Schools -- always ask the main office if you need to take pictures inside a school. Usually if your press with a real press badge and have a story to cover no big deal, but otheriwse its as bad as a hospital and the military base combined. The exception is sporting events where you should be allowed to take pictures with your camera
Fires-Rescues -- Never ask anyone in charge if you because they will tell you no. no matter what. But, if your there stay back out of the way behind the yellow tape or parked fire trucks and take whatever you like and you usually can get away with it depending on what is going on. Sometimes if their is a dead person,body lied out etc they will ask you to leave, but most of the time they will give you a funny look and move on. Never!!!! get in the way. As soon as you get in the way or cross the yellow tape you will be escoted away by police. Keep your distance is the best policy and then zoom in (use a 200 - 300mm range lens on the long end).
Airports: Some airports allow you to take pictures inside and we have all seen pictures of the neon colored walkway at Chicago's airport etc. and some will not. In Atlanta I have been able to photograph out the window looking at the runway, taxiway etc without any issues while waiting for a dealyed flight. But at Dullues TSA was asking people left and right to pack up their camera (even little point and shoot things).