what the different between using Nitrox and Normal Air to dive???

[Elvistheking]

Are you suggesting deep tech divers go back to deep air? I'm shaking my head....

Trimix has a lower percentage in deeper depths to manage oxygen toxicity. Displacing that O2 with N2 would be equally dangerous because of the significant impairment it provides at depths. Helium is a great choice to displace the N2 as it's inert in the body and releases more easily from tissues. It's also a thinner gas offering an easier work of breathing. In recreational technical diving it has very little to do with managing the shakes.

You should start a voodoo gas thread.

I think the problem is that he has gone straight from Nitrox is evil and straight onto the problems with Heliox (He and O2 only), and yes trimix (i.e. He,O2 and N2) was developed because of problems using just heliox (HPNS,although I don't think the current *theories* are due to it's narcotic nature that helps prevent shakes!) as well as being slightly cheaper!

Helium is generally considered a fast gas so that yes it does off-gas faster (and on-gas faster) which isn't always a good thing, a He bend is generally considered worse than a N2 bend.

That being said I'm starting to think this guy is a troll too.

 

[PfcAJ]

I think the helium bend thing might be a bit of a misnomer, too. I think I recall reading of a study that found a disproportionally high amount of nitrogen in bubbles (compared to helium) following a rushed ascent to 1 ata.

 

[Elvistheking]

I think the helium bend thing might be a bit of a misnomer, too. I think I recall reading of a study that found a disproportionally high amount of nitrogen in bubbles (compared to helium) following a rushed ascent to 1 ata.

Possibly but then maybe He2 produces more bubbles?, it's all based on exploding goats and guess work pretty much anyway, no one *really* knows what is going on ;-)

I do love the fact that the more you learn about deco theory the more you realise how much "art" there is in the "science".

(Oh crap this isn't in the Tech section are we allowed to let that little secret out)

 

[PfcAJ]

I doubt it. My personal hypothesis is that divers were originally doing inadequate decompression and just got bent. Helium got the blame.

 

[616fun]

I doubt it. My personal hypothesis is that divers were originally doing inadequate decompression and just got bent. Helium got the blame.

6 minute accents for the win!!

 

[Rich Keller]

I think the problem is that he has gone straight from Nitrox is evil and straight onto the problems with Heliox (He and O2 only), and yes trimix (i.e. He,O2 and N2) was developed because of problems using just heliox (HPNS,although I don't think the current *theories* are due to it's narcotic nature that helps prevent shakes!) as well as being slightly cheaper!

Helium is generally considered a fast gas so that yes it does off-gas faster (and on-gas faster) which isn't always a good thing, a He bend is generally considered worse than a N2 bend.

That being said I'm starting to think this guy is a troll too.

While helium is safe to use, it is a shock to the nerves system at depth until your body has time to adjust. The percent of nitrogen in trimix is very low and even with that when you get blowed down to the 600 to 700 foot range you are still shaking to the point of being useless for most of the first day. I have no problem with trimix as it also has a lower percent of oxygen, it is the higher percent of oxygen in nitrox that concerns me. As for trimix on scuba you are not going deep enough or staying long enough to run into the problem with helium or the benefit of the nitrogen in the mix. So I do not understand why you would even bother with it?

 

[Rich Keller]

OK, I just read the entire section of the Navy manual on nitrox, and I don't see anything in there that is inconsistent with a typical recreational nitrox course, such as the one I teach. I don't see any hint of a suggestion that the risks outweigh the benefits. In fact, it appears to me that it is pretty much advocating nitrox use within the identified range. I don't see a single word about a recommendation for oxygen tolerance testing.

The section on oxygen toxicity (10.3) says that dives need to be conducted with a PPO2 of 1.4 or less, and such dives "can be conducted using the full range of bottom times allowed by the air tables without concern for CNS or pulmonary oxygen toxicity." It goes on to identify a table that if followed should eliminate any concerns for oxygen toxicity on repetitive dives.

I get that he believes the risks outweigh the benefits and that nitrox users should pay for an expensive oxygen tolerance test, but there is no validity in referring to the Navy Dive Manual for support in those positions.

The statment "The Navy Experimental Diving Unit said the increased risks of using Nitrox at depth far out weigh any benefits." came from a phone conversation I had with a Navy Master Diver at the NEDU when I called to ask about nitrox. Unlike most of the people here I do not think I know it all so when I have a question I ask the NEDU. I will give his opinion far more credence then any I have heard here so far.

"NITROX breathing gas mixtures are normally used for shallow dives. The most benefit is gained when NITROX is used shallower than 50 fsw, but it can be advantageous when used to a depth of 140 fsw."

The above quote is from the Navy Dive Manual. It seems to me they favor the use of nitrox above 50' which is what it was intended for in the first place. I am equating "normally used" with "identified range" when I come to that conclusion. Going below that is where you start to push the limits more and open yourself up to more risk.

 

[Rich Keller]

Rich, I think you just need to stop. So many of your posts are dead wrong. The stuff on oxygen cleaning, the stuff on nitrox, and now you're making highly questionable comments about trimix and when it should or shouldn't be used.

People have continued to provide you with scientific research, industry standards, and practical experience. You've chosen to ignore all of that and pontificate about things you (clearly) don't know too terribly much about. Unfortunately, your commercial dive experience is somewhat non-applicable to recreational scuba (to include the use of oxygen and helium). It seems like you're just trolling.

I have just been quoting the Navy Dive Manual and the NEDU on nitrox use. Clearly you think you know better then they do which in my opinion is the hight of both arrogance and ignorance. As for trimix I was just explaining why nitrogen was in trimix not condemning its use, that is you putting words in my mouth. I also never said or suggested you blindly follow anything, that is again you putting words in my mouth. Though the only thing I can think of off hand about the Navy Dive Manual that I do not agree with is the Navy's idea of who wrote it and on what day he wrote it. If you ask a Navy Master Diver who wrote it he will tell you something along the lines of the following. "After creating the universe God did not rest on the seventh day, he wrote the US Navy Diving Manual." I will stick with what the professionals have to say not the amateurs like yourself!

 

[LiteHedded]

he did a pretty big trimix dive with one of those NEDU Dr's last weekend. im not sure he's as ignorant about this as you think

 

[ianr33]

Possibly but then maybe He2 produces more bubbles?

He2 ?