As businesses adjust to the new normal that is the pandemic, air quality is a top concern that must be addressed. Our collective understanding of COVID-19 is constantly evolving. Currently, we understand that it spreads via droplets expelled through talking, coughing, and breathing. Although, most of these droplets fall to the ground, research suggests smaller particles may linger in the air. Hence this is where clean room air purifiers or extraoral suction systems that remove aerosols and other particles with HEPA filters may help. However, the question remains: are HEPA filters effective when it comes to COVID-19?
How big is the COVID-19 virus?
Researchers have determined the diameter of the COVID-19 virus to range between 60 nanometers (0.06 microns) to a maximum diameter of 140 nanometers (0.14 microns).
What size particles can HEPA filters capture?
Medical grade H14 HEPA filters like the ones featured in the PAX 2000X extraoral dental suction systems are able to filter 99.995% of particles down to 0.1 microns.
HEPA Filters accomplish this feat through the following filtration mechanisms:
- Inertial Impaction
- Inertia works on large, heavy particles suspended in the flow stream. These particles are heavier than the fluid surrounding them. As the fluid changes direction to enter the fiber space, the particle continues in a straight line and collides with the media fibers where it is trapped and held.
- Diffusion works on the smallest particles. Small particles are not held in place by the viscous fluid and diffuse within the flow stream. As the particles traverse the flow stream, they collide with the fiber and are collected.
- Direct interception works on particles in the mid-range size that are not quite large enough to have inertia and not small enough to diffuse within the flow stream. These mid-sized particles follow the flow stream as it bends through the fiber spaces. Particles are intercepted or captured when they touch a fiber.
- Sieving, the most common mechanism in filtration, occurs when the particle is too large to fit between the fiber spaces.
Does that mean smaller COVID-19 Viruses pass through HEPA Filters?
As established by studies, some COVID-19 viruses can be as small as 0.06 microns, below the 0.1 threshold of HEPA filters. It would seem to indicate that they bypass the filters then. However, experts say that this is not the case as virus particles don’t exist alone. Importantly, viruses like COVID-19 are always bonded to something, attaching to water droplets or aerosols that are generated by breathing, talking, coughing, etc. Subsequently, these consist of water, mucus protein and other biological material and are all larger than 1 micron.
“There is never a naked virus floating in the air or released by people.”Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who specializes in airborne transmission of viruses.
How to proceed in the face of uncertainty.
“The prudent and pragmatic approach is to acknowledge that airborne transmission is happening and put in the controls. If we find out in five years, that airborne was 5% of transmission, then OK… But what if it’s 20% or 30% and we failed to acknowledge it? That’s a problem.”Joseph Gardner Allen, director of the the Healthy Buildings program at the Harvard T.H. Chan School of Public Health
As our understanding of COVID-19 is changing, there are no concrete regulations we can follow yet, but many experts agree that it is better to be safe than sorry when it comes to aerosol and air transmissions. As we have definite proof that HEPA filters are able to effectively stop particles the size of COVID-19 viruses, it follows that implementing them through products such as extraoral suction systems or air purifiers is something that all dental practices and other businesses should seriously consider.