Interesting snip from the first article:
So in the 1970s, the Bureau of Mines and the National Institute for Occupational Safety and Health teamed up on creating the first criteria for what they called “single use respirators.” The first single-use N95 “dust” respirator as we know it was developed by 3M, according to the company, and approved on May 25, 1972. Instead of fiberglass, the company repurposed a technology it had developed for making stiffer gift ribbons into a filter, by taking a melted polymer and air-blasted it into layers of tiny fibers. “They look like somebody dropped a bunch of sticks—and they have huge spaces between them,” says McCullough.
As particles, whether silica or viruses, fly into this maze of sticks, they get stuck making turns. 3M also added an electrostatic charge to the material, so even smaller particles find themselves pulled toward the fibers. Meanwhile, because there are so many big holes, breathing is easy.
The longer you wear an N95 respirator, the more efficient it becomes at filtering out particles. More particles just help filter more particles. But breathing becomes more difficult over time as those gaping holes between the fibers get clogged up with particles, which is why an N95 respirator can’t be worn for more than about eight hours at a time in a very dusty environment. It doesn’t stop filtering; it just prevents you from breathing comfortably.
N95 respirators were used in industrial applications for decades before the need for a respirator circled back to clinical settings in the 1990s with the rise of drug-resistant tuberculosis. HIV had a lot to do with its spread across immunocompromised patients, but tuberculosis infected many healthcare workers, too. To stop its airborne spread, N95 standards were updated for healthcare settings, and doctors began wearing them when helping tuberculosis patients. Even still, respirators are rarely used in hospitals to this day because it’s only outbreaks like COVID-19 that necessitate so much protection.
I can't remember what the concern was, but during one of my three hospital stays in 2014 the staff was concerned with a particular outbreak. I was tested everday and the result of the test dictated how my visitors had to dress prior to a visit.
Some days they arrived in the clothes they wore coming into the hospital. Other days they arrived fully gowned with head coverings and masks. It was a challenge to know sometimes what was expected.