Let’s clear the air on air purifiers and COVID

·3 min read

From 10 members of the Department of Civil, Construction, and Environmental Engineering at North Carolina State University.

The Wake County Public School System is not keeping pace with our evolving knowledge of COVID-19, its variants, and how to keep children safe while learning in person.

Covid infection rates among children are rising and Triangle area pediatric intensive care units are near capacity. Parents are understandably concerned about their childrens’ safety in school, but WCPSS can take actions to address those concerns in a meaningful way.

WCPSS has adopted a mask mandate, installed MERV13 filters and increased building ventilation rates, and encourages social distancing. However, these efforts are not enough, and we should not wait to act on low-cost, low-risk solutions for our children.

The most recent research shows COVID-19 is primarily transmitted through aerosols, tiny particles emitted to the air as we exhale. These aerosols linger for hours and pose a risk to people in an indoor space long after an infected person has left. A recent study by leading researchers concludes that adopting a layered approach to risk mitigation is the best way to navigate the pandemic.

Unfortunately, this evidence has not reached local authorities. In a recent N&O article, we were dismayed to read that ABC Science Collaborative claims “There are no scientific data to support that the use of HEPA filters and ventilation work to prevent spread of COVID-19 when everyone is masking.” This statement appears to be based on an outdated and limited study conducted last winter, before classrooms were full and the far-more-infectious delta variant became the dominant form of this coronavirus.

Since then, several studies have confirmed that aerosol-removing air filtration units reduce the risk of transmission in classrooms.

We fully support mask mandates, but they alone are not a silver bullet. As any parent or teacher can attest, kids’ attention to proper mask wearing is imperfect at best. Thus, other layers of protection are essential. Air filtration should be used as a complement to enhanced building ventilation.

Despite the ventilation upgrades undertaken by WCPSS, many buildings do not meet the Harvard Healthy Building target of five to six air changes per hour (the number of times fresh air replaces indoor air per hour). Bridging this gap requires improved filtration, such as through the use of High Efficiency Particulate Air (HEPA) portable air purifiers. Properly sized HEPA purifiers can provide additional air changes, ensuring aerosols are removed at a rate that keeps our children safe.

The combined effect of proper masking along with improved ventilation and filtration is substantial: it may reduce the risk of COVID exposure by over 90%. These purifiers cost approximately $20/student per year to purchase and $4/student per year for filter replacements, compared to over $9,000 to educate a student each year.

A safe, less-expensive DIY air purifier is also available: a Corsi-Rosenthal (CR) box. Tests show this design performs similarly to HEPA purifiers at one-fifth the cost. They could be deployed across WCPSS to address the inequitable distribution of HEPA filters, but WCPSS has inexplicably banned their use, even though they have been tested and deemed safe by Underwriters Laboratories.

As scientists and concerned parents, we implore WCPSS to do two things:

1. Keep pace with the latest in our scientific understanding of COVID.

2. Act quickly to implement low cost, low risk solutions equitably.

Many of the additional layers of protection come with multiple benefits, such as the use of improved air filtration long-term to keep school air healthy, and spending more time outdoors. These investments can improve our schools for many years to come.

The following members of NCSU’s Department of Civil, Construction, and Environmental Engineering signed this op-ed: Tarek Aziz, Ashly Cabas Mijares, Douglas Call, Joseph DeCarolis, Fernando Garcia Menendez, Andrew Grieshop, Angela Harris, Jeremiah Johnson, Meagan Kittle-Autry, Brina Montoya

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