Magnet safety

I’ve got a couple of magnets that my son and I want to use for his science fair project. I don’t know their composition, but they’re about 100mm by 175mm by 20mm thick, the poles are on the faces, and they’re held in a cage so that the poles are aligned N-S-N-S. They’re out of a SEM and had to be used for beam bending, but they’re a lot bigger that any Wien filter I’ve seen. They can affect a monitor’s display from several feet away (it has taken twelve hours for my TV to nearly recover.) On the other hand, I was able to buy something by credit card shortly after carrying them near my wallet.

I’m starting to wonder how safe it would be to place these things in the middle of a school auditorium. Does anyone have enough experience with magnet safety to give a give a very rough estimate of their safety or to give some basic suggestions on safety tips. I am already planning to put up a warning for people with pacemakers; I assume that shielding is beyond my capabilities.

Also, I started to get a headache after playing with these things for an hour. It would take a hypochondriac to link the two events, right?

Wondermagnet.com has a brief FAQ that deals with magnet safety. They also have some links on their site that may prove useful.

http://www.wondermagnet.com/dev/faq.html#q20

Magnets cannot harm you in that way. In a previous job I ran Hall Effect experiments that required a rather large electromagnet. I guarantee this magnet was a thousand times stronger than the one you have and I sat within 2 feet of it while it was running for several hours every working day. No ill effects, no harm, nothing whatsoever. I did always leave my wallet in another room to prevent CC destruction though.

That was a fun job. I got to play with a “cold finger” that would chill a sample down to 12K. I also got to play with Mercury (the element, not the planet) and liquid Nitrogen. None of those things harmed me, but then I didn’t do anything stupid like drinking the Mercury or bathing in the liquid Nitrogen. :smiley:

Thanks folks. I thought that they would be ok.

Well, never underestimate the power of supermagnets to cause harm by pinching - some of the really, really powerful ones can trap a web of skin between them, resulting in a very nasty bruise…

Yup, been there Anthracite; I dismantled a hard drive for the magnets once; they were powerful enough that you could put one in your palm and another on the back of your hand and even at that separation, the pinching would be uncomfortable - I made the mistake of letting them pinch my fingertip and I ended up with a blood blister.

Another potential danger with powerful magnets is that they can shatter into sharp pieces as they snap together

Actually, the gap between the magnets when in the frame is just wide enough for a sledgehammer on edge. Also, the change in flux is apparently highest between the magnets. My son may title the (2nd grade) project “how I hit my dad with a sledgehammer, and why it was ok.”