most adds a few minutes to the total deco. But what it does is allow me to drop the PO2 should I want to and not affect the total decompression time.
There are times when i will "pull" the 10 foot stop down to 20 foot for operational consideration but that's done by choice. By having both 20 and 10 foot info i can control how to manage the oxygen exposure.
If the dive requires 20 min or more of pure oxygen at 10 / 20 combined I will just split the time up equally between the two depths. If it will require 20 min or more at the 20 foot stop only and then more at 10 foot - i will then add in "air breaks" for 5 min for every 20 min of oxygen at 1.6 atm.
What decompression model are you using ? This has an overall effect on how much oxygen is used. Neo haldanean models will call for long shallow stops whereas bubble models will spread the deco time out over greater depth range and will usually lower the oxygen time.
When we moved over from classic Hamilton DCAP to the Hamilton Bubble model we saw a big shift in how the deco was calculated. More bottom gas, less oxygen.
If you can post a profile it would be helpful.
Cheers
JDS
when it climbs over 20-ish minutes I do 12-6-12 counting the backgas time towards the deco.
entire stop before a switch is on backgas
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