25 replies to this topic

[chinacat46]

Did you ever wonder if Nitrox was the original gas for SCUBA diving and then air came along if they would charge extra for air. Hey you can dive deeper with this air gas.

- Chuck

[jextract]

Geez!!! I can get double 104's filled to 3500 psi with my blend of choice for $20... I think I'd buy my own compressor before I paid anyone $15 for a fill.

There's a lot of mythology surrounding the whole O2 cleaning thing, Jextract. Banked Nitrox shouldn't dirty up your tanks. Generally any air clean enough to pass breathing air standards is clean enough to mix with. Hyperfiltration is a bonus, but not necessarily required IMHO.

I have heard bad things about one particular shop in your area, though. I'll dig through my files and PM you about it later...

I appreciate any 411 you can give me. I usually get filled at Scuba Schools of America in Woodland Hills. The LDS closest to me is Hollywoodivers in Universal City and they're the ones who told me that while the air in the bank was fine it was the membrane that they had the problem with. As you alluded to, I'm not too worried about my safety on this, more the guy who would be filling a potentially dirty tank with pure O2. In fact, I use the same regulator for both Nitrox and air, which is supposedly verboten ... I just open the valve very slowly to avoid the heat associated with rapid pressurization. I check my o-rings fanatically for any signs that there might be a problem. Any further guidance you might give me will be hugely appreciated.

[jextract]

The reason I dive nitrox is BOTTOM TIME!!!

BT is exactly the reason why I got certified and dive with it!

[Coo's Toe]

I appreciate any 411 you can give me. I usually get filled at Scuba Schools of America in Woodland Hills. The LDS closest to me is Hollywoodivers in Universal City and they're the ones who told me that while the air in the bank was fine it was the membrane that they had the problem with. As you alluded to, I'm not too worried about my safety on this, more the guy who would be filling a potentially dirty tank with pure O2. In fact, I use the same regulator for both Nitrox and air, which is supposedly verboten ... I just open the valve very slowly to avoid the heat associated with rapid pressurization. I check my o-rings fanatically for any signs that there might be a problem. Any further guidance you might give me will be hugely appreciated.

Well, first off, you can treat anything up to 40% pretty much like it's air, even going so far as to pump it through a compressor, when the danger factor would be at it's greatest. O2 cleaning a regulator is just plain silly unless you plan on using it with 50% or 100% O2 for advanced decompression. The reg manufacturers seem to be coming around on this too, and you don't see all the green regs for Nitrox like you did a few years ago. A lot of regs are starting to come standard with Viton or EPDM o-rings now, and most are coming straight from the factory with O2 friendly lubes. But if you are just using stanard mixes like 32%-36%, no special precautions are required for your regs.

But really the thing to worry about is your tank valves, which will see 100% during partial pressure fills, and that's where most of the heat is concentrated during the fill. Valves and tanks should be O2 cleaned. What I was saying was that it would be really hard to contaminate a cleaned tank to an unsafe level with just one airfill, especially if you trust the shop is pumping clean air to begin with. Sure, they might not be willing to guarantee the O2 clean status of your tank ( remember this is sue happy America we're talking about ), but that's not saying they are actually going to make your tank unsafe for future partial pressure fills.

I'm kind of hoping Lubold will weigh in on this subject too, he's pretty knowledgeable about all this techie stuff, and seems to know his way around regulators and mixing issues.

[WreckWench]

I'm kind of hoping Lubold will weigh in on this subject too, he's pretty knowledgeable about all this techie stuff, and seems to know his way around regulators and mixing issues.

Hey where is Lubold? I haven't seen him in a long time....HEY WE MISS YOU!!!

[Diverbrian]

Ok...my 2psi as someone always says other then me....

The reason I dive nitrox is BOTTOM TIME!!! No not 'bums' or 'bottoms' but BOTTOM TIME!! In the venues I usually dive...aka my beloved North Carolina you can double your bottom time using nitrox vs. air. Now at the depths we dive we use a non-standard mix of 30% as we can't predict if we'll dive 80 ft or 125 ft but with the lower mix we still dramatically extend our bottom time AND do it more safely then on air.

I'll let the techno wizards give you all the 'why's and wherefores' and if you really push me, heck I can do it....but the bottom line is....its all about "BOTTOM TIME" and I like mine on nitrox thank you please!!!

