Ventilation of ordinary face masks

Wearing of face masks has been identified as an essential means of reducing COVID-19 infection during the pandemic. However, air leakage into ordinary face masks decreases the protection they provide. Wearing a mask also causes both CO(2) and humidity to accumulate inside, imposing breathing difficulty and discomfort. To remedy the above problems, this investigation proposed to ventilate ordinary masks by supplying additional HEPA filtered air. The N95, surgical, and cotton masks available on the market, were modified into ventilated masks. The air inside the masks was extracted for measurement of the PM(2.5), CO(2), and water vapor concentrations. The protection provided by the masks was evaluated in terms of their effectiveness in shielding wearers from ambient PM(2.5). Mask comfort was examined in terms of both CO(2) concentration and humidity ratio. In addition, a mathematical model was established to solve for the exchanged air flow rates via different routes. Subjective voting by 20 mask wearers was also conducted. Performance of the ventilated face masks were compared against the non-ventilated ones. It was found that the protection provided by the ordinary non-ventilated masks is much lower than that claimed for the filter materials alone due to significantly total inward leakage. The accumulated CO(2) and humidity inside masks resulted in discomfort and complaints. For contrast, the ventilated face masks not only enhanced protection by suppressing the inward leakage of ambient airborne particles, but also significantly improved comfort. The wearers preferred a filtered air flow rate ranging from 18 to 23 L/min.