Influence of fire heat release rate (HRR) evolutions on fire-induced pressure variations in air-tight compartments

Abstract

The paper presents experimental results indicating the influence of the fire heat release rate (HRR) evolution on the fire-induced pressure variation in air-tight compartments, which increasingly appear in modern buildings. The fire evolution is stipulated according to a power law with variations in fire growth/decay rate coefficient, maximum steady state HRR, fire growth/decay exponent and fire duration. It is illustrated that the higher the fire growth/decay rate coefficient, the higher the over-pressure/under-pressure peaks become. The peak values approach a maximum level when the fire growth/decay rate coefficient exceeds a certain level (0.0926 kW/s2 in the present cases). Besides, the over-pressure and under-pressure peak values increase monotonously with the increase of the maximum steady state HRR. For cases with fire growth/decay exponent below 1, the pressure reaches peak values before the HRR reaches a steady state (maximum value or zero) because the net heat gained per unit time in the gas phase already reaches its peak values then. In cases with fire growth/decay exponent above 1, the pressure reaches peak values at the moment where the HRR reaches the steady state. Finally, in one test low-frequency oscillatory behavior is illustrated with gaseous fuel during the well-ventilated phase.