Ratio Deco on 32%

[gwilson]

Originally Posted by Garf

the fraction of what gas?

Thats what i wasnt to clear on i think he was meaning the percentage of oxygen using EAD tables. So if at 13 metres 60% has an EAD of 1.6 metres what is the fraction of o2 ? (I think).

I dont do this deco thing yet so havent got a clue.

[RichW]

Originally Posted by Howard Payne

Perhaps a GUE Instroketor could just check that over for me and pick holes in it if there are any - just for the sake of accuracy and clarity Particularly bearing in mind the fact that most of the time - we haven't got a bloody clue what we're doing.....

That looks pretty reasonable to me, Howard.

However, 30m deco dives can be a tricky one, particularly as you start to accumulate any significant deco. Many of the models, rules of thumb, etc seem to fall over in not a very predictable way as you get beyond an hour of bottom time. Oxygen at 6 obviously helps the decompression, and I'd generally consider taking it as the 6m stop gets much longer than 10-15mins or so.

Hope that helps,,
Rich

[Mal Bridgeman]

Originally Posted by gwilson

Thats what i wasnt to clear on i think he was meaning the percentage of oxygen using EAD tables. So if at 13 metres 60% has an EAD of 1.6 metres what is the fraction of o2 ? (I think).

I dont do this deco thing yet so havent got a clue.

Fraction of O2 is constant. ppo2 varies proportionately to the ATA.
HTH
Mal

[Howard Payne]

Thanks Rich - thoroughly recommmeded for Fundies if anyone wants to learn some of this stuff formally - I did mine with him - learnt loads and had a great time.

It seems that on the longer dives - not skimping on the increased time at 12 + 9m becomes more important?

[Garf]

Originally Posted by RichW

That looks pretty reasonable to me, Howard.

However, 30m deco dives can be a tricky one, particularly as you start to accumulate any significant deco. Many of the models, rules of thumb, etc seem to fall over in not a very predictable way as you get beyond an hour of bottom time. Oxygen at 6 obviously helps the decompression, and I'd generally consider taking it as the 6m stop gets much longer than 10-15mins or so.

Hope that helps,,
Rich

using O2 as a deco gas in the 30-35 metre range is something I discovered to my joy this year. It works really, really well.

[lloydwatkin]

Originally Posted by Garf

using O2 as a deco gas in the 30-35 metre range is something I discovered to my joy this year. It works really, really well.

I'm guessing there'd be no point (well not much point) in taking 50% on one of these dives as the decrease in deco time over a 32% mix would be negligible?

[RichW]

Originally Posted by Howard Payne

Thanks Rich - thoroughly recommmeded for Fundies if anyone wants to learn some of this stuff formally - I did mine with him - learnt loads and had a great time.

It seems that on the longer dives - not skimping on the increased time at 12 + 9m becomes more important?

Thanks Howard.

You're absolutely right about the 9 & 12's as well. These longer dives tend to load up the intermediate and slower tissues, so you really do need to be wary of this and not forget about these stops. If you do too little time here, there's a danger of picking up some minor damage, and the O2 doesn't do very well at "fixing" it.


Rich

[Garf]

Originally Posted by lloydwatkin

I'm guessing there'd be no point (well not much point) in taking 50% on one of these dives as the decrease in deco time over a 32% mix would be negligible?

correct. If you stop at 21M to maximise the PPo2 you are probably still ongassing. If you go shallower to increase the gradient, you can't maximise the PPo2, so 50% is not worth the effort.

[RichW]

Originally Posted by lloydwatkin

I'm guessing there'd be no point (well not much point) in taking 50% on one of these dives as the decrease in deco time over a 32% mix would be negligible?

Lloyd,

The 50% has limited useability here, as you don't really start to decompress with any "vigour" until you're shallower than about 15m. You're effectively using the pressure gradient here to elimitate N2, and consequently the 50% won't have much effect on the off-gassing. O2 is a better choice for these dives, as Garf points out.

Rich

[David]

if Howard is starting to make sence have i done something wrong........

did I not take the right deco pills last night..........