What grade breathing air is used in SCUBA cylinders?

Answer 1

* The CGA Grade "E" quality verification level has become the specification most widely referenced for sport diving. CGA Grade "E" is generally considered to be the absolute minimum acceptable breathing gas quality for Scuba diving, and many consider it to be too liberal. Filling an "Oxygen Clean" cylinder with CGA Grade "E" will introduce hydrocarbon contamination such that the cylinder is no longer considered O2 clean and may not be used for partial-pressure blending.

* "Oxygen-Compatible" is CGA Grade "E" with reduced maximum acceptable carbon monoxide, hydrocarbon and particulate levels. The International Association of Nitrox Divers (IANTD) and American Nitrox Divers International (ANDI) created this designation for gases used in technical diving and gas blending. The U.S. Navy and the American Academy of Underwater Sciences (AAUS) have also issued "Oxygen-Compatible" specifications. All the "Oxygen-Compatible" specifications are similar but not identical. For the purposes of this discussion we'll use the IANTD "Oxygen-Compatible"