Is Air A Medical Or Industrial Gas?

Air can be used for breathing or for industrial/analytical applications. The production and analytical requirements may be specified by the FDA or OSHA, depending on the usage. Let’s consider three case studies for air applications.

Industrial/Instrument Air
“Instrument Air” is often used for purging instruments or powering pneumatic actuators. “Dry Air” is often used for drying out piping/samples. “Hydrocarbon Free Air” (Zero Grade, Ultrazero Grade, THC Free Grade, etc.) is commonly used to support flame ionization detectors in analytical labs. These applications are not intended for breathing and are typically not covered by FDA or OSHA air specifications. The supplier determines the specifications, fill procedures and analytical requirements.

OSHA Breathing Air (Grade D)
“OSHA Grade D Air” is often for compressed breathing air. The testing requirements are specified in 29 CFR 1910.134(i). The regulations specify the CGA document Commodity Specification for Air G-7.1 (1989). (CGA G-7.1 has been updated and the current version is 2004.) Also see CGA document Compressed Air for Human Respiration G-7 for more details.

Analytical Specifications for OSHA Grade D Breathing Air

If OSHA Breathing Air is produced by reconstitution (blending oxygen and nitrogen), be aware that you may be able to omit certain detector tube tests if you use prequalified oxygen, USP and nitrogen, NF to blend the medical air. Both the oxygen and nitrogen must have been produced by the air liquefaction method. (See CGA G-7 and G-7.1.)

Medical Air
“Medical Air” is also called “Air, USP.” This product is a drug and should be prescribed by a physician or used in drug manufacturing operations. The analytical specifications are defined by the United States Pharmacopoeia (USP).

As of April 2009, the electrochemical oxygen analyzer is the official test method for the assay of medical air. If you use the paramagnetic oxygen method for this assay, be sure you have a copy of the validation report/SOP at each location using the method.

If the medical air is produced by reconstitution, the contaminant detector tubes may not be required if you use prequalified oxygen, USP and nitrogen, NF to blend the medical air. Both the oxygen and nitrogen must have been produced by the air liquefaction method. You may need to confirm the identity of the balance gas (nitrogen) depending on your SOPs and fill process.

When any breathing air (OSHA or medical) is produced, especially by reconstitution, it must be analyzed for oxygen content. There have been fatal incidents where cylinders supposedly containing air were used for life support and were deficient in oxygen concentration.

Follow the analyzer manufacturer’s specifications for calibration and operation. Individually sample each cylinder for oxygen content. Analyze each cylinder when a group of cylinders is manifolded together. Introduce nitrogen into the analyzer before each cylinder is tested to assure the regulator and detector cell are purged of the prior sample. Allow the instrument reading to fall below 15 percent. For more details, see CGA SA-16, Safety Alert, Blended Breathing Air Fatalities.

It is critical to know the intended use of the air you produce since your FDA/OSHA compliance can be affected by not knowing the ultimate purpose of the air.

Gases and Welding Distributors Association
Meet the Author
GAWDA’s FDA & Medical Gases Consultant Thomas L. Badstubner is president of AsteRisk LLC in Blackstone, Massachusetts. Members can reach him at 508-883-0927 or at