Good Respirators have Check valves to Protect Filters: COVID-19 Safety

A good respirator will provide extremely easy exhale, no heat/moisture build-up and a long lasting filter.  The long lasting filter is probably most important.

Home-made masks are far better than nothing. They catch plenty of potentially dangerous droplets expelled by others. Unfortunately, like most other masks, they catch close to 100% of the droplets expelled by the wearer. Home-made and most other masks become unsanitary rapidly. Most people might be better off  keeping things simple and just wear a 3 ply face mask that is disposable. For those that like to focus on details and are not easily bored, I wrote this complicated post.

A good respirator contains valves that plumbers call “check valves”. Most of these are only designed to make exhaling easier. It is hard to find respirators that use check valves that filter incoming AND outgoing air. 

Check valves only allow flow in one direction. If you focus on details concerning some Respirators, you will notice two check valves. Most of these make it easy to exhale UNFILTERED breath.  Both valves only open as the wearer exhales. This type of respirator expels UNFILTERED breath.

It is safer for others  to wear a mask like the 3 ply listed above or a  much more complicated one.  A check valve on the inhale (filtered) part of a respirator prevents the wearer’s breath (droplets) from causing premature failure of the inhaling filter. Meanwhile, to protect others, properly designed respirators should filter exhaled air. Easier exhaling and longer lasting inhaling protection can be provided by a properly constructed-but-hard to find respirator. Otherwise, it is probably best to use a 3 ply disposable mask.

Most masks and some respirators waste about 80% of the life of the filtering material. If a filter only has to trap particles in the incoming air it can last much longer. When a filter has to catch the wearer’s droplets at close range and often containing food particles, it clogs and begins breeding organisms quickly.

One “rule of thumb test” concerning filter contamination (wear out) is called “the smell test”. A rancid or other strange smell usually indicates filter replacement is past due. Often, homemade masks are so porous that the smell test provides little to no benefit.

Much like printer makers selling ink cartridges, many respirator makers are beginning to make most of their profit by selling filters. Some people are probably saving lots of money buying specially made fabric like Zosakonc non-woven filter fabric to make their own filter replacements.

Soon, people might start looking for eye protection that is neatly coordinated with a respirator. Eventually when we have to reduce our “safe distance” we might choose to add eye protection to our respirators. Working and researching together, we can find ways to feel safe.