LDS Filling Nitrox - Partial Pressure Blending

[Jimmer]

If cracking the valve quickly before attaching the fill whip to blow off water/dust/debris is pretty effective - qualifies as being O2 cleaned for this section/path of the overall filling system?

What gives? O2 cleaned is more of a gimmick than reality. I am sure I am wrong so hopefully someone will chime in on the real reason.

OK, we're not talking about a valve face smeared in motor oil after it's been through 5000 miles in an old beatup chevy half ton. We're talking about a little bit of dust or debris. If the valve face truly got dirty, then yes the shop would clean the face and maybe put a new O-ring in. O2 clean isn't a mystical magical bit of rocket science. We're not dealing with lab coats and masks and vacuum chambers. O2 clean really comes down to common sense. Things don't blow up automatically just because a piece of dirt got on them and then O2 hit them. I've talked to the guys at Praxair, who have told me about welding O2 tanks being opened up for a vis, and finding rust and even a lil bit of oil in the bottom, and they had been used and refilled multiple times. They also told me that when they refill industrial O2 bottles, they don't slow fill them like we do, they slam them fill as quick as they can to keep up to demand.

O2 clean for diving is just common sense. Clean your gear, use the right lube, and handle the O2 carefully. I know guys that don't use Viton rings, and their gear doesn't explode. I know guys that haven't even O2 cleaned their deco regs, and they didn't explode (I personally don't advise that). There is no magic formula to know what is going to cause an ignition. Use clean parts, christo-lube, slow fills, and chances are very very good that you'll be just fine. Just because a spec of dirt got on a valve, doesn't mean you need to tear the tank and valve apart and reclean it all.

Go buy a copy of the Oxygen Hacker's Companion, and read it through. Honestly, you seem to be trying to find things to be afraid of with regards to oxygen handling. Afraid of oxygen isn't necesarry, respectful of oxygen is.

 

[do it easy]

In essense, the rules are there to keep you safe, but they are drawn through thick gray fog. Think of it like the speed limit- if you go over 55/65/75/80 (whatever your particular speed limit is), you aren't going to immediately get into a wreck or get a ticket. However, as you go faster and faster, your chances of a getting a ticket or ending up as twisted metal get higher and higher.

As far as keeping valves clean, my tanks usually have a DIN plug or a regulator in them to keep the dust out. And when the reg is on the tank, the dust cap to the reg is on the DIN plug. Do I need to be this obsessive? No, but it helps me sleep at night.

 

[UaVaj]

We're talking about a little bit of dust or debris. If the valve face truly got dirty, then yes the shop would clean the face and maybe put a new O-ring in. O2 clean isn't a mystical magical bit of rocket science. We're not dealing with lab coats and masks and vacuum chambers.

We are getting a little side track from the original topic. One more post please. Just to pick you brains a little more. Don't take it the wrong way. It meant this in a good way. This is very educating.



To get to the point.

As sensitive as my LDS make O2 sounds. If there is something visually wrong. A wipe or quick open of the valve is obviously insufficent as being 100% O2 cleaned.

My LDS said that if I take my nitrox tanks to the Florida Keys and use it there. Refill it there once. I will have to pay $50 for each tank to be O2 cleaned, $35 for each valve to be O2 cleaned, and $15 for a new VIP before the will refill my tank with nitrox.

That the filling stations in the Keys are suppose to be no good and will introduce contaminants. Are diver dying in the Keys (1) dying due to bad air or (2) LDS blowing up due to nitrox tank refilling?

Here is a twist. How about I do visit the Keys. Refilled my tanks in the Keys. Come back in town. Take it to my LDS for a refill and say no mention of the Keys. Leave for a short lunch. Is my LDS gonna blow up when I come back to pickup my tanks?

 

[Puffer Fish]

Pure oxygen is also flammable, which is another consideration.

PPB is also cheaper to get started, where as a membrane system costs more.

And we were doing so well here.. Oxygen is not flammable.. it is an "Oxidizing agent", meaning it needs a fuel to burn with.

 

[Puffer Fish]

If cracking the valve quickly before attaching the fill whip to blow off water/dust/debris is pretty effective - qualifies as being O2 cleaned for this section/path of the overall filling system?

What gives? O2 cleaned is more of a gimmick than reality. I am sure I am wrong so hopefully someone will chime in on the real reason.

You have to reach the minimum amount of combustion material, plus have the right O2 and usually some heat. Normally the amount of material that might be in the gas stream from the valve area is not enough...as only a small amount would ever get in the air stream.

Blowing out, and looking for any excess is normally good enough.

 

[Jimmer]

We are getting a little side track from the original topic. One more post please. Just to pick you brains a little more. Don't take it the wrong way. It meant this in a good way. This is very educating.



To get to the point.

As sensitive as my LDS make O2 sounds. If there is something visually wrong. A wipe or quick open of the valve is obviously insufficent as being 100% O2 cleaned.

My LDS said that if I take my nitrox tanks to the Florida Keys and use it there. Refill it there once. I will have to pay $50 for each tank to be O2 cleaned, $35 for each valve to be O2 cleaned, and $15 for a new VIP before the will refill my tank with nitrox.

That the filling stations in the Keys are suppose to be no good and will introduce contaminants. Are diver dying in the Keys (1) dying due to bad air or (2) LDS blowing up due to nitrox tank refilling?

Here is a twist. How about I do visit the Keys. Refilled my tanks in the Keys. Come back in town. Take it to my LDS for a refill and say no mention of the Keys. Leave for a short lunch. Is my LDS gonna blow up when I come back to pickup my tanks?

