Why is Nitrox so expensive (and so hard to get)?

[Peter69_56]

Given the paranoia about filling a potentially contaminated tank with pure O2 under pressure, I'm not sure where the requirement to purge tanks before filling comes from.

Not sure what your point is here? I suspect the reason they evacuate the Medical/aircraft cylinders before filling is simply a documented and trackable trail to demonstrate that the cylinder (by their procedures) only contains oxygen at their specified purity. Evacuating ensures that there is no residual gas of any sort, prior to the fill.

In the case of standard industrial gas, they usually just refill and don't evacuate as the requirement to have traceability is not there. I assume if you have delicate welding work you ask for a different industrial oxygen? or perhaps aircraft grade??? The risk with standard industrial oxygen is the potential to have LPG or acetylene contamination in the oxygen cylinder due to faulty non return valves and back pressure from the acetylene cylinder to the oxygen cylinder.

---------- Post added April 7th, 2015 at 02:01 PM ----------

I monitor the CO all the time. So far have never seen it over 0.0 except when testing.

I don't believe tanked O2 is cheaper than a membrane system after you have bought the membrane system. Two shops I bought from in Mexico charged an extra $1.50 for 32% over air. That is less than my cost of welding oxygen in 32%.

I suspect the LDS are using Nx as another form of revenue and using the mystery of Nx as a way of charging a little more than perhaps they should, given the pricing you are being charged in Mexico?