EAN versus "no-Fly" delay

[tbone1004]

you aren't going to find literature on this because all of the official recommendations are either laid out in the USN tables, or you follow the recommendation of your agency/computer on what you want they think is safest for you to do

 

[Edward3c]

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.

Its the BSAC ‘88 Decompression Tables: Levels 1 to 4 that are required, not the manual.

 

[KenGordon]

you aren't going to find literature on this because all of the official recommendations are either laid out in the USN tables, or you follow the recommendation of your agency/computer on what you want they think is safest for you to do

So do agree yet that planning the dive as an attitude dive but executing it at sea level does not allow a diver to then immediately go to altitude?

 

[EFX]

But when you dive at altitude you have LESS N2. Both at the start of the dive if acclimatised and at the end of the dive due to the lower contribution of surface pressure to the ambient pressure during the dive.

The planning of an altitude dive MUST account for the lower ambient pressure at surfacing and MAY account for the reduced ppN2 before and during the dive.

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.

Had to rethink numbers. may post a reply later.

 

[tbone1004]

So do agree yet that planning the dive as an attitude dive but executing it at sea level does not allow a diver to then immediately go to altitude?

no because of the questions that I posed earlier about being able to dive at 10ft for an infinite amount of time, descent to depth until you hit your NDL's, and stay at 10ft for as long as you want before you surface. that can be immediately, or it can be an infinite amount of time, doesn't matter because you are within NDL's

 

[Storker]

But could you stay an infinite amount of time if your ascent wasn't from 10' (1.3 ATA) to sea level (1 ATA), but from 10' (1.3 ATA) to some higher altitude (<1 ATA)?

 

[tbone1004]

the 10ft to surface is the same ATA change as going from sea level to 8,000ft

 

[boulderjohn]

This discussion is probably best continued in the Ask Dr. Decompression forum. Dr. Decompression is Dr. Michael Powell. He is not as active as he was years ago, but he still joins in from time to time. He was one of the researchers who developed the PDI RDP, but his primary job was working on decompression issues for NASA. If anyoone knows about this topic, it will be him.

 

[Charles2]

Its the BSAC ‘88 Decompression Tables: Levels 1 to 4 that are required, not the manual.

Can you post a link? All the links that I have found want a credit card to look at these tables.

 

[Charles2]

you aren't going to find literature on this because all of the official recommendations are either laid out in the USN tables, or you follow the recommendation of your agency/computer on what you want they think is safest for you to do

Since I cannot get your theory to calculate close enough to tables, I guess that I will just go with the old USN/NAUI tables that I learned with. I am comfortable with that. Thanks for the mental exercise.