Effect of a motorcycle helmet on the airborne dust concentration near a rider's nose and mouth: wind tunnel study and field test

摘要

Wind tunnel experiments were performed to investigate how the presence of a driver wearing a motorcycle helmet affects the airborne dust concentration near the driver's nose and mouth relative to the ambient dust concentration. Data were collected for different grain size fractions of dust ranging from less than 20 mu m to approximately 100 mu m. The wind tunnel data were also applied to a field experiment with motorcycles and quads. Results show that the presence of a driver wearing a helmet significantly affects dust concentration. For the helmet tested, the concentration at the mouth position was about 50 % lower than the ambient concentration. At the nose position, the concentration depended on the particle size considered. For fine particles (smaller than approximately 30 mu m), the dust concentrations at the nose position were lower than the ambient concentrations, similar to the situation near the mouth. For particles larger than 30 mu m, which represent most dust released during typical off-road driving on natural surfaces, the dust concentration at the nose position was higher than the ambient concentration. The reason is most probably the chin guard of the helmet, which disturbs the trajectory of the dust particles and brings many particles to a higher elevation as they flow over the chin guard. Most helmets currently on the market have a chin guard and will behave similarly to the one tested in this study. Applying the wind tunnel results to the field experiment showed that the dust concentrations near the nose of the driver were more than 10 % higher than the ambient concentration, but only for particles coarser than 30 mu m. For finer particles, they were lower, up to 70 % lower for particles smaller than 20 mu m. On the other hand, the dust concentration near the mouth was significantly lower than the ambient concentration, less than half for all particle size classes investigated. This study shows that the effect of wearing a helmet should be taken into consideration when calculating human exposures to airborne dust.