In a study published in JAMA Internal Medicine, researchers studied 29 different face masks and used fit and use guidelines by the Occupational Safety and Health Administration to evaluate the FFEs in a variety of breathers worn by a male and female volunteers.
When two people wearing masks interact, chance of SARS-CoV-2 transmission is drastically reduced. Some masks were as much as 79 percent effective at blocking particles that could carry the virus. UNC scientists researched the protectiveness of various kinds of consumer-grade and modified masks. Researchers used an approach based on the OSHA Fit Test to determine the fitted filtration efficiency of facemasks. The top-of-the-line N-95 mask proved to be 98 percent effective.
Fitted filtration efficiency tests were conducted in a custom-built exposure chamber. Masks were fitted with sampling probes using a Fit Test Probe Kit for Disposable Facepieces 8025-N95 (TSI) to allow sampling of aerosol inside the face mask. Three respirator sterilization methods were tested on used masks: ethylene oxide (EtO), steam (121 °C, 15 minutes), and vaporized hydrogen peroxide (8 g/min, 260 PPM, 100-minute cycle) The FFE of these sterilized, used masks was measured after a single sterilization cycle as described above.
N95 respirators fitted to the face are the preferred choice of protection from bioaerosols. However, availability of these items may be compromised during periods of high demand, such as in a pandemic. Recently, sterilization and decontamination of face masks has emerged as a novel method to prolong the limited supply of existing respirators. The study evaluated particle penetration for commonly available face masks and alternatives. The most effective face mask achieved only 79.7% FFE, and masks with elastic ear loops were the least effective when moving the head left and right (21.2% F FE) and bent at the waist and looked up and down.
The most penetrating particle size was found to be 30 to 60 nm, which is similar in size to those used for measurements in this study. A limitation of this study is the decision to test each mask on a single man (and woman for a few comparisons) rather than a large number of individuals with a full range of facial configurations.
Even face masks with less than 95% FFE (eg, surgical masks) are effective in preventing acquisition of epidemic coronaviruses. N95 respirators had no increased prevention benefit over surgical masks. The CDC and Infectious Diseases Society of America has recommended the use of N94 respirators.
Cover Photo Credit: UNC School of Medicine