In the radioactive parts of the US DOE lab that I used to work at, it smells a lot like a machine that cuts plastic. Sort of that smell in a machine shop when someone is cutting plexiglass. Mix in laser printer, or maybe one of those really old copiers also, but a lot stronger. Thanks to neil for helping me place that part of the smell. There is also something else, something bad, but I can't relate it to anything else in the world. It is a bit like spent model rocket engines, but different.