can hepa Air purifiers capture the coronavirus

Can HEPA Air Purifiers Capture the Coronavirus? Yes and No.

Air purifiers with HEPA filtration can efficiently capture particles that are the size of the new coronavirus, and many Wirecutter readers have asked whether air purifiers can therefore help protect against infection. The answer is yes in theory and largely no in reality.

The virus that causes COVID-19 is approximately 0.125 micron (125 nanometers) in diameter. It falls squarely within the particle-size range that HEPA filters capture with extraordinary efficiency: 0.01 micron (10 nanometers) and above. Many media outlets have incorrectly stated that HEPA filters don’t filter below 0.3 micron and therefore can’t capture the new coronavirus. That claim is flat wrong. (This NASA study of HEPA filtration is quite technical, but the graph on page 7 and the preceding paragraph do a good job of explaining why HEPA filters are actually most efficient—almost 100 percent at 0.01 micron—at capturing ultrafine particles below the 0.3-micron HEPA test standard.)

But that doesn’t mean an air purifier can protect you. While scientists are still researching how the new coronavirus spreads, the current consensus is that it is not an airborne virus, and that’s the position of both the CDC and other global health agencies. Rather, experts believe that the coronavirus is transmitted by person-to-person contact and by contact with virus-laden droplets expelled by an infected person’s coughing and sneezing. Coughs and sneezes certainly suggest “airborne” to most people, but such droplets travel only about 6 feet before falling out of the air and settling on surfaces. This is one reason health agencies worldwide are recommending 6-foot (2-meter) “social distancing” and related efforts like frequent handwashing and disinfection of surfaces as the primary means of protecting yourself.

Photo: Sarah Kobos

It’s also the reason HEPA purifiers must not be considered a first line of defense against the virus that causes COVID-19. “The big thing with trying to say that a HEPA filter would do any good is whether you’re getting anything to the filter or not,” said Kathleen Owen, a consulting engineer with nearly 40 years of experience in air filtration. “If it turns out—and this is the big if; I’m not sure you should even mention it—but if there’s stuff that’s getting into the air, HEPA would catch it.” Owen noted that the coronavirus that caused the SARS outbreak in 2003 was primarily transmitted person-to-person but is thought to possibly have been airborne as well. (A preliminary study suggests that the virus behind COVID-19 can become aerosolized and remain airborne for several hours, but the study’s authors note that even should this prove to be the case, person-to-person contact would likely remain the chief mode of transmission.)

Owen, too, reemphasized that as far as researchers know now, air is not the vector by which the virus spreads, and that air purifiers should not be considered protective.

So, follow the CDC’s best practices: Self-isolate, wash your hands frequently, and disinfect frequently touched surfaces. A HEPA purifier won’t hurt. But it probably won’t help.