They make breathing in a mask more comfortable, but face coverings bearing filter valves have been banned from military health facilities and increasingly at bases as well, under guidance issued by the Defense Health Agency and the Army Public Health Center.
Masks that contain plastic filters or vents protect the wearer against any germ-laden moisture droplets or exhaled air, but they allow breath to be emitted without passing through the protective cloth barrier, potentially exposing others to the wearer's germs, according to Dr. Steven Cersovsky, a scientific advisor to Army Public Health Center.
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As such, Cersovsky said, "these face coverings should not be authorized for use."
"The Army Public Health Center does not recommend the wear of face coverings with exhalation valves," he added.
The Centers for Disease Control and Prevention updated its face mask guidelines in August recommending against the use of masks with exhalation valves. Army Public Health Center experts also evaluated the popular face masks, and finding them lacking, issued an operations order in August to all Army medical personnel restricting their use.
"APHC has its own experts in personal protective equipment who have evaluated these products and confirmed their inability to adequately prevent potential transmission of viruses and other infectious organisms," he said.
The Defense Health Agency also issued guidance recommending against use of these types of masks at its facilities, including domestic U.S. military hospitals and clinics. Some installation and operational commanders have also prohibited them within their units or on base.
U.S. Forces Korea banned masks with valves beginning in early September, around the same time the Republic of Korea's Ministry of Food and Drug Safety recommended against their use.
Personnel, employees and dependents on U.S. military installations in South Korea are required to wear masks indoors and outside when they can't socially distance, and they are allowed to use cloth masks, neck gaiters, bandannas or scarves. But masks with valves are no longer allowed.
The announcement was met with frustration by some of those affected by the ban. They voiced their feelings on Facebook, with many complaining that they purchased their masks at post exchanges and some types of these masks that have valves that are lined inside with cloth, providing similar protection to an all-cloth mask, they argued.
U.S. Forces Korea has upheld the ban, however.
“The CDC now says the purpose of masks is to keep respiratory droplets from reaching others to aid with source control. However, masks with one-way valves or vents allow air to be exhaled through a hole in the material, which can result in expelled respiratory droplets that can reach others," wrote U.S. Army Garrison Daegu on Facebook.
In announcing the ban on vented masks at Joint Base San Antonio medical facilities, officials asked staff members, patients and vendors to "continue to do your part to slow the spread of the virus."
"Wear a proper face covering, wash your hands regularly and socially distance from others, both at work and in your communities. That is the best way to preserve the health of our patients and staff," they wrote in a release.
As of Wednesday, the Defense Department had logged 66,375 cases of COVID-19, including more than 11,000 new cases in September alone. More than 45,000 military personnel, 6,092 dependents, 10,210 civilians and 4,314 contractors have tested positive for the illness.