John, I think maybe I can explain it this way, stand by, I might get on a roll. Even though Argon is heavier, Graham's Law comes into play, it talks about the way gases act when together. Think about liquids such as gasoline and water, the gas floats on top and blankets the water. Gases don't behave like that. The molecules pass each other because they are spread out. Like having 6 people in a room and having 6 more enter the same room, the original 6 aren't forced to leave. (Unless they are chewing on garlic). They occupy the same space. Even though you add an inert gas, there will still be oxygen present unless you flood the area with lots and lots of gas. Gases don't stratify quite like liquids. I know that is no where near a scientific explanation and the scientists (Mike) will have a fit. I agree, short term protection. As a side note. I have seen co2 used in flex tanks. Since it is absorbed, you have to open the tanks to top off with more gas since it partially collapses the tank, by creating sort of a vacuum. Nitrogen is cheaper than Argon by the way and serves the same purpose.