Hey guys. Just got back from a shooting trip down in LA. At the Seattle end they did what they always do-- swab my boxes of sheet film and let me on through. On my return, however, I had a box of exposed film that the security people at LAX insisted on opening. They that said because the factory seal was broken, I could have a plastic knife in the box, and they couldn't let me through without either x-raying the box or opening it for visual inspection. Only after summoning the supervisor of the supervisor and getting into quite a shouting match, did they finally let me pass with my film.
I then asked the highest-up person what I should do in the future if I had to carry a box of exposed undeveloped film with me, and she said the best thing to do is bring a changing bag-- then they could open the box and feel the film manually in the dark and check if there's anything sharp in there. That made good sense as a last-resort measure, especially for airports that don't have the swabbing system.
Then, after our 20 minutes of intense argument about the possible contents of a thin flat cardboard film box that weighs about an ounce, just for kicks I showed them what they had let me pass through with inside my carry-on bag: My camera's monorail, which is a heavy tube of thick metal just a few inches shorter than a baseball bat. Seems to me it would be pretty easy to fashion a samurai sword that would fit inside that thing, but they were unphased.
In any event, carrying a changing bag seems to be a good safety measure for exposed sheet film-- I'll have one with me on my next trip.