Are there any studies that measure the loss of mask performance over time while is storage?
Re: 1813:
“Frequently Asked Questions: 3M Health Care Particulate Respirator and Surgical Masks Storage Conditions and Shelf Life”
Probably similar to SPAM. It might not taste as good, but it is safe to eat and gives you the nutrients.
Although I did throw away a bunch of masks my old-man sent me in 1984(?) when Mt. Saint Helens blew. I tossed them around 2009 I'm guessing (bird flu). But, IIRC, the only thing bad was the foam on the nose bridge was deteriorated. The rubber bands will get loose over time with use. I got some UV resistant bands to replace the bands on my masks. The masks can be dried out, or zapped with UVC light or ozone to decontaminate them. The ozone however causes the regular bands to go bad.
If they have an expiration date they have likely degraded to a point that they are no longer effective. This can be from bands, nose bridges, or even the material itself will degrade to a point they can no longer meet the NIOSH standards for safety and effectiveness. You may not be able to see the degradation on the mask itself.
“Particulate respirator The particulate respirator is the simplest, least expensive, and least protective of the respirator types available. These respirators only protect against particles. They do not protect against chemicals, gases, or vapors, and are intended only for low hazard levels. The commonly known “N-95” filtering facepiece respirator is one type of particulate respirator, often used in hospital to protect against infectious agents. Particulate respirators are “air-purifying respirators” because they clean particles out of the air as you breathe. Even if you can’t see the particles, there may be too many in the air for this respirator to provide adequate protection.”
Read this last line. And once you are in a situation where the particles overtake the mask the mask is what is call spent and needs to be replaced. This is likely what is happening in hospitals where nurses and doctors are getting sick with Covid-19. They are not changing out the mask regularly probably due to lack of supply.
https://www.cdc.gov/niosh/docs/2003-144/default.html