Tech Nitrox Intro

[padiscubapro]

Big-t-2538 once bubbled...
But what I do know is that once you extend the PO2 above 1.4 to 1.6 you run a severe risk of getting an ox tox hit.

From my quick math, if you are diving to 150' the MAX O2% you should have is 28.8%...that works out to a PO2 of 1.6 ATA. For 100', max O2% is 39.6%

Thus, you say you normally dive 32 to 34% O2....and you normall dive to 100ft...that's an avg PO2 of 1.37....now according to my IANTD EANx text...the maximum recreational limits for O2 exposure at that PO2 in 24 hours is 180min....if your doing more than 4 dives...I think you might have exceeded this.

Anyway, this is just what I learned in my basic EANx class through IANTD. I wouldn't exceed these limits...you might want to check into an IANTD class?

As for more of my illustrious theories, if you are going to be using an 80% mix for DECO, I believe DECO stops are done at a high PO2 in order to off-gas, and you would be having to DECO at (approximately) 33 ft. as opposed to (I believe) 20ft. with 100% O2. I think most of the tech divers are now steering away from 80% for that reason, and using 70% for a deeper stop, then switching to 100% O2 for their final stop....I'm sure someone will correct me if I'm wrong.

Anyway, I too am going to be looking in the direction of deeper dive before too long...it seems to be interesting to me, but I am going to be sure I get some good education and knowledge before I jump in feet first.

I dont recommend 80% for a deco gas, depending on the profile using 50% from 70 feet or 100% at 20 are preferable..

If you are running high CNS loads you are much better on 50%, the time differance on hangs between o2 and 50% overall are minor and you get out of the water with a much lower cns. this said I always carry 50%as a deco gas (even when on a ccr for deco bailout). oxygen is useless to carry since you can only use it at 20ft or above.. if all goes well I'll do my deco on 50% and switch to o2 (hung below the boat or staged)otherwise I just finish it on 50%. Using both gases does decrease the decompression obligation since you started decoing deeper.. o2 by itself is only a marginal gain.. 80% is only 1 stop deeper and shorter than the 20ft stop.. so you really don't gain on the deco

 

[AquaTec]

padiscubapro once bubbled...

I dont recommend 80% for a deco gas, depending on the profile using 50% from 70 feet or 100% at 20 are preferable..

what do you have against 80%

I don't see it as an alternative to 50% it is an alternative to the 100% gas.

 

[Wendy]

What sort of profiles do you have on your dives? I know when you chase fish you may have a tendency to bounce a little in your depths. Are you doing these dives from a private boat?

 

[padiscubapro]

Big-t-2538 once bubbled...
But what I do know is that once you extend the PO2 above 1.4 to 1.6 you run a severe risk of getting an ox tox hit.

Not true.. The agencies take a more cautious approach now than in the past... I used 1.6 as a bottom gas for about a decade and in currents without incident..
ther is nothing wrong with going with a more cautious mix but above 1.4 isn't a magic number saying you'll otox.. There are alot of factors and total expossure time has to be taken into account.

Another fact there is only ONE documented case of a OTOX hit at 1.6 and this one is unclear as the person already had a history of epileptic attacks. I have had many dives with po2s higher than 1.6. I am not advocating using a 1.6 as a bottom mix just pointing out data doesn't support it as a danger.. If you are running long exposures it is probably prudent that you use a lower Po2 to stay within NOAA established normal exposure limits.. They also have a chart called exceptional limits which if you havent seen allow exposures and times considerably higher than the standard limits.

The NAVY uses a 1.8 with some of its rebreather divers!

Do some research yourself or find a knowledgeable instructor who knows more than the standard "text book responses". There is lots of reference material out there, a good starting point is the Navy manual..
BTW as you are reading youll find out most (all for nitrox)training agencies name trimix,heliox and nitrox incorrectly, they state ox-he or ox-nitrogen in the naming.. its not really oxyni or oxyhe is it??

The commercial industry, and the navy use intert gas then oxygen you don't see them calling a 84% heliox 16% oxygen mixture as heliox 16 its heliox 84-16.. also the navy calls nitrox 36 as nx 74-36.. ANDI follows this designation for trimix/heliox but goes with the recreational nomenclature for nitrox use.

Look at other commercial gas mixtures they are always presented with percentages in the way its named.

 

[roakey]

padiscubapro once bubbled...
also the navy calls nitrox 36 as nx 74-36..

Only the government would have a total of 110%!

[yhea, it's a typo but it struck me as funny ]

Roak

 

[AquaTec]

padiscubapro

you raise some good points, I remember back in the 80's when PADI said you do not dive deeper than 130 feet, if you do you will get dcs or worse the rapture of the deep will just swallow you up and you may never return.

We now believe the same thing about Po2 of 1.6
just like PADI we are taught by technical diving agencies that you are sure to die if you excede this limit.

I support exploration and the questioning of what is believed to be safe. yes some will die in this exploration but we must explore and push the limits of what we know today so we can discover what we will know tomorrow

 

[Big-t-2538]

I'm just looking in the direction of taking tech courses. I am trying to gain as much knowledge as I can before I do anything. What I said before was based on what I had learned in my recreational Nitrox class. It was a good class, and I feel like I took a lot away from it. Diving, much like engineering, is an ongoing learning process. I just hope to learn more.

 

[SM Diver]

Hey, Uncle Pug, why don't you let up a bi! Why so many posts laced with sarcasim? Yeah, everyone knows you're knowledgeable, but if you don't want to share that knowledge with Dan, either because he is a spearfisherman or you don't like his prior posts, why lay in to him?

Having said that, Shooter Dan is not only an outstanding spearfisherman, but an excellent diver, as well. I have hunted with him several times.

Hey, Dan. Chris was talking to me about taking that advanced nitrox course with you guys in December. Can't do it. I'm starting a cave diving course next month. See you this Friday at the Captain's meeting for the Southern Open Derby.

 

[SM Diver]

AquaTec once bubbled...
Well I think you guys ran him off

Yeah, I'm sure Dan was real intimidated.

 

[100days-a-year]

!!!DANGER DO NOT TRY THIS AT HOME.get credible instruction before trying any of the following.!!!West Coast spearfishermens try www.mobilescuba.com for info and classes.Very few folks on this board are experienced in this type of diving so thier input while generally helpful is not always applicable.This board is very polite and well mannered if you are......usually.The only way to do this type of diving realistically is with 1 of 3 methods.1.Methodically check your BTs,SIs+depths and carry a palm or laptop to cut custom tables.2.Dive within a conventional "diveplan".Planned depth and times with pre-cut tables and back-ups.3.Get a multi-gas computer and dive it conservatively.1 and 2 suck for a spearfisherman.#3 is iffy too,but looks the best to me based on the already hi task loading involved.We currently use method 2 but use longer BTs and limit dives to 3-4 per day .OTOH commercial spearfishermen here just dive thier liberalest computer 6-8 times a day and max out PO2 by either lying to the computer or varying thier depth enough to keep from being locked out.PM me for more.