What Are HEPA Filters? Will They Keep Me Safe When Flying?

If there’s one thing we’ve heard wheeled out by practically every airline as they look to resume flying, it’s the concept of HEPA filters. In a bid to encourage passengers back to the skies, airlines are shouting loud about the quality of the air onboard the plane, and their ‘hospital-grade’ filtration systems. But what are HEPA filters, and can they really make flying safe again?

737 Silhouette
As we return to flying, can we rely on HEPA filters to keep us safe? Photo: Getty Images

What is a HEPA filter?

Standing for High Efficiency Particulate Air filter, the HEPA technology onboard aircraft is used in other products around the world, including vacuum cleaners. They work through the use of close-knit fibers that trap impurities from the air, removing them from circulation.

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The structure of a HEPA filter. Photo: LadyofHats via Wikimedia

It’s not just dust and dirt that the filters remove. They are so good at removing particles, they can extract bacteria, moisture and, crucially, viruses. Since the 1980s, most commercial aircraft have had these types of filters fitted to maintain the cleanliness of the cabin air.

Do HEPA filters protect from coronavirus?

According to the Centers for Disease Control and Prevention (CDC), HEPA filters capture 99.9% of particulate matter from the air, including fungi, bacteria and viruses, from 0.1 – 0.3 micrometers in diameter. Studies of the coronavirus linked to COVID-19 have shown that the viral particles, or virions, range in size from 0.06 to 1.4 micrometers, with an average size of 1.

While that doesn’t sound great, it’s important to remember that the virus is not airborne. Although the smallest individual virions could indeed slip through a HEPA filter, they would never end up there unless they were contained within a respiratory droplet.

Respiratory droplets, produced when people, cough, sneeze, breath and even talk, range in size from 5 micrometers up to as big as 10. They are still invisible to the naked eye, but in terms of HEPA filtration, they’re huge.

The downside of the coronavirus not being airborne is that, by piggybacking on respiratory droplets, it has the opportunity to land on flat surfaces. In a home environment, a HEPA air purifier would be unable to eliminate the droplets at a sufficient rate to stop them from settling on surfaces. For this reason, home-based air purifiers, even those with HEPA filters, would be unlikely to protect you from COVID-19.

However, on an airplane, it’s a different story.

What Are HEPA Filters? Will They Keep Me Safe When Flying?
The HEPA filters being changed on an aircraft. Photo: Emirates

Why HEPA filters work on planes

The reason HEPA filters do provide protection on a plane but wouldn’t at home is because of the rapid circulation of air in the cabin. On a typical narrowbody (A320, Boeing 737), the air is completely renewed every two to three minutes, or 20 – 30 times every hour. The cabin air is a mix of fresh air (around 60 – 70%) and recirculated air.

Even more crucially, the air is not circulated around the aircraft in a way that would allow the virus to pass by other passengers. Air is sucked out of the cabin using vents in the floors, passed through HEPA filters, mixed with fresh air from the outside and injected back in through air outlets and individual vents.

This vertical movement of air forms a protective barrier between rows, making it highly unlikely that the virus could pass between passengers seated in front or behind each other.

This, coupled with the enhanced cleaning measures being undertaken by airlines as well as the ever-expanding requirement for face coverings, will ensure that passengers are as safe as possible when they are ready to return to flying.

Do you feel confident in the capabilities of HEPA filtering? Let us know in the comments.