Reference Exposure Levels for Hexamethylene Diisocyanate (Monomer and Polydiisocyanates) (HDI)
Notice of Adoption of Reference Exposure Levels for Hexamethylene Diisocyanate (Monomer and Polydiisocyanates)
Download Reference Exposure Levels for Hexamethylene Diisocyanate (Monomer and Polydiisocyanates) (HDI)
The Office of Environmental Health Hazard Assessment (OEHHA) is adopting new Reference Exposure Levels (RELs) for Hexamethylene Diisocyanate (Monomer and Polydiisocyanates) (HDI) for use in the Air Toxics Hot Spots Program. RELs are airborne concentrations of a chemical that are not anticipated to result in adverse noncancer health effects for specified exposure durations in the general population, including sensitive subpopulations. The adopted RELs cover different types of exposure to HDI 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 HDI. The HDI RELs were developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for the Derivation of Noncancer Reference Exposure Levels” (OEHHA, 2008). These chemicals will also be added to the list of Toxic Air Contaminants that may disproportionately impact children, pursuant to Health and Safety Code Section 39669.5(b)(1).
A draft document for the HDI RELs was released on December 1, 2017, to solicit public comment and was discussed at public workshops in Sacramento and Diamond Bar, CA during the subsequent 75-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 March 2019 before being finalized.
The REL values are as follows:
HDI monomer:
Acute REL (for a 1–hour exposure): 0.3 micrograms per cubic meter (µg/m3)
8–Hour REL (for repeated 8–hour exposures): 0.06 µg/m3
Chronic REL (for long–term exposures): 0.03 µg/m3
HDI polyisocyanates:
Acute REL (for a 1–hour exposure): 4.5 µg/m3
8–Hour REL (for repeated 8–hour exposures): 0.8 µg/m3
Chronic REL (for long–term exposures): 0.4 µg/m3
Please direct any inquiries concerning technical matters or availability of the documents to:
Dr. John Budroe, Chief
Air Toxicology and Risk Assessment Section
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA 94612
E–mail: john.budroe@oehha.ca.gov