Nitrox PPB

[Packhorse]

As Perronford mentioned the descrepancy is probably due to the lack of temperature considerations in my speadsheet.

It does seem to work with either PSI or Bar though so all you vintage divers can use it too.

 

[SparticleBrane]

"Divers in the US" might be a more appropriate term, as we still currently use PSI.

 

[Packhorse]

"Divers in the US" might be a more appropriate term, as we still currently use PSI.

My bad

 

[SparticleBrane]

It's all good.

 

[Azza]

I only really made this so I can learn a bit more about PPB. That and I got a bit bored over the weekend because I couldnt go diving.

Lucky you. My wife made me do stuff around the house... Doesnt look like the weather this weekend is going to be much better either.

 

[Packhorse]

Lucky you. My wife made me do stuff around the house... Doesnt look like the weather this weekend is going to be much better either.

My bet is the forecast will change and it will be all good!!
At least I hope so, I got my first nitrox dives coming up.
Well no, all my dives have been nitrox up to now. These will be the first EAN dives

Anyway as I said earlier a similar speadsheet NZAndy sent me added 1 bar to the fill pressures. Which get me woundering, If I fill a tank to 230 bar does it have 230 bar in it or is it 230 bar above atmospheric pressure? eg 231 bar
Does it really matter anyway? Can the gauges be accurite to 1 bar? Probably not but I would still like to know the correct way. How accurite is good enough?
Also how does pressure play apart? Is 100bar of H N or O2 100 times as dense as 1 bar? or should I say does 100 bar of gas have 100 times the mass as 1 bar given the same temp and volume.

 

[MikeFerrara]

Not quite. Although I will preface this by saying that I haven't taken a trimix class either.

"Nitrox" is any mix of nitrogen and oxygen. Air is usually considered a mix of 21% nitrox.
Trimix is a blend of nitrogen, oxygen, and helium, but there is less oxygen than normal everyday air. Examples are: 18/45, 15/55, 12/60, and 10/70.
Helitrox is a mixture of nitrogen, oxygen, and helium, where there is equal to (I believe some people call this "normoxic trimix" ?) or more oxygen than we breathe in normal everyday air. Think of this as nitrox, but with helium added. Examples are 25/25, 21/35, 30/30...the list goes on.

Helitrox has both an EAD and an END. The EAD comes from having MORE oxygen than what we breathe, and and also having helium, which reduces narcosis.
Trimix only has the END, since the helium reduces narcosis. The oxygen is LESS than what we breathe in normal air, so there is no EAD.

If you check out the PDF link that I posted above, most of this is fairly self explanatory.

Why make it so complicated? I never saw these names for hyperoxic trimix like helitrox or triox until the fairly recent introduction of recreational trimix courses which use hyperoxic trimix.

Traditionally, trimix is any mixture of helium, oxygen and nitrogen. It can be hypoxic, normoxic or hyperoxic. It's all trimix so why screw with other silly names? Besides, the proper new wave name for hyperoxic trimix depends on which agency certified you. Right? If you are NAUI trained, you have to call it helitrox and if you are GUE trained you are rule 1ed unless you refer to it as triox. the rest of us just use a non-agency specific name and call it trimix. LOL but you could call it Fred if you want. If you wish to trademark a name, I'm thinking you'll need to come up with your own but comming up with a new horse **** name doesn't give you license to screw with the math.

I realize that some people (GUE?) dive mixes like 30/30 as EAN32. However, traditionally speaking, since there is helium in any trimix, we would want to take that into account when calculating decompression. Therefor the term EAD has no meaning. Strictly speaking, EAD does not come from having more O2 as you stated above but rather from having less N2. EAD is the equivilant depth of air that we could base our decompression clacs on. If we take the helium into account there is no such thing as EAD with any trimix.

END is an estimate of the breathing gasses narcotic effect as compared to air. If you look at the traditional equation for EAD you'll see that it's just the depth where the
PPN2 is the same so the equation for END is very similar to EAD. If we consider O2 as non-narcotic the equation is END in FSW= (d+33)/.79 (FN2) - 33. Does that Look familiar? If we wish to consider O2 as narcotic, as many do these days, the equation simplifies to... END in FSW = (d+33) (1-FHE) - 33

 

[MikeFerrara]

Anyway as I said earlier a similar speadsheet NZAndy sent me added 1 bar to the fill pressures. Which get me woundering, If I fill a tank to 230 bar does it have 230 bar in it or is it 230 bar above atmospheric pressure? eg 231 bar
Does it really matter anyway? Can the gauges be accurite to 1 bar? Probably not but I would still like to know the correct way. How accurite is good enough?
Also how does pressure play apart? Is 100bar of H N or O2 100 times as dense as 1 bar? or should I say does 100 bar of gas have 100 times the mass as 1 bar given the same temp and volume.

The difference between guage pressure and absolute pressure. Typically a guage is calibrated so as to read zero at atmospheric pressure (usually at sea level). When the pressure of a tank measures 3000 psi on your guage it's 3000 psi above atmospheric pressure...assumming a perfectly calibrated guage. When the tank reads zero on the guage there is still some gas in there right?

You could take that into account in your mix calcs but I think you'll find that it's pretty insignificant.

 

[PerroneFord]

END is an estimate of the breathing gasses narcotic effect as compared to air. If you look at the traditional equation for EAD you'll see that it's just the depth where the
PPN2 is the same so the equation for END is very similar to EAD. If we consider O2 as non-narcotic the equation is END in FSW= (d+33)/.79 (FN2) - 33. Does that Look familiar? If we wish to consider O2 as narcotic, as many do these days, the equation simplifies to... END in FSW = (d+33) (1-FHE) - 33

Are we aware of any agency these days that is NOT teaching that oxygen is narcotic? The three technical agencies I've studied with have all counted o2 as narcotic.

 

[MikeFerrara]

Are we aware of any agency these days that is NOT teaching that oxygen is narcotic? The three technical agencies I've studied with have all counted o2 as narcotic.

As I recall, both TDI and IANTD give (d+33)/0.79 (FN2) - 33 as the equation for END. This equation makes the comparison only on the basis of nitrogen rather than O2 + N2 as in the equation (d+33) (1-FHE) - 33

The later equation assumes that everything in air is narcotic and everything other than helium in trimix is narcotic. In reality of course, O2 is probably less narcotic than N2 and HE has some narcotic effect, just far less than N2. Also the difference in answers isn't all that great. There are probably other factors that introduce much greater uncertainty about our own level of narcosis on any given dive than which equation we use.