No building of any of the grades referred to in this act shall be used for human habitation unless it is equipped with a fire-escape or fire-escapes as required by law: Provided, That any building of such grades having less than four (4) stories, and used as a rooming-house or tenement, the third story of which shall contain not more than five (5) rooms and a bath-room, and such third story is not occupied by more than ten (10) persons, and has at least one stairway therefrom, shall be exempt from the provisions of the acts of Assembly requiring fire-towers and outside fire-escapes for such buildings, if every apartment above the second floor in any of said buildings shall be equipped with a satisfactory wire, chain, or other safe fire-escape.