As I was going through my closet, a can of silly string dropped from one of the highest shelves. It hit the ledge of one of the other shelves quite hard before landing on the carpet. This can has standard warnings for aerosol cans written on it: "Don't store at 120 degrees plus", etc. My dad tested it out and it worked fine even after the drop. Is there any risk of this can exploding if it's used? If I put it back and don't touch it again for another few weeks, will there still be any risk?
As long as the can isn't exposed to high heat or flame, and isn't punctured, it's not going to explode.
Soda pop cans can explode after a hard impact. The reason is the carbonation, the carbon dioxide that is dissolved in the liquid. The agitation tries to release it back into the air, but the amount of air in the can is too small to hold that much extra gas. On rare occasions the can can pop open from this internal pressure, but I've never actually seen a documented instance of this happening. What usually happens is that when you open the can all the pressure suddenly has an escape valve. The extra gas, plus a whole bunch of the liquid, will shoot out of the opening with great force. I have seen this happen many times. It's often very funny, as long as it's happening to someone else and it's not your house or office that now has to be cleaned from floor to ceiling, and Murphy's law says that your cat will always be in the line of fire. People say "the can exploded," but that's not really what happened. Aerosol cans don't work the same way, they don't have carbon dioxide dissolved in a liquid. So dropping an aerosol can isn't going to have the same effect as a soda pop can.
The contents of the can are under great pressure, but even if the can's structural integrity fails (i.e. you put a hole in it by dropping it in your closet) it isn't going to "explode" with flames, etc. It could very well make some noise and scare you, but if the can didn't do this after you dropped it, it is highly doubtful that the can's structure will fail over the next few weeks. And as Fraggle Rocker mentioned, "shaking" the can has nothing to do with increasing the pressure, therefore letting it sit for a couple of weeks is meaningless.
