The researchers, from the University of Cambridge, carried out 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 performs no better than a cloth mask. Minor differences in facial features, such as the amount of fat under the skin, make significant differences in how well a mask fits.
The results, published in the journal PLoS ONE, also suggest that the fit-check routine used in many healthcare settings has high failure rates, as minor leaks may be difficult or impossible to detect by the wearer. While the sample size was small, the researchers hope their findings will help develop new fit tests that are quick and reliable, in the case of future public health emergencies. The current study only evaluated the impact of fit on the wearer of the mask – the team will evaluate how fit impacts the protection of others in future research.
The COVID-19 pandemic has made well-fitting face masks a vital piece of protective equipment for healthcare workers and civilians. While the importance of wearing face masks in slowing the spread of the virus has been demonstrated, there remains a lack of understanding about the role that good fit plays in ensuring their effectiveness.
“We know that unless there is a good seal between the mask and the wearer’s face, many aerosols and droplets will leak through the top and sides of the mask, as many people who wear glasses will be well aware of,” said Eugenia O’Kelly from Cambridge’s Department of Engineering, the paper’s first author. “We wanted to quantitatively evaluate the level of fit offered by various types of masks, and most importantly, assess the accuracy of implementing fit-checks by comparing fit-check results to quantitative fit testing results.”
Image: Doctor in the Fight Against Ebola in Sierra Leone
Credit: Defence Images
Reproduced courtesy of the University of Cambridge