Nitrox exam question

[Boss Bozo]

So I have this nitrox exam question which I cannot get right, if you can figure out the answer, please reply the answer and explanation to that answer.The question is as follows:

Using NOAA air tables a diver deceides to do 3 dives:

1st at 39meters for 15minutes using Nitrox I.
After a 55minute surface interval the diver does the
2nd dive at 24meters for 20minutes also using Nitrox I.
After an Hour surface interval the Diver wishes to do a third dive at 18meters this time using NitroxII.

a) What is the maximun bottom time allowed, and
b) the total number of UPTD?

NB: I managed to figure out (a) using these tables:
http://www.ndc.noaa.gov/pdfs/nitrox32.pdf and http://www.ndc.noaa.gov/pdfs/nitrox36.pdf
but cannot work out (b)

[Superlyte27]

Sounds like this is a question for your instructor.

[bletso]

Use the appropriate NOAA air tables as the question states, not the NN1 and NNII tables. Convert to EAD (Equivalent air depth) and solve as you would any air dive. EAD = ((FN2 / .79) * (D + 10)) - 10 FN2 is fraction of nitrogen in the mix.

First depth EAD is therefore 29.7 msw. Try it. If you still have a problem PM me.

Dale

[Doppler]

Firstly, the question asks you to use the AIR tables.

OK, part two. The pulmonary toxicity level from these two dives is insignificant, but since this is an exam, here's what you do.

Somewhere in your textbook there is a table for pulmonary toxicity units per minute at a specific oxygen partial pressure. Find it. Now work out the PPO2 at depth for each dive and look that up in the table. Now multiply that per minute dose by the number of minutes of exposure to those partial pressures. Add the products for each dive and that's your answer...

Compare your answer to the allowable daily limits (850 single day 300 multiple day) and my guess is that you will agree that loosing sleep over whole body or pulmonary toxicity at the level you're diving is at is a total waste of effort.