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<font color='#000080'>Right then. Tiewrapdiver, who unfortunately lives in my house, is now insisting that the HSE thinks 22% is still air. Someone please tell him he's wrong, because he just won't believe me that he's wrong.

20.9% and I'm sticking to it.

Back me up here guys. Otherwise he's going to be moaning on about this for days. Please. I couldn't stand it.
 

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Digger is trying to start a big arguement here about something i read.

I know the air is 20.9% oxygen!
 

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<font color='#000080'>I read not so long ago about the dangers of Dihydrogen Monoxide. Doesn't make it true.

Nor does it make it sensible. Are you admitting you're wrong then? Jesus. That hasn't happened in a while.
 

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A mix of 22% air and 78% nitrogen might still be equivalent to air in terms of its *nitrogen* content, perhaps? Assuming you'd mixed two pure gases, and didn't have all the CO2 etc that's in normal air.

Or I might just be talking crap.
 

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I'm not wrong, i'm just saying what i read
 

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wibble
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<font color='#000080'>When i was at the dive shop buying my analox doodah i was told that 20.9% was more accurate for the percentage of oxygen in normal air.  Now i have buggered about with small fluctuations in O2 content with deco software and it does make a difference (not much but it IS there, 51% instead of 50% knocks a minute off a deco time of 20 odd mins, all this because deep blue gave me a richer fill than i wanted......)
 

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<font color='#000080'>From my first search on Ask Jeeves I came up with:

78.1% Nitrogen
20.9% Oxygen
0.93 Argon
Trace (<0.1%) amounts of Noble trace gasses, Carbon Dioxide and air polutants.

With these facts? to hand, where does all the carbon dioxide we breath out (around 1 lpm) go? All those little plants must be working over time. Any good Sientists out there? Anyone able to help me sepll too?? Oh F**c it.  


p.s Digger, How old is that picture of yours? From the previous picture you had on it looks like you've put on a little weight? Or was it a bad angle?  
 

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<font color='#000080'>Helen, Reading my new Nitrox Manual from TDI, it says that the measuring instruments have a tolerance of about 1%. 50+/- 1% = 49% or 51%. Then when looking at what depth for what mix they tell you to round to the nearest integer.
 

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Ginger, Irish, sometimes stroppy
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The amount of oxygen in air does vary dependent on the environment. E.g. if there is a high level of combustion then the level could drop below 21. In student accomodation you'd be lucky if there is any o2 at all


20.9 is average for the 'open air' but it does fluctuate so the HSE probably mean that 22% is within normal tolerances and so can be treated as normal air. They may well define normal O2 content as a range, say between 20% and 22%, outside of that range you may need special procedures etc.....I'm assuming that this was a general HSE statement but not diving specific???

By the way I made all that up, sounded pretty convincing didn't it?
 

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[b said:
Quote[/b] (Digger @ Feb. 12 2004,17:31)]Right then. Tiewrapdiver, who unfortunately lives in my house, is now insisting that the HSE thinks 22% is still air. Someone please tell him he's wrong, because he just won't believe me that he's wrong.

20.9% and I'm sticking to it.

Back me up here guys. Otherwise he's going to be moaning on about this for days. Please. I couldn't stand it.
Well I've searche the HSE pages (www.hse.gov.uk) and can't find any definition of air and O2 %, but as a diver with nitrox quals and a scientist with several years of working on biological oxidative processes, you can tell TWD that Dr Stevil say's you're right and he's wrong  

added later: actually, Conor's got it I reckon with the  "acceptable tolerance range", after all science isn't an exact science  (eh???)


Dave, we will also accept the terms "Boffin" or "Lab Rat" much easier to spell  

 

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Is this what you were thinking about ?

Divers gases include pure oxygen and oxygen mixtures where the oxygen percentage is more than 22%.  (22% is the upper limit for oxygen in air as stated in BS EN 12021 and has been used as the figure for EN diving equipment standards that require the equipment to be fit for oxygen service.)

HSE Letter
 

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<font color='#0000FF'>Just had a thought.

If I'm at the top of a mountain, where the air is "thin", I assume this to mean less o2 in the mix.

If there is less o2, am I still breathing air?.

Or is it all down to pressure?

er..PressurE.
 

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<font color='#000080'>I think we have now tracked down the document of which he speaks. I like Dr. Stevil's verdict, so I'm going with that one. I'm right. For once.

Acceptable tolerances aside, his statement was that some training agencies think that air has 22% O2 content. Not only is the HSE not a training agency, they don't think that air has 22% O2.

You'd be breathing lower O2 levels, that's still "air", but not air as we know it.
 

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<font color='#000080'>And Dave, this is an old photo used to sttract women. I'll show you the full size photo wen you're up for the Stoney gig. Make sme look dead technical, and like I've had food poisoning. Which I had. Also makes me look really well built I reckon, which I wasn't really. Strange.

Digs.
 

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I think this is a grey area with regards to terminology and tolerence, O2 clean rules and certs etc.

Air is somewhere around 20.9% by definition.

Nitrox tolerences are usually accepted to be + or - 1%  therefore I think this is where the definition from the HSE comes into play.

A nitrox mix of 21.9% could analyse as 20.9% using the accepted tolerences, so is it air or nitrox?

Basically I think you can both be considered correct.  


You can argue the toss but the HSE do have some strange definitions.

Of course if you want to find out 100% phone the HSE.

Daz
 

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Ginger, Irish, sometimes stroppy
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[b said:
Quote[/b] (PressurE @ Feb. 12 2004,22:48)]Just had a thought.

If I'm at the top of a mountain, where the air is "thin", I assume this to mean less o2 in the mix.

If there is less o2, am I still breathing air?.

Or is it all down to pressure?

er..PressurE.
If I understand it correctly, you would still have the same percentage of oxygen in the air, but the pressure would be lower and so the partial pressure would be lower. So there would be less oxygen molecules in an average lungfull, and the body would be less efficient at extracting that O2.
 

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Digger, is that avatar actually you? Because in that pic you look remarkably like the chap in dive kit on the flyers for Coral Cay Conservation, no doubt there's some of these flyers in your Uni bioloical sciences dept.
 

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<font color='#000080'>Cheeky monkey! Has anyone got a link to this chap from Coral Cay? Maybe I've got another clone! I've already got one Mini-Digger, he's coming to the social after the 21st, I'm fully expecting at least 2 or 3 people to ask him if he's me. The likeness used to be really bad, but I've been coaching him to choose his own clothes and think for himself now.
 
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