Compressed air for breathing purposes is used by firemen and by professional or sport divers. A sport diver, using self-contained underwater breathing apparatus (SCUBA), is probably the most susceptible to potential dangers from impure air due to the lack of trained supervision or control and the great degree of individual freedom enjoyed by sport divers. It is likely that members of this group, often poorly trained and ignorant of the need for care of equipment, would be most susceptible to the dangers which result from compressed air gas cylinder corrosion.