Section 27-754. Minimum quantity of outside air for mechanical ventilation

The minimum quantity of outside air required for mechanical  ventilation
  in  any  occupiable  room,  where  not  otherwise  prescribed,  shall be
  determined according to table 12-2.
 
         Table 12-2 Required Minimum Outdoor Air Supply and Exhaust
                              (cfm per sq. ft.)
  ========================================================================
                 Ventilated Rooms    Ventilated Rooms
                   with Natural        without Natural
  Index for         Ventilation         Ventilation     Air Conditioned
  Ventilation        Openings            Openings            Rooms
  ------------------------------------------------------------------------
                 Supply    Exhaust   Supply  Exhaust    Supply   Exhaust
  ------------------------------------------------------------------------
     0- 300...     2.5      2.0        2.5     2.0        1.5     1.5
   301- 520...     2.0      1.5        2.0     1.5        1.2     1.2
   521- 850...     1.5      1.25       1.5     1.25       0.9     0.9
   851-1250...      ..      1.0        1.0     1.0        0.6     0.6
  1251-1650...      ..      0.67       0.67    0.67       0.5     0.5
  over 1650...      ..       ..        0.33    0.33       0.4     0.4
  ========================================================================
 
    (a) Window requirements. To be credited as ventilating openings  under
  the  provisions of this subchapter, windows or other openings shall meet
  the requirements of section 27-749 of article six  of  this  subchapter,
  and  where  mechanical  supply ventilation is not provided, shall have a
  free openable area of at least one square foot per  one  hundred  square
  feet of floor area.
    (b) Air conditioning.
    (1) In air conditioned rooms, the windows and other openings shall not
  be  credited  as  such  in  computing  the  index  for  ventilation. Air
  conditioned rooms shall be considered as interior rooms.
    (2) Air that has been exhausted from an air conditioned space  may  be
  reconditioned   by   air  conditioning  apparatus  and  recirculated  as
  equivalent outdoor air, provided that the total of  supply  air  is  not
  less  than required for air conditioned rooms by table 12-2 and that the
  amount of actual outdoor air is at least thirty-three and one-third  per
  cent  of  the  required  total. The actual outdoor air supply shall not,
  under any circumstances, be reduced to less than five cfm per  occupant,
  except  that these minimum requirements may be reduced by fifty per cent
  as provided in section 27-755 of this article.
    (c) Required exhaust. Required exhaust may be accomplished by  raising
  the  pressure within the space with consequent leakage through doors and
  windows, or by drawing the vitiated air from air conditioned spaces into
  the return air duct of air conditioning apparatus  or  into  an  exhaust
  duct discharging directly to the outdoor air.
    (d)  Make-up  air.  A  sufficient  quantity of air to make the exhaust
  system effective shall be provided to the space being exhausted  by  one
  or by any combination of the following methods:
    (1) By supplying air to the space by means of a blower system.
    (2)  By  infiltration  through  louvres, registers, or other permanent
  openings in walls, doors, or partitions, adjoining spaces where  air  is
  supplied by one of these methods.
    (3) By infiltration through cracks around window sash and doors.
    (4) By other methods acceptable to the commissioner.
    (e)  Prohibited  use  of  recirculated  air. Air drawn from any of the
  following spaces may not be recirculated; mortuary rooms;  bathrooms  or

  toilet  rooms; or any space where an objectionable quantity of flammable
  vapors, dust, odors, or noxious gases is present. Air drawn  from  rooms
  that  must  be  isolated to prevent the spread of infection shall not be
  recirculated, except that air drawn from hospital operating rooms may be
  recirculated, if in compliance with the following requirements:
    (1)  There  shall  be  a  minimum of twenty-five total air changes per
  hour, of which five air changes per hour shall be outdoor air.
    (2) All fans serving exhaust systems shall be located at the discharge
  end of the system.
    (3) Outdoor air intakes shall be located  at  least  twenty-five  feet
  from   exhaust   outlets   of  ventilation  systems  and  other  exhaust
  discharges,  combustion  equipment  stacks,  medical   surgical   vacuum
  systems,  and  plumbing  vent  stacks,  from  areas  which  may  collect
  vehicular exhaust such as off-street loading bays, and from areas  which
  may  collect  other  noxious  fumes.  The  bottom of outdoor air intakes
  serving central systems if installed above a roof, shall be  located  at
  least three feet above roof level.
    (4) Positive air pressure shall be maintained at all times in relation
  to adjacent areas.
    (5)  All  ventilation  or  air conditioning systems serving such rooms
  shall be equipped with a filter bed of twenty-five per  cent  efficiency
  upstream  of  the  air conditioning equipment and a filter bed of ninety
  per cent efficiency downstream of  the  supply  fan,  any  recirculating
  spray  water  systems  and  water reservoir type humidifiers. All filter
  efficiencies shall be average atmospheric dust spot efficiencies  tested
  in accordance with ASHRAE standard 52-68.
    (6) A manometer shall be installed across each filter bed.
    (7) Duct linings shall not be used in ventilation and air conditioning
  systems  serving  such  rooms unless terminal filters of at least ninety
  per cent efficiency are installed downstream of linings.
    (8) Air supplied shall be delivered at or near the  ceilings  and  all
  exhaust air shall be removed near floor level, with at least two exhaust
  outlets not less than three inches above the floor.
    (f)  Outdoor  air  intakes.  For  high-rise  office  buildings erected
  pursuant to new building applications filed on or  after  the  effective
  date  of  this  section,  outdoor  air  intakes serving spaces above the
  second story and serving spaces greater than ten thousand square feet of
  floor area shall be located at least twenty feet above ground level,  at
  least  twenty feet from exhaust outlets of ventilation systems and other
  exhaust discharges, and at least twenty feet from areas that may collect
  vehicular exhaust such as off-street loading bays.