Knowing my PPO2

JG40 · 10th July 2006, 20:52

Hi Folks,
first daft question here goes...
I am not the brightest in the world at maths and only just scraped an O level all those years ago (Grade C I think!! I was better at other things!!)

When I am reading in the bnooks that I have to know and understand my PPO2 at all times, does that mean that I need to have a mental spreadsheet running in my head all the time and that I need to know what % mix I am using at each depth?? I hope not because that seems bloody impossible for my pea sized brain!!
What does this phrase really mean in simple terms...? Anyone able to explain??
Sorry but this is bound to be only the first of a whole load of newby questions!!

***ScubaDadMiami*** · 10th July 2006, 21:31

There is the easier answer, and then there is the less easy (but not too big of a deal) answer to your question.

Your gauges/computer will show you what your PPO2 is. However, even with multiple oxygen sensors, there is a chance that none will be reading correctly (or perhaps only one will read correctly) at times. When this happens, you will need to know what your PPO2 should be based upon your diluent and depth. This means doing a little math.

You should already know what the deepest diluent PPO2 will be before doing the dive, taking care of the math before entering the water (since you will be considering PPO2 in your planning anyway). Otherwise, if you use the same diluent mixes (a/k/a standard mixes) a lot, it will make the calculations easier since you will have used these mixes, and made the calculations for them, so many times on previous dives.

Unfortunately, you will not be able to completely eliminate the math. However, if you keep doing the calculations again and again, it get's easier.

Timbo · 10th July 2006, 21:33

Know your PO2 simply means that if the setpoint on your unit is say 1.3, then look at the displays and make sure you see 1.3 or thereabouts on all 3 sensors. So if u look and see something different a cell may be wrong or solenoid is stuck open/closed or other problems.
So a good way to verify which cells are okay is below.

It is useful to have on a slate on your wrist what PO2 you would expect to see if you did a diluent flush at 10M increments. eg

On air 21% O2

10M = 2Bar so dil flush is 0.21X2=0.42
20M = 3Bar so dil flush is 0.21X3=0.63
30M = 4Bar so dil flush is 0.21X4=0.84
40M = 5Bar so dil flush is 0.21X5=1.05

So on your slate just write
10M=0.42
20M=0.63 and so on.

So if you want to verify cells do a diluent flush and say you were at 38M then expect to see the cells crash down to around 1.05.
If they are near to this all is okay.
If 2 read around 1.05 and say one read 0.63, then that cell has probably had it.
Always know that you PO2 is what you want, if it is wrong do what you were trained to do on the course to rectify it.
In early days, if in doubt BAIL OUT TO OPEN CIRCUIT.
Hope this helps.
Tim B

Timbo · 10th July 2006, 21:36

PS.

You could do it at 5M increments as well

Again air=21% O2

so eg

25M=3.5BarX0.21=0.73 ect ect
however you would need a bigger slate!!

JG40 · 10th July 2006, 21:50

Hey guys thanks for your help. That has made it clearer now. I was worried but I think I am ok with what you have all explained
Thanks again....

PS Paid the money for the unit this morning...Pick it up on 4th Aug form AP...
Wife & kids not being fed for the next few months!!!

Simon A · 11th July 2006, 07:33

Quote: (Originally Posted by JG40)

PS Paid the money for the unit this morning...Pick it up on 4th Aug form AP...
Wife & kids not being fed for the next few months!!!

You didn't just trade them in against the unit? So you'd have more time to go diving.

Simon A

10th July 2006, 20:52	#1 (permalink)
JG40 New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Jul 2006 Location: UK Posts: 3	Knowing my PPO2 Hi Folks, first daft question here goes... I am not the brightest in the world at maths and only just scraped an O level all those years ago (Grade C I think!! I was better at other things!!) When I am reading in the bnooks that I have to know and understand my PPO2 at all times, does that mean that I need to have a mental spreadsheet running in my head all the time and that I need to know what % mix I am using at each depth?? I hope not because that seems bloody impossible for my pea sized brain!! What does this phrase really mean in simple terms...? Anyone able to explain?? Sorry but this is bound to be only the first of a whole load of newby questions!!
(Offline)

10th July 2006, 21:31	#2 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,939	Re: Knowing my PPO2 There is the easier answer, and then there is the less easy (but not too big of a deal) answer to your question. Your gauges/computer will show you what your PPO2 is. However, even with multiple oxygen sensors, there is a chance that none will be reading correctly (or perhaps only one will read correctly) at times. When this happens, you will need to know what your PPO2 should be based upon your diluent and depth. This means doing a little math. You should already know what the deepest diluent PPO2 will be before doing the dive, taking care of the math before entering the water (since you will be considering PPO2 in your planning anyway). Otherwise, if you use the same diluent mixes (a/k/a standard mixes) a lot, it will make the calculations easier since you will have used these mixes, and made the calculations for them, so many times on previous dives. Unfortunately, you will not be able to completely eliminate the math. However, if you keep doing the calculations again and again, it get's easier. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
(Offline)

10th July 2006, 21:33	#3 (permalink)
Timbo New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Join Date: May 2006 Location: Hertfordshire UK Posts: 63	Re: Knowing my PPO2 Know your PO2 simply means that if the setpoint on your unit is say 1.3, then look at the displays and make sure you see 1.3 or thereabouts on all 3 sensors. So if u look and see something different a cell may be wrong or solenoid is stuck open/closed or other problems. So a good way to verify which cells are okay is below. It is useful to have on a slate on your wrist what PO2 you would expect to see if you did a diluent flush at 10M increments. eg On air 21% O2 10M = 2Bar so dil flush is 0.21X2=0.42 20M = 3Bar so dil flush is 0.21X3=0.63 30M = 4Bar so dil flush is 0.21X4=0.84 40M = 5Bar so dil flush is 0.21X5=1.05 So on your slate just write 10M=0.42 20M=0.63 and so on. So if you want to verify cells do a diluent flush and say you were at 38M then expect to see the cells crash down to around 1.05. If they are near to this all is okay. If 2 read around 1.05 and say one read 0.63, then that cell has probably had it. Always know that you PO2 is what you want, if it is wrong do what you were trained to do on the course to rectify it. In early days, if in doubt BAIL OUT TO OPEN CIRCUIT. Hope this helps. Tim B
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10th July 2006, 21:36	#4 (permalink)
Timbo New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Join Date: May 2006 Location: Hertfordshire UK Posts: 63	Re: Knowing my PPO2 PS. You could do it at 5M increments as well Again air=21% O2 so eg 25M=3.5BarX0.21=0.73 ect ect however you would need a bigger slate!!
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10th July 2006, 21:50	#5 (permalink)
JG40 New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Jul 2006 Location: UK Posts: 3	Re: Knowing my PPO2 Hey guys thanks for your help. That has made it clearer now. I was worried but I think I am ok with what you have all explained Thanks again.... PS Paid the money for the unit this morning...Pick it up on 4th Aug form AP... Wife & kids not being fed for the next few months!!!
(Offline)

11th July 2006, 07:33	#6 (permalink)
Simon A Escapee from DIY Rebreather's Current Rebreather/s: Inspiration Classic Other Rebreather/s: Not Bought Yet Join Date: Feb 2005 Location: Reading, UK Posts: 282	Re: Knowing my PPO2 Quote: (Originally Posted by JG40) PS Paid the money for the unit this morning...Pick it up on 4th Aug form AP... Wife & kids not being fed for the next few months!!! You didn't just trade them in against the unit? So you'd have more time to go diving. Simon A
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