Although I haven never worked with respirators, the thought of using one with a beard has always intrigued me. I have experience with a diving mask and that tends to seal reasonably well with the moustache, though small leakage occurred. I could imagine a helmet like construction to be placed over your head as a solution, but I don't know if such a thing exists or is really practical. I can imagine you wouldn't want the hazardous materials ending up in your beard so your beard would also have to be protected.