D.C. Mun. Regs. tit. 25, r. 25-B1811
Heating, ventilating, and air conditioning systems shall be designed and installed so that make-up air intake and exhaust vents do not cause contamination of food, food-contact surfaces, food packaging materials, equipment, or utensils.
Adequate ventilation or control equipment shall be provided to minimize odors and vapors, including steam and noxious fumes, in areas where they may contaminate food; and fans and other air blowing equipment shall be located and operated in a manner that minimizes the potential for contaminating food, utensils, equipment, food-packaging materials, and food-contact surfaces.
Intake and exhaust air ducts shall be cleaned and filters changed so they are not a source of contamination by dust, dirt, and other materials.
Ventilation systems may not create a public health hazard or nuisance or unlawful discharge, if vented to the outside.
D.C. Mun. Regs. tit. 25, r. 25-B1811