Section 690-232 - Overcasts and undercasts(a) Arrangement of ventilation.--Ventilation shall be so arranged by means of air locks, overcasts or undercasts that the passage of trips or individuals along the entries will not cause interruptions of the air current. In face areas where it is impracticable to install air locks, single doors may be used with the permission of the department. An air lock shall be ventilated sufficiently to prevent accumulations of methane in it.(b) Doors.--(1) A door controlling ventilation shall be kept closed, except when men or equipment are passing through the doorway. Motor crews and other individuals who open a door shall see that the door is closed before leaving it.(2) It shall be unlawful for an individual to knowingly leave a door or a check-curtain open.(c) Hanging of doors.--A door controlling ventilation shall be hung in such a manner as to be self-closing.(d) Construction materials.--Overcasts and undercasts shall be constructed tightly of incombustible material, such as masonry, concrete, concrete blocks or fire-resistant prefabricated material of sufficient strength to withstand possible falls from the roof. Overcasts and undercasts shall be of ample area to pass the required quantity of air and shall be kept clear of obstructions.2008, July 7, P.L. 654, No. 55, §232, effective in 180 days [ 1/5/2009].