What is a gas I can use that has no side effects?

Question

I need it for a story. It needs to nock out about sixty gaurds for about 3 hours. They need to be questioned straight after they wake up so they can't be to sleepy. and they must be able to be transported in a truck without waking up.

Answer 1

How about Xenon?  Not a conventional general anaesthetic, as it is rather expensive to produce, but is effective, and is kinder to the environment than nitrous oxide.  

http://en.wikipedia.org/wiki/Xenon#Anest...