I have been through 3 different ALICE training classes. Barricades can be made out of desk, or whatever is in the room to wedge against the door. Just not a person.
I found all 3 had good points but they are conflicting with some info. One said have a place to gather... No thanks. One said leave lights on one said off. Both made good points depending on the situation. All my classes are for a factory/office setting. My new job has me as the first person you see walking in. I am not at my desk very often.
I wish I could carry at work.