I was wondering if it was safe to have your CPU running at 100%. Whenever i try a blender game or animation outside of blender, My processor jumps to 100% and the fan starts spinning madly. If i keep it going after it hits 100, will i fry it?
As long as the temp stays reasonable it’ll be fine. I have long render times (5+ hours) quite frequently where the cpu runs at 100%. Haven’t had any problems in 5 years.
Only thing you need to worry about is the temperature of the CPU. The temperature will be higher when your processor is at 100% than when it’s idle. But as long as your CPU cooler works there’s nothing to worry about(unless you like overclocking).
I rendered an animation a year ago that took 48+ hours and had no problems(except that I had messed up with some materials making the renders useless to me afterwards). 
You should be worried when the cooler stays still.
If it is at 100% it means it is at its full capacity, in other words, it is doing what it is expected to do.
I used to run dnetc clients for years on end 24/7. No problem, as long as your cooling works.
/Nathan
anyway, if u have a intel processor, the worst thing can happen is a cpu hang.