Are Fibers From HEPA Filters Harmful to Health?

HEPAs are air filters often used in air purifiers or central air systems to clean indoor air. They’re made from a mat of randomly aligned fibers that are usually made from polypropylene (PP) or fiberglass.

That fact has made some people afraid of HEPA filters. There’s a controversy over whether fiberglass particles can cause lung disease and cause cancer. Some people are worried that fibers in HEPA filters will break off, enter the air, and enter people’s lungs.

Are HEPA filter fibers dangerous? Let’s break the question of whether HEPA filters are harmful to human health into two parts:


1. Can The Fibers from HEPA Filters Break Off and Enter Our Body?

A team of scientists looked into whether or not commercially available filters shed fibers in both the lab and real-world conditions. They tested a fiberglass filter and a filter made from plastic fibers (polycarbonate and polyester). Both filters tested were rated to capture 95% of particles in the air (H11 HEPA filters or MERV 16).

In the lab, they blew clean air at each filter for 6 hours. While they did that, they captured and measured the number of fibers breaking off the filter and traveling downstream.


But wait, fibers breaking off from HEPA filters could be tiny, right? So how do the scientists know that they can actually detect fibers coming off of the filter?

To make sure they could detect the fibers, the scientists used a tiny filter with gaps that were just 0.4 microns big. That works because the fibers that broke off the filters were on average 1.5 microns in diameter and 24 microns in length. That’s over 50 times bigger than the gaps in the capture filter.


And indeed, they were able to capture fibers coming off the filters. They capture 300 fiber particles per cubic meter of air from the synthetic filter and 700 for the fiberglass filter.

Comparing Fibers Shed From HEPA Filters With Everyday Air

Seven hundred fibers sounds like a lot, but let’s compare it to something we know more about: PM2.5. These fiber particles are in the size of range of PM2.5, and PM2.5 is in the air we breathe every day.

The World Health Organization sets a PM2.5 annual limit of 10 micrograms per meter cubed. Using a simple formula, that’s equivalent to 25,225 PM2.5 particles per meter cubed, or 35 times what the filters were shedding.

Let’s compare that to some of the cleanest cities in the world, like Bredkalen in Sweden or Sinclair in the US. In those places, PM2.5 averages 2 micrograms over a whole year. 2 micrograms is equivalent to 7 times more tiny particles than what would come off a HEPA filter.

In short, air purifier filters do shed fibers, but the number of fibers is negligible. What’s more, the researchers also found that the number of fibers shed reduced over time.

2. Are Tiny Microscopic Fibers That are Inhaled Into our Body Harmful to our Health?

OK, so HEPA filters only shed a small number of fibers. But maybe that’s still important because maybe those fibers are really harmful to our bodies. Maybe they’re harmful because they’re so long, thin, and brittle? Perhaps the fibers can get trapped in the our wind pipe or lungs, causing leading to serious health impacts? For example, asbestos fibers are more harmful than the average particle.

Research showing fibers unlikely to cause irreversible damage

Many researchers have studied the health impacts of fiberglass on the body, yet there’s still no agreement on whether fibers are harmful or not. One study by the American College of Chest Physicians looked at the effect of fibers on the lungs of animals and humans. After analyzing over 30 studies, the physicians concluded that glass fibers could be irritant to lungs. However they also found the fibers are unlikely to cause irreversible damage or cancer. They concluded that fiberglass be classified as a nuisance dust.

Research showing elevated risk of respiratory cancer due to fibers

Despite this, other reports [1, 2] have found some evidence of the harm from fibers. One study analysed 32,110 workers in the US. They looked at the effects of fiberglass over a long period of time (more than 30 years). The results weren’t conclusive, but the study found there could be an elevated risk of respiratory cancer for people who work with fiberglass on a daily basis.

The NIOSH Exposure Limit for Fibers

Despite the harms of small fibers on the body , the National Institute for Occupational Safety and Health (NIOSH) in the US recommends a fiber count of no more than 3 fibers/cm3, averaged over a 10-hour work shift. NIOSH suggests that people may experience irritation to the eyes, skin, nose, throat or difficult breathing.

Here’s how that compares to the number of fibers shed from the HEPA filters in the study above.

Of course, with many things, we probably want to breathe even less than the workplace limit, but the number of fibers is far less than the NIOSH exposure limit. The difference is from a few hundred to 3 million.

Bottom Line on the Harms of HEPA Filters to Human Health

Bottom line: HEPA filters shed very few fibers over their lifetime, with the highest rate of shedding when they’re new. Although some studies have linked fiberglass to cancer, a summary of research suggests that the fibers are no more harmful than other dust in the air. Even for new HEPA filters, the number of fibers shedded are less than one thousandth the occupational limit.

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