By: Christopher Sirota, CPCU
A recent study looked at indoor airflow generated by a building's ventilation system and how a person's breath moves within it: spoiler alert, masks seem to help steer particles away, which could mitigate viral exposure.
We previously posted that there is reportedly a risk that the novel coronavirus (SARS-CoV-2), which causes COVID-19, may be transmitted through the air as an aerosol emitted from an infected person. For example, an April 2020 National Health Institute report regarding healthcare worker exposure to SARS-CoV-2 noted that "[s]neezing and coughing are effective aerosol generators, but all forms of expiration produce particles across a range of sizes."
Back in June 2020, we posted that researchers at the National Institute of Standards and Technology (NIST) modified one of its airflow analysis models, called CONTAM, to develop software that can reportedly simulate how much aerosol might be expelled by people indoors, and how long that potentially contaminated air might linger or dissipate depending on various factors.
Now, EurekAlert has reported that researchers at the University of Cambridge have actually analyzed the movement of exhaled breath indoors by tracking volume of carbon dioxide. The researchers reportedly analyzed exhaled air from people-- both wearing and not wearing a mask--talking, nasal breathing and laughing.
The article explains that:
airflow in rooms is complex and depends on the placement of vents, windows and doors, and on convective flows generated by heat emitted by people and equipment in a building. Other variables, such as people moving or talking, doors opening or closing, or changes in outdoor conditions for naturally ventilated buildings, affect these flows and consequently influence the risk of exposure to the virus.
Regarding building ventilation systems, per the article, the researchers determined that the method more commonly used in buildings - the mixed air method - is likely not as effective at extracting potentially contaminated air as a system that uses the so-called displacement method. The displacement method reportedly relies on positioning vents high and low in a room such that warmer air - like exhaled breath - that rises will be extracted efficiently.
That said, the researchers reportedly found that wearing a mask seems to reduce the momentum of exhaled particles, which may result in leaked particles being carried upwards toward the ceiling of the room which likely increases the chance for extraction by a ventilation system, especially one that uses the displacement method. Thus, wearing a mask indoors in a building with a ventilation system actually can reportedly provide viral mitigation beyond the filtration provided by the mask itself.
Of interest, "[t]he researchers found that laughing, in particular, creates a large disturbance, suggesting that if an infected person without a mask was laughing indoors, it would greatly increase the risk of [viral] transmission."