O2 partial pressure

[Frog]

Thanks for the confirmation Jon. GUE have allsorts of cert levels including a recreational course which marries it with DIR fundamentals. This course requires that you have 25 open water dives. All my equipment is DIR Jon and i agree with most if not all of the stuff that i have read about DIR thus far. However i believe the term "Doing it Right" is a poor idea for a name for obvious reasons that i am not going to point out (because i dont want to distort the educational value of the thread by provoking hardcore DIR divers).

Yes PADi are recreational and are in my opinion designed for people to have fun, namely the holiday diver. Thas what i was pointing out. But at the same time i understand that there are probably excellent PADI instructors out there that will go out of there way to provide a little extra knowledge. I agree Jon but i am going to stick at AOW level and get some rock solid ocean diving experience (around ~150 dives). Perhaps i will do the Rescue diver cert in a few months when and if i can find a good enough instructor (which is proving difficult). Cheers

PS: Could someone tell me what resting pO2 means please. Thanks alot in advance.

 

[100days-a-year]

Resting po2=po2 of your mixture while you are resting and able to sustain a higher po2(it gets involved) Working po2=po2 of your mixture while working (such as swimming around a wreck.etc...)It is recommended to decrease your exposure to o2 by .05 per stressor(cold,work,deep,lo vis etc...)phew... you ever wonder why the DIR get so uptight sometimes..this is one reason

 

[mattiedread]

... but never asked or looked it up. 1ATM=14.7 psi, so 3000 psi = 205 ATM. So, the 'BAR' measurement system is in ATM or metrics? Why don't we all just switch, everything is divisible by 10?
Thanks Greg, I knew I would stumble into that number on this board one day. It is a relative measure, so there was never any great incentive to go look it up, but I learned (or relearned, probably saw it in a physics/chem class one day) something new today. Thanks. Although I'm American I'm bad with British Equivalents, so it was like getting a broken cog in a wheel fixed.

 

[Warhammer]

Frog here is a few formulas that you might find interesting/useful:

To figure EAD (Equivalent Air Depth):

EAD = ((1 - 02%) x (Depth + 33) / .79) - 33


This formula allows you to calculate the exact EAD for any depth and mix. EADs are used to dive nitrox on air tables.

Say you have an PADI RPD and you want to use it to dive EAN32 to a depth of 80ft. You want to know how long you can stay at 80ft on that mix. You must first determine the EAD.

EAD = ((1 - .32) x (80 + 33) / .79) - 33
EAD = ((.68) x (113) / .79) - 33
EAD = 76.84 / .79 - 33
EAD = 97.27 - 33
EAD = 64.3 ft

So now that we know our EAD is 64.3ft, we can use the RPD to determine our NDL. Since the RPD doesn't have 64ft, we use 70ft to determine it and come up with an NDL of 40 minutes. That's 10 minutes longer than an air dive to 80ft.

To figure 02 Partial Pressure:

02 PP = (Depth + 33) / 33 x 02%

You use this formula to determine any mixes partial pressure at any given depth.

Example:

Say we want to know EAN32's partial pressure at 80ft.

02 PP = ((80 + 33) / 33) x .32
02 PP = (113 / 33) x .32
02 PP = 3.42 x .32
02 PP = 1.09

Maximum & Contengency Depth Formulas:

PADI and most other recreational agencies believe that that maximum partial pressure you should expose yourself to is 1.4ata and that the contengency (emergency only) is 1.6. These may be conservative, but they are safe nonetheless. Here's the formulas:

Max Depth = (46.2 / 02%) - 33

Contingency Depth = (52.8 / 02%) - 33

Example:

Say you want to know what the max and contingency depths are for EAN 32.

Max Depth = (46.2 / .32) - 33
Max Depth = 144.375 - 33
Max Depth = 111.375 ft

Contingency Depth = (52.8 / .32) - 33
Contingency Depth = 165 - 33
Contingency Depth = 132ft

[red]Disclaimer: This information is posted as a reference only and is not intended to take the place of nitrox instruction by a certified instructor. I just posted it to give you an idea of some of the things you'll learn in a nitrox course and this only touches on that course. You should never dive nitrox without completing a sanctioned nitrox course.[/red]

 

[turnerjd]

Blatanely plagarised from Warhammer
Frog here is a few formulas that you might find interesting/useful:

Note - when warhammer wrote %O2 he means as a figure between 0 - 1 (called the decimal percentage equivalent) this is the save as %/100 as I've written (ie 37% = 37/10 = 0.37 DPE)

To figure EAD (Equivalent Air Depth):

Using pl in bar (local pressure ie (depth/10)+1 )

EAD = (D x (1-(%/100)))/0.79

This formula allows you to calculate the exact EAD for any depth and mix. EADs are used to dive nitrox on air tables.

