While universal masking alone provided a reduced level of exposure to infectious particles, researchers with the National Institute for Occupational Safety and Health (NIOSH) found evidence supporting a layered approach—physical distancing, ventilation, and masking—to control the transmission of SARS-CoV-2, the virus that causes COVID-19. Results of a study out of NIOSH’s Health Effects Laboratory in Morgantown, West Virginia, appear in the journal Indoor Air.
“Universal masking” means everyone in an indoor space, regardless of health, infection, or vaccination status, wears a mask. The NIOSH researchers evaluated the effectiveness of a three-ply cotton mask.
Universal masking reduced exposures to coughed or exhaled aerosol particles by over 77% compared with no masking.
Universal masking acts as a source control for infectious particles, blocking coughed or exhaled particles, rather than as a protective device for the wearer.
Researchers continue to study the role of respiratory droplets or aerosols in COVID-19 disease transmission. However, increasing evidence showing that asymptomatic and presymptomatic individuals are responsible for the spread of COVID-19 in the community suggests that very fine droplets and aerosols factor into infections.
Factors affecting the effectiveness of masks for either protection or source control include variations in filtration efficiency, air flow resistance, mask fit, and user compliance.
The NIOSH team simulated very fine respiratory droplets and aerosol particles like those generated through breathing and coughing. The micron and submicron scale particles produced by breathing and normal speech can remain airborne for minutes to hours.
Loud speech and singing can increase the distances that droplets and aerosols travel.
A single symptomatic case of COVID-19 resulted in 32 confirmed and 20 probable cases following a 2 ½-hour choir practice at the start of the pandemic.
Coughing produces particles and aerosols that can travel up to 26 feet (8 meters).
The NIOSH team acknowledged the difficulty in evaluating the effectiveness of increased ventilation because ventilation is unique to each indoor space. The NIOSH researchers concluded that the layering of engineering and administrative controls remains an important intervention for reducing SARS-CoV-2 transmissions.
The Occupational Safety and Health Administration’s (OSHA) current employer guidance for COVID-19 recommends:
- Facilitating employee vaccination by granting time off for vaccination and recovery from vaccine side effects;
- Instructing infected workers or unvaccinated workers who have had close contact with an infected individual to stay at home to reduce workplace transmission;
- Implementing physical distancing in shared indoor spaces;
- Providing nonrespirator face coverings, such as surgical masks, for employees;
- Informing employees of corporate COVID-19 policies and procedures;
- Maintaining ventilation systems and following the recommendations of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE);
- Performing routine workplace cleaning and disinfection; and
- Requesting or requiring customers and visitors to wear face coverings.
OSHA established two emergency temporary standards (ETSs) last year for workplace COVID-19 exposures. The agency’s June 21, 2021, healthcare ETS expired in December, but the agency intends to pursue a permanent healthcare industry infectious disease standard that would include COVID-19, as well as measles, tuberculosis, and other diseases. The agency withdrew its vaccination and testing ETS after the U.S. Supreme Court issued a stay of enforcement.