When I was in the Navy, my first Command was USS NIMITZ. We would dry dock the ship after every 6 mth cruise for any moderate to major repairs to the screws and shafts, the hull, and to update the tech onboard. I was tasked with rehabbing our Aviation Ordnance Support Equipment storage spaces.  Anyway, because of the work and the chemicals/debris involved, I had to wear a respirator in these spaces all day.  BUT, as with everything in the military, these respirators required certification classes from OSHA, EPA, CDC, AND NAVOSH, the Navy's Occupational Safety Hazard agency. Guess what they made sure to remind us of throughout the class? 2 hr work intervals while masked, followed by 30 min breaks with no respirator in a clean air environment and to wash both your fave and the respirator before and after each use. They had the same rules for the paper masks, too as not all the work I did required a respirator.  I quickly learned that their rule in masks and respirators HAS to be followed to the "T" after my first day. I disregarded their warnings about the side effects and it reulted in a rash and migraine.  If the fucking agencies that make the mask safety guidelines and the scientists that study this stuff we're saying in the 90's not to be masked for more than 2 hrs at a time, then why do all these idiots out here keep doing it?