By Kathleen Berger, Executive Producer for Science & Technology
D.I.Y. face masks are now a trend based on necessity. There are some basic dos and don’t’s, but there is a science behind it.
PhD student David Dhanraj in the McKelvey School of Engineering at Washington University in St. Louis is testing materials to determine best alternatives to the N95 masks used by health care workers. At the Aerosol and Air Quality Research Laboratory in the Center for Aerosol Science and Engineering, Dhanraj is testing filtration efficiency of accessible materials.
“The shortage of the N95 is the biggest reason,” explained Dhanraj. “People do not have access to N95’s so people tend to use whatever they find around the house.”
While it’s no surprise some common cloth fabrics don’t have nearly the filtration efficiency as an N95, some available materials are at least closer to N95 performance. But even the more efficient available materials are a function of particle size, as well as mask design and coverage.
For example, two layers of Halyard fabric, a medical grade fabric cloth used for hospital gowns or sterilization wraps, have a maximum filtration efficiency of about 80%. However, the more penetrating particle size of the COVID-19 virus can lower its efficiency to about 45%. And if the mask doesn’t fit the face well enough, Dhanraj said leaks alone might drop an efficiency level by about 20%, no matter the particle size the mask has the potential to filter.
Dhanraj said a Swiffer is another option with good results.
“We were expecting something around 60%, but then it was higher and we were a little surprised,” he said.
A Swiffer filter alone, which would be sewn into a cloth mask, has the potential to be 75% efficient with two layers. Against the more penetrating viral particle sizes, the same Swiffer filter is about 40% percent efficient. And leaks account for a loss of about 20% regardless of particle size.
Dhanraj said D.I.Y. mask makers could at least have some peace of mind knowing which materials offer better protection than others.
Dhanraj provided a list of tested materials in the order of highest to lowest efficiencies.
- Halyard fabric
- HVAC filter
Details on test results for the various materials are included in HEC Media’s video story.