Fire induced flow in building ventilation systems

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Insinööritieteiden korkeakoulu | Master's thesis
Mechanical Engineering
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Master’s Programme in Mechanical Engineering
69 + 31
Fast growing fires inside compartments with limited paths for expanded gases to escape leads to a rapid pressure rise. High pressure can cause smoke to flow through supply vents into the adjacent rooms and can also cause structural damage. In Finland, apartments are fitted with a distinctive double door system and the inner door opens inwards into the apartment. The opening of this door could be difficult under high pressure conditions and the effect of pressure on egress possibilities of occupants was an issue of discussion in Finland. Extensive studies have not been made to better understand the influence of ventilation networks on pressure and smoke spread possibilities. The main objective of this thesis work is to investigate the development of pressure during fires in residential buildings and the influence of ventilation networks on pressure and smoke spread through buildings. It also aims to validate the efficiency and accuracy of the CFD code, Fire Dynamics Simulator for modelling HVAC networks and provide fire safety designers with guidelines to model and simulate pressure development and ventilation system response. The first phase of studies deals with the validation of the HVAC module in FDS. The Swedish-FOA experimental studies of pressure rise in compartments and smoke spread via ventilation ducts are used as validation cases. The FOA experiments were conducted in a sealed test chamber of size 4.0m x 5.5m x 2.6m with different opening diameters to model leakage and different ventilation configurations. In the second phase of the thesis work, fire tests were carried out in a 1970s apartment building. Different types of fire situations were created by altering the ventilation duct configurations. The pressure, gas temperatures in the room, gas concentrations and outlet smoke temperatures were measured and the effects of fire pressure in the ventilation networks were studied. The leakage rates of the test apartment were determined using a multi-point blower door test. A numerical simulation of these tests were performed using FDS. The studies show that the pressures developed during a compartment fire can be high enough to pose risk to the safety of its inhabitants and also cause significant damage to property. It was also found that the ventilation systems play an important role in relieving the fire pressure. The possibility of egress of occupants is compromised as opening the inner door became difficult. The FDS validation model predictions of temperatures and pressure rise in compartment fires are within the range of acceptable uncertainty.
Hostikka, Simo
Thesis advisor
Korhonen, Timo
FDS, fire, pressure, smoke spread, HVAC
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