Every school building of more than one classroom shall have at least two widely separated exits and in no case shall the distance from the door of a classroom, laboratory, study hall, assembly room or auditorium be more than one hundred feet from the nearest exit. Every auditorium or assembly room shall have at least one exit from the stage and at least two independent exits from each floor and in no case shall one exit serve more than two hundred and fifty people. Every exit shall be easily accessible without obstruction to all the persons that it is intended to serve.