Help from an instructor or DM on a PADI divemaster question

[Akapp]

Im in the process of studying for my divemaster and have ran into a brick wall with the physiology section of the book. Hopefully one of you guys thats a PADI instructor can clear some of this up for me in simple terms.


The question I am stuck on is -

In metres/feet of pressure, how much nitrogen would the 5, 10, 20 and 60 minute halftime compartments each have after 60 minutes at 60 fsw?


Ive reviewed the chapter this question is from several times over and still cant figure it out.

 

[vladimir]

Second result from a search for halftime+compartment that took me 2 minutes, including this post:

http://www.scubaboard.com/forums/going-pro/310490-halftimes.html

 

[Cave Diver]

Im in the process of studying for my divemaster and have ran into a brick wall with the physiology section of the book. Hopefully one of you guys thats a PADI instructor can clear some of this up for me in simple terms.


The question I am stuck on is -

In metres/feet of pressure, how much nitrogen would the 5, 10, 20 and 60 minute halftime compartments each have after 60 minutes at 60 fsw?


Ive reviewed the chapter this question is from several times over and still cant figure it out.

The 5 minute compartment would saturate as follows:

5 minutes - 30'
10 minutes - 45'
15 minutes - 52.5'
20 minutes - 56.25
25 minutes - 58.125
30 minutes - 59.063'

etc.

Every 5 minutes that compartment increases to halfway from current pressure to max pressure (60' in this case). For all intents and purposes, the 5 minute compartment would be fully saturated after 30 minutes at 60'.

10 minute compartment:

10 minutes - 30'
20 minutes - 45'
30 minutes - 52.5'
40 minutes - 56.25'
50 minutes - 58.125
60 minutes - 59.063'

So it's fully saturated at 60' for 60 minutes

20 minute compartment:

20 minutes - 30'
40 minutes - 45'
60 minutes - 52.5'

Not quite fully saturated

60 minute compartment:

60 minutes - 30'

Halfway saturated.


(damn I hope I explained that right!)

 

[TMHeimer]

Those were my figures, just wanted to check first if someone agreed.

 

[Cave Diver]

Those were my figures, just wanted to check first if someone agreed.

Great, make me the guinea pig!

 

[sam1]

I agree with the math...but "since a compartment is 98.4 percent saturated after six halftimes, most models treat six halftimes as saturated."

 

[Thalassamania]

I get about the same as CD:

5 min => 60'
10 min => 60'
20 min => 52'
60 min => 30'

 

[vladimir]

(1-e^{-(time* ln(2)/halftime}) * depth

 

[boulderjohn]

OK, now...

Do you understand why?

 

[Web Monkey]

Im in the process of studying for my divemaster and have ran into a brick wall with the physiology section of the book. Hopefully one of you guys thats a PADI instructor can clear some of this up for me in simple terms.

The question I am stuck on is -

In metres/feet of pressure, how much nitrogen would the 5, 10, 20 and 60 minute halftime compartments each have after 60 minutes at 60 fsw?

<hijack mode>
Why is this even on the test? Modeling decompression is certainly fascinating, but wouldn't the class time/course content be better spent on teaching how to safely manage groups, avoid problems and handle the stuff that can't be avoided?

Out of all the posts in the A&I forum, I've never seen a single incident or accident that was caused by the DM not being able to calculate compartment values.
</hijack mode>

Terry