Totally off the usual topics I thought I would post about Magnetic Resonance Imaging safety, prompted by a web site I came across.
If anyone has ever had an MRI, you are always told to remove all metal objects before you go into the imaging room where the machine is. Now we have all played with magnets and picked up paperclips, but I don't think many people realize how strong magnets can be.
I remember in our physics lab at college we had two industrial horseshoe magnets that were each about half the size of a shoebox. You had to be very careful when putting them together that your fingers did not get in between them, because they were very strong and were very difficult to get apart.
An MRI machine has an even more powerful magnet. I learned this first hand when I had an MRI done last year. They had me remove all metal objects, and I did ... except that I forgot to remove my belt which had a metal buckle on it. The technician also failed to notice it. Anyway, they prep me then she pushes me into the machine, which was one of those tight ones that claustrophobic people have touble with (thankfully I am not very claustrophobic). As she was pushing me in, I thought the opening was too small and my belt buckle had hooked onto the outside of the opening, but then I realized the pulling was in the opposite direction. By the time I had been pushed all the way in, my belt buckle was now hovering about 2 inches above my waist (I could put my hand between the buckle and my stomach). Obviously the belt kept the buckle from flying up to the magnet, but it made me realize how powerful those magnets are. Which is why MRI technitians have to be very vigilant about metal in the room for safety purposes.
Which brings us to a site which has a few pictures of when people weren't that vigilant in the imaging rooms.
Danger! Flying Objects! (MRI Physics and Safety)
If that doesn't convince you, see how difficult it is for these techs to get a light weight office chair from out of the magnetic field.
or how slowly a chunk of metal falls in the field.