NC State Experts Study Performance, Fit Testing for Face Masks for the Public
By Laura Oleniacz
Researchers at the North Carolina State University Textile Protection and Comfort Center are working on consistent and reliable ways to test the effectiveness of cloth face masks used by the public to limit the spread of the coronavirus, building on their expertise in testing protective equipment for firefighters and first responders.
“In March, we saw that people were making cloth masks, and we realized there were no specifications or consistent testing for them,” said Bryan Ormond, assistant professor of textile engineering and chemistry in the NC State Wilson College of Textiles. “We started looking at: How do we look at making better tests?”
The Center for Disease Control and Prevention recommends the general public wear multi-layer cloth masks to prevent transmission of SARS-CoV-2, the virus that causes COVID-19, by reducing spread of the virus through respiratory droplets as well as to reduce inhalation of droplets by the wearer.
To learn about strides in testing cloth face masks, the Abstract sat down with Ormond to talk about research into testing cloth masks for the public, which are considered the last line of defense against the spread of the coronavirus.
The Abstract: Can you describe some of the tests you’re doing on face masks worn by the general public?
Ormond: We worked during the pandemic at our homes, some in the lab, to put together a couple tests to be able to just get a screening level using ambient air particles. We wanted to see how well the materials filter.
We essentially put fabric in a cell, passed air through it and counted the particles on either side. That gives us an idea of the filtration efficiency. We recently added an aerosol generator to give us a consistent level of particles at a consistent size because you can’t really control ambient air from day to day.
The other approach is to look at the full product. When you make a cloth face covering, it is not a flat piece of material. It has the openings around the face, the nose. It has a fit factor that also affects the performance.
We have an animatronic breathing head form that we can control. Testing masks on our articulated head form allows us to simultaneously get a measure of filtration efficiency and fit.
TA: How do cloth face masks protect people?
Ormond: Any time you’re dealing with some sort of hazard you’re trying to protect people from, you look at this hierarchy of strategies for how you can control the hazard. Typically, you’re starting with administrative and engineering controls. In this case, that refers to keeping 6 feet of distance, washing your hands and staying at home – those are going to separate you from the hazard.
The PPE, the respirators and the face coverings are a last line of defense in any situation, not just in respiratory protection.
The other is this idea of getting everyone to realize that a mask, a face covering is just one of the tools that we can use. It’s a public health strategy. Every single person wearing a mask just cuts things down a little bit from spreading.
TA: Are there standards for cloth face masks?
Ormond: Right now there is no certification process or specification for cloth face coverings for the general public. The American Association of Textile Chemists and Colorists, AATCC, came out with a design specification or guideline on how to construct them.
Now, a task group of ASTM International’s subcommittee on respiratory protection – with experts from around the country – is coming together to put together a specification. That involves setting design and performance requirements so every mask can be certified through a process. We also have to pick the correct test methods that provide relevant performance to the use conditions
TA: What do you look for in a face mask?
Ormond: There are three main performance characteristics you want to look at. One of those is filtration efficiency. If you pass air with particles through that fabric, how many particles does that fabric actually stop?
The next thing that you want to look at is breathability. Filtration and breathability typically have an inverse relationship, so as you increase the filtration performance, the material or composite becomes less breathable. So the balance between these two is critical for an effective face covering.
The last one that’s most important for providing any protection to the wearer is the fit. If the mask doesn’t fit and seal to the face, you can have the best filtration material possible, it can block everything in a material level test, but if you put it on your face, what’s going to happen is the air you’re breathing in is actually going to follow what we call a “path of least resistance” and move around the material instead of through it. This is less of a concern if you are intending the face covering to only function as a means to limit spread and protect others from the wearer.
TA: What’s your ultimate goal for face mask testing?
Ormond: We want to be able to develop a rating system. Right now a regular person shopping for a mask is looking at four, five different masks, and has no real way of comparing those. If you have a specification in place, you at least know that these have been through a process, that they have been tested, shown to work to some level that has been agreed upon by a group of experts.
The other thing you could do is you can show how one varies in breathability or material filtration. What you want to have is to get a measurement or a rating of how breathable something is so people can make an informed decision.
This post was originally published in NC State News.