N95 masks can reduce hospital visits for wildfire smoke inhalation by up to 40 percent: study

Cloth masks provide very little protection against dangerous particles emitted by wildfire smoke, but N95 respirator masks do, according to a recent study in GeoHealth.  

Mass adoption of N95 masks could cut wildfire-induced emergency room admissions by 20 to 40 percent, according to coauthor Jack Kodros, who studies atmospheric science at Colorado State University. 

The findings from the study match recommendations from public health authorities like the California Air Resources Board, which advised residents to wear N95 masks to help protect against smoke from wildfires. The N95 masks pull all air through a respiratory filter. He noted that wearing two layers of fabric masks, as recommended by the Centers for Disease Control and Prevention (CDC), could also provide protection. 

“While cloth face coverings offer protection against COVID-19 virus spread, they do not provide protection against smoke particles,” the Board wrote.  

Much of the research such suggestions were based on, however, came from surveys that asked participants how often they wore a mask, and about their health conditions from smoke, Kodros said. This kind of data made it harder to quantify the effectiveness of a mask against the smoke. 

As a former resident of California, Kodros had friends who, “during the fire season, because of mask mandates, were starting to ask — should I hold onto my mask for fire season, would it help? And I realized there was not a lot of quantitative research about which masks would or wouldn’t be useful for air pollution.”

By attaching masks to a pipe and pushing smoke-filled air across them to simulate breath, Kodros’s team was able to test the effectiveness of N95 masks, as well as synthetic, cotton and surgical masks. The study found that a cotton mask blocked “20-40 percent of smoke, if you are wearing it correctly for most of the day.”

Surgical masks were nearly as ineffective. While the tight weave of surgical mask fabric was 90 percent effective in capturing smoke particles, those masks are made to keep sneeze and cough droplets from emerging in the air, not protect the wearer against a dangerous environment. Only about half the air inhaled by people wearing surgical masks gets filtered through the mask, Kodros said, with the rest traveling around the chin and nose.

By contrast, N95 respirator masks cut the dangers of inhaling contaminants by a factor of 16 if worn correctly. 

While surgical masks by themselves were ineffective, combining them with a cloth mask to compensate for the surgical mask’s loose fit was about as effective as an N95 as long as the seal around mouth and nose was good, Kodros said.

“That’s one of the reasons the CDC suggested the double-mask: to increase the fit of the surgical mask,” Kodros said. “One of those cloth masks that fits really well on the face — but it’s not so good at particles. A surgical mask is very good at particles, but it doesn’t fit well on your face.”

Part of the discrepancy comes from the different kinds of particles that cause pollution-induced respiratory illnesses versus COVID-19.  

The most dangerous particles from fire or other forms of combustion, like vehicle or factory exhaust, are so small they bypass both sneeze and cough reflex, as well as the protective hairs and mucus in your nose and throat. The particles are called PM 2.5, because they’re particulate matter of less than 2.5 microns, or 2500 nanometers.

These particles can penetrate the bloodstream and cause a broad range of long-term health problems ranging from asthma to heart disease to premature birth.

The coronavirus is far smaller than these particles, around 0.1 microns, according to the National Institutes of Health. But the cough and sneeze droplets that it tends to travel on are far larger, around twice the size of PM 2.5 particles. Infection from droplets, therefore, are dramatically curtailed even by relatively coarse, cotton masks.

“The big difference with a covid mask is you want to reduce viral emissions as well as protect what you’re breathing in,” Kodros said. “That’s a big difference: this double aspect of protecting what you breathe out.”