Entry Hallway - Hospital 4F (Resident Evil 3: Nemesis)

On every play-through the game, there will be an encounter with zombies when the elevator stops on one of the three accessible floors of the hospital, thus making it a 33% chance that you will encounter zombies on this floor.

Appear after acquiring the Vaccine Base from Room 402, but only if you did not encounter Zombies when exiting the elevator on this floor, and you have already acquired the Vaccine Medium from the basement.