Characteristics of air pressure fluctuations in high-rise drainage stacks

Maximum air pressure in a drainage stack can deplete the appliance water trap seals that prevent the ingress of foul gases and odors into a habitable space. This study investigates the air pressure fluctuation frequency, as well as the maximum and average air pressures with their respective standard deviations, in a 38 m high drainage stack of a full-scale experimental tower under steady flow conditions of flow rates 1 Ls-1to 4 Ls-1discharging at a height between 15 m to 33 m above the stack base. Mathematical expressions are proposed to correlate the maximum air pressure with the probability density function of the data measured. The average prediction and the maximum under-prediction of the absolute peak pressure were determined with the margin of error taken within certain confidence levels. It was demonstrated that water seal failure would likely be occurred at some heights below the discharge locations. The outcome enhances the understanding of the characteristics of air pressure fluctuation within a drainage stack of a high-rise building.