Aviator oxygen...thanks for the info. Talked to my supplier yesterday and asked what type of oxygen he was selling me. He said 'its just the plain stuff'. Time for a change.
It's classified in the US as Grade E. Aviator Oxygen (min 99.6% purity) is a nick name.
It's the gas required by high flyers and ultra deep divers. It's importance is in having been "dried" before going into a cylinder, so that ice can't form in line or inside the regulator at high altitude. The drying and the sterilant value of Oxygen renders it perfectly aseptic, which is what we want for brewing.
There's a lot of myth about what grade of O2 is "best" for brewing. For decades in the United States (and I believe UK countries, too), there has not been a real "industrial" or welding grade because the need for a higher standard has made that an obsolete issue. All oxygen is USP listed (meaning its listed as a drug licensed for use in the US), making is "safe" for human consumption.
Respiratory and Medical grade O2 get a tank purge before refilling to prevent blended gasses. They don't get a drying process, so can freeze regulators and lines in high flow circumstances. The only meaningful difference between the two is that many states require a prescription for "Medical" grade. There is no special filtration or treatment applied when filling the tank.
Believe it or not, Grade A Oxygen has the loosest standards. It's most often sold as welding Oxygen. Purity is rated at 99% (aviator is 99.6%) It can have as much as 10ppm CO and 300 ppm CO2 (aviator requires <2 ppm).