CFR /  Title 30  /  Part 57  /  Sec. 57.8531 Construction and maintenance of ventilation doors.

Ventilation doors shall be--

(a) Substantially constructed;

(b) Covered with fire-retardant material, if constructed of wood;

(c) Maintained in good condition;

(d) Self-closing, if manually operated; and

(e) Equipped with audible or visual warning devices, if mechanically operated.