Most structural damage from safes is not caused by the weight suddenly ripping through the floor, but rather the floor sagging over time from the weight of the safe.
I have seen stairways collapse under the weight of a safe, and broken floor joists, but in 15 years, have never seen a safe fall through a floor (except during fire).
If you can jump up and down on your floor without falling through, 500 pounds will not be a problem. I always suggest placing the safe along an exterior wall or interior load bearing wall. This will help eliminate sagging issues. I also suggest that you max out the weight in a residential setting at 1,100 pounds. Anything over 1,100 pounds, and you should seriously consider additional support for the safe.
With all of this said, if you are unsure of anything, you should seek the advice of a local engineer.