Oxygen Purity Grade Chart

industrial specialty oxygen gas

Oxygen is graded based on the contaminants in the stored gas and if it is medical grade certified.

The use cases for compressed oxygen are endless. From hospitals, laboratories, food production, fabrication, industrial manufacturing and even cryospas - these customers all use oxygen gas in their processes.

Not only are there several ways to obtain oxygen, but there are also different oxygen purity grades, depending on the percentage of oxygen by volume and the allowable contaminants in the tank. 

While we hear customers ask questions like “What should my oxygen concentration be?” or “Am I using the right oxygen monitor?" they don't realize the importance of selecting the right oxygen grade for their application. 

To get pure oxygen, oxygen plants start by separating oxygen from the air and liquefying it at -297.3°F (-182.96°C) or lower.

As the gas is collected it is tested for purity, then bottled and labeled according to grades. The Compressed Gas Association (CGA) has identified seven grades of oxygen, to show how pure the gas actually is.

Below, we talk about the most common oxygen purity grades: medical oxygen and industrial oxygen.

Industrial Grade vs. Medical Grade Oxygen

Oxygen gas in air is critical for humans and animals to breathe. Many believe air is made up of 100% oxygen. In fact, only about 21% of air is oxygen by volume.

However, there is a need in both medicine and industry to use 100% oxygen. Since it is nearly impossible to maintain this purity, different grades of oxygen have been defined to meet specific applications.

The two main classifications are medical grade oxygen and industrial grade oxygen. While both may be "pure," medical grade oxygen is certified for human use. Industrial grade oxygen is certified for everything else.

The key difference between both grades is how the tank refill process, testing and certification process is regulated. While medical oxygen has strict parameters set by the Food and Drug Administration, industrial grade oxygen does not. This allows a greater chance for contamination. Using industrial oxygen in a medical environment can be dangerous.

To save costs, many oxygen production facilities meet the purity requirements of medical grade oxygen when producing industrial grade. However, if the gas is not properly tested and certified, it cannot be sold as medical grade.

Medical Grade Oxygen

Medical grade oxygen is essential for caring for individuals and especially vital for patients in the healthcare system. It is used for many hospital treatments like surgeries, trauma, heart failure, asthma, pregnancy, and pneumonia. 

If you have a chronic disease you may need additional medical oxygen for your organs to function normally. This is especially common for people who have respiratory illnesses or breathing problems.

As with any medication or treatment, medical oxygen must meet specific requirements to ensure safety and proper purity standards. In fact, medical grade oxygen is actually considered pharmaceutical and is classified by the FDA as a drug meeting specific standards for medical use only.

Here are some helpful hints to ensure you are gaining "medical grade" oxygen:

  • For starters, medical oxygen can only be generated by medical air compressors.
  • The FDA regulates medical oxygen and sets strict parameters as it pertains to cleanliness and elimination of harmful contaminants.
  • Ask your supplier to verify their quality through an independent ISO-certified lab.
  • If you are gaining medical oxygen you should be required to visit your primary care physician to gain a prescription and/or have necessary documentation.
  • A chain of custody is required to verify that the cylinder is only being used for medical oxygen and safeguard against any contamination that could have taken place.

All in all, medical grade oxygen is only designed to be used and regulated specifically for patients demonstrating a medical need. All other uses of oxygen are considered "industrial." 

Industrial Grade Oxygen

Industries use industrial oxygen for combustion, oxidation, cutting, processing, and chemical plants. Other uses include:

  • Fabrication, welding, cutting, and cleaning
  • Steel cutting and manufacturing
  • Chemical process plant production
  • Paper-based manufacturing and bleaching
  • Bio-reaction processes

Here are some tips when selecting industrial grade oxygen:

  • Industrial grade oxygen is not regulated by the FDA
  • Industrial grade oxygen may have impurities. You should ask your supplier to confirm this for your industrial setting.
  • Ask your supplier to verify their quality through an independent ISO-certified lab.

Oxygen Purity Grade Chart

Oxygen Purity Grade Concentration Maximum Contaminants
Research Grade > 99.999% Water < 1 ppm
Total Hydrocarbons (like CH4) < 0.5 ppm
Nitrogen < 4 ppm
Argon < 4 ppm
Carbon Dioxide < 1 ppm
Carbon Monoxide < 1 ppm
Ultra High Purity Grade > 99.994% Water < 1 ppm
Total Hydrocarbons (like CH4) < 0.5 ppm
Nitrogen < 10 ppm
Nitrogen < 100 ppm
Argon < 35 ppm
Carbon Dioxide < 1 ppm
Carbon Monoxide < 1 ppm
High Purity Grade > 99.8% Water < 5 ppm
Total Hydrocarbons (like CH4) < 50 ppm
Nitrogen < 100 ppm
Carbon Dioxide < 10 ppm
Carbon Monoxide < 1 ppm
Zero Grade > 99.6% Total Hydrocarbons (like CH4) < 0.5 ppm
Industrial Grade > 99.5% Water < 50 ppm
Aviator Breathing Grade > 99.0% Water < 6.6 ppm
Identity: Positive
Odor: None
Food Grade > 99.0% Identity: Positive
Odor: None
Medical Oxygen: USP Grade > 99.0% Odor: None
Identification: Positive
Carbon Dioxide < 0.03% (300 ppm)
Carbon Monoxide < 0.001% (10 ppm)


Download the chart to print

Note that for cryogenic applications, many require a high 99.5% minimum requirement. Pharmaceutical companies also require oxygen purity of not less than 90.0% but not more than 96.0% for oxygen. 

What is a dangerously low oxygen level?

The Occupational Safety and Health Administration (OSHA) Respiratory Protection Standard ("the Standard"; 29 CFR 1910.134) uses 19.5% oxygen as the level below which an oxygen-deficient atmosphere exists and requires, generally, that all oxygen-deficient atmospheres be considered immediately dangerous to life or health ("oxygen-deficient IDLH").

For example, normal ambient air contains an oxygen concentration of 20.9% oxygen by volume. When the oxygen level dips below 19.5% air is considered oxygen-deficient.

In addition, OSHA defines "oxygen enriched" atmospheres as any atmosphere that contains more than 22% oxygen.

Oxygen Gas Supply and Recommendations

Because oxygen is so vital it also is complex at times. Access to oxygen continues to meet many challenges surrounding availability, quality, affordability, supply, human resources, and safety. 

Because of these common hurdles, organizations like WHO continuously provide resources to overcome them and can be found here as a helpful reference.

No matter what your business or application is you should always contact your gas supplier and ask the following questions:

  • What grade/purity gas are you delivering to me?
  • Can you provide me with a certificate that states the purity?

Any qualified gas provider will be able to not only answer those questions immediately but they should also be able to demonstrate the gas quality as well. Do not settle for purity any less than what your application calls for.

In addition, you should always consider the main differentiators:

  • Medical oxygen is used to maintain healthy oxygen levels and is FDA regulated for impurities and contaminants. 
  • Industrial oxygen is used to support industrial functions and does not need regulation or concern with impurities in the gas.

Oxygen Safety Monitors

oxygen safety meter

Regardless of what grade O2 you use, in order to test the accuracy of a oxygen safety monitor, detector, sensor or alarm, you should purchase a gas monitor that meets oxygen specific levels and requirements.

The RAD-0002-ZR Oxygen Deficiency Alarm does just that as well as protect individuals when working in hazardous areas where nitrogen, helium, or argon could pose severe personal injury. 


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