Actually, if you read the directions on most fix-a-flat cans, it specifically tells you to drive it somewhere where you can air it up, bleed the gas from the can out of the tire, then fill it back up with air. The reason for this is not only to get the flammable propellant out of the tire, but also because the slimy stuff that fixes the hole in your tire stays liquid until it hits air.
That's really the reason why tire guys hate people that use that stuff.....cuz most of them don't follow directions, meaning the tire guy has to not only deal with a tire full of flammable gas, but also full of slimy liquid fix-it material, which only starts to harden AFTER they've broken the bead on the tire and started dripping that crap all over EVERYTHING. :roll: