LDS Filling Nitrox - Partial Pressure Blending

[Puffer Fish]

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

I don't put anything in my tanks except NITROX (whether banked or partial blended), but as a diver using different locations to get tanks filled, I am still at the mercy of each locations.

Clearly, from a shop perspective, every tank coming in has to be a bit suspect, as the chain of custidy is long been broken. (it left the shop, it came back.. that is all that is known).

I have always wondered about having a fill log for tanks, and if that would be of any benefit.. you have any thoughts on that?

 

[UaVaj]

Given my Key West example. Simply because a tank has a current O2 cleaned sticker plus a current VIP sticker does not mean that such tank is STILL in O2 cleaned condition. I could just imagine how many people are bring in tanks that WAS O2 cleaned in the past but is CURRENTLY contaminated for whatever reason.

How does a partical pressure shop determine if they want to fill it or not. If it safe or not? Is the risk worth the $10 charge per tank? I know these shop are filing these possible contaminated tank day in day out and obviously the $10 charge is not worth the risk of accidentally blowing up their struggling business.

Given that said - It be very possible that this "O2 cleaned" is taken way out of proportion.