Asking questions is how we learn, so go ahead and ask. A quick visual look at the valve face is all we really need to do. The chance of something on the valve face being a big enough contaminant to cause a problem is very slim. If something on the face were that big of a problem, you'd probably see it. Such as a big grease mark or something similar. Playing it by ear as far as that goes is how I would play it. If it's just a little dirt, then I'd wipe it off with a clean rag, blow a little air out of the valve to blow everything out and away you go. If it were grease and was "in" the face of the valve, then yeah maybe I'd take the valve out and clean it properly. I'm the same as Do it Easy, I always have valve plugs or a regulator in my DIN valves.

The Florida Key's question. Yes it is possible that if you get air fills from a questionable source that doesn't use O2 clean air, it wouldn't be a terrible idea to have them at least vis'd before putting O2 in the tanks. Some people may not agree with my next statement but here it is. The engineer is me sees non-O2 clean air this way. I wouldn't want to put non "O2 clean" air on top of pure O2 in a tank, but if I had non O2 clean air in my tank, and it was properly filtered and was good enough to breathe, then I have a hard time thinking it would actually contaminate the metal walls of my cylinder. My reaction would be to drain the tank, have it vis'd and if there was no visual indication of contamination, or no evident smell, I'd put the valve back in and partial pressure blend some Nitrox.

The question of death. If the air in a tank is bad, chances are you'll get a headache, might be a good idea to go on the boat's DAN O2 kit after the dive, and get your tank cleaned. To actually die from bad air, you would need a fair bit of CO or CO2 in the tank to cause that. Is it possible? Yeah probably, but I personally haven't read of any accounts like that, if anyone has, please mention them. I think very few LDS' have blown up from filling Nitrox. Again I'm sure it's possible, and probably has happened very few times, but trust me, shops blowing up while filling Nitrox just simply isn't a regular occurance. Now as for your LDS blowing up when you drop off your tanks that were in the keys. If they fill them with air, no. If they fill them with pre-blended Nitrox, no. If they partial pressure blend, well they would likely be emptying the cylinder first to add the O2, removing the non-O2 clean air. As I mentioned before, I would personally at least want to spin out the valve and have a look and smell before putting O2 in a tank that has unknown fill history. The odds of your LDS blowing up because you got a fill from a non-O2 clean source is very remote, provided that the air was at least properly filtered and was clean enough to breathe, since you would be removing that air before adding O2.

I do wholeheartedly support any LDS that reserves the right to at least demand a vis before partial pressure blending in a tank of unknown fill history. I know the LDS that I work for vis' every single rental tank that gets filled somewhere other than their shop.

 

[Hoyden]

If you want a good look at this topic, I'd recommend The Oxyge Hacker's Guide by Vance Harlow.

 

[bdshort]

I'll throw in another recommendation for The Oxygen Hackers Companion. I just received my copy a few days ago... I'm not that far along in it yet, but it's an excellent primer for someone who is interested in blending, which it seems like you are. My dive buddy PP blends his own nitrox mixes using a leased O2 tank, and topping off at the fire station. I'm considering doing this myself, but I'm wondering about storage for O2 tanks... is it unwise to store something like an O2 K cylinder inside an apartment?

 

[Puffer Fish]

I'll throw in another recommendation for The Oxygen Hackers Companion. I just received my copy a few days ago... I'm not that far along in it yet, but it's an excellent primer for someone who is interested in blending, which it seems like you are. My dive buddy PP blends his own nitrox mixes using a leased O2 tank, and topping off at the fire station. I'm considering doing this myself, but I'm wondering about storage for O2 tanks... is it unwise to store something like an O2 K cylinder inside an apartment?

Having an O2 tank in your apartment is much, much safer than having any flammable gas. What could it do... leak out and raise you O2 level a small amount? Ok, if it is a big tank, and a small apartment, and you turned it open to drain... that would not be a good idea, as there are lots of potential heat sources.

Other than than... don't know of any issue.

There are lots, and lots of O2 tanks already in apartments and homes. I have one for a torch.

 

[PhilEllis]

......I would personally at least want to spin out the valve and have a look and smell before putting O2 in a tank that has unknown fill history......

My store inspects approximately 400 nitrox cylinders a year. We use all of the proper equipment, lights, and everything else available to dive stores to improve the quality of our inspections. We know of no way to visually inspect for the presence of the small level of hydrocarbons (parts per million) necessary to cause a problem with partial pressure filling, short of some sort of test like a millipore resolved weight test. Obvisiously, this sort of test is not available to a dive store. The only proper defense availalbe to dive store and divers is proper and frequent cleaning to remove hydrocarbons.

In my opinion, it is extremely dangerous to engage in any conversation or practice that minimizes the importance of proper and frequent cleaning of cylinders intended for oxygen service in scuba diving. Proper cleaning is necessary becasue we lack an adequate method of testing. Frequent cleaning is required because the repeated act of filling a cylinder exposes it to the potential of hydrocarbon build-up from the trace amount of hydrocarbons present in even clean gases. The fact that people with cavalier attitudes toward oxygen cleaning continue to survive and prosper is NOT evidence that proves their practices safe. It is luck and the law of large numbers and probability. A search on the other board will yield evidence of about three or four accidents JUST IN THE PAST COUPLE OF YEARS involving oxygen fires in scuba bottles. None were fatal, but one in particular caused quite a bit of damage to the divers hand. Even more cases of "soot" or other evidence of potential fires are noticed on valve seats during routine inspection. Luckily, these "events" did not cause explosion or fire.

The duration of a fire in an oxygen-rich cylinder is typically very short (parts of seconds). If there is enough fuel (hydrocarbons) in the cylinder to allow the fire to burn longer (a few seconds), eventually the valve, its components, and the cylinder itself become part of the fuel source.

Don't play around with this stuff. I agree with others......handled safely, oxygen is safe. The dispute is exactly what does "safely" mean.

Phil Ellis