With the advent of COVID-19 infection in November 2019 there has been increasing interest in the use of face masks. Face masks can be respirators for surgical masks. The level of protection offered by surgical masks and respirators differ. The history of face masks go back to late 1800s. Early face masks were made of cotton gauze and were aimed to prevent infection of open surgical wounds. Today surgical masks are worn in wide range of healthcare settings and are aimed to protect the wearer again possible infective respiratory emissions.
The goal of face mask is to prevent inward transport of hazardous airborne particles and outward movement of user-generated aerosol. A surgical mask is a loose-fitting, single use, disposable device that is aimed to serve both the above goals. A surgical mask may come with or without face shield. Since OSHA issued the blood borne pathogen standard in 1991, surgical masks have been recommended as a part of universal protection to protect user against direct splashes and sprays of infectious blood or bodily fluids.
Level of protection offered by any surgical mask is based on its filer performance. The filter used in modern surgical masks is considered fibrous in nature and are made of flat, non-woven mat of fibres. How well a filer collects particles depends on its thickness, porosity and filter diameter. Broadly three mechanisms operate in fibrous filters to capture particles. One is inertial impaction, second is interception and third is diffusion. Larger particles are collected by inertial impaction and interception while smaller particles are captured by diffusion. However, some face masks made from charged fibres have an additional mechanism of electrostatic attraction. Electrostatic attraction helps to capture both small and larger particles. In all cases once a particle comes in contact with filter fibre, it is removed from the air stream and strongly held by molecular attractive forces. It is very difficult for such p[article to be removed once it is collected.
All surgical masks and respirators are put through stringent testing as per the standards set in place by NIOSH (The national institute of occupation safety and health). These stringent quality standards ensure that PPE surgical masks provide high level of particle collection efficiencies. Manufacture of surgical masks need to demonstrate that their mask is atleast as good as ones currently available in the market. However, loose fit of surgical masks can impact their efficacy to a great extent and in studies comparing the efficacy of surgical masks using standardized airflow have resulted in collection efficacy ranging from 10% to 90%. It is important to keep in mind that overall performance of surgical masks depends a great deal on the seal they make on your face. A loose seal can reduce their effectiveness to a great extent. Similarly their effectiveness also depends on good filter performance. Masks with good face seal and good filter performance will provide you the optimum protection you deserve.