NIST Airflow Model Could Help Reduce Indoor Exposure to Aerosols Carrying Coronavirus

Researchers at the National Institute of Standards and Technology have built an online tool that could help decrease the concentration of aerosols containing the novel coronavirus in the hospital rooms of COVID-19 patients and other spaces such as offices, retail stores and residences, potentially reducing the likelihood of building occupants becoming infected.

The Fate and Transport of Indoor Microbiological Aerosols tool considers factors including ventilation, filtration and aerosol properties to estimate the concentration of aerosols a person might encounter in a room. Using the new tool, building managers and engineers can evaluate their options for reducing occupant exposure to the novel coronavirus. A new report serves as a FaTIMA user guide.

When people breathe, cough and sneeze, they release respiratory droplets and smaller aerosols less than five millionths of a meter in size. Compared with respiratory droplets, the smaller aerosols can remain in the air for longer periods of time. The current data suggest the novel coronavirus is primarily transmitted through contact with larger droplets, but tiny aerosols can also harbor the virus and may pose a threat to people, especially indoors. To establish a sound defense against these aerosols, informed management of airflow and airborne contaminants could be critical.

For FaTIMA to perform its calculations, the user must provide details about a room’s geometry, ventilation rates, air filter efficiencies and the presence of portable air cleaners, all of which can influence the concentration of small airborne particles to varying degrees.

The tool also requires specifics about the virus-containing aerosols, such as their size and how quickly they deposit onto surfaces. Although the properties of aerosols containing the novel coronavirus are not yet clearly defined, aerosols carrying the more well-studied influenza virus can be modeled in FaTIMA to approximate their behavior.

Users are free to adjust the aerosol property inputs as they see fit but, by default, the values in the tool are based on previous studies of influenza-containing aerosols, which are referenced in the report.

FaTIMA users can vary factors such as ventilation rates, air filter ratings and emission rates (to account for the effects of masks, for example) to identify approaches that reduce aerosol concentrations. Informed by the tool, building managers and engineers can then develop strategies and implement them in real buildings, producing a safer environment for occupants such as healthcare workers on the front line.

Both the tool and its associated report are available online.