I took out a can of Fix-a-flat, filled the tire, and drove to the nearest gas station to add air. I was able to drive home without losing pressure, and the next morning I went to the friendly folks at Firestone to get the flat fixed.
A few hours later the manager called me and said that the Fix-a-flat chemical messes up the rubber and a patch won't bond, so I had to replace a tire with just 4K miles on it.
On Monday of this week, I started driving to work, and the car sounded funny. I stopped, looked around, and saw that the new tire was flat. I drove two blocks back to my house, and rather than take a chance with the dreaded Fix-a-flat, I filled the tire from my compressor, and drove my wife's van to work.
The next morning, the formerly-flat tire still looked OK (except for the screw in the tread), and I drove back to Firestone for another flat fix. I was thrilled when the manager said they'd give me a break and fix it for free, since I was a good customer and only had the tire a few weeks.
A few hours later, the manager called. Of course, there was no problem from Fix-a-flat pollution this time; but I would still have to pay $116 for ANOTHER new tire because I had damaged the sidewalls when I drove a few blocks.
I am perfectly capable of changing a tire, but it's a PITA to do it in a dark airport garage or on a rainy day.
Just how far is it safe to drive on a flat? 200 feet? 20 feet? Or is the damage done by the time you realize that the tire is flat?

Were they BS-ing me about sidewall damage?