Experimental study on the effect of mechanical ventilation conditions and fire dynamics on the pressure evolution in an air-tight compartment

The paper presents a comprehensive set of experiments on the effect of mechanical ventilation conditions and fire dynamics on temporal pressure evolution in a reduced-scale, air-tight and mechanically-ventilated enclosure. A square propane burner with flow controller imposes a quadratic fire growth followed by a steady-state (0.1 or 0.2 g/s) and then a quadratic decay phase. Eight tests are discussed with different ventilation conditions in terms of flow resistances and initial ventilation flow rates ranging from 12 to 40 m(3)/h, corresponding to air renewal rates of 6.4-21.3 h(-1). The pressure evolution is characterized by an over-pressure peak (up to 900 Pa) followed by a quasi-steady state and then, an under-pressure peak (up to -760 Pa). The pressure variation is due to the mechanical effect (i.e., ventilation configurations), while also influenced by thermal effects. The pressure amplitudes increase with ventilation resistances. Both the total network resistance and individual resistances in admission and extraction ducts are important for the pressure variation. The enhancement and reduction of ventilation flow rates depend on both the fire-induced pressure and ventilation resistances. Experimental results show that the mechanical effect does not strongly affect gas temperatures.