This supplement gives recommendations relating to the safety of portable compressed air cylinders used in self-contained underwater breathing apparatus. The dangers associated with cylinders are listed, and recommended safe practices and precautions to be observed during selection, handling, charging and maintenance are then given for eliminating or minimizing of these dangers. Owners and users of cylinders must comply with any relevant statutory requirements existing in the State where they will use the cylinders. They should also observe the manufacturers' or suppliers' instructions for use and maintenance, and should follow the recommendations given hereunder.