If Your Mask Has a Valve, It Is Half Useless
If you wear a face mask with a small plastic flap built into it, you should be aware that valves reduce the mask’s effectiveness – and this is true whether your mask is a store-bought N95 or a designer cloth mask.
These valves allow the exhaled air to bypass the filter. When you breathe in, the air you breathe is filtered by the mask; when you breathe out, it is not. (The valve works in one direction only.)
This video from the government agency NIST shows unfiltered air bursting from the mask valve with each breath. The person in the valveless mask still exhales the same amount of air, but all of his air is filtered through the material of the mask.
One-way valves make sense if you’re collecting sawdust in your basement, walking around California during the bushfire season, or working in a factory where particles you definitely don’t want to breathe could be in the air. In these cases, the mask’s job is to protect you. The valve makes it more comfortable to wear, so you can go through a work day or factory shift without feeling too overwhelmed. But that’s not why we are all wearing masks now.
Why valves aren’t good for fighting infections
In the COVID-19 era, we wear masks outside for two reasons: First, we hope they can protect us from other people at least a little. (The science of this is not very convincing.) The second reason is more important: they protect us from infection of others, if it turns out that we are infected and do not know about it.
The valves defeat this second target. The valve mask allows you to exhale without filters; the valve acts as a small escape hatch for any droplets containing the virus that you breathe out. Some municipalities requiring masks indicated that valve masks are not counted . For the same reason, you also don’t usually see valve masks in healthcare settings. As the CDC explains :
Respirators with exhalation valves should not be used in situations where a sterile field must be maintained (for example, during an invasive procedure in an operating room or treatment room) because the exhalation valve allows unfiltered exhaled air to escape into the sterile field.
If you have a stock of N95s that you’ve previously used as dust masks, or if you’re considering buying a designer cloth mask with a valve (for some reason, all the fancy ones seem to have valves), keep in mind that they only filter yours. inhaled. air, not exhaled air. And now this is not enough.
If these masks are all you have, you can tape the valve or check if the valve can be closed (some of the plastic valves on reusable masks can rotate to close until they click). As the saying goes, “your mask protects me, my mask protects you,” so please use a valveless mask to do your part to reduce transmission.
This post was originally published in April 2020 and was updated on November 11, 2020 to include video from NIST and advice on closing or closing a valve on valve masks.