I have two different types of respirators from the big box home improvement store(s).
How do you determine when to change the filters?

I used to work in health care and they had a test for fit of the masks--they sprayed some solution and if you could taste it while the mask was on the mask was not adjusted correctly. (I could not be tested because I could not taste the stuff before putting on the mask.

What routine do people use to make sure the mask is doing what it is intended to do--protect our lungs

Thanks