Inflow Of Air Required At Wall And Ceiling Apertures To Prevent Escape Of Fire Smoke

Expe r iments have been conducted to determine cr I tical Froude numbers associated with required inflow of air to a fire space through wall and ceil ing apertures to prevent escape of smoke. The exper iments were conducted mostly on reduced, model scale, with verification in a 2.4 m high test room. Critical Froude numbers, as formulated, were insensitive to aperture geometry. Those for wall apertures varied slowly and predictably with the vertical temperature distribution in the room, consistent with a discharge coefficient of 0.64 for the inflow. Those for ceiling apertures exhibited a dependence on an aperture Grashof number, with both a highGrashof number asymptote and an apparent low-Grashof number asymptote. While discharge coefficients for wall apertures can be considered constant near 0.64 for aperture Froude numbers larger than cr itical, the discharge coefficient for ceiling apertures increased from 0.19 near the critical Froude number, toward the familiar isothermal value for sharp-edged orifices of 0.61 near a Froude number seven times larger than the critical.