Copper Tube Handbook: II. Minimum Recommendations for
Nonflammable Medical Gas Systems Use Medical Gas tube Types K or L, suitably cleaned for oxygen service per NFPA Standard No. 99, Health Care Facilities. Air-Conditioning and Refrigeration Systems Copper is the preferred material for use with most refrigerants, including newer, natural refrigerants like CO 2 , propane, isobutane and others ( copper is not recommended for use with ammonia ).