Every hospital that has an MRI machine has stories about it. Those things use supraconducting magnets cooled by liquid helium, generating fields on the order of Teslas. This is unbelievably strong. I've heard they show instruction videos to the people that need to work with them where they get a pair of scissors to fly across the room and embed themselves in a wooden board. Walk into the room with keys in your pocket, and you'll have to rip your pants off to get out - shutting down the magnet is expensive and dangerous. The energy release when it stop superconducting is huge.

There's a little site dedicated to things flying into MRI machines: http://www.simplyphysics.com/flying_objects.html