A team of researchers studying the effectiveness of different types of face masks found that in order to provide the best protection against COVID-19, the fit of a mask is as important or more important than the material it is made of.
Researchers at the University of Cambridge performed a series of different fit tests and found that when a high-performance mask – such as an N95, KN95 or FFP2 mask – is not properly fitted, it does not perform better than a masking cloth. . Small differences in facial features, such as the amount of fat under the skin, make significant differences in the fit of the mask.
The results, published in the journal PLoS ONE, also suggest that the fit verification routine used in many healthcare environments has high failure rates, as small leaks may be difficult or impossible to detect by the user. Although the sample size is small, the researchers hope that their findings will help to develop new rapid and reliable fit tests in the case of future public health emergencies. The current study evaluated only the impact of the adjustment on the mask user – the team will assess how the adjustment affects the protection of others in future research.
The COVID-19 pandemic made well-fitting face masks a vital piece of protective equipment for healthcare professionals and civilians. Although the importance of using face masks to slow the spread of the virus has been demonstrated, there is still a lack of understanding about the role that a good fit plays in ensuring its effectiveness.
“We know that unless there is a good seal between the mask and the wearer’s face, many aerosols and drops will leak out of the top and sides of the mask, as many people who wear glasses know very well,” said Eugenia O ‘Kelly , from the Cambridge Department of Engineering, the article’s first author. “We wanted to quantitatively assess the level of adjustment offered by various types of masks and, most importantly, assess the precision implementation of adequacy checks by comparing the results of the adequacy check with the results of quantitative adequacy tests. “
For the study, seven participants first evaluated the N95 and KN95 masks by performing an adjustment check, according to the NHS guidelines. Participants then underwent a quantitative adjustment test – which uses a particle counter to measure the concentration of particles inside and outside the mask – while wearing N95 and KN95 masks, surgical masks and tissue masks. The results assessed the protection of the mask user, which is important in clinical settings.
The N95 masks – which are a similar pattern to the FFP3 masks available in the UK and the rest of Europe – offered higher degrees of protection than the other categories of masks tested; however, most N95 masks did not adapt properly to the participants.
In their study, the researchers found that when fitted correctly, N95 masks filtered more than 95% of airborne particles, offering superior protection. However, in some cases, ill-fitting N95 masks were only comparable to surgical or cloth masks.
“It is not enough to assume that a single N95 model will fit the majority of the population,” said O’Kelly. “The most suitable mask that we saw, the 8511 N95, fit only three of the seven participants in our study.”
One observation the researchers made during the study was the width of the mask flange – the area of the material that comes in contact with the skin – can be a critical feature for the fit. Masks that fit the largest number of participants tend to have wider, more flexible flanges around the edge.
In addition, minor facial differences were noted to have a significant impact on quantitative adjustment. “Adjusting the face perfectly is a difficult technical challenge and, as our research has shown, small differences like a centimeter-wide nose or slightly fuller cheeks can make or break the fit of a mask,” said O’Kelly.
Adjustment checks performed automatically are attractive because they save time and resources and are often the only fit test method available. However, this study and studies of adjustment verification systems in other countries indicate that such adjustment verification systems are not reliable.
The researchers hope that their results will be useful for those working on new technologies and programs to assess suitability, so that health professionals and other frontline professionals are adequately protected in the event of any future pandemic. In addition, they hope that these results will draw attention to the importance of fitting clinical-grade masks, especially if such masks are widely used by the public. This study did not assess the impact of the adjustment on protecting others, which is an area of future research.
Reference: “Comparing the fit of N95, KN95, surgical and tissue facial masks and evaluating the accuracy of the fit check” by Eugenia O’Kelly, Anmol Arora, Sophia Pirog, James Ward and P. John Clarkson, January 22, 2021, PLOS ONE.
DOI: 10.1371 / journal.pone.0245688