There are 17 floors. As a survivor, you can go down one or two floor without dying, then you have to wait for your health to get back up before jumping down again. Else you break your legs.
The survivors on the top floor can pick any weapon they want from The Platform, but the survivors from the lower levels can only choose among the weapons that have been left by those above... if any.
Psycopaths (the infected) climb up from below for the first 30 seconds, and come from above after that. If you get killed by a psycopath, you become one. They can jump up and down each level without taking damage, unlike the human survivors.
Survivors can go down safely with with platform.