I-169 truuk lagoon

[RJP]

I'm not surprised you have questions like this after being certified for Nitrox via Padi. Fundamentals will actually teach you more about best mix and standard mix. Do some self study and brush up on the math before doing the course using the Daltons diamond equation etc. All diving is somewhat technical and in my opinion all divers should acquire at least that level of knowledge which Padi most often fails to teach.

As long as we're hijacking this thread, let's go a step further and keep in mind that no one has ever been "nitrox certified by PADI" nor does PADI teach (or fail to teach) anything. INSTRUCTORS "teach" and INSTRUCTORS "certify." I learned about best mix, standard mixes, Dalton's diamond, etc from a PADI instructor. Hell, that stuff is even in the course materials.

 

[clownfishsydney]

Last Saturday in Sydney I dived the wreck of the SS Tuggerah which is a maximum of about 48 metres (160 feet) but averages about 45 metres (150 feet). I used 26%. As others have said, you can use "Nitrox" deeper than what you thought, you just need to get the right mix.

 

[Doubler]

Why is 32% considered the standard when it does not take you to recreational depths?

 

[RJP]

Why is 32% considered the standard when it does not take you to recreational depths?

MOD of EANx 32% at 1.6 P02 = 132fsw

So, technically, 32% can get you to the bottom of recreational limits.

That said, given a standard AL 80cf cylinder and the SAC of a standard recreational diver... you'd run out of gas long before you ran out of bottom time at 132fsw.

At 1.4 PO2, MOD for 32% = 111fsw, which is perfect for the relatively standard "100ft or shallower" depth of 99.999999% of dives that recreational divers conduct.

 

[clownfishsydney]

MOD of EANx 32% at 1.6 P02 = 132fsw

So, technically, 32% can get you to the bottom of recreational limits.

That said, given a standard AL 80cf cylinder and the SAC of a standard recreational diver... you'd run out of gas long before you ran out of bottom time at 132fsw.

At 1.4 PO2, MOD for 32% = 111fsw, which is perfect for the relatively standard "100ft or shallower" depth of 99.999999% of dives that recreational divers conduct.

You might run out of gas, not one of the people I dive with would run out of gas on such a dive.

The bottom time for 132 feet (40 metres) has a bottom time of at least 9 or 10 minutes. If I did this dive within deco limits using my 88 cf aluminium tank I would come up with about 150 bar (say 2200 psi).

On the dive I mentioned above last weekend, I averaged over 45 metres and did a 16.5 minute bottom time (2.5 minute descent). I was using a steel 12 litre tank (say 100 cf). I surfaced with about 90 bar (say 1300 psi), although I did breath 59% from 6 metres for about 8 minutes.

Virtually everyone in our dive club could run out of bottom time at any depth (deeper than say 50 feet) before they would run out of air.

 

[scubadada]

Hi I-169

Your MOD is determined by the pO2 you're willing to dive at maximum depth. The oft quoted pO2 of 1.4 is reasonably conservative and yields a MOD of 132 feet with 28%, 111 feet with 32% and 95 feet with 36%. Some of us, at times, will dive a higher pO2. At a pO2 of 1.6, the MOD of 32% is 132 feet.

Good diving, Craig

 

[RJP]

You might run out of gas, not one of the people I dive with would run out of gas on such a dive.

Do note that I referenced "the standard recreational diver" in my comments.

According to V-Planner, I'd use 34cf of gas on a 10min no-deco dive to 130ft.

I'd also never do a wreck dive to 130 on a single tank, irrespective of tank size.

But we've now wandered too-far-afield from the OP's original question.