COVID-19 is still circulating in the U.S. and may once again gain traction as families and friends gather indoors over the holidays. There are several measures that, combined with vaccination, could curtail a new wave of infections. One often-overlooked approach for homes is managing air flow and air cleaning.

Leveraging ventilation and filtration has been an underutilized strategy for many residents throughout the pandemic because of the technical know-how required to implement these strategies. To help more people use this approach effectively, researchers at the National Institute of Standards and Technology (NIST) have developed a simple interactive webpage featuring the new Virus Particle Exposure in Residences (ViPER) tool. With ViPER — and some basic knowledge about their homes — homeowners and renters can learn how much certain actions, such as upgrading air filters or opening a window, may lower their risk of exposure to particles in the air that could potentially transmit COVID-19.

ViPER is based on an earlier tool developed in 2020 by NIST researchers with expertise in creating airflow and containment transport models. Called Fate and Transport of Indoor Microbiological Aerosols (FaTIMA), the web-based program estimates the concentration of exhaled aerosols — a collection of liquid and solids floating in the air, also often referred to as particles — a person would encounter in a single space.

Oftentimes, these particles are harmless, but in other instances, they can harbor pathogens, such as the virus that causes COVID-19. It is generally difficult to predict how many particles would be carrying a virus in a given scenario, but FaTIMA’s calculations cover all bases by describing exhaled particles whether or not they contain pathogens.

The tool’s specific purpose is to guide people in selecting strategies to reduce the number of airborne particles indoors in general, which could in turn mitigate COVID-19 transmission. However, it is mostly geared toward engineers, building managers and others familiar with heating, ventilating and air conditioning (HVAC) systems, as it requires users to provide a great deal of technical information about a space and its HVAC system.

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