Static Pressure Measurements of Enclosure Fires

Some enclosure-fire static pressure measurements are presented for both full and scale model rooms and are compared with the present hydraulics-orifice flow model for fire induced flows into and out of enclosures. Results indicate that the vertical pressure differential (enclosure to ambient) follows the expected hydrostatic distribution quite well and accurately reflects the doorway inflow and outflow gas velocities. Measurement of ceiling and floor differential pressure using different numbers of gas burners yields insight into gross plume entrainment and illustrates how the neutral plane and thermal discontinuity vary with upper gas temperature. Correlating upper gas temperature with fire size and enclosure height makes it possible to predict at what heat release rate a given enclosure might become fully involved, i.e., by using the temperature at which the thermal discontinuity approaches the floor. In terms of present fire plume modeling large entrainment coefficients (0.3-0.4) are required in order to reproduce the enclosure flows for both the small and large scale results. A noted deficiency in the plume model appears in the small scale results where the data suggest that the entrainment should exhibit a much stronger dependence on the fuel injection rate than that predicted by the theory.