I would divide up such areas into two groups - places where the environment makes it a bad idea, and places where your status makes it a bad idea.
1) Environment includes areas with high magnetic fields:
As was mentioned by chieftain in post 22,
Magnetic Resonance Imagers (MRIs) are a bad idea. Here's the article about the incident:
http://www.ajronline.org/cgi/content/full/178/5/1092 "Spontaneous Discharge of a Firearm in an MR Imaging Environment". Also, other areas with high magnetic fields (though these are generally only found in research labs) are NMR spectrometers and any sort of particle accelerator.
High temperature environments (fire-fighters) could cause a cook off (I know that it would be a temperature beyond what a person could survive, but ifyou passed on, a cook off could endanger your colleagues).
2) For your own status:
I would also say anyplace where you could not control the weapon (and this will vary by person). It will include any time anesthesia is used, and might include other situations where awareness and ability are impaired (for example, getting your eyes dilated at the ophthalmologist's). Participation in sports where grappling, tumbling, and falling would be another class. Activities like roller-coasters and bungee-jumping might be included if your firearms lacks a firing-pin safety, or other device to prevent an inertial discharge.
