I recently visited an industrial plant where workers were using sign language. No, the workers were not deaf; they simply could not hear each other over the din of workplace noise. Turbulent flames from furnace burners, the clatter of metal, and the whine of combustion blowers, all contributed to high noise levels. Workers had little choice but to communicate via hand signals.
Is this the most efficient way to operate a facility? Lower productivity due to high noise is a significant hidden cost in industrial plants.