Describes an experimental study of ventilation in the occupied zone in the waiting area of nine railway concourses in Hong Kong. The performance of the mechanical ventilation systems in those areas was also evaluated by evaluating the age of air, local air velocity and carbon dioxide levels. States the results show that ventilation effectiveness may not necessarily be improved with increasing supply or extraction flow rate. Also calculates the revised jet momentum numbers for the stations and compares them with the mean CO2 concentration and the local age of air. States it appears that this parameter can be used for evaluating the performance of the ventilation systems. A linear relation is fitted empirically to correlate the mean local age of air with the revised jet momentum number for the nine stations.

KEYWORDS: year 1997, Ventilation, mechanical ventilation, experiment, China, railway stations, performance, carbon dioxide, air jets