It’s not an unreasonable idea, and HSE guidance does recommend this in larger premises. The practice makes individuals think about different scenarios and puts a bit more thought into the process of evacuating; rather than just following your work colleagues out of the building the way you came in earlier in the day!

I would suggest though that you have undertaken at least one drill will all exits being available before you try this. The best way is to just put a little note up or stand someone at the exit turning people away. (Don’t lock the exit of block with furniture this is dangerous and sets a bad example.)