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Machinery rooms shall be mechanically ventilated to the outdoors. Mechanical ventilation shall be capable of exhausting the minimum quantity of air both at the normal and emergency conditions. Multiple fans or multi-speed fans shall be allowed in order to produce the emergency ventilation rate and to obtain a reduced airflow for normal ventilation. Location of the openings shall be based on the relative density of the refrigerant to air. The free-aperture cross section for the ventilation of the machinery room shall be not less than:
where:
F = The free opening area in square feet (m
2
).
G = The mass of refrigerant in pounds (kg) in the largest system, any part of which is located in the machinery room.
Exception: Where a refrigerating system is located outdoors more than 20 feet (6069 mm) from any building and is enclosed by a penthouse, lean-to or other open structure, natural or mechanical ventilation shall be provided. Location of the openings shall be based on the relative density of the refrigerant to air.