One year into the pandemic and a half million American deaths later, our understanding of how Covid-19 spreads has grown and changed significantly. However, federal safety guidelines are still largely based on old science and in desperate need of updating in order to control the virus and bring the pandemic to an end. The need is particularly urgent to protect frontline workers in essential industries who face much greater risk of infection and death, but it will also be important in the months to come for any employer who wants to reopen an office or other workplace safely.
Although the Occupational Safety and Health Administration, the federal agency that regulates workplace safety, is moving quickly to issue new stronger Covid-19 workplace safety measures, it is critical that these new protections be based on current knowledge and that in particular they address a problem that so far has received too little attention: inhalation exposure.
At the beginning of the pandemic, the most common routes of virus transmission were thought to be droplet spray (the propulsion of large droplets into the face, nose, eyes, and mouth of someone nearby) or touch (transferring respiratory fluids by hand to your eyes or mouth from surfaces where they have deposited). Since droplets are heavy and generally don’t travel far before they fall, the Centers for Disease Control and Prevention recommended staying six feet apart, frequent handwashing and surface disinfection. When it became clear that the virus could spread by asymptomatic persons, CDC recommended wearing masks when near other people.
While it is still important to prevent person-to-person transmission via droplet spray, there is now a large body of scientific evidence that particles much smaller than droplets can also spread the virus. These tiny particles, called aerosols, are emitted by infected people during breathing, talking and singing, and waft away in plumes of exhaled breath. The particles are so small they stay aloft for minutes to hours and can be carried distances by air currents.
In enclosed indoor spaces, these particles can accumulate, particularly if the ventilation is poor and the air is not filtered. There are now numerous studies of people infected with Covid-19 due to small particle inhalation, at distances far greater than the few feet that droplets travel.
To understand how far aerosols travel, consider cigarette smoke, which moves through the air in a similar fashion. If you are next to a smoker, you may inhale a big dose of their smoke. But even 10 or 20 feet away, you can still smell the smoke. If there are many smokers, even more smoke will fill the air. Small particles containing the SARS-CoV-2 virus behave similarly, giving the biggest dose and most infections to people within a few feet, but also potentially infecting some people at a greater distance from the source. If there are more infected people in one room or an infected person is talking loudly or singing, the danger increases because more virus is likely to be in the air.
Surgical masks and cloth face coverings stop droplet spray but don’t perform as well in preventing exhalation or inhalation of tiny aerosols. They may be fine for a quick trip to the store where shoppers keep six feet apart, but workers who spend many hours in crowded indoor settings, especially settings with inadequate ventilation and jobs that involve being close to other people, need much more protection. And it’s exactly those working conditions that are driving the high rates of Covid-19 among workers in nursing homes, correctional facilities, transportation, food processing, grocery stores and similar jobs involving long hours in poorly ventilated spaces. These jobs are ones in which people of color are over-represented, contributing to elevated risk of Covid-19 disease and death among Blacks, Latinos and other racial and ethnic minorities.
Clean, well-ventilated air is the most important way to make workplaces safe. Fresh air brought in by increased ventilation dilutes the concentration of the virus in the air, and High Efficiency Particulate Air (HEPA) filters can remove virus from environments. As a last resort, a worker who spends long periods in poorly ventilated settings or in close contact with many other people may need an approved respirator, like an N95 respirator, instead of a surgical mask or face covering. That’s because respirators don’t just block the virus from getting into the air, but also filter the virus out of the air that the wearer breathes — something surgical masks and cloth masks don’t do very well.
President Joe Biden has promised to reinvigorate OSHA, which had been handcuffed in the Trump administration. The agency is expected to soon issue an Emergency Temporary Standard for Covid-19 that will require employers to assess the risks of exposure in their workplace and take steps to limit it. The president has also committed to “follow the science,” and that now clearly calls for strong measures to limit small particle and aerosol inhalation, including ventilation and respiratory protection for workers at increased risk.
There are two steps to making that happen. First, CDC can and must update its guidance to make clear that aerosol exposure is a major source of Covid-19 transmission and provide recommendations for control. Second, OSHA should address the danger posed by infected aerosols in its upcoming workplace standards, including recommendations for proper ventilation and the wearing of respirators where necessary.
A failure by the CDC to provide an updated and consistent science-based explanation of how the virus spreads will lead to more confusion and will undermine public acceptance of CDC and OSHA recommendations. And that’s important if employers want to avoid taking measures that are less likely to be effective and will ultimately lead to more Covid-19 infections and worker deaths — among both workers who’ve been on the job through the pandemic, and the millions who’ve been working from home and hope to return to their usual workplaces someday soon.
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March 08, 2021 at 04:30PM
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