What gas mixture for what depth range?

[headhunter]

I'm asking this question as a currently recreational level diver that has rarely exceeded 100 foot depths (planned not accidental). My reason for the inquiry is purely academic at this time and prompted by the reading of an article who's URL was posted in another thread. Someday, I believe my curiosity and drive toward the unknown will lead me to technical diving, but I'm not in a hurry. I figure I'll get there when I get there.

Let me be clear about one thing. I am not asking the question, so that I can go out and start experimenting on my own without proper training. I believe that one should be properly trained for any diving that exceeds one's current level of training and experience. The only time this changes is when you are a pioneer doing something no one has ever done before and have already gone through all other levels of training available in your endeavor. I probably won't have to worry about that for a while.

This is the URL that prompted my question and it was interesting to read from a historical perspective:

http://www.umich.edu/~oseh/abolish.pdf

The following mixtures were mentioned in the article, but I'm also interested in knowing if there are others.

Air
Nitrox (Does this differ from EANx?)
Trimix
Heliox
Hydrox (Isn't that also the name of a midwestern cookie or cracker?)
Hydreliox

Q: What are the currently accepted depth "ranges" for air and each of the mixed gases by today's standards? :06:

What I'm looking for in otherwords is, "air would be used from zero to no more than 'x' feet deep, heliox would be used from 'x' feet deep to no more than 'y' feet deep", etc. Of course, the reasons "why" would also be helpful.

Thanks for your help in starting to understand this stuff.

Christian

 

[MikeFerrara]

That article is way out of date I just skimmed it but while it tells about some of the stunts that have been pulled over the years it doesn't tell about all the divers who have died pulling the.

the 130 ft limit that the article questions is only a limit for certain training levels. The recommended max limit printed on an TDI advanced trimix card is 330 ft.

 

[headhunter]

That article is way out of date I just skimmed it but while it tells about some of the stunts that have been pulled over the years it doesn't tell about all the divers who have died pulling the.

the 130 ft limit that the article questions is only a limit for certain training levels. The recommended max limit printed on an TDI advanced trimix card is 330 ft.

I realized that the article was old and I'm not advocating removing the 130 ft rec limit from any organization's manuals or curriculum, but it got me to wondering what the current thoughts are about the depth "ranges" that different mixes should be used at.

From reading through other threads and websites, I'm under the impression that certain mixes are of benefit at certain depths, but could have undesirable or dangerous results if used at the wrong depths.

Am I not thinking the right way about the topic of mixed gases? Are there ranges of use for each gas?

Thanks.

Christian

 

[H2Andy]

Air

good down to 185 or so due to oxygen toxicity, but really,
should not be used below 100 or so due to narcosis
issues.

Nitrox (Does this differ from EANx?)

nitrox and EANx are basically the same thing (technically,
nitrox is any mixture of oxygen and nitrogen other than air,
and enriched air is any mixture of oxygen and nitrogen with
more than 21% oxygen).

this gas is excellent for 0-100 feet diving, and it shines in the
60-100 foot range. it does have a more serious oxygen toxicity
limitation than air, and it still doesn't keep you from getting
narced.

heliox

helium and oxygen. pretty expensive, but reduces narcosis
and o2 toxicity issues. diving down from 100 to 350 feet.
different mixtures can be mixed for different depths.

Trimix

oxygen, helium, and nitrogen. less narcosis and oxygen toxcity issues, and lets you dive
down to about 350 feet. a lot cheaper than heliox. also can be mixed for various depths.

as for the others, i don't know too much about them,
but hydreliox is a mixture of hydrogen, oxygen and helium
and hydrox is a mixture of hydrogen and oxygen.
these gases are just not in my vernacular.

by the way, the 350 depth i am quoting comes from NOAA;
i am sure people are diving deeper than that on a regular basis,
and the scuba depth record is over 1,000 feet.

oh, also, don't forget about decompression gases, which will
be as rich in O2 as possible given the depth, with 100% O2
starting at 20 to 15 feet.

 

[MikeFerrara]

We use 32% to about 100 ft

21/35 trimix to 150 ft and sometimes a mix like 28/30 or 30/30 between 100 and 130.

18/45 trimix to 200 ft
15/55 trimix to 250 and 10/70 belopw that.

For decompression we use 100% at 20 ft and or EAN50 at 70 ft and/or EAN35 at 120 ft.

I havenb't needed a decompression gas below 120 ft yet

A gas mixture with less than about 0.16 ATA PPO2 won't keep you alive.

A mix with to high a PPO2 and/or for too laong can make you convulse and drown.

Too high a PPN2 and the narcosis is too much.

Too little N2 and very deep HPNS can be an issue.

BTW PP = partial pressure...ATA = pressure in atmospheres absolute.

I know that wasn't very detailed but it gives an idea of some of the issues.

There are of course other mixtures that divers use but these are the ones that we use.

 

[headhunter]

Thanks Andy and Mike.

That's exactly the kind of info that I was looking for.

Obviously, everyone has to be somewhat on the same page with this information due to the physics involved. Although, I imagine that actual mixes vary somewhat from one person to the next for reasons that I have yet to understand.

Are there different schools of thought on the subject?

Is there a particular book (or are there a few) that I should read that would let me study the topic in depth?

I'd like to learn a lot of the details and principles behind using mixed gases through reading about it first and then take classes to further my education through more of a hands on exposure down the road. I find that doing a lot of research about something first and then taking classes involving its practical application help me learn things best.

I'm just one of those people that does well reading technical manuals. Guess that's why I work with computers and networks. I don't dive with a computer, but I did play with an Orca Edge in the '80s. I just didn't see the value in it for me since I found the tables comfortable to use.

Thanks again and I'm open to more suggestions and comments.

Christian

 

[Kim]

If you haven't done a basic Nitrox course yet I'd start with that. It will BEGIN to give you understanding of the issues - and reasons - and explain in detail stuff like PPO2, PPN2, oxygen toxicity, etc. It will make it easier to understand the rest!!

 

[chrisch]

Here here, Kim. I also agree with Mike's list. I use EAN32 to 30M and trimix after that.
If you can get a copy there is a book called "Mixed Gas Diving" by John Crea with contributions by Brett Gilliam and Dick Rutkowski (apologies on spelling if wrong on these names). I think it is Underwater Publications.
That will tell you everything you need to know.
If not try IANTD - they have an encyclopedia, but I have not seen that. I have the book and it is well worth finding a copy.
Chris

 

[chrisch]

Found it:
http://www.amazon.com/exec/obidos/t...f=sr_1_3/002-0347165-3049664?v=glance&s=books

Chris

 

[J1M1]

hydreliox is used to better offset hpns at extreme depth, ie-500fsw-2000fsw i believe. The mix is heated while it is delivered to the diver via his umbilical because of the gas mixes heat loss properties. Hydrox is unstable and will explode if the mixture of O2 is to high ie-above 4 or 5 % i think...JD