AIR CHANGE RATES IN STATIONARY AND MOVING MOTOR-VEHICLES

The project was carried out to determine the likely infiltration rate of a gas into a stationary motor vehicle for different wind speeds and directions. Measurements were first made on five vehicles under both positive and negative pressures to determine their leakage characteris tics both with the vents open and with them closed. A tracer gas metho d was then used to determine the air change rates in the vehicles for different wind speeds and directions. Measurements on one vehicle enab led a constant to be evaluated which enabled infiltration rates to be found for other vehicles in terms of leakage characteristics and wind conditions. Predicted values of air change rates can be used to estima te the build-up of a contaminant infiltrating into a vehicle. In the s econd part of the project the scenario considered was that of a vehicl e moving through a cloud of contaminant. Measurements of air change ra tes (ACH) were made on a vehicle driven at constant speeds of between 35 and 70 mph (15 and 32 m/s). Although the variation of ACH with spee d was similar to that for the stationary vehicle in an airflow, a high er ACH was found for the moving vehicle than would be predicted for th e stationary vehicle, using the leakage characteristics.