Photo: Washington Post Photo by Carolyn Van Houten
Those face masks you see with coin-shaped valves on the front may seem intriguing but they are not as good at preventing the spread of the new coronavirus as the apparently low-tech, non-valved masks.
Some masks designed for hot and dusty construction jobs – where the intent is to filter the dust before it hits the lungs of the wearer – have “exhaust” valves that allow the exhaled air to flow out more easily, to maintain cooler who wears it.
The 3M company, which manufactures valve masks for such occupations, illustrates on its website how they work: the inhaled air is filtered through the fabric part of the mask and the hot and humid exhaled air exits through the valve. The system may be what you want when you destroy a kitchen to remodel it, but the valve defeats the purpose when you are trying to slow down the spread of a virus.
Public health experts have recommended wearing a mask to prevent respiratory droplets from spreading in the air when you exhale, speak, cough or sneeze and the valves allow it to pass.
Medical masks, you will notice, have no valves.
In its guidelines for wearing the mask, San Francisco states that valve masks do not meet its standards.
“Any mask that incorporates a one-way valve (typically a raised plastic cylinder about the size of a quarter on the front or side of the mask) designed to facilitate exhalation allows you to release droplets from the mask, placing others in the vicinity at risk”, says the order.
The Centers for Disease Control and Prevention recommend simple cloth masks for the public to prevent the spread of covid-19. Some layers of cotton prevent most potentially infectious respiratory droplets from leaking into the air around you and are also much cooler than the N95 masks that adapt to the shape.