Face Mask 101: USF researcher shares best mask-wearing practices

Dr. Sarah (Ying) Zhong is an Assistant Professor in the USF College of Engineering: Department of Mechanical Engineering, who specializes in Energy Management Technologies and Smart Health Improvement Systems. She operates the Green Research for Energy Efficient Innovations (GREEN) Lab, and is a recipient of the COVID-19 Rapid Response Research Grant -- a program created by USF to facilitate potential treatment, technology and social mitigation strategies to combat the global COVID-19 pandemic.

Zhong seeks to address PPE shortages with a technology designed to sterilize and re-charge N95 and surgical masks, making them safe for re-use in under five minutes. Her team is also designing tech to sterilize shared surfaces in heathcare settings, homes, restaurants, and other public spaces -- reducing the use of disinfectants and promoting sustainable sterilization practices.

Zhong estimates testing to be complete by the end of June, and looks to move forward quickly in developing affordable, portable PPE sterilization devices -- in the $50 range -- for healthcare workers as well as the public.

In the meantime, as Florida businesses gradually open to the public and more people venture out, 83 Degrees connected with Zhong to learn best practices for safely and effectively using masks.

83D: In this stage of the COVID-19 pandemic, who should be wearing masks?

Sarah (Ying) Zhong, an Assistant Professor in the USF College of Engineering, is a recipient of the COVID-19 Rapid Response Research Grant.Dr. Zhong: Everyone in a shared area who may have a chance to be in contact with others should wear masks to protect themselves and others because at this time, asymptomatic [COVID-19] patients are difficult to identify.

83D: What types of masks are there and how do they differ? 

Dr. Zhong: The most common masks can be categorized into three major types:

First, there are home-made cloth masks which have a pore size in the range of tens of micrometers -- but the SARS-CoV-2 virus is about 100 nanometers. Its major carriers, droplets, range from several micrometers to millimeters. Cloth masks can block spreading or contraction of large droplets but are not effective for blocking droplets in the smaller micrometer range -- which can stay in the air for minutes or longer. When you are wearing cloth masks, social distancing is highly recommended.

The second major type of mask is the three-layer surgical mask. The external layer is hydrophobic [repels water]. The middle layer is non-woven polypropylene fiber, which has a much smaller pore size than cloth. The inner layer is hydrophilic [attracted to water]. During the manufacturing process, static charges are “injected” in the polypropylene fibers. Electrostatic attraction is an important mechanism for the mask to stop the contaminated small-size droplets because most droplets are negatively charged and the non-woven fibers are positively charged. Once the droplet gets close to the mask, it will be attracted to and stopped by the mask, so the chance of the contaminated droplet getting into contact with the mouth or the nose is extremely reduced. The static charge allows surgical masks to prevent infection while being breathable. The suggested lifetime of surgical masks is about four hours because the humidity from the mouth or nose will reduce the static attraction function.

The third type is the N95 mask. Also made in three layers, the functional middle layer of an N95 mask is 7-8 times thicker than a surgical mask, so better filtration efficiency can be reached -- approximately 95%. Static charges also play an important role. The inventor of N95 masks, Dr. Peter Tsai, said static charges can make a significant difference in filtration efficiency: about 37% without versus 95% with a static charge. The tight rubber band and design of N95 also offers better sealing than surgical masks. The typical lifetime for an N95 mask is about 10 hours.

83D: Do masks eliminate or reduce the need for social distancing? 

Dr. Zhong: When wearing a cloth mask, social distancing is essential and necessary. Cloth masks are not enough to protect yourself or others. If you are wearing a surgical mask, social distancing is still recommended. Even though surgical masks can protect you in most situations, they are not 100% effective -- especially because the sealing of surgical masks is not as good and many people cannot wear them properly. N95 masks are what healthcare workers wear during close contact with patients. These masks can protect the wearer in situations where they cannot practice social distancing. N95 masks are not comfortable to wear, and, most importantly: They should be saved for the healthcare workers. 

83D: Can you share best practices for using and re-using masks?

83 Degrees writer Jessi Smith demonstrates the proper nose fit and coverage for a homemade mask, this one designed by Sarasota artist Kari Bunker. Dr. Zhong: Wash or sterilize your hands before you put on the mask. Press the aluminum strip along your nose while you are putting on the mask to get the best sealing effect. Never touch your mask or your face while you are wearing it. If you want to take off the mask, sterilize your hands first, then fold the outside inward. Do not expose yourself to the possibly contaminated side after wearing.

If you want to sterilize and reuse the mask, the best way, for now, is dry-heating [baking] for 30 minutes at 70 degrees C (158 F). Cloth masks should be sterilized every 1-2 hours, surgical masks approximately every 4 hours, and N95 masks every 10 hours. Sunlight, disinfectant wiping, alcohol dipping, steaming, boiling, and one-side treatment with UV are not enough to 100% kill the virus. 

83D: If people are crafting fabric masks at home, are there any materials and techniques you recommend that might be most effective?

Dr. Zhong: Hydrophobic microfibers may be more effective than cotton, as cotton may easily get wet and droplets can still get in contact with you easily. You can try to make a two-layer mask with an outside layer made by hydrophobic microfibers and an inside layer made by cotton to make the mask more efficient. But remember: Cloth masks are not effective enough to avoid social distancing.

Dr. Libin Ye from the USF Department of Cell Biology, Microbiology, and Molecular Biology, is the co-Principal Investigator on Zhong's project. Ye's lab is leading and contributing significantly in the sterilization efficacy test. 

For more information, visit these links:
Enjoy this story? Sign up for free solutions-based reporting in your inbox each week.

Read more articles by Jessi Smith.

Jessi Smith (she/they) is a freelance writer who is passionate about sustainability, community building, and the power of the arts and transformative storytelling. A fourth-generation Floridian, Jessi received her B.A. in Art History and English from Florida International University and began reporting for 83 Degrees in 2009. When she isn't writing, Jessi enjoys taking her deaf rescue dog on outdoors adventures, unearthing treasures in backroads antiques and thrift shops, D.I.Y. upcycling projects, and Florida-friendly gardening.