Aberdeen Proving Ground, MD — When the Centers for Disease Control and Prevention, the Department of Defense, and many state government began recommending or requiring that people wear face coverings when out in public and unable to maintain proper social distancing, the Combat Capabilities Development Command (CCDC) Chemical Biological Center put more than 100 years of filtration experience to use in testing materials for homemade masks.
Since the COVID-19 epidemic began, the Center has been contacted by dozens of defense agencies, federal agencies and health organizations to see if its experts can help with the national shortage of personal protective equipment. The Center is one of only a handful of agencies that is experienced in performing tests that precisely measure materials’ filtration efficiencies in strict accordance with National Institute for Occupational Safety and Health (NIOSH) standards. It is also one of a very few organizations that have the TSI Model 8130 Automated Filter Tester. So the Center was the obvious choice to perform this research.
“The challenge is to pick a material that effectively blocks the virus particles from going through the material while not being too hard to breathe through,” said David Caretti, chief of the Center’s Chemical Biological Protection & Decontamination Division and leader of the team testing homemade face covering materials. “If the resistance is too high, airflow will simply bypass the covering and go around the edges.”
“We knew that claims about masks and face coverings were exploding all over the internet, and we wanted to make sure that any decisions about materials these agencies make will be based on proven science,” said Caretti.
The Center performs its testing by spraying a salt aerosol at a swatch of material. The testing team measures the density of salt aerosol suspended in the air on one side and compared it to the density on the other side after it passes through the material. These material screening trials utilize the same aerosol challenge and instrumentation that is used when N95 filters are certified to NIOSH standards.
The team started out by testing materials sent to them by organizations seeking their expertise, then broadened out to testing materials likely to be found in the home that members of the public could use to make their own face coverings.
They found that one of the best readily available materials to use in a homemade face covering is four-ply microfiber cloth which can be found in the cleaning section of most big box stores. It filters out over 75 percent of particles. In comparison, the N95 mask used by healthcare workers in hospitals can filter 95 percent of particles or greater. The team also found that even a polyester bandana can be reasonably effective if it is used in layers. It will filter out 40 percent of suspended particles.
Thus far, the Center has run more than 300 trials and continues to test new materials. Armed with this information, the Center is now able to give other agencies the best filtration efficiency information possible for them to pass on to their stakeholders.
How to hand sew a face mask: https://www.nytimes.com/article/how-to-make-face-mask-coronavirus.html
How to machine sew a face mask: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html