A. Ventilation shall be so arranged by means of air locks, overcasts, or undercasts that the passage of haulage trips or persons along the entries will not cause interruption of the air current. Air locks shall be ventilated sufficiently to prevent accumulations of methane therein.

B. Air lock doors that are used in lieu of permanent stoppings or to control ventilation within an air course shall be (i) made of noncombustible material or coated on all accessible surfaces with flame-retardant material having a flame spread index of 25 or less as tested under ASTM E 162-187 and (ii) of sufficient strength to serve their intended purpose of maintaining separation and permitting travel between or within air courses or entries.

C. To provide easy access between the return, belt and intake escapeway entries, substantially constructed man-doors properly marked so as to be readily detected shall be installed in at least every fifth crosscut in the stopping lines separating such entries.

D. Doors shall be kept closed except when miners or equipment is passing through the doorways. Motor crews and other miners who open doors shall see that the doors are closed before leaving them.

E. Overcasts, undercasts, and regulators shall be well constructed of incombustible material, such as masonry, concrete, concrete blocks, or prefabricated metal. They shall (i) be of sufficient strength to withstand possible falls from the roof, (ii) be of ample area to pass the required quantity of air, and (iii) be kept clear of obstructions.

Code 1950, § 45-60.4; 1954, c. 191; 1966, c. 594, § 45.1-60; 1993, c. 442; 1994, c. 28; 1996, c. 774; 2005, c. 3.