Say you have an PADI RPD and you want to use it to dive EAN32 to a depth of 25m. You want to know how long you can stay at 25m on that mix. You must first determine the EAD.

EAD = (3.5 x (1-(0.32)))/0.79
EAD = 3.0 Atm = 20m

So now that we know our EAD is 20.m, we can use the RPD to determine our NDL.

To figure 02 Partial Pressure:

(%value / 100) x ((depth/10)+1) =pp(whatever gas you have the % of)

You use this formula to determine any mixes partial pressure at any given depth.

Example:

see above where frog has already done a metric calculation

Maximum & Contengency Depth Formulas:

PADI and most other recreational agencies believe that that maximum partial pressure you should expose yourself to is 1.4ata and that the contengency (emergency only) is 1.6. These may be conservative, but they are safe nonetheless. Here's the formulas:

Max Depth = (1.4/(%/100)) = local pressure (ie (pl-1)x10 = actual depth)

Contingency Depth = (1.6/(%/100)) =local pressure

Example:

Say you want to know what the max and contingency depths are for EAN 32.

Max Depth = (1.4/(%/100))
Max Depth = 1.4/0.32
Max Depth = 4.37 Atm = 33.7m

Contingency Depth = (1.6/(%/100))
Contingency Depth = 1.6/0.32
Contingency Depth = 5atm = 40m

[red]Disclaimer: This information is posted as a reference only and is not intended to take the place of nitrox instruction by a certified instructor. I just posted it to give you an idea of some of the things you'll learn in a nitrox course and this only touches on that course. You should never dive nitrox without completing a sanctioned nitrox course.[/red]

 

[Texass]

I see you've gotten lot's of good answers to your original post. The one thing that I would recommend is the disclaimer from Warhammer & Turnerjd - TAKE THE NITROX COURSE!

It's a short classroom only class - sorry no getting wet. PADI's is a 1 night 3hr class. I took mine with TDI, which was a 2 night 5hr class. The prices range from $99 - $150.

Nitrox in a nutshell: since you're using a higher % of Oxygen, you've got a lower % of Nitrogen. This means you absorb less nitrogen, which in turn increases your NDL. That translates into longer bottom time before reaching your NDL or a shorter SI between dives. It also gives you a greater margin of safety when doing multiple dives.

The other side of the coin is that you now have to pay close attention to your O2 limits. Oxygen toxicity is not forgiving like passing up your NDL's. That's why you hear all the chat centered around Po2 levels.

The other consideration is that Nitrox limits your depth. It's primarily benificial for depths in the 40-95' range.

Take the course, you'll be glad you did.

 

[turnerjd]

Originally posted by Texass
It's a short classroom only class - sorry no getting wet. PADI's is a 1 night 3hr class. I took mine with TDI, which was a 2 night 5hr class. The prices range from $99 - $150.

Not quite, The PADI course involves 2 dives. There are no special requirements underwater for doing these dives, but you still have to do them (called 'transfer of learning' rather than 'skill development'). It is supposedly so that you demonstrate to the instructor that you have learned what they have told you.

Unfortunately, the prices I have seen are all starting at £130 or so ($220) for the full (PADI) course, although you can usually get it for less if there is more than one of you.

Jon T

 

[Texass]

I see your quoting pounds, not dollars. Hmmm, maybe that explains the difference in requirements (and price!).

 

[turnerjd]

Originally posted by Texass
I see your quoting pounds, not dollars. Hmmm, maybe that explains the difference in requirements (and price!).

PADI requirements are PADI requirements........ They should be the same the world over.

TDI courses.... I haven't seen one advertised so I can't give you a price.

Jon T

 

[Texass]

My Nitrox cert was all done in a classroom. I called around to other shops and their courses were "dry" as well.