I am interested in what tests you use to conclude that a mask is safe. I work in a research area where my guys have to process equipment that can carry pathogens or have carcinogens/ debris, etc...
Every year they have to go to be fit tested for the appropriate mask. We are told that the guys have to have everything completely shaved that will touch the perimeter of the mask or they will not pass and it is not safe.
They use a dummy mask with a nipple on the end and it is hooked to a machine by airline tubing. The machine puts off a saline vapor and the entire unit is hooked to a computer.
There are multiple tests that they have to take IE:Turning head side to side, up and down,leaning forward, speaking, etc... Each of the tests lasts a few minutes and you get a pass or fail for each section.
I have seen guys go through 5 or 6 masks until one passes the testing regime. Funny, there is a metal guard at the nose area of the mask and it is very specific how you mold it to the face. It needs to be done from either side of the nos and not pinched from the top or the seal is broken.
Sorry to ramble I was just curious as to how you guys determine proper fit. It seems to be quite a science in my industry.