Oxygen window

[Mark]

Andy,

The profiles will look very simular if you use software to generate a profile using 50% and then one using 32&80%. The Dplan profiles look very simular in shape but I'm not using software to generate my 50% profiles (I have to for the 32% & 80% ones though).

Just so we are talking about the same thing, please run a profile for 30mins @ 51m on 21/35 using 32% & 80% using your software.

Cheers,

Mark.

[Andy Phillips]

Ok, 51M 30 mins 21/25 gas

32/80___________50
39 - 4_________27 - 7
21 - 7_________24 - 1
18 - 1_________21 - 2
15 - 2_________18 - 1
12 - 4_________15 - 3
9 - 5_________12 - 4
6 - 23_________9 - 5
_______________6 - 32

Bear in mind Noah used this software to plan his dives to his house to get his kettle for a cup of tea.
If you don't want to post up the GUE profile, please PM me, this is all begining to bug the c**p out of me.

Andrew

[Mark Chase]

Plus we only need to take one stage which is a whole lot less complicated and less drag etc etc.....

Yes but it limits the dive too much…

Granted its less hassle but with the bottom times Andrew and I run I would need a 10ltr or 12 ltr stage of 50% to safely complete the dive in a worst case scenario. Carrying a single 10 or 12 as a stage is a PITA. I find two 7's a balanced rig when worn one left one right. Also two 7's = 14ltrs of gas so a greater margin for error is present. I appreciate this doesn’t affect you as you where them all on one side so there is no advantage of two small tanks over one big one.

Moldavia 50m Max dive 50min bottom time: Planned both ways:

Gas 25/25 Deco 32 and 80% GF20/80 Ascent in run time safety off ascent rate sub 10m/min :

Back Gas required 226bar on twin 12s with a 50bar reserve
32% deco required 169 bar 50 bar reserve 7ltr
80% required 192 bar 50 bar reserve on a 7ltr

3 @ 40m for gas switch to 32%

2 @ 18
4 @ 15
7 @ 12
7 @ 10 Gas switch to 80%
32 @ 6

Total deco 54mins plus 3min for the gas switch

Gas 25/25 Deco 50% GF20/80 Ascent in run time safety off ascent rate sub 10m/min:

Back Gas required 256 bar with a 50 bar reserve ( you would need twin 15's)
Deco gas required 233 bar in a 10ltr with a 50 bar reserve ( not enough reserve you would need a 12ltr for deco)

1 @ 27
3 @ 24
3 @ 21 Gas switch so extended
2 @ 18
4 @ 15
6 @ 12
8 @ 9
45 @ 6

Total deco 71min plus 2min for gas switch

Apart for the additional 17mins of deco, the gas management just doesn’t work for me on this dive. The depths and run times are typical of a max 50m dive for me and using the VR3 I will often extend the bottom time if the wreck is actually shallower. So this being the Moldavia I am aware that I will spend most of the dive at 46m so may manage 60mins on the bottom. This would only push my real time deco to 67mins and is still achievable on two 7ltr stages.

Frankly I don’t think the single deco gas argument stands up at these depths. You have to make the dive fit the gas, which is IMHO all wrong you should make the gas fit the dive. I would single gas deco max 40m

ATB

Mark Chase

[MattS]

We appear to have moved off the original thread but I am quite interested in all the normoxic talk. To date I have only used hypooxic mix past 60m but now that Den at O-View has Helium in I was thinking about normoxic for shallower dives.

What strikes me about 21/35 or 18/45 using a single stage, is that you must be relying on having that single stage available. What contigency plans do you have for the stage being disabled?

For a 50m 30min (bottom time) dive I was planning on something like 24/24 with a single stage of 80% for deco. Should the stage go tits I could, just about, get out using the 1/3 backgas reserve. It should be clear that I don't regard total back gas failure as a huge risk, however that risk is somewhat mitigated by the fact that a buddy would be configured to supply gas up to 10m by way of the long hose. If anyone cares to comment on the sense of this plan I would appreciate it.

[Andy Phillips]

Originally Posted by MattS

We appear to have moved off the original thread but I am quite interested in all the normoxic talk. To date I have only used anoxic mix past 60m but now that Den at O-View has Helium in I was thinking about normoxic for shallower dives.

What strikes me about 21/35 or 18/45 using a single stage, is that you must be relying on having that single stage available. What contigency plans do you have for the stage being disabled?

For a 50m 30min (bottom time) dive I was planning on something like 24/24 with a single stage of 80% for deco. Should the stage go tits I could, just about, get out using the 1/3 backgas reserve. It should be clear that I don't regard total back gas failure as a huge risk, however that risk is somewhat mitigated by the fact that a buddy would be configured to supply gas up to 10m by way of the long hose. If anyone cares to comment on the sense of this plan I would appreciate it.

They are GUE trained and as such dive DIR, therefore all gas planning allows for the fact that the buddy is the backup supply........They carry enough for two, some of the post's above are not concerned with an actual dive but are there as illustrations as we discuss this deco question.

