They must be helping, since he said he didn't feel hoarse after wearing the mask. It may be worth doing some experimentation. I wonder if a simple dust mask would provide some benefit. They don't restrict breathing as much as the respirators and are easier to use.When you say 3M mask I'm guessing you mean a cartridge type respirator. When was the last time you changed the cartridges and do you have the correct cartridges installed? Having cartridges for organic vapors, cleaning, painting fumes won't give you the level of protection you need if you being more exposed to fine airborne particulates.
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