I assume we are talking about rock breakers attached to the end of heavy equipment? Your employer is legally responsible for telling you the hazards and precautions of your job. Each hammer may have different manufacturer instructions. Most injuries from this type of equipment comes during servicing the hammer itself. Due to the weight of the different parts, there is a crush hazard. During operation there is: noise hazard (most likely well above 85dB), vibration hazard to the operator, dust hazards from breaking up concrete, rock, etc, and the obvious track hoe and other heavy equipment hazards.