Measurement of air pressure fluctuations at lower levels in a high-rise drainage stack

Drainage system is a basic and essential provision for all buildings. The maximum air pressure in a discharging drainage stack can deplete the appliance water trap seals that prevent the ingress of foul gases and odors into a habitable space. The control of air pressures in discharging drainage stacks has been identified as an important factor in ensuring the performance of a building drainage system. This study reports air pressure fluctuations at a stack at the lowest floor of a high-rise building induced by a consecutive operation of water closet flushes. Mathematical expressions proposed earlier for steady flow conditions are examined to correlate the maximum air pressure with the probability density function of the data measured. The average prediction of the absolute peak pressure is determined. The results showed that the maximum air pressure at the discharging stack with unsteady flows could be described by the probability density function of the measured data using earlier proposed mathematical expressions with a modified constant. Such outcome enhances the understanding of the characteristics of air pressure fluctuations at a drainage stack at lower floors of high-rise buildings and it is useful for further development of stochastic models for air pressure fluctuations at a drainage stack.