Just how long can you wear a surgical mask? How often you should replace your mask depends on who you ask. If you ask the WHO, they recommend surgical masks be changed every 4 hours. That could mean many masks a day. That’s a lot of masks and a lot of waste.
To find out how long a surgical mask stays effective, Smart Air ran tests on surgical masks worn by two of the Smart Air team for 40 days and over 30 hours.
How Surgical Mask Effectiveness Varies Over Time
We tested two surgical masks worn by Keer and Vivian from the Smart Air team.
These were 3-layered masks bought from a local supermarket in Beijing. They claimed to meet the Chinese YY-0469 standard, at filtering out 95% of 3.0 micron particles, and at least 30% of 0.1 micron particles.
Both Keer and Vivian wore their surgical masks every day for 43 days as they commuted to the Smart Air office. Keer’s daily commute involved a 20-minute cycle and a 40-minute bus ride.
On the other hand, Vivian’s involved a 10-minute cycle, 10-minute walk, and a 40-minute subway ride.
Throughout the experiment, the masks were stored both on a desk, as well as occasionally left hanging in the open air. At the end of the 40 days, the masks were not visibly dirty other than a bit of makeup and lipstick. The masks also had no bad smell.
We recorded the number of hours of mask usage and tested their effectiveness at different points in time.
How We Tested Surgical Mask Effectiveness
We mimicked a setup commonly used by researchers called a Henderson apparatus. In our setup, a fan on the left end blows air and particles through the mask material on the right.
On the other side of the DIY mask material, a Met One GT-521 laser particle counter measures the number of particles that penetrate the mask material.
Results – Surgical Masks Remain Effective After Prolonged Usage
Data showed that both masks retained high effectiveness in blocking both 0.3 micron and 1.0 micron particles, even after 6 days. Specifically, the effectiveness of Keer’s mask at filtering 1.0 micron particles decreased from 100% to 99.87%.
Similarly, the effectiveness of Vivian’s mask at filtering 1.0μm particles decreased from 100% to 99.94%.
On the other hand, the effectiveness of Keer’s and Vivian’s masks at filtering 0.3 micron particles decreased from 98.13% to 95.24% and 97.49% respectively.
This data supports the findings in our previous article about N95 longevity – masks still remain effective after being worn a long time. After 30 hours, the surgical masks still roughly meet NIOSH standards, having at least 95% protection against 0.3 micron particles.
Greater Usage Leads to Greater Breathability
When we set out with this experiment, we expected the masks to get more and more difficult to breathe through as they were worn. The thinking here is that as the masks get more and more clogged with particles, they become harder to breathe through.
Our data showed the opposite. The masks actually became easier to breathe through. This is most likely due to the loosening of the fabric material over time which allows more air to pass through.
After 30 hours, differential pressure (a measure of breathability) for Keer’s and Vivian’s masks decreased by 8.1% and 6.9% respectively. As lower pressure means greater breathability, Keer’s Mask became 8.1% more breathable, whereas Vivian’s mask became 6.9% more breathable. This highlights that prolonged usage of the masks increases their breathability.