Ventilation of ordinary face masks

• Published in: Building and environment Vol. 205; p. 108261
• Main Authors: Huo, Shigao, Zhang, Tengfei (Tim)
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.11.2021; Elsevier BV
• Subjects: Air flow; Air leakage; Carbon dioxide; Carbon dioxide concentration; CO2; Cotton; COVID-19; Discomfort; Face mask; Flow rates; Flow velocity; Humidity; Humidity ratio; Leakage; Masks; Mathematical models; Pandemics; Particle; Particulate matter; Shielding; Ventilation; Voting; Water vapor; Particle; Humidity ratio; Ventilation; Voting; CO2; Face mask
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2021.108261

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 CO2 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 PM2.5, CO2, and water vapor concentrations. The protection provided by the masks was evaluated in terms of their effectiveness in shielding wearers from ambient PM2.5. Mask comfort was examined in terms of both CO2 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 CO2 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. •Ordinary face masks were provided with additional HEPA filtered air for ventilation.•The masks were comprehensively evaluated by measurement, modeling, and voting.•Ordinary non-ventilated face masks have significant inward leakage.•The ventilated face masks enhanced protection and comfort.•The appropriate filtered air flow rate into the face masks was determined.