Both parents and teachers are quite reasonably worried as school administrators decide how to resume classes safely amid a surging COVID-19 pandemic.
“This is the biggest adaptive challenge in my career, and in the history of public education,” said Cindy Marten, superintendent of San Diego public schools in the New York Times.
One thing is certain: Coronavirus transmission is primarily airborne. This article focuses on how HEPA Air purification can play a vital role in reducing the threat of COVID-19 in classrooms. More specifically:
- How viral transmission takes place indoors
- Why airflow is key to decreasing the likelihood of infections
- How HEPA filtration can capture viruses in shared spaces like classrooms
The Big Picture
Doctors and scientists believe schools can be reopened safely under certain conditions. In our view, there's one thing we must not overlook: How adequate airflow and effective HEPA filtration can work together to decrease risk by keeping airborne viral concentrations to a minimum.
THE THREAT: COVID-19 Transmission from Indoor Air
The science is clear: coronavirus spreads via aerosol droplets mainly indoors. Shared indoor spaces occupied for prolonged periods pose one of the most acute risks.
“Converging lines of evidence indicate that SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, can pass from person to person in tiny droplets called aerosols that waft through the air and accumulate over time,” according to the scientific journal Nature.
In an urgent open letter, "It is Time to Address Airborne Transmission of COVID-19," an international group of 237 doctors, scientists, and engineers convinced the World Health Organization to revise its stance on airborne transmission. The letter said:
Studies have “demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1-2 m (3-6 feet) from an infected individual… traveling tens of meters (30-60 feet), much greater than the scale of a typical room.”
THE INFECTION: How People Catch Coronavirus Indoors
According to Dr. Erin Bromage, the Dartmouth Immunology and Infectious Disease professor who emerged as an authority on airborne transmission, the Golden Rule of indoor COVID transmission is this:
SUCCESSFUL INFECTION = EXPOSURE TO VIRUS X TIME
In other words, the degree of concentrated exposure over time is the crucial factor.
Indoor spaces account for 90% of all transmission events, Bromage wrote, and any enclosed environment with poor air circulation and a high density of people spells trouble.
Referencing a restaurant and a call center where known coronavirus infections took place (see below), Bromage said:
“Social distancing guidelines don't hold in indoor spaces where you spend a lot of time, as people on the opposite side of the room were infected.”
THE SOLUTION: How HEPA Captures Viruses & How Airflow Reduces Risk
True HEPA filtration (or H13, according to the U.S. Department of Energy) is the most effective air-purifying technology available today. It’s used by hospitals, high-tech clean rooms, and scientific labs as a proven method of removing airborne impurities.
The True HEPA filters used by Alen can capture over 99% of particles in the virus range. But doing so effectively requires a purifier with enough capacity to clean an entire room or “box.” Here’s how it works:
- Ultrafine virus particles (.080 - .120 microns) are carried by small and large aerosol droplets (5-500 microns) dispersed by coughs, sneezes, talking, and laughing.
- Small droplets can quickly spread up to 16 feet before evaporating, leaving virus particles floating weightlessly to circulate even further.
- A HEPA purifier with sufficient airflow capacity for the room draws in virus particles.
- Trapped viruses die (or loses infectiousness) inside the HEPA filter within hours/days.
Successfully purifying a room requires a purifier to move lots of air—completely circulating air throughout a room with and without an HVAC system. (Later, we’ll discuss why HVAC-only improvements can offer false confidence.)
In the context of coronavirus, we know particles can simultaneously float and settle. HVAC ventilation can help by dispersing particle concentrations (as infected air isn’t blown directly from person to person).
But purifiers play a critical by drawing in contaminated air, trapping virus particles within its HEPA filter (where they’ll lose infectiousness within hours), and circulating clean air back into the room, further dispersing viral particle concentrations.
A room ideally needs four full-volume air changes per hour (ACH) for the maximum degree of safety. For that reason, a purifier MUST not only have adequate capacity but be able to work quietly. Here at Alen, our engineers have been perfecting that formula for over 15 years.
The CDC recommends using portable air purifiers like Alen alongside other best practices as “part of a plan to protect people indoors.” The EPA states that “air cleaning and filtration can help reduce airborne contaminants, including particles containing viruses.”
TOP 3 TAKEAWAYS: Air-Related Recommendations for a Safer Back to School
In their letter to the WHO, the 200+ doctors and scientists said handwashing and social distancing are appropriate but insufficient. Here are three key recommendations:
- Practicing cohorting to avoid overcrowding and limit spread - The CDC recommends that groups of students, teachers, or staff form cohorts or ‘pods’ that stay together throughout the school day to minimize exposure across the school environment.
- Prioritize airflow: Ample ventilation can disperse the virus - Be outside when possible. Wind, even in perceived stillness, can rapidly decrease concentrations of viral particles. Bring in clean outdoor air when appropriate and minimize recirculating air. Direct HVAC airflow to not blow directly from one person to another. And avoid restrictive HVAC filtration upgrades, which significantly reduce airflow that could otherwise disperse virus particles.
- Use True HEPA (H13) Air Purifiers for Classrooms - Supplement general ventilation with airborne infection controls such as portable True HEPA filtration. Choose an effective purifier that’s able to draw in contaminated air and circulate pure air throughout your entire breathing space or 'box' quietly enough not to disturb the class. Alen is proud to make top-rated purifiers that do just that—guaranteed for life.
THE MYTHS: Why HVAC Improvements (like Filters and UV) Aren’t a Silver Bullet
A myth making the rounds is that installing HVAC (Heating Ventilation and Air Conditioning) improvements alone—such as high-MERV return filters or UV bulbs—can make indoor spaces safe. The EPA recommends that airflow improvements include HEPA filtration with the overall goal of INCREASED airflow.
- Upgraded HVAC filters can make things worse. More restrictive air return filters installed with the intent of trapping COVID can actually reduce the airflow that would otherwise help disperse virus particles and minimize the likelihood of infection.
- Many UV (ultraviolet) light applications are unproven for clearing the full volume of air in every room - While massive, powerful lighting arrays pointed directly into a space (as in hospital operating rooms) will work, the effectiveness of adding UV to HVAC ducts is unproven outside the condenser core and plenum. Further, the physics of how air moves through HVAC systems suggests that virus particle concentrations or clouds may not be exposed to enough UV light due to a “shadow effect” from larger particles like dust.
“Inside an enclosed ‘box,’ millions of viral particles become more concentrated with every breath—even with a mask on—unless they are dispersed by HVAC airflow,” said Alen CEO, Andy Graham. “Shared-air indoor spaces need their own air purifiers to effectively trap the virus within each ‘box’ in tandem with HVAC airflow.”
Alen’s mission is to provide safe and healthy air for all the spaces we share. That includes ensuring our invaluable learning environments are free of harmful particles—from pathogens to allergens to pollutants.
We offer a customizable line of True HEPA (H13) air purifiers backed by an exclusive lifetime warranty and an in-house team of air quality experts who can help you quickly build protective solutions for spaces of any size.
Contact us at B2BPurchaseOrders@alen.com, chat at alen.com, or call 855-200-5483.
IMPORTANT: Alen does not provide medical advice. Consult your doctor or a medical professional with healthcare questions.