City University of Hong Kong Department Name



Public-transport-interchange ventilation

Breathing diesel fumes raises a person¡¯s risk of lung cancer. In addition to promoting cancer the fumes are likely to damage lungs in other ways such as causing irritation and inflammation in the lungs. In Hong Kong, the provision of mechanical ventilation in a semi-confined public transport interchange (PTI) is mandatory. The authority recommends the general use of low-level supply and high-level exhaust airflow scheme. This is different from the traditional ventilation concept in that the low-level emitted vehicle pollutants are best to be removed at source. Computer analyses of the air quality at typical PTI environment were examined with these two alternative airflow schemes. The CFD simulation cases were generalized by studying both light and heavy traffic conditions with adjusted ventilation rates to match the change in vehicle emission levels. Pollutant concentrations at the passenger waiting areas and the elevated footbridge were examined. The results show that while the conventional high-level-supply and low-level-exhaust scheme could perform better during light traffic loads, the difference diminishes with increased traffic load during peak hours. On the other hand, the high-level exhaust scheme has an advantage of serving as a smoke extraction system during a fire outbreak.


Physical model used in a comparative study of PTI ventilation schemes

 NO2 concentration at the ground level for high-density traffic, (i) Scheme 1: low level supply and high level exhaust, and (ii) Scheme 2: high level supply and low level exhaust.


Related publications :


Lin Zhang, Jiang Feng, Chow TT, Tsang CF, Lu WZ. CFD analysis of ventilation effectiveness in a public transport interchange. Building and Environment, 41(3), 2006, 254-261.

Chow TT, Lin Zhang, Bai Wei. Assessment of alternative ventilation schemes at public transport interchange, Transportation Research Part D: Transport and Environment, 11(6), 2006, 447-458.

Lin Zhang, Chow TT, Tsang CF, Fong KF, Chan LS, Shum WS. Effect of ventilation system on smoke and fire spread in a public transport interchange. Fire Technology, 44(4), 2008, 463-479.


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