N.Y.C. Admin. Code § 27-428: § 27-428 Ventilation.

Mechanical ventilation systems in moderate hazard plants shall be adequate to effect ten complete air changes per hour. Low hazard dry cleaning establishments shall be provided with mechanical ventilation adequate to effect four complete air changes per hour. Ventilating systems shall be arranged in such manner as to prevent solvent vapors from being admitted to the combustion area of any device requiring an open flame. Sufficient make-up air shall be introduced into all parts of the establishment to equal the air exhausted by the dry cleaning units, dryers, and exhaust ventilating system. Such air shall not contain any flammable vapors. Openings or stacks discharging solvent vapor-air mixtures to the outdoors shall be located in accordance with the provisions of subchapter thirteen of this chapter.