Daltons law

[readysalted]

Hi guys,

I have just started to read a book involving ccr's, and they are going deeper than 150 meters, and only putting .4 o2 on the ccr, whilst I think I understand the small amount of o2 " due to dpp law " should you not have nitrogen narcoses ?, so if you only have .4 o2 does that mean you have 99.8 nitrogen ?
Please help my head hurts !!!!

 

[Kern]

Have a look at your numbers, they don't add up. When you get the numbers sorted, think about replacing some of the N₂ with He.

 

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hey there,
not to sure of the numbers as they are from a "story" book so its hard to tell what is fact or what is story line!!
there was nothing said about helium ?
thats more like a trimix ?
i thought that it was just O2, is there a post where i can read more about this ?
thanks for the help so far !!

 

[battles2a5]

hey there,
not to sure of the numbers as they are from a "story" book so its hard to tell what is fact or what is story line!!
there was nothing said about helium ?
thats more like a trimix ?
i thought that it was just O2, is there a post where i can read more about this ?
thanks for the help so far !!

Do some searching or go to wikipedia to find out how a CCR works. A closed-circuit machine uses 2 gases; pure oxygen and a diluent. The purpose of the diluent is to dilute the oxygen as the depth increases so you keep the partial pressure of oxygen at the appropriate level. On a dive like this you are definitely using trimix. You already know what one of your gases will be (oxygen) so you have to figure out the appropriate diluent, and that's all Dalton's. So in simple numbers:

150m = 16 bar

Preferred Dil Po2 = 1 bar
Preferred Dil PN2 = 3 bar
Balance PHe= 12 bar
Total= 16 bar

That works out to about 6/74 for dil (6% O2, 74% He, 20% N2) as an ideal dil mix. So the mix in the tank has 6% oxygen which extremely hypoxic.

This should go without saying since you obviously aren't diving at these depths but please don't even think about using a gas like this until you know what you are doing. Diving hypoxic gases on CCR is fraught with risk. Doing it without the appropriate training and experience is suicidal.

 

[Kern]

Sorry, I didn't realise I was in the RB forum when I first responded, so I'll leave the discussion on RB's to those that really know.

As to your numbers, I think you may have confused 0.4 or 40% O2 (a hyperoxic mix) as written in the OP, with 0.04 or 4% O2 (a hypoxic mix) which is more likely for a dive to these sort of depths.

 

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Thanks battles
I'm not thinking of doing anything with a ccr for a very long time yet!!, I did think of the wiki thing but thought I would get better info from you guys, sorry if it's a bit of a stupid question, but it was one I did not know the answer to, now I understand !!
Cheers to all