Construction of protective enclosures for pumping equipment shall be of noncombustible materials throughout and, adequate ventilation shall be provided for such enclosures to prevent the accumulation of flammable vapors in hazardous concentrations. Design of ventilation systems shall take into account the relatively high specific gravity of the vapors. Ventilation may be provided by adequate openings in outside walls at floor level, unobstructed except by louvers or coarse screens. When natural ventilation is impracticable, mechanical ventilation shall be provided. Mechanical systems for removing flammable vapors shall be designed, installed, and operated in accordance with approved standards.
34 Pa. Code § 14a.103