EAN versus "no-Fly" delay

[Basking Ridge Diver]

example using naui tables.

I am getting a kick out of this one. I tried to show folks how to use Naui tables to do multi level dives... Using less than 10 min surface intervals in between the levels and you would have thought I was insane...

Don't go to crazy with the explanations - some folks won't believe you no matter what you say or how you try to prove it...

 

[BRT]

I am getting a kick out of this one. I tried to show folks how to use Naui tables to do multi level dives... Using less than 10 min surface intervals in between the levels and you would have thought I was insane...

Don't go to crazy with the explanations - some folks won't believe you no matter what you say or how you try to prove it...

We agree

 

[KenGordon]

what? if you use air tables, and adjust the depth to account for 8,000ft of altitude, then you have a shorter dive time because your nitrogen loading is set to account for a surface at 8,000ft. The exposure is the same as it would have been as if you were at altitude in terms of actual water depth and dive time. The difference is because the exposure is much shorter than it would have been if you hadn't accounted for altitude.

The plan is accounting for surfacing at altitude AND diving at altitude. If you do not dive at altitude the plan does not stand.

Consider dive A to X feet for Y minutes at altitude. Assume Y is the NDL. When I executed there will be a leading/limiting ppN2 of P That leading ppN2 will have been calculated by whatever means you plan, it may be have been scaled up if that is how your tables work to something like Q=Z/0.75 but we do not care as that is simply an artefact of the method.

The same dive (X feet for Y minutes) at sea level starts with a higher ppN2 and is exposed to a higher ppN2 throughout the actual dive. When you get out the leading ppN2 is R.

Clearly R is greater than P as at all times the ambient ppN2 on the dive was higher and the initial tissue ppN2 was higher.

Since P is the maximum ppN2 that can be allowed at altitude going to altitude with a higher ppN2 (R) is a risk.

 

[tbone1004]

@KenGordon

quick questions
how long can you stay at 10ft on air and surface immediately?

Are you allowed to go to depth, hit your NDL, come back to 10ft for some length of time, then go back to depth for an abbreviated NDL, come back to 10ft for however long, or not, and immediately surface? Essentially two dives with a SIT at 10ft instead of the surface

The point of this example is you start your dive at 10ft, descend to whatever depth you have, dive to your NDL, return to 10ft, stay there for however long, then surface. The trick is getting the tables/computer/planning software to account for that. It's not terribly difficult, albeit a bit annoying, but it is possible, and it really isn't that scary or complicated.

 

[BRT]

Not worth it.

 

[KenGordon]

@KenGordon

quick questions
how long can you stay at 10ft on air and surface immediately?

Are you allowed to go to depth, hit your NDL, come back to 10ft for some length of time, then go back to depth for an abbreviated NDL, come back to 10ft for however long, or not, and immediately surface? Essentially two dives with a SIT at 10ft instead of the surface

The point of this example is you start your dive at 10ft, descend to whatever depth you have, dive to your NDL, return to 10ft, stay there for however long, then surface. The trick is getting the tables/computer/planning software to account for that. It's not terribly difficult, albeit a bit annoying, but it is possible, and it really isn't that scary or complicated.

Starting a dive at 10ft and decending and ADDITIONAL X ft is not the same as starting at the surface and decending X ft.

My point is that the Cross scheme, and other altitude planning schemes, only apply ONCE you are at altitude and not to a dive at sea level FOLLOWED by moving to altitude. The dive at sea level, given same depth and time, WILL result in higher ppN2 NOT accounted for by the planning.

Doing a sea level dive and then going to altitude is covered by well developed process, you do not need to make one up, especially one which is wrong. See section 9.14 of the US Navy diving manual for example.

 

[tbone1004]

9-13 in the current manual btw and page 9-55 if you want the page with the table, but that table only applies if you use the USN or NAUI dive tables. They don't correlate to PADI etc. or any other computers.

by your logic, how do you plan altitude diving if you haven't had 12 hours for your tissues to stabilize? You have to account for it somehow, how are you doing it? The tables certainly don't, and unless your computer has a built in ambient pressure sensor and was turned on when you left whatever lower altitude and is programmed to track tissue loading with altitude *most aren't btw*, then you are in the exact same scenario.

 

[victorzamora]

Actually, I think most altitude tables/procedures say that you have to stabilize before they become applicable. IIRC, the PADI ones make it clear....but it's been a while since I looked.

 

[KenGordon]

9-13 in the current manual btw and page 9-55 if you want the page with the table, but that table only applies if you use the USN or NAUI dive tables. They don't correlate to PADI etc. or any other computers.

From Naval Sea Systems Command > Home > SUPSALV > 00C3 Diving > Diving Publications

http://www.navsea.navy.mil/Portals/...ev 6 with Chg A.pdf?ver=2016-02-26-123349-523

9-14 ASCENT TO ALTITUDE AFTER DIVING / FLYING AFTER DIVING

Which discusses the subject at hand. It is the process which is important. Understand that and application using whatever tools is easier.

by your logic, how do you plan altitude diving if you haven't had 12 hours for your tissues to stabilize? You have to account for it somehow, how are you doing it? The tables certainly don't, and unless your computer has a built in ambient pressure sensor and was turned on when you left whatever lower altitude and is programmed to track tissue loading with altitude *most aren't btw*, then you are in the exact same scenario.

You use the tables as designed. In the BSAC and USN tables there are transfer tables which change your tissue code when moving from one altitude to another. In BSAC88s the tissue codes are A-G increasing (relative) saturation. When going from surface to 8000ft you look at the transfer table (page 29) which says that if you start on an A you arrive on a C. Now you plan your dive using table C for the altitude. There are four levels. If you did not dive straight away there is a surface interval table. Wait 8 hours and you are back to tissue code A and so dives are planned on the more liberal A table.

For the case the OP is talking about you do the dive, end up with a tissue code and then look up (page 29 again) the resulting tissue code if moving between altitudes. So starting on a C (for example) at sea level you are not allowed at 8000ft. Then you look at tissue code B and that is ok so you look at the surface interval table and it says it takes 120 minutes to get to a B from a C. So now you know how long to spend in the bar before getting on the plane.

The USN tables have a similar scheme but with different mechanics and more exciting examples involving pneumofathometers and other stuff only found in Frank Zappa lyrics.

 

[Charles2]

All of this cyphering makes my brain hurt.

@TBone - Your logic makes a great deal of sense; however, I cannot get most of the examples I tried to agree with the Navy Table 9-6. It's somewhat close at deeper levels, but not at all when shallower. I suspect that the variation is caused by the nitrogen equilibrium level differences between sea level and 8,000 ft. Is there some literature that explains this further?

@KenGordon - I am not sure that I followed your last post. I don't have a copy of the BSAC manual, but do have the U.S. Navy manual. It gets a little complicated for us lesser folk when we change from USN to BSAC, or to PADI or NAUI. Thanks.