Smoke spreading in vertical shafts in buildings with scale modelling technique

Abstract

A vertical shaft is a building enclosure with large height-to-span ratio passing through floors vertically with openings to different levels. Smoke spreading through a vertical shaft is identified as an important key issue and of the primary concern of fire safety for old highrise buildings in Hong Kong. This study investigates the smoke movement in vertical shafts due to a fire at various locations in a building. A scale-down model was constructed and the scaling laws were applied to study the smoke travelling time from the fire location to other building locations through the shaft. Scaling parameters considering the conservation of enthalpy were selected for the experimental study. It found that the location of fire would be important in determining the smoke travelling time in vertical shafts. Scenarios of a fire in a compartment at different levels adjacent to the shaft were considered. Five different locations were studied with different fire sizes. Smoke spreading patterns were observed and empirical correlations were derived to predict the smoke travelling time of the plume front in the shaft. These empirical correlations would be very useful for professionals such as building design engineer, law draftsmen and property owners in predicting the smoke travelling time in full scale buildings. Finally, the experimental results were used to describe the smoke spreading through a lift shaft in a reported fire case, the Garley building fire. The times required for smoke to travel inside the lift shaft were obtained from the correlation derived. This information would be helpful for fire investigation.