Introduction Motorcyclists could be exposed to high PM2.5 up to 460 μg/m3. The aim of this work was to develop a full faced helmet (FFH) that provides clean air and cool temperature inside the helmet to reduce particulate exposure and increase comfort for motorcyclists.
Methods A commercial FFH was modified to generate cool and clean air in a way similar to the powered-air-purified-respirator, commonly used in industrial settings. Three different clean air supply locations (A: upper rear of the head, B: zygomatic side, and C: lower chin) were applied to investigate the location effect. A small wind tunnel was used to simulate the turbulence that motorcyclists might encounter while riding on the road. The operating parameters included: the supply air flow rate to the helmet (Qs), the velocity in the wind tunnel (U0) and breathing flow rate which is a combination of tidal volume and breathing frequency. To minimise infiltration of aerosol outside the helmet into the breathing zone, the FFH was tightly surrounded with a neckerchief made of different materials. The stiffness of the neckerchief was measured by using a 45° angled Cantilever. A condensation particle counter was used to measure particle number concentrations both inside and outside the FFH, to calculate the protection factor, PF.
Results The PF of the FFH increased with increasing Qs, but decreased with increasing wind speed and breathing flow rate. At breathing flow rate of 7.5 L/min with the FFH sealed using neckerchief, PF increased from 1 to 900 as Qs increased from 0 to 50 L/min under calm air condition, with air supply through location A. Meanwhile, the PF decreased from 900 to 3 when wind velocity increased from calm air to 10 m/s. The PF increased significantly when the FFH was sealed with a neckerchief made of soft shell (stiffness 19.2 mm, 28 cm long). In addition, the temperature on the top of head decreased with increasing supply air flow.
Discussion Applying a higher Qs up to 100 L/min is necessary, not only to maintain a positive pressure inside the helmet but also to decrease the concentration of carbon dioxide exhaled by the wearer. The use of the soft shell neckerchief is also critical to reduce the infiltration due to external turbulence.
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