Modeling and management of fire-induced pressures in a model apartment

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Insinööritieteiden korkeakoulu | Master's thesis
Structural Engineering
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Rakenne- ja rakennustuotantotekniikan koulutusohjelma
Fire developing in a mechanically ventilated airtight compartment can induce high pressure. The significance of this arisen pressure and the risks involved with it were explored in this study. Previously, no effort has been made to study the impact of realistic fire growth rates over compartment pressures in a residential setting. This research is based on a fire development scenario exhibiting a model apartment in a multi-story residential building. This thesis study documents the behavior of fire-induced compartment pressure relative to involved variables. This thesis also devises an alternate method of computing fire-induced pressures in airtight compartments. Finally, this thesis proposes solutions for the management of the encountered overpressure under apartment fire scenarios. Fire-induced pressure as a function of fire growth rate, envelope airtightness, and damper configuration was studied using Fire Dynamics Simulator (FDS). Pressure behavior, peak pressure values, and variable trends were the focus of this study. Results suggest that pressure increases with faster fire growth rate and overall airtightness of the compartment. In addition, the sensitivity of pressure to a parameter value seemed to increase when moving towards a faster fire growth or increased overall air-tightness of the compartment. It was found that the pressure rise can risk the occupants’ escape from the inward-opening door for medium and faster fire growth rates. Overpressure can cause structural damage to a near-zero envelope with a fast or ultra-fast fire growth rate. An analytical model was developed from the basic assumption of an ideal gas as an alternate way to capture the pressure rise related to compartment fire scenarios. The model was validated with the known FOA and AALTO experiments’ simulation and experimental data. In comparison to FDS results, the analytical model captured the pressure behavior in an apartment fire scenario with reasonable accuracy. The positive peak pressures were captured with an average difference of 5%. The model was found reliable in all configurations of input variables. In order to deal with the overpressures encountered, recommendations were made for additional leakage areas required to diminish the overpressure under the threshold safety limits of occupant safety and structural integrity. The findings were also verified using the FDS simulations. Finally, for managing the pressure in practical scenarios, the pressure threshold limits were converted into their equivalent bulk leakage area limits for different ventilation configurations.
Hostikka, Simo
Thesis advisor
Janardhan, Rahul Kallada
fire-induced pressure, analytical model, pressure management, apartment fire, envelope airtightness, damper configuration
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