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I was watching a program about disaster preparedness, and it was suggested that the metal enclosure of a common shipping container (of the intermodal variety) would be sufficient to protect its contents from a large electromagnetic pulse (the kind that could affect an entire region or continent).

I have my doubts that this is true, as it seems like a misunderstanding of how electromagnetic pulses work—but I can't find any reliable resources on the subject.

What does physics have to say about this? Would a metal enclosure (such as a shipping container) protect its contents from the effects an electromagnetic pulse large enough to affect a large geographic region?

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Looks like a metal enclosure would be OK, provided its seams and joints are electromagnetically closed , see http://www.wbdg.org/ccb/FEDMIL/std188_125_1.pdf , however, I am not sure this requirement is satisfied in off-the-shelf containers, so some extra electromagnetic hardening of seams and joints may be required.

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this link is useful en.wikipedia.org/wiki/Farraday_cage – anna v Feb 19 '12 at 8:28
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There is a case to be aware of when thinking about a solid (as opposed to woven) Faraday cage: smooth, high-quality conductive surfaces will absorb the radiation, but they promptly to re-readiate the same signal. The conditions under which this is efficient are complicated; for some signals a box may suffice, for others it may not. I met the situation experimentally when a carefully fitted, smooth covering of aluminium foil barely reduced a signal at all, but replacing it with a ugly layer made of crumpled then re-opened foil got nearly two orders of magnitude. – dmckee♦ Feb 19 '12 at 18:45
@dmckee: I don't know. I would say conductive surfaces reflect, rather than absorb signals. In the case that you describe, I suspect the frequency was very low, and the foil thickness was very small, so the thickness was comparable or smaller than the skin-depth. A shipping container's panels are thick and corrugated. Another possibility in your example: the radiation penetrated through the seams/joints, and its frequency was close to a resonant frequency of the enclosure. – akhmeteli Feb 20 '12 at 0:05
It was sub-nanosecond scale pulses, and there were no seams in the original that were not also present in the working copy: the only difference was the roughened surface (same material, same construction; just no care taken to make it "neat"). I've talked to other people who have had similar experiences. The free charges in the conductor move under the influence of the field and that acceleration means they radiate. Work it your self. Your big advantages on the shipping container are that the surface is rough at the few cm scale, and that steal is only a pretty good conductor. – dmckee♦ Feb 20 '12 at 0:21
@dmckee: So maybe the second possibility was realized in your example: while the seams were the same for the smooth and crumpled foil, so the radiation penetrated inside to the same extent, but the properties of the resonator formed by the smooth and crumpled foil were very different. By the way, conductivity of aluminum and steel is of the same order of magnitude, as far as I know. – akhmeteli Feb 20 '12 at 0:34
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