OSHA requires annual hearing testing for any person exposed to 85 dBA or more for an 8-hour time-weighted average(TWA). 85 dBA is about the amount of noise made by a lawnmower or truck at 50 feet.
OSHA calls the 85 dBA TWA the “action level”, i.e., the exposure at which you must apply hearing conservation measures.
Note that all workers with a TWA of 85 dBA or more must be included in a noise monitoring program. Dosimetry should be done after any significant change in the work environment, such as installing new equipment.