Super-strong magnets... deadly?

The season finale of Lost got me wondering… would a sufficiently strong electromagnet kill someone? how?


Static fields have no discernable effect on humans.

However, there are effects from varying fields.

An MRI machine that you’d find in a hospital is about 1.5T, and they’re huge. I wouldn’t like to imagine how big, and how much power would be drawn by a 5T electromagnet.

Well theres transcranial magnetic stimulation, an experimental technique currently being researched where an electromagnet is put on the head to change brain activity.

“Side Effects: To date, the most serious side effect of TMS has been the induction of grand mal seizures in seven subjects. Five of the seizures occurred prior to the introduction of safety guidelines in 1993. These guidelines subsequently were revised in 1996. Other reported side effects include headache. In addition, 3 percent of patients reported a nonspecific sense of discomfort experienced during treatment that usually resolved after the first few treatment sessions.”

So it can apparently induce seizures in at least some people, I dont know how strong it needs to be though, or what more can be induced if the effect is even stronger.


A 3.0T MRI machine’s not hugely larger than a 1.5T MRI. Looks to be a foot or so wider, but that’s it.
(PDFs showing typical MRI suite construction)

Power draw’s not hideous either- the 3.0T needs about 100 amps of 480-volt 3-phase power. Surprisingly, the power supply specs for the 1.5T are essentially the same, despite half the field strength. This doesn’t mean that a hypothetical 5.0T MRI would also only draw 100 amps, but just is menat to show that power draw is not as tightly linked to the field strength as one might have guessed…
For the technologically-impaired, the links are all PDFs from General Electric, one of the prime makers of medical MRI systems.

I think we’re looking at getting a 9T for animal studies. So 1.5T really isn’t that crazy (although it is still immensely powerful when compared to normally encountered magnetic fields).

All right, I’ll ask the naive and stupid question: Aren’t there trace amounts of iron in our blood? Wouldn’t a sufficiently strong magnetic field eventually start doing funny things to them?

According to this, it looks like a magnetic field of around 10T is enough to allow you to levitate a frog. Not sure what the status of the frog was afterwards though.

Not really. At least not until the magnetic fields are strong enough to do funny things to the rest of your body.
All atoms are slightly magnetic; it’s just that in most materials the atoms are pointing in all different directions so the small magnetic forces just cancel each other out.
The reason chunks of iron are magnetic is because in the metallic state, atoms are free to turn and line up with each other (and they do, when you get a magnetic field going). Since now all the tiny forces are in the same direction, they add up and you end up with a force large enough to notice.
Iron in our blood is mostly individual atoms, held in hemoglobin, so they have no neighbors to line up with. That means no noticeable magnetic effect greater than any other material.

It might reset your moral compass?
A strong electromagnet can have lethal side effects.
Warnings are posted around or at access points to the areas around the magnet to keep magnetic objects/material ouside the area.
An oxygen bottle can be drawn into the magnet with great accelleration and resultant force.

The Nevians deployed a magnet powerful enough to suck the iron right out of hemoglobin in EE Doc Smith’s Triplanetary. But in real life, ferromagnetism is a property of bulk materials. Single iron atoms bound to proteins are not strongly affected by magnetic fields.

I’m regularly around a 12T magnet, and haven’t experienced any ill-effects. The major precaution we take is making sure that signs are posted warning of effects on pacemakers and ferromagnetic bulk objects.

I assume you’re referring to an MRI’s magnet.

You’re right about the side effects - they’re of the blunt trauma variety. All sorts of things have been carelessly or absent-mindedly brought into MRI suites and sucked into the bore. If a person is in the bore or simply between the object and the bore, they’ll be clobbered.

In that regard, super-strong magnets can be quite deadly. This page has some photos of things sucked in, as well as an account of a fire fighter that was sucked into the bore via his air tank and folded in half. One of the more notorious fatalities was a young boy that was killed by a flying oxygen tank.

There’s been at least one MRI-caused shooting as well. This one was lucky that the bullet didn’t hit anything other than a wall.

I have a question regarding this sort of thing, I keep meaning to ask at work but never get round to it because my contact with radiographers is quite limited.

I have probably 75-150 surgical staples (which I presume are stainless steel) inside my abdomen, if I were to get into close proximity to an MRI machine, would they be affected (i.e. ripped out of me)?

Or would it be reasonably safe for me to have a scan?

I don’t believe that stainless steel is subject to magnetic fields. Possibly something to do with the chrome not allowing the iron to line up correctly. But that’s just a guess.

It’s not just the magnets in MRIs that can be dangerous. Regular rare earth magnets, especially larger ones (anything above a couple of inches), have to be handled very carefully if you don’t want to get hurt.

Check out the pictures on this page.

I have a bunch of smaller rare earth magnets (none over an inch) and even they can give the skin a nasty pinch if they come together quickly when the user isn’t exercising caution.

There are many different alloys of stainless steel, of course, but I’ve never encountered a stainless steel object which did not stick to a magnet. Not as strongly as other forms of iron, perhaps, but with multi-Tesla fields, you wouldn’t need much. Then again, they might also be titanium or some other material.

Even metals without iron are affected by a very powerful magnetic field. A close friend of mine was told he could not get an MRI, because he has a mechanical valve in his heart.

My brother works on MRIs for several clinics. He says if you stand an aluminum sign inside the magnet, it will very slowly fall down.

Well, everything is magnetic to some degree, but most things a lot less so than iron, and some things are actually repelled by a magnet.

This isn’t because the aluminum is magnetic, though, but because it’s conductive. When a conductor has a magnetic flux going through it, it tries to keep the same amount of magnetic flux. A fallen-down piece of aluminum would have a different amount of flux through it than an upright piece of aluminum, so there’s a force on the aluminum acting to try to prevent it from falling. You can do a similar demonstration dropping a strong magnet through a length of copper pipe: The magnet will fall, but only very slowly (with the setup we have for class demonstrations, the magnet takes about 20 seconds to fall through a meter-long pipe).

Read this short news clip.