Multi store parking spaces are complex buildings that pose specific problems to hazard management resulting from fire and pollutant release from the exhaust gases of automobiles. They are often characterized by large open spaces which do not prevent the spread of fire and smoke. The presence of large quantities of fuel just adds to the risk. In addition, the random occupancy of the space and existence of large openings make difficult the hazard containment. Structural details such as columns and beams can facilitate the accumulation of smoke in pockets. A combination of fire resistant doors and forced ventilation are the usual methods for smoke/fire mitigation.
The current legislation defines the acceptable limits for CO concentration for both continuous (50 ppm over 8 hours) and peak (200 ppm) conditions. If the parking space is above ground and has side openings, forced ventilation is not mandatory and it is acceptable that risk prevention and management can be dealt by natural ventilation only.
The commissioning of the space often requires that tests are carried out in which a smoke tracer is released into the space in order to evaluate its dispersion over time. This is performed at ambient temperature and the thermal effects on the plume are not taken into account resulting in a lower dispersion rate.
The objective of the present work is to evaluate the influence of the temperature of the release source into the smoke dispersion in a parking space. This is a large public space 113 m long, 76 m wide and 3 m in height. The computational model is implemented within the Ansys Fluent. In this, the continuity, momentum, energy and species equations are solved for the physical model which includes the building structural details and vehicles. The fluid is assumed as a mixture of CO, N2 and O2. The boundary conditions assume various conditions for the external wind through the side openings and the heat source is modeled as that resulting from the combustion of gasoline from an open fire. The time dependent variation of the heat load is assumed with a peak of 8 MW.
The results show that the temperature at the source promotes a stratification of the plume to the ceiling of the building leaving the occupied (lower) levels with a much clear atmosphere. Beams also facilitate the concentration of high levels of CO in isolated pockets. These proved to be stable while the atmosphere temperature remains high; subsequent cooling drives the smoke/pollutants to the power levels. Such behavior is also dependent upon the entrance of fresh air through the lateral openings.