I worked with an NMR machine in college and would always have to empty my pockets before entering the room. I'm not sure I really understood the danger. I heard stories about people having piercings ripped out though.
Some system or another was running low on oxygen, someone panicked and grabbed a tank carelessly, next thing you know a tank is free where it shouldn't be.
Projectile injuries are one issue. Heating, induced current, hearing loss are others. FDA is investigating setting up a registry for safety problems to help reduce the frequency of accidents. http://www.auntminnie.com/index.aspx?sec=sup_n&sub=bai&#.... There are some shockers out there.
Metal detectors on doors etc. Stopping the guy with a pacemaker is important too.
And those, i think, are just from the fixed magnets (which may be a type of superconducmting electromagnet thats just normally on.). During a scan, dont mangetic fields go way way up? The fixed ones are just there for stability and whatnot.
They are superconducting magnets kept that way through cryogenic helium. They can lose their magnetism through a process called quenching. If you search on youtube for "MRI quench" there are several videos of people messing around with MRI's before they get decommissioned. Not exactly safe.
http://www.simplyphysics.com/flying_objects.html
I worked with an NMR machine in college and would always have to empty my pockets before entering the room. I'm not sure I really understood the danger. I heard stories about people having piercings ripped out though.