909.7 Air Flow Design Method

When approved by the department, smoke migration through openings fixed in a permanently open position, which are located between smoke control zones by the use of the airflow method, shall be permitted. The design air flow shall be in accordance with this section. Air flow shall be directed to limit smoke migration from the fire zone. The geometry of openings shall be considered to prevent flow reversal from turbulent effects.

The minimum average velocity through a fixed opening shall not be less than:




where:

h	=	Height of opening, feet (m).
T f	=	Temperature of smoke, °F (°K).
To	=	Temperature of ambient air, °F (°K).
v	=	Air velocity, feet per minute (m/minute).

This method shall not be employed where either the quantity of air or the velocity of the airflow will adversely affect other portions of the smoke control system, unduly intensify the fire, disrupt plume dynamics or interfere with exiting. In no case shall airflow toward the fire exceed 200 feet per minute (1.02 m/s). Where the formula in Section 909.7.1 requires airflow to exceed this limit, the airflow method shall not be used.