The public health concern of coronavirus transmission has led to widespread use of protective measures. Masks and physical barriers, such as glass or plexiglass, are common in public settings. Many question their effectiveness in preventing virus spread. This article explores how masks and physical barriers function to reduce coronavirus transmission.
Understanding Mask Protection
Masks primarily protect against coronavirus transmission by blocking respiratory droplets and aerosols expelled when an infected person talks, coughs, or sneezes. They serve two main functions: source control and personal protection. Source control involves preventing an infected person from spreading the virus by largely blocking droplets from contacting others. Personal protection refers to reducing the wearer’s exposure to infectious particles.
Different types of masks offer varying levels of filtration efficiency and fit. N95 respirators are designed to filter at least 95% of airborne particles, including those as small as 0.3 micrometers. These respirators form a tight seal around the face, filtering both large and small particles when the wearer inhales. Surgical masks, also known as medical masks, are loose-fitting and typically composed of three layers of synthetic nonwoven materials. They protect the wearer from contact with droplets and sprays, filtering large particles.
Cloth masks, made from multiple layers of fabric, trap respiratory droplets from the wearer and block droplets from others. While their filtration efficiency varies depending on the fabric and construction, layered cloth masks can have efficiencies similar to some surgical masks. Masks with exhalation valves are not recommended as they allow unfiltered air and droplets to escape, defeating the purpose of source control.
Understanding Glass and Physical Barrier Protection
Physical barriers, such as glass, plexiglass, or plastic shields, provide protection by creating a physical separation between individuals. These transparent shields obstruct the direct trajectory of respiratory droplets. They prevent the rapid exchange of respiratory particles between individuals. This obstruction reduces the risk of close-range transmission.
These barriers are commonly seen in various settings, including cashier stations, reception desks, and open workspaces. They create a protective layer between employees and visitors, blocking respiratory droplets. By redirecting respiratory emissions, physical barriers can allow ventilation and air cleaning systems more time to reduce particle concentrations. While primarily effective against larger droplets, well-designed, solid barriers can reduce exposure to aerosolized particles.
Limitations and Layered Protection
Neither masks nor physical barriers offer absolute protection alone. For masks, improper fit can allow particles to bypass the filter material through gaps around the face. Prolonged use can lead to masks becoming moist, reducing effectiveness. While masks are effective against droplets, very fine aerosols can still penetrate or circulate, particularly with less protective mask types.
Physical barriers also have limitations; they often feature gaps, reducing their effectiveness. These barriers do not filter air and are less effective against airborne aerosols that circulate around or over them, especially in spaces with poor ventilation. Improperly placed barriers can hinder air mixing and trap aerosols in a localized area, potentially increasing exposure.
Given these individual limitations, public health strategies emphasize “layered protection,” known as the “Swiss cheese model.” This model illustrates that while each protective measure has imperfections, combining multiple layers of defense significantly reduces the overall risk of transmission. For instance, wearing a mask, maintaining social distancing, ensuring good ventilation, practicing hand hygiene, and using physical barriers together create a more robust defense against coronavirus spread. No single intervention is 100% effective; their combined application provides a higher level of prevention.