909.6 Pressurization Method

The primary mechanical means of controlling smoke shall be by pressure differences across smoke barriers. Maintenance of a tenable environment is not required in the smoke control zone of fire origin.

The minimum pressure difference across a smoke barrier shall be 0.05-inch water gage (0.0 124 kPa) in fully sprinklered buildings. In buildings permitted to be other than fully sprinklered, the smoke control system shall be designed to achieve pressure differences at least two times the maximum calculated pressure difference produced by the design fire, but in no case less than the values indicated in Table 909.6.1:

TABLE 909.6.1
MINIMUM PRESSURE DIFFERENCES ACROSS SMOKE BARRIERS

CEILING HEIGHT	MINIMUM DESIGN PRESSURE DIFFERENCE
Less than 15 feet (4572 mm)	0.10-inch water gage (0.0259 kPa)
Equal to or greater than 15 feet (4572 mm), but less than 21 feet (6401 mm)	0.14-inch water gage (0.0349 kPa)
Equal to or greater than 21 feet (6401 mm)	0.18-inch water gage (0.0448 kPa)

The maximum air pressure difference across a smoke barrier shall be determined by required door-opening or closing forces. The actual force required to open exit doors when the system is in the smoke control mode shall be in accordance with Section 1008.1.3. Opening and closing forces for other doors shall be determined by standard engineering methods for the resolution of forces and reactions. The calculated force to set aside-hinged, swinging door in motion shall be determined by:



where:

A	=	Door area, square feet (m2).
d	=	Distance from door handle to latch edge of door, feet (m).
F	=	Total door opening force, pounds (N).
Fdc	=	Force required to overcome closing device, pounds (N).
K	=	Coefficient 5.2 (1.0).
W	=	Door width, feet (m).
ΔP	=	Design pressure difference, inches of water (Pa).