What must be done to ensure that breathing air is of high purity?

Paragraph (i) of the standard provides references which establish parameters for breathing air quality. Compressed and liquid oxygen are required to meet the specifications for breathing air outlined by the United States Pharmacopoeia (USP); compressed air, at a minimum, is required to meet the specifications outlined in the ANSI/Compressed Gas Association (CGA) Commodity Specification for Air, G-7.1-1989 for Grade D breathing air. Cylinders of purchased breathing air must have a certificate of analysis for purchased breathing air quality obtained through the supplier.