Free online calculator helps examine aerosol travel in indoor environment
By Matt Phillion
Indoor air quality isn’t a new issue for healthcare facilities. Ensuring the quality of the air we breathe is a safety concern all organizations take into consideration both in daily life and when planning for alterations, updates, or improvements. The advent of COVID-19, however, has given healthcare facilities a fresh reason to examine the air quality in their buildings, with an eye to new risks and ways to prevent those risks from harming patients and staff.
Fortunately, tools are available to make that research easier. The indoor air quality experts at the National Institute for Standards and Technology (NIST) have developed a free tool, recently featured in a new article in the ASHRAE Journal. It estimates exposure to potentially infectious aerosols for people in a room. Calculations are based on information about the aerosols themselves as well as the room’s HVAC system and air filters.
The tool is designed for building managers and engineers to better identify strategies, such as adjusting ventilation rates or setting up portable air cleaners, that could help reduce exposure to the coronavirus in indoor spaces—like hospital rooms, waiting areas, or offices.
The tool, called the Fate and Transport of Indoor Microbiological Aerosols (FaTIMA), determines what happens with infectious aerosols in a building environment, as well as the impact of different control measures. It takes into consideration the effects of ventilation, filtration, deposition, and inactivation. Although FaTIMA doesn’t examine risk of infection, it can be of particular use for anyone working to determine the effectiveness of planned control measures for COVID-19 safety protocols.
New views on an age-old problem
COVID-19 is just the latest in an ever-evolving series of challenges that give researchers a new angle to apply decades of solid science.
“We at NIST have been studying airflow for decades, with a variety of motivations,” says Andrew Persily, chief of NIST’s Energy and Environment Division. “Using less energy, improving indoor environments, improving the productivity of the occupants under normal situations.”
When new challenges like COVID-19 arise, NIST has a chance to look at methods for improving indoor environments. After 9/11 and a series of anthrax-related events years ago, for example, the organization was able to investigate issues surrounding airflow and quality and how they related to those sorts of threats. Today, the pandemic has opened the door for more research on airborne viruses.
“Fortunately, while the challenges change, the physics hasn’t—air moves for the same reasons,” Persily says. “Ventilation has always been important. Ancient civilizations did all kinds of cool things to make buildings comfortable. And as we and our buildings evolved and things like urbanization increased, we’ve devoted more awareness and attention to airflow.”
The team is able to leverage their decades of applicable research to tackle new problems and build tools like FaTIMA to address current challenges.
How it works
The FaTIMA tool can be used to look at key removal mechanisms for the coronavirus, running simulations for 24 hours and displaying a time history of how much airborne concentration and surface loading occurs. Variables it examines include:
- Filtration (within the ventilation system and via room cleaner)
- Deposition of particles onto walls, floors, ceilings, and other surfaces
Organizations looking for ways to limit the spread of COVID-19 in their environments can use the tool to study potential options.
“Ventilation is one strategy for reducing aerosol disease transmission in buildings,” Persily says. “Over the years, we’ve learned that, with respect to the way air moves around buildings and the way ventilation systems work, there’s often a disconnect between design intent and what actually happens. Now, if a system is not operating as intended, it can have more serious consequences.”
Tools like FaTIMA offer a way to predict air, and therefore contaminant, movement throughout a building. To do this, “FaTIMA makes use of a software called CONTAM, which has been available for decades,” Persily says. (See the sidebar for more on this software.)
Making use of FaTIMA does require some knowledge about buildings and ventilation systems, so hospitals or healthcare organizations will want a bit of in-house expertise from their facilities or building planning teams. For example, the user would want to know and understand information like ventilation rates and related information to be able to add the correct inputs into the tool.
“In general, it could be used by anyone who has some sense of building ventilation, filtration technology, airborne particles, or aerosols,” Persily says. “They don’t need to have a PhD, but should have some familiarity with those phenomena. It could be a building ventilation designer or an operator who has had time to work with a tool like this.”
“In response to COVID, we wanted to create an online tool or calculator to make it easier for people to look at the relative impact of ventilation and filtration,” Persily says.
FaTIMA is somewhat limited in scope, focusing on a single zone representation in a building, so it can only approximate an entire building’s airflow. But the tool is designed to make analysis easier as organizations seek to limit the spread of COVID-19 in their facilities.
Who is using FaTIMA?
So far, NIST has seen organizations like public school systems use the tool to help decide how to keep students safer. Researchers are also using it to look into calculating the benefits of filtration versus ventilation versus indoor mask wearing.
“Ideally, what they’ll get out of it first is some understanding of how more ventilation would stack up to high-efficiency filtration versus a portable air cleaner, for example,” Persily says. “It helps with understanding how these options compare with each other.” If you better understand the potential air quality impacts of a change, you’ll be able to make a more informed decision regarding measures to help prevent COVID-19 spread within a building.
The tool isn’t strictly for COVID-19, either, so facilities looking at other airflow improvements can make use of it as well. FaTIMA allows the user to select the particle size, so it is adjustable to the needs of the problem being addressed. “Another application that comes to mind is protection against wildfire smoke particles getting into the building, and [exploring] what you can do to reduce indoor exposure,” says Persily.
Both uses of the tool can help organizations examine occupants’ particle exposure and possible measures to counteract it. And FaTIMA could play a role in future public health crises as well. “We are all reading that this isn’t going to be our last epidemic, and that we can’t let our guard down,” Persily says. “Assuming we get this one under control, we can then look to what could be next.”
NIST hopes organizations in healthcare and beyond can take advantage of the tool to better understand the impact of airflow during a crisis. “It’s in the public domain, so anyone can go there and make use of it,” Persily says. “It allows you to do the calculations reliably without having to create your own tool.”
What is CONTAM?
FaTIMA employs the solver of the CONTAM program, which was developed by NIST and has been used for decades for multi-zone, whole-building airflow and contaminant transport analysis. CONTAM predicts:
- Contaminant concentration
- Personal exposure
CONTAM’s ability to calculate building airflow rates and relative pressures between zones of the building is useful for:
- Assessing the adequacy of ventilation rates in a building
- Determining the variation in ventilation rates over time
- Determining the distribution of ventilation air within a building
- Estimating the impact of envelope air-tightening efforts on infiltration rates and associated energy implications
Matt Phillion is a freelance writer covering healthcare, cybersecurity, and more. He can be reached at email@example.com.