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CFD study of fire-induced pressure variation in a mechanically-ventilated air-tight compartment

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The present work describes Computational Fluid Dynamics (CFD) simulations of fire-induced pressure rise and ventilation duct flow rate in a mechanically-ventilated air-tight compartment, which represents a passive house. Overlapping wooden slats were used as fire source in the experiments and were represented in the simulations by a 0.4 m × 0.4 m × 0.4 m cube with a prescribed HRR based on the experimental results. The maximum ventilation volume flow rate was set to 80 m3/h in the experiments, in line with Belgian requirements for residential ventilation. Two methods were used to set up the ventilation volume flow rate in the simulations to meet the requirement of maximum ventilation flow rate by modifying the fan curve, and adding dampers. As expected the combination of the real fan curve and dampers, which resembles reality better, is morein line with the experimental results. The maximum over-pressure in the fire room was about 420 Pa, resulting in a reverse flow in the supply duct and an enhanced flow in the exhaust duct. The reversed inlet volume flow rate and increased outlet volume flow rate reached 137 m3/h and 175 m3/h respectively. The fire-induced pressure is high enough to hinder evacuation and fire rescue operations due to the impossibility of opening inward-open doors over a certain period of time. Moreover, the pressure rise in the adjacent room also reaches a dangerous level. Reducing the gap area between rooms can significantly decrease the pressure rise in the adjacent room, but leads to an increase of pressure in the fire room. As expected, when applying mechanical ventilation, the influence of leakage pressure exponent on pressure rise is smaller compared to cases without ventilation.
Book: Proceedings of the 9th International Seminar on Fire and Explosion Hazards
Volume: 1
Pages: 574 - 583
ISBN:9785742264965
Publication year:2019