This document provides an overview of breathing apparatus used in hazardous work environments. It discusses self-contained breathing apparatus (SCBA) which provides compressed air from a cylinder carried by the user. The key parts of an SCBA including the backplate, shoulder straps, pressure gauge, and face mask are described. Proper inspection, donning, doffing, and cleaning procedures are outlined. Various toxic gases commonly found in oil and gas work like ammonia, carbon monoxide, hydrogen sulfide, and their hazards are also summarized.