Equivalent nitrogen depth

[wedivebc]

Well, I thought so. I just checked my notes and see where I wrote both EAD and END formulas. But It's possible that the instructor, not the book material, is the source of the END formula.

Later today I'll dig up the books and double check.

The give-away is whether they use (1-%he) or the (fraction N2/ 0.79) to calculate END in their trimix training .

 

[Jim Lapenta]

Usually 100ft but we often mix for 80-90. I have yet to use a deeper END. But then again my max depth to date with deco obligation is only 157ft.

 

[MikeFerrara]

My recommendation: Drop the term "Equivalent Nitrogen Depth" from your diving lexicon and follow the NOAA guidelines for figuring your END (Equivalent Narcotic Depth).

The formula is... END(in Atmospheres)=(1-He fraction)*ATA



Rick

For those who don't know...
That is absolute narcotic pressure in atmospheres. If you convert it to pressure in FSW and subtract 33, you have END (depth)... (D+33) X (1- FHe) - 33 = END

Which is absolute pressure in FSW multiplied by the fraction of narcotic gas which gives the "absolute pressure of narcotic gas in FSW". Subtract one atm (in FSW) and you get equivilant depth.

Of course, you could do the same thing using units of "meters" (or whatever).

 

[Rick Murchison]

For those who don't know...
That is absolute narcotic pressure in atmospheres. If you convert it to pressure in FSW and subtract 33, you have END (depth)... (D+33) X (1- FHe) - 33 = END

Which is absolute pressure in FSW multiplied by the fraction of narcotic gas which gives the "absolute pressure of narcotic gas in FSW". Subtract one atm (in FSW) and you get equivilant depth.

Of course, you could do the same thing using units of "meters" (or whatever).

Since Meters to ATA is 10 to 1, dealing with meters and atmospheres (Bar, essentially) for all the calculations is soooo much easier! (So if I'm dealing with feet, I convert to meters first, (depth in feet * .3 = depth in meters) then do the calculations, then convert back to feet - that way I can do it all without paper ) In my previous example of 165 FSW/50 meters, that's 6 Bar pressure (50/10 + 1). END for 16/50 (50% He) is half that - 3 Bar, which is 20 meters (3*10 -1).
The conversion from meters to feet is then just a matter of dividing by .3:
20/.3 = 66.6666etc, within a foot of the 66' you'd come up with using the FSW method, and close enough...

Rick

 

[Mike Edmonston]

Since Meters to ATA is 10 to 1, dealing with meters and atmospheres (Bar, essentially) for all the calculations is soooo much easier! (So if I'm dealing with feet, I convert to meters first, (depth in feet * .3 = depth in meters) then do the calculations, then convert back to feet - that way I can do it all without paper ) In my previous example of 165 FSW/50 meters, that's 6 Bar pressure (50/10 + 1). END for 16/50 (50% He) is half that - 3 Bar, which is 20 meters (3*10 -1).
The conversion from meters to feet is then just a matter of dividing by .3:
20/.3 = 66.6666etc, within a foot of the 66' you'd come up with using the FSW method, and close enough...

Rick

That's just crazy VOODOO Math Rick!

 

[limeyx]

Since Meters to ATA is 10 to 1, dealing with meters and atmospheres (Bar, essentially) for all the calculations is soooo much easier! (So if I'm dealing with feet, I convert to meters first, (depth in feet * .3 = depth in meters) then do the calculations, then convert back to feet - that way I can do it all without paper ) In my previous example of 165 FSW/50 meters, that's 6 Bar pressure (50/10 + 1). END for 16/50 (50% He) is half that - 3 Bar, which is 20 meters (3*10 -1).
The conversion from meters to feet is then just a matter of dividing by .3:
20/.3 = 66.6666etc, within a foot of the 66' you'd come up with using the FSW method, and close enough...

Rick

Yah, or ... since for me 25/25, and 18/45 are the same price.
Dive 32% or 25/25 to 120 (average)
dive 18/45 for anything up to 200

zero calculations

 

[Rick Murchison]

Yah, or ... since for me 25/25, and 18/45 are the same price.
Dive 32% or 25/25 to 120 (average)
dive 18/45 for anything up to 200

zero calculations

Umm Hmmm... standard mixes... that's a whole other subject, ain't it. Personally, I like to standardize END and PO_2max rather than the mix itself... that is, mix for the planned MOD, topping helium with EAN32 with an END of 100' (4 Bar) (which automatically sets my PO_2max at 1.28), so my target He% is always (Target Depth in ATA - 4) / Target Depth in ATA. So, for a dive to, say, 200' (7 ATA), my target He% is (7-4)/7 (3/7 or 43%) and my target O₂% is 1.28/7 or 18%.
If I'm just mixing to have some gas on hand with no specific site in mind I usually mix 16/50, which is good for anything down to 230FSW (250 @ 1.4) and as deep as I'm planning to go unless it's a very special circumstance.

Rick

 

[limeyx]

Umm Hmmm... standard mixes... that's a whole other subject, ain't it.
Rick

Possibly, but it just seems a whole lot less hassle than all the other stuff!
Calc the gases once and use about 3 bottom gases and 2-3 types of deco gas

Also means I can fill with one gas (18/45) and do any kind of dive from 60 feet to 200 feet as long as I bring some deco bottles with me.