As for feeling better...the others have captured my feelings exactly!!! Of course there is a whole school that says dive nitrox like it is air for the safety margin....only problem with that is that its too EXPENSIVE to do that. If nitrox cost a few bucks more then air...I'd be all over it...but unless you work a boat or have free nitrox...its too expensive to dive as air!! :dltears: -ww

This is where you have people again talking about nitrogen absorption and money at the same time.

I agree. It is not economical to dive nitrox as air. My dive shop fills my 120's for $15.00 /tank and my double 100's for $25.00/fill. I dive large capacity tanks for a reason and that is see all the historic wrecks and pretty fishies. I paid good money for that charter, I am using the time that I have out there.

Next point: when I was in Florida I saw the safety margins on nitrox first-hand. I was diving next to a group of air divers (I knew them and they are not nitrox certified.) and I was using EAN36. I had to leave that group on the last day as I had too much bottom time left, LOL. Nearly all of the other divers on that trip kind of looked away when you asked them where they wound up on the tables or about the stops that they made on the way up that were a little deeper than a safety stop. (Hmmmm!) I was nowhere near my NDL's the whole trip and I was normally one of the first in and last out (as my group had a known diver with the lungs of a bird ::envy:: ). I know that if you are pushing NDL's that tightly, you are building up significant nitrogen that needs to be off-gassed. You are likely to be tired. Also the chance of DCS just went way up.

Now, Lubold, could you please get in here to discuss those tanks?

PS I own exactly one reg that has been O2 cleaned. As Erin says, it goes on my stage bottle which has EAN50 in it. Needing to dedicate a reg for nitrox when you are diving mixtures below 40 percent is unnecessary. I have five tanks O2 cleaned. That is for PP blending which is the most common method of making nitrox that I run into although the dive shop here preblends EAN36 and banks it.

[Laura]

Hi everyone,

Just wanted to say thanks again to everyone for posting such good info. I really appreciate it.

Have a great wekkend,
Laura

[jextract]

Did you ever wonder if Nitrox was the original gas for SCUBA diving and then air came along if they would charge extra for air. Hey you can dive deeper with this air gas.

- Chuck

Hey, you can dive as deep as you want with Nitrox ... of course there's that whole inconvenient "seisure and drowning" thing, but once you get past that it's all good, right?

[chinacat46]

You can dive as shallow as you want on air too and no seisures.

[domino22]

I dive nitrox as much as I can. Some times it can become $$ but when you can get a weekly deal on a trip and do allot of dives I think it is safer for multi dives. Plus I dive with a Suunuto and they do not like air. The more nitrogen you take out of the mix the less you can absorb- well this is my thought not fact so do not take that as a fact but it sounds good.

[Lubold8431]

I'm kind of hoping Lubold will weigh in on this subject too, he's pretty knowledgeable about all this techie stuff, and seems to know his way around regulators and mixing issues.

Hey where is Lubold? I haven't seen him in a long time....HEY WE MISS YOU!!!

Sorry guys, I guess I missed this thread!!!

Well, basically, the issue is contamination. There are two things that can get you into trouble with high pressure O2. Particle impingment (particles causing a spark) and the cleanliness of the cylinder or valve (must be pure of all hydrocarbons). Your air is being pumped by a compressor that uses oil for lubrication, and gets its air from the normal air that we breath, and we all know there are contaminants in there. So, most compressors have some type of moisture separator to make the air dry, and then a filter stack to reduce the hydrocarbons in the gas. This air is normally tested and could be Grade E scuba air (normal scuba air that most of us breath). There are NOAA standards, and other agencies standards for hydrocarbons, moisture, and other contaminants (CO, CO2, etc...). These standards are readily available on the net. Modified Grade E air is what you want for an O2 cleaned and O2 service rated cylinder. Modified Grade E air goes thru another set of filters to further reduce contaminants. Most agencies (IANTD, specifically) advise to use Modified Grade E air for all nitrox mixing. If your LDS makes premix, it will be OK for an O2 clean cylinder because it should have been mixed using straight O2 and modified grade E air. So, it wont contaminate your cylinder. Now, if they partial pressure mix in your cylinder (adding a certain amount of O2 and topping off with air), you are good as well, because they should be using hyperfiltered (modified grade E) air. Membrane systems are a little different. I dont have alot of experience with these systems. This system may or may not be hyperfiltered air or clean for your cylinder. My advise is to listen to what the LDS is telling you. If they say that their air or nitrox is NOT O2 compatible, then dont get your cylinders filled there with O2 clean cylinders.
All of my cylinders are O2 cleaned, and as such only see Nitrox or hyperfiltered air.

There, hows that Kamala and Erin??? I hope that helps...