Do HEPA Filters Capture the COVID Virus?
Get a clear explanation of how HEPA filters capture virus-carrying aerosols and their practical place in managing indoor air quality.
An increased focus on indoor air quality has accompanied concerns about airborne pathogens like the virus that causes COVID-19. This has led many to investigate High-Efficiency Particulate Air (HEPA) filters, a type of mechanical air filter that works by forcing air through a fine mesh that traps extremely small particles.
How HEPA Filters Capture Airborne Viruses
To be classified as “HEPA,” a filter must meet a strict standard by removing at least 99.97% of airborne particles that are 0.3 micrometers (µm) in diameter. This particle size is used for testing because it is the most difficult for filters to capture. Both smaller and larger particles are trapped with even higher efficiency.
The virus that causes COVID-19, SARS-CoV-2, is approximately 0.125 µm in diameter. However, the virus does not travel through the air on its own. It is carried within larger respiratory droplets and aerosols generated when an infected person breathes, speaks, or coughs. These virus-laden particles fall well within the range that HEPA filters capture efficiently.
HEPA filters physically remove particles from the air using three primary mechanisms: impaction, interception, and diffusion. Impaction catches larger particles whose inertia causes them to collide with a filter fiber. Interception traps medium-sized particles that follow the air but get stuck to a fiber as they pass. The smallest particles, including individual viruses, are captured by diffusion as their random movement causes them to collide with a fiber.
Choosing and Placing HEPA Air Purifiers
When selecting a portable HEPA air purifier, consider the Clean Air Delivery Rate (CADR). This rating, measured in cubic feet per minute (CFM), indicates how quickly the purifier cleans the air in a specific room size. Choose a unit with a CADR rating appropriate for the room’s square footage, ensuring it is at least two-thirds of the room’s area.
The placement of an air purifier impacts its performance. For maximum air circulation, place the unit in a central location, away from walls and corners that can obstruct airflow. Ensure there are a few feet of clear space around the unit. Placing the purifier in a bedroom or main living area helps capture particles where people spend the most time.
Consistent upkeep is necessary for a HEPA purifier to function correctly. Filters become clogged with trapped pollutants over time, which reduces their efficiency. Follow the manufacturer’s recommendations for filter replacement and look for products labeled “True HEPA” to ensure the filter meets the required standard.
HEPA Filters as Part of a Layered Strategy
HEPA filtration is one component of a layered strategy to lower transmission risk. A multi-layered approach combines several mitigation efforts for the best protection. These other layers include improving ventilation by opening windows, vaccination, and wearing well-fitted masks in certain settings.
HEPA filters lower the concentration of viral particles in a room’s air, reducing transmission likelihood over time. They are beneficial in spaces with insufficient ventilation, like rooms without windows or in buildings with older HVAC systems. Their use is also valuable in households with vulnerable individuals or during periods of high community transmission.
Air purifiers do not eliminate all risk and cannot prevent transmission from close, face-to-face contact with an infected person. The effectiveness of filtration is additive to other safety measures. Combining HEPA filtration with improved ventilation and personal protective actions creates a safer indoor environment.