Protection And Comfort Performance Of Ventilated Facial Mask

Since the end of 2019,the COVID-19 has caused a global epidemic.Masks become the last line of defense to protect people.However,gaps of causing leakage are easily formed between the mask and the face when ordinary masks are worn.Air leakage into ordinary face masks decreases the protective effect of the mask.Meanwhile,wearing a mask also causes both CO₂ and water vapor to accumulate inside,which causes a decrease in the concentration of inhaled oxygen,then resulting in a feeling of breathing difficulty and hot-humid feeling.In order to improve the protective effect and wearing comfort of masks,this article proposes to transform ordinary masks into ventilating masks.The independent supply air filtered by HEPA is sent into the mask,and the positive pressure in the mask is maintained to reduce the leakage of environmental aerosol into the mask,thereby improving the oxygen content inhaled of the wearer and exhausting the water vapor accumulated in the mask effectively.In this study,N95,surgical and cotton masks were transformed into ventilating masks,and clean air filtered by HEPA was sent into the inside of the mask through a silicone hose.Experimental tests,mathematical modeling and subjective questionnaires are used to evaluate the protective effect and comfort of ventilating masks.Build a test chamber in the laboratory that can independently supply HEPA filter air.The HEPA filter air supply range is 0～36.84 L/min.The extracted air of inside the masks was for measurement of the PM_2.5,CO₂,and water vapor concentrations when a real person wears a ventilating mask is taken for testing.The effect of removing PM_2.5 is used to evaluate ventilating masks protective performance,while the CO₂ concentration and humidity ratio in the mask are used to evaluate the comfort.In order to further evaluate the performance of ventilated masks,the conservation equations of air exchange flow,PM_2.5concentration,CO₂ concentration and water vapor content are established for ordinary masks and ventilating masks respectively,and HEPA air supply and leakage flow are analyzed for the protection and comfort of masks.In addition,20volunteers were recruited to vote on the acceptance and comfort of ventilated masks on subjective questionnaires.The voting content included AMSV（Air movement sensation vote）,AMAV（Air movement acceptance vote）,weight change,breathing difficulty and hot-humid feeling.Among them,AMSV and AMAV are five-level indicators.Weight change,breathing difficulty and hot-humid feeling are three-level indicators.The study found that:（1）Ordinary non-ventilated masks have obvious leakage problems.The protective effect provided by the mask is far lower than that of the filter material itself.In addition,carbon dioxide and water vapor accumulate in the mask,causing breathing difficulties and discomfort.（2）Ventilating masks can not only inhibit the leakage of particles in the surrounding air into the masks,but also improve comfort by reducing the CO₂ concentration and water vapor content inside the masks.The greater the HEPA filter supply air volume,the lower the concentration of particulate matter,CO₂ and water vapor in the mask.（3）The most acceptable HEPA filtered air supply for volunteers is 18 to 23 L/min.N95masks with a hard shape are most suitable for transforming into ventilating masks.However,because of the soft texture of surgical masks and cotton masks,the silicone air supply pipes connected to these two kinds of masks easily touch the lips of the wearer,resulting in bad experience.The ventilating mask proposed in this article is very suitable for places with personalized air supply such as airplanes and buses,and can also be connected with a portable HEPA filter unit for air supply use.