I have just finished a 41 year career as a car painter and used an activated carbon respirator from day one! It's doubtful I could have lasted to my age, working in the environment I worked in without it. I also used gloves for most of the time. Most of my working life was working flat rate in car dealership body shops, so I have probably sprayed thousands of gallons of chemically hardened paint. I painted in high-end down-draft spray booths for most of that time, but if I was painting large vehicles I would switch to a full-face air-supplied mask if the overspray was intense.

Wear a respirator when using epoxy, whether it's wet or you're sanding it. It's toxic, and just because you can't smell anything doesn't mean it isn't emitting fumes. Some auto paint manufacturers purposely add an unpleasant scented feature to their paint to encourage users to use a respirator!

The filters in activated charcoal filters have a life span based on usage, which is determined by number of hours they are exposed to atmosphere, so when finished using them they should be stored off the mask in a sealed plastic bag. This action will halt the clock on their life span. To test them, mask manufacturers have purpose made intense scent that you put in front of a mask user to see if the carbon is still active in the filters. When they are deactivated the scent can be smelled. 3M suppliers supply these products.