That bag expanded because the pressure outside dropped, not because the pressure inside increased.(incidentally those bags are filled with Nitrogen to displace the Oxygen so the contents won't go stale
) At that altitude change the pressure dropped by a few psi and so the gas in the bag was allowed to expand and if taken higher it would have exploded but this would be due to the bag, unlike a tire, being unable to contain the few PSI difference and even at 50,000 ft it would not be enough to cause a tire to explode. To say that the pressure in an aircraft tire would double and result in explosion at altitude due to being inflated with air instead of Nitrogen is simply ridiculous. The difference in pressure change in a car tire using Nitrogen instead air because of heat build-up may very well be enough to make a difference in tread wear, I had not thought of that. I think it was about a year ago that someone asked about spraying paint with Nitrogen or CO2 because the location did not lend itself to using a compressor and now it has been asked again. There may be some legitimate reasons for the need for this and it does no harm to examine it since it seems anyway that it might be more practical than at first thought. If the cost could be held to less than $25 or so per job then in comparison to other costs it may not be too expensive, key word here being "if". Once the tanks are set up then refill would not be that costly and one would have zero problems with air line contamination and possibly even some other benefits (or maybe drawbacks?) that we have not covered yet.