Oxygen Enrichment

By Tabitha Mishra
Last updated: September 7, 2022

What Does Oxygen Enrichment Mean?

Oxygen enrichment refers to an excess of oxygen in the ambient air. While there are competing definitions of enrichment, atmospheres with more than 21% oxygen concentration can be considered enriched.

Oxygen enrichment is a significant concern for anyone working in a confined space, where safe oxygen levels fall between 19.5% and 23%.

Safeopedia Explains Oxygen Enrichment

Oxygen concentration in confined spaces is a concern at both extremes. Low oxygen levels puts workers at risk of asphyxiation, while excessively high (enriched) oxygen levels make combustion easier and more devastating. At concentrations of 24% of greater, fires start more easily, burn hotter, and are more difficult to extinguish.

Since oxygen is colorless, odorless, and has no taste, an oxygen enriched atmosphere is difficult to detect without the use of gas monitors.

Industry-Specific Definitions of Oxygen Enrichment

The precise concentration at which an atmosphere is considered oxygen enriched differs across standards and regulations.

For instance, OSHA 1910.146 and 1926 Subpart AA deem an atmosphere with a 23.5% concentration of oxygen to be enriched and hazardous. OSHA 1915 Subpart B, however, places the cutoff at 22%.

The following table provides an overview of oxygen-enriched atmosphere (OEA) levels (for complete details, please refer to WHA International):

Organization OEA Definition Reference
National Fire Protection Association (NFPA) 21% NFPA 53 (General)
Occupational Safety and Health Administration (OSHA) 22% OSHA 29 CFR 1915.11 (confined spaces in shipyards)
Compressed Gas Assocation (CGA) 23.5% CGA G-4.1 (2009), CGA P-39 (2015), GA P-45 (2018), CGA PS-13 (2007)
European Industrial Gases Association (EIGA) 23.5% EIGA IGC Doc 33/18, EIG IC Doc 04/18
International Organization for Standardization (ISO) 23.5% ISO 10156:2017
NFPA 23.5% NFPA 99 (2018), NFPA 99B (2018) (health)
OSHA 23.5% OSHA 29 CFR 1910.146 (permit-required confined spaces)
International Marine Contractors Association (IMCA) 25% IMCA D 031 – May 2003, IMCA D 048 – Jan 2017


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