Air breaks

[milldog]

just a follow on from the thread deep air, as i don't want to hijack Brains thread

if your last stop on a dive was 36 minutes on O2 how would you break that up if at all?

would you count the back gas breaks as part of the deco?

if you don't break it up how long would you stay on O2 before you would have breaks?

or are you happier using the 80%?

Graham

[Clare Gledhill]

If I wanted 36 minutes personally I'd do:

12 on
6 off
12 on
6 up (staying on O2)

Whether you count it or not depends on how you feel, how aggresive the deco is, how short the O2 time is (and therefore how much as a percentage of O2 time you are missing by counting the 'off' time). If in doubt or unhappy with the pattern then do more time.

I'd happily do up to 20 minutes on O2 and then a 5 minute ascent without taking a break but a 12 on 6 off pattern is a reasonable pattern to adopt for longer exposures. Would 10 and 5 work just as well? Of course it would, so choose what suits you for your diving.

[Andy Kerslake]

Originally Posted by milldog

just a follow on from the thread deep air, as i don't want to hijack Brains thread

if your last stop on a dive was 36 minutes on O how would you break that up if at all?

would you count the back gas breaks as part of the deco?

if you don't break it up how long would you stay on O before you would have breaks?

or are you happier using the 80%?

Graham

Our concerns with high POP gases are the effect that the O2 has on the lungs. As we know O2 is an irritant and anything above 0.5 PPO2 has a negative effect. So it does not really matter whether you use 80% or 100% both over time will have act as an irritant to the lungs ( pulmonary toxicity)

So what we are attempting to do with air breaks is to reduce to a minimum the effect of the O2 and keep the alveoli running at full speed.

Pulmonary toxicity is time dose dependent, so if you had been running high PPO2's during the bottom phase of the dive, then additional high exposures during deco would not only increase pulmonary tox, but also the likelihood of Oxtox.

Due to the effect of the gas breaks our lungs maintain a greater level of efficiency than without - I guess the secret is the how often should the gas breaks be? (a gas break is a break to the lowest breathable PPO2 that you have with you)

Over long periods of time 20 on and 5 off seems to start frying lungs, but anecdotally 12 on 6 off does not appear to have the same impact.

So with Graham's 36 minutes on O2, you could do 12 on 6 off, 12 on and 6 up. This keeps the clock running

Andy

PS I would not use 80%, as it still contains Nitrogen, and I would still be ongassing Nitrogen.

[Gene_Hobbs]

For a little more history on how they picked 20 on/ 5 off protocol to start with:

Extension of oxygen tolerance by interrupted exposure.
Clark. Undersea Hyperb Med. 2004 Summer;31(2):195-8.
RRR ID: 4009

Andy gave an excellent explanation of the development of 12 on/ 6 off here.

[gobfish1]

If your worried about 36mins on 1.6 slide to 5 half your load ,

I don’t do air brakes but if I did I would not count air as part of my deco ,

the old numbers were 1min @ 1.6ppo2 = 5 mis on air

newer numbers are about 1min @ 1.6ppo2 = 2,5 0n air

so if you went with the old numbers you could still do one or two 5 min air brakes
and still have done the right amount deco to come out ok ,

but if you go with the new thinking , then you have missed a bit of deco

ps

if your running your deco with a big Safety margin then you will be o.k.
as your getting more dceo to do in the first place

hope that BS helps

[Andy Kerslake]

If you read the reference in Gene's post you will see that 20 on and 5 off does lead to a 4% vital capacity reduction over time.

So if we use this method we are reducing the efficiency of our lungs, for short deco times 30/40 minutes this probably does not really matter, but for longer exposures it must make a difference.

So apart from shortening the exposure times its good to have a protocol thats nice and simple to remember.

Andy

[gobfish1]

Originally Posted by Andy Kerslake

If you read the reference in Gene's post you will see that 20 on and 5 off does lead to a 4% vital capacity reduction over time.

So if we use this method we are reducing the efficiency of our lungs, for short deco times 30/40 minutes this probably does not really matter, but for longer exposures it must make a difference.

So apart from shortening the exposure times its good to have a protocol thats nice and simple to remember.

Andy

yes its all down to time , and milldog is diving Oc for less than 140 mis in water time i would think , Do you can class that as short exposure time

[Andy Kerslake]

Originally Posted by gobfish1

yes its all down to time , and milldog is diving Oc for less than 140 mis in water time i would think , Do you can class that as short exposure time

Its time and dose dependant, so it would depend on what PPO2's are being run on the dive. 140 mins is not a long dive (its long enough in the sea !) but it makes sense to have a simple protocol, rather than keep changing it based on shorter/longer durations.

Andy

[milldog]

there is talk that on 100% after leaving the water you feel better than if you were on the 80% until the O2 calming effect happens and wipes you out, but thats another thread.

the sort of run times i would be looking at were in the 124 to 145 minutes with ppo2 of 1.4 bottom and 1.6 deco running on 15/55, 21/35, 50% and 100% funny but the GUE planner doesn't do air breaks? anyway this would be a short exposure.

I'm interested to see who would go straight through the 36 Min's on the 100% without breaks

Graham

[gobfish1]

Originally Posted by Andy Kerslake

Its time and dose dependant, so it would depend on what PPO2's are being run on the dive. 140 mins is not a long dive (its long enough in the sea !) but it makes sense to have a simple protocol, rather than keep changing it based on shorter/longer durations.

Andy

i can live with that