p.p. calculations.

[nigelH]

...begun doing shallow reef dives on 80%, very shy at first, i keep on playing with PP. of 1.6 at various depth for small intervals of time, them slowly increasing the level of complexity on more demanding dives.

Well when I started on Nitrox 1.6 was a good conservative number and 2 bar was what people used to do. Also I admit to getting in a fight with people over only using 1.1 bar or below on a rebreather, which I think is going too far, but I will admit that routinely using 1.6 at the bottom, finning part of a dive is pushing it. I'll do 1.6 hanging on a string in chill out mode but not rooting about looking for something interesting and especially not if it was a rather tense, not been here since I got hurt big time, dive.

[dreammermaid]

Originally Posted by Lazlo

The calculation for Maximum Operating Depth (assuming max 1.6ata for PPO2) is:

MOD = (16 / F02) - 10

where F02 is the fraction of O2 in the mix e.g. 0.21 for Air, or 1.0 for pure O2.

If you work on 1.4 as your max PPO2 then the calculation becomes

MOD = (14 / F02) - 10

and so on.

So plugging in 80% O2 on a 1.6 gives 10m.

As the turbaned one says though - 1.4 is considered safer for the working part of the dive.

That covers O2 CNS toxicity. There are a few ways to calculate oxygen pulmonary exposure as well, but you need tables or a PC for that.

hth

You can be on my expedition team anyday. Thanks for adressing the question, not discussing my ignorance(maybe I should have known but I didn't which is why I asked), and getting sidetracked by petty details. A green spot for you, the only one who actually wrote out an equation. I'm quoting it in case someone missed it the first time. Please keep future dicussion on tis topic. If you would like to know why I don't know something, have a similiar experience or anything to share please do so with a private message and I will be happy to answer.
Thanks, Lazlo and others who focused on the question.

[Freeflow]

Running a pO2 of 1.6 would allow the following depths:

% O2 Depth [m]

100..........6

90............8

80...........10

70...........13

60...........16

50............22

40............30

30............43

21............66

Without seeing the original emails it is difficult to know what you and your correspondant were looking at but from a 'conservative' pO2 of 1.6, they may be a military diver used to running 2. As you can see, running 1.6 doesn't mean that you are shallow.

[jb2cool]

Does this help anyone?

Nitrox depth table.zip

[NotDeadYet]

Some of the earlier responses highlight the best bit of advice I can give: some questions are best not asked on the internet. The people to ask about diving medicine are diving medics, the live and breathe this stuff and are not the enemy -- they aren't trying to stop you diving, they are trying to stop you dying. They tend to be very conservative so I listened to what they said and maybe changed it by about 10-20%.

Everyone is different. After my last bend I was diving five days later because I felt that it was appropriate. I'm sure plenty of people will tell me I was wrong to do it and I certainly wouldn't advise anyone to do it -- my circumstances were probably very much different. As the medics will tell you what diving capability you have will depend on scar tissue, predisposition to further bends, nervous/circulatory damage, pre-existing questions (PFO, etc) and what your own body is capable of tolerating. You need to get these assessed. As my trimix instructor used to say, only take advice on diving from someone who is willing to push your wheelchair afterwards. And as the other old saying goes, opinions are like rectums (polite version), everyone has one...

FWIW, I'm not certified to do 95% of the diving I do, I'm not cert'd to mix my own trimix or service my own kit. Please feel free to berate me from commenting on subjects I don't have a plastic ticket that qualifies me to talk about.

[wreckweasel]

Originally Posted by dreammermaid

The other tech courses were a bit of a joke. My instructor was only interested in having me pass as quickly as possible. All calculations were done on the computer. At the end of the course I definitely did not feel competent to mix gas (other than nitrox) let alone call myself an instructor.

Just a couple of questions....

Did you pay money for this course? Were you happy with ending a course where you didnt feel you'd been sufficiently taught?

[aquayle]

Sort of following on from the pp bit, what about accumulated O2 exposure. If on a liveaboard you are diving Nitox to max pp, you could well be up to 100% exposure all the time - I guess its the same on a YBOD. The first exposure only 'drops off' after 24hrs, so you could end up on repetative dives with over 100% O2 exposure??

[Freeflow]

Originally Posted by aquayle

Sort of following on from the pp bit, what about accumulated O2 exposure. If on a liveaboard you are diving Nitox to max pp, you could well be up to 100% exposure all the time - I guess its the same on a YBOD. The first exposure only 'drops off' after 24hrs, so you could end up on repetative dives with over 100% O2 exposure??

That's the PADI way of calculating it, IANTD use a CNS exposure half time of 90 minutes.

[dreammermaid]

Originally Posted by wreckweasel

Just a couple of questions....

Did you pay money for this course? Were you happy with ending a course where you didnt feel you'd been sufficiently taught?

I paid a lot of money for these courses. I felt awful ending a course that I didn't feel competent to teach (gas blending). All the courses he tried to do as little as possible. We did a night dive and still came up before the sun had set. When I went to BKK for the dive show, I learned he was receiving an award. - probably for certifying so many students.

I won't mention his name other than to say he's a Brittish course director for PAdi living in Phuket...last I heard.

[Harlequin]

Originally Posted by dublinbay

Heliox, 80% ,O2, deep dives.............. And he/she(you) are asking for what exactly? How to calculate CNS/UPTD loadings, run times? Anyone who dives He should know this shit.

Just to add to this and re-enforce what others have said. I recently completed my PADI Nitrox course and even at this level I am aware of how fool hardy pushing your PPO2 rate can be. Sure, the navy (I believe) use a PPO2 rate of 2.0 but their divers are uber fit, dare I say "expendable" young men.

I know know how to calculate MOD, PPO2 rates and have the tables for O2 saturation but would I play with a PPO2 rate of 1.6...? No way, it's there as a warning and absolute limit, not to be tinkered with at all.

I hope your friend gets the correct advice from a doc along with the pre-requisite training required for diving on high O2 mixes as he could find himself in the pot... or worse.