I was watching an interview on Fox earlier this evening where the guy being interviewed said it was broadcast to the occupants that there was no need to worry, nothing was wrong, this tower is OK the only problem is with the other tower, stay in your offices, etc. No evacuation, no alarms, no nothing. It wasn't until the second airplane hit and rocked the building that they realized thngs were very bad and took off.

At least according to this interview.

Also heard interviews about the progress down the stairwells. Seems it was rather orderly (no panic, no pushing, etc.)