Why are simple valveless fabric masks better at stopping the spread of COVID-19?


Those face masks you see with coin-sized valves on the front may seem intriguing, but they’re not as good at preventing the spread of the new coronavirus as the apparently low-tech valveless masks.

Some masks designed for hot and dusty construction jobs, where the intent is to filter dust before it reaches the wearer’s lungs, have “exhaust” valves that allow exhaled air to flow more easily, to keep the wearer from the cooler mask.

The 3M company, which manufactures valve masks for such occupations, illustrates on their website how they work: inhaled air seeps through the fabric portion of the mask, and hot, humid exhaled air exits through the valve. . The system may be what you want when you start up a kitchen to remodel it, but the valve doesn’t serve the purpose when you try to delay the spread of a virus.

Public health experts have recommended the use of masks to prevent respiratory droplets from spreading into the air when you exhale, speak, cough, or sneeze, and the valves allow those droplets to pass.

You will notice that medical masks do not have valves.

In its guidelines for mask use, San Francisco states that valve masks do not meet its standards.

“Any mask that incorporates a one-way valve (typically a quarter-size raised plastic cylinder on the front or side of the mask) that is designed to facilitate easy exhalation allows droplets to be released from the mask, placing other close at risk, “says the order.

The Centers for Disease Control and Prevention recommends simple cloth masks for the public to prevent the spread of covid-19. A few layers of cotton prevent most potentially infectious respiratory droplets from escaping into the air around them, and are also much cooler than fitted N95 masks.