Notice of Adoption of Revised Reference Exposure Levels for Benzene

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The Office of Environmental Health Hazard Assessment (OEHHA) is adopting new and revised Reference Exposure Levels (RELs) for benzene.  RELs are airborne concentrations of a chemical that are not anticipated to result in adverse non–cancer health effects for specified exposure durations in the general population, including sensitive subpopulations.  The three adopted RELs cover different types of exposure to benzene in air: infrequent 1-hour exposures, repeated 8-hour exposures, and continuous long term exposure.

OEHHA is required to develop guidelines for conducting health risk assessments under the Air Toxics Hot Spots Program (Health and Safety Code Section 44360(b)(2)).  In response to this statutory requirement, OEHHA develops RELs for many air pollutants, including benzene.  The benzene RELs were developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for the Derivation of Noncancer Reference Exposure Levels,” finalized by OEHHA in 2008.  These three RELs may now be used as appropriate in Air Toxics Hot Spots program risk assessments. 

A draft of the benzene RELs was released on June 21, 2013 to solicit public comment, and was discussed at public workshops in Sacramento and Diamond Bar, CA during the subsequent 60-day public review period. The document was revised to reflect public comments, and peer reviewed by the State’s Scientific Review Panel on Toxic Air Contaminants (SRP) in November 2013 and again in February 2014. The document was modified based on the comments of the SRP and finalized. 

The REL values are as follows:

  • Acute REL (for infrequent 1–hour exposure): 27 micrograms per cubic meter (µg/m3), equivalent to 8 parts per billion (ppb)
  • 8–Hour REL (for repeated 8–hour exposures): 3 µg/m3, equivalent to 1 ppb
  • Chronic REL (for continuous long–term exposures): 3 µg/m3, equivalent to 1 ppb

Please direct any inquiries concerning technical matters or availability of the documents to:

Dr. John Budroe
Chief, Air Toxicology and Risk Assessment Section
Air, Community, and Environmental Research Branch
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA, 94612


Telephone: (510) 622-3145


Information about dates and agenda for meetings of the Scientific Review Panel can be obtained from the California Air Resources Board web page at