Self-pollution, the intrusion of a bus's own exhaust into the bus cabin, leads under some conditions to very high exposures. This study attempted to elucidate how and where self- pollution occurs, and to test various methods to mitigate this phenomenon. The mechanism of self-pollution was investigated by evaluating the magnitude of exhaust system leaks, searching for exhaust entry points using a tracer gas, and determining the overall leak rate of the bus cabin. Comprehensive detection of leaks in the exhaust system using SO2 from the exhaust as a tracer gas and a survey of leak potential using back pressure measurements showed that exhaust system leaks in a well-maintained system were insignificant. However, identifying specific exhaust entry points into the passenger compartment using tracer gas was found to be infeasible due to the large number of potential entry points. To quantify overall air tightness of cabins, the leak rate of 17 buses was evaluated by pressurizing them with an air blower with a constant flow rate and measuring the pressure differential between the inside and outside of the bus (blower door method). Pressure differentials ranged over a factor of five, but in general, newer buses showed lower leak rates.


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    Title :

    Evaluation of Mechanisms of Exhaust Intrusion into School Buses and Feasible Mitigation Measures


    Contributors:
    D. R. Fitz (author) / A. M. Winer (author)

    Publication date :

    2006


    Size :

    102 pages


    Type of media :

    Report


    Type of material :

    No indication


    Language :

    English




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