Can someone help me with this question?

[pilot fish]

Sorry to just butt in here, but don't be too hard on yourself pilot fish. After you jump through the equation hoops and pass the class, keep it simple and just use the 20% reduction rule. Take 20% off the depth and this is basically your EAD when diving 32%. This method is quite adequate when using tables, as rounding is required.

If I'm being hard on myself it's beause all you guys get it and I don't.

20%? That I can do.Take 20% off air depth? You think it's easy being this dense? :06:

 

[lragsac]

If I'm being hard on myself it's beause all you guys get it and I don't.

20%? That I can do.Take 20% off air depth? You think it's easy being this dense? :06:

Oh, I don't know, I don't find it hard being dense It keeps me from doing tedious math problems. Easy=good, Tedious=Bad...sounds like a principle Homer Simpson would back

 

[simbrooks]

I would have thought to go nearer 15%, 0.79/0.68 N2, but 20% seems to work on air tables.

Another rule worth remembering is the rule of 120 (ie depth (ft) + ndl (mins) = 120), you can use rule of 140 (ie. 20 mins or 20ft more) for ndl calcs. If you see it was 140/120 that is also 115% just to further clarify to the first point of 15%) That doesnt help so much with repetative dives though unless you can account for your rbt due to you previous on-gassing and off-gassing.

Approximately 1/3 reduction seems to work for 36% (even though its about 20% from 0.79/0.64 N2), not sure if there is an addition rule there as well - havent checked that closely I havent got my tables in front of me, not the time at work to work each one out.

 

[rab]

OK, I'll take the EANx32 table with me, the most common, to look at, and match to my puter, but I'm not doing any alegegra.

Here's a table that you can use to take any EANx mix from 21% to 40% and find out what Air depth to use.

It can be used two ways.

1. (planning) Take the known depth on the left (the 21% column) and move right to the last available non-gray cell. Use the EAN for that column.
2. (post-dive pressure group to back up computer) Starting from top of EANx column, move down to the first cell that exceeds your actual maximum depth, and use the EAD from the 21% column to determine pressure group.

It's meant to be adaptive so you can change the pO2 values from 1.4/1.6 and the table will automatically adjust. I want to make it English/Metric, too, by adjusting the value for "1 bar" at the top, but the first dive NDLs don't get completely changed. (Hint: if someone would PM me the DSAT NDLs in meters, I could fix this!)

Enjoy,
-Rob

 

[MaxBottomtime]

Here's a quick reference for NDLs using 21%, 32% and 36%
http://www.scubadivers.ws/tables.htm

 

[mdsd]

Here's a quick reference for NDLs using 21%, 32% and 36%
http://www.scubadivers.ws/tables.htm

I like the table, thanks. (Good for first dive only)

 

[pilot fish]

Here's a quick reference for NDLs using 21%, 32% and 36%
http://www.scubadivers.ws/tables.htm

Did not understand why some of the cells are blank in the table you provided, like 35 ft air 2:05 but X32 & X36 is blank and 40ft air 1:40 but X32 &X36 blank? Also, why is 45ft air blank X32 2:20 but X36 blank. Im feeling more more dense

 

[rab]

Did not understand why some of the cells are blank in the table you provided, like 35 ft air 2:05 but X32 & X36 is blank and 40ft air 1:40 but X32 &X36 blank? Also, why is 45ft air blank X32 2:20 but X36 blank. Im feeling more more dense

While I don't know exactly why the author chose to put the page like that, it does seem to be explained by the "disclaimer" paragraph that follows:

Figures are for first dive reference only and do not consider residual nitrogen from previous dives. Figures are averages from several table. Consult an actual table for exact numbers. Figures are intended to demonstrate on difference between Air and Nitrox.

The Air table(s) used probably didn't have 45 or 55 ft entries and the Nitrox tables probably didn't have entries below 45 or 50 ft.

Practice the math until you at least kinda understand it, but don't worry if you can't do it in your head. You can always just keep my spreadsheet. (Where the empty cells are beyond the MOD of the mix.)

-Rob

 

[simbrooks]

Did not understand why some of the cells are blank in the table you provided, like 35 ft air 2:05 but X32 & X36 is blank and 40ft air 1:40 but X32 &X36 blank? Also, why is 45ft air blank X32 2:20 but X36 blank. Im feeling more more dense

At those depths your EAD is essentially a shallow/deep safety stop, the NDL on those is almost unlimited. Look at the NDL on both 32 and 36 at 40-50ft, its almost identical to that of air at 35ft - far longer than any tank could keep you down for, 200+ mins is a long time! Even if i did back to back shore dives (say 25ft) on air, just the surface swimming and swapping out time would off-gas enough that i could do it almost all day, my NDL would be huge - of course i could do it on a hookah, but i might get chilled - dehydrated by that time. As for deeper depths - just in case this question comes up, they are greater than the MOD of the mix.

 

[BigJetDriver]

I'm feeling more more dense.

Pilotfish,

I just got your PM. Sorry I didn't get to it earlier, but I had to run in to work. Looks as if the others have it well covered.

Hang in there. You'll get it.

Cheers!

Rob