Andrew

[MattS]

They are GUE trained and as such dive DIR, therefore all gas planning allows for the fact that the buddy is the backup supply

I am aware of the general DIR mantras. I was interested in the details of this one specifically. It is not much use having enough gas for two unless two have access to it. How do 2 DIR divers share a single stage? Buddy breathe, two 2nd stages, something else?

some of the post's above are not concerned with an actual dive but are there as illustrations as we discuss this deco question.

I am glad that has been made clear.

The academic discussion is all very interesting but ultimately I need to apply the science practically. Balancing narcosis, deco and bailout risks is part of the application. I can understand where MarkC and yourself are coming from, but I am more interested in normoxic using a single stage. I would appreciate any input people who are normoxic diving have to make before I finalise my personal RAs.

[Andy Phillips]

The stage is rigged in a pretty standard manner, they simply buddy breath. Fine, but it is one of the reasons I am not entirely convinced by the DIR solution and prefer to dive with my own back up. Mind you, there have been occaisions where we have pushed our gas to the limit and would have struggled to get out with out additional gas getting to one of us.

Hopefully one of the GUE trained mob will reply with a more complete answer.

Take care,

Andrew

[And]

Hi

We don't buddy breathe the deco gas. If it is lost we deco on backgas reshaping the deco accordingly. The buddy stays with us, but obviously he will breathe his deco gas. If one is unluky enough to lose backgas and the deco bottle then the buddies deco bottle will be passed over. Our backgas reserve is enough to get ourselves and our buddy to the next gas supply at the end of the dive. On the 51 mtr example this is around 90 bar, not rule of thirds. This reserve gives plenty to do the deco on backgas if required.

If, during the gasplanning you decide you do not have enough backgas to deco on then you add O2 as a second deco gas. The aim is not to rely on all the gasses. If one breaks then you should be able to deco on another or backgas, or provide support to deliver extra gas should you require it.

One other point not mentioned yet about using 50%. By getting on it earlier and knowing that most of the deco is complete by the time you get to 6mtrs, if you need to get out of the water for any reason at the 6 mtr stop, you can, knowing that getting on oxygen out of the water will probably limit any DCI event. On the 51 mtr dive at 6 mtrs we have completed 27 mins of a 47 minute schedule on a 30/85 GF profile and already used the 1.6 ppo2 of the 50% bottle.

Andy

[Mark Chase]

For a 50m 30min (bottom time) dive I was planning on something like 24/24 with a single stage of 80% for deco. Should the stage go tits I could, just about, get out using the 1/3 backgas reserve. It should be clear that I don't regard total back gas failure as a huge risk, however that risk is somewhat mitigated by the fact that a buddy would be configured to supply gas up to 10m by way of the long hose. If anyone cares to comment on the sense of this plan I would appreciate it

IF you believe the hype, dropping to a PP02 of 0.5 then jumping on a PP02 of 1.6 all of a sudden can spike the 02 and cause problems.

Personally I don’t think much of this suggestion as back gas breaks and other big PP02 jumps seem to happen a lot in technical diving without incident.

My personal feeling is the deco curve is crap and the options for bail out are wayyyyy to limited for this coward. I am doing a 35m-40 on Sat and I will use 32% back gas 50% for deco for both these reasons. 40 plus and its two stages for me thanks.

Normoxic Trimix is a great way to dive. On a 40m wreck I would use 28/20 and be totally confident with wreck penetration or low viz diving.

ATB

Mark Chase

[MattS]

Thanks for the input Mark

IF you believe the hype, dropping to a PP02 of 0.5 then jumping on a PP02 of 1.6 all of a sudden can spike the 02 and cause problems.

I have a mate that suffers with this. He sometimes gets mild O2 tox symptoms, mainly visual disturbance, using 80% or higher. It soon subsides though. I regularly jump from .42 to 1.6 without problems but thats on Air+80. Might be worth a thought as to how He is going to effect O2 spiking.

My personal feeling is the deco curve is crap

The bailout last stop is around an hour which I find acceptable. Could you be a little more specific?

and the options for bail out are wayyyyy to limited for this coward.

If I can effectively deco out on back gas within my reserve I am comfortable with the bailout. Having looked at the plan again I am reducing the BT by 5 mins.

40 plus and its two stages for me thanks.
Normoxic Trimix is a great way to dive. On a 40m wreck I would use 28/20 and be totally confident with wreck penetration or low viz diving.

I basically view this as a risk analysis. Narcosis is one risk, the DCI implications of Helium and the complexity introduced with two stages are others. There is also a minor logistical consideration with an additional stage.

I would be comfortable with this dive on air + 80. I really don't want to get into a 'What is deep air?' conversation. If I can use normoxic as simply as I use Air + 80 then great, if not I will carry on with what I know. I want to see if I can reduce narcosis risk, without increasing complexity. I am looking for information rather than approval.

Thanks again for the point on O2 spiking.