For the purposes of CERCLA release notification requirements, hazardous substances are listed in 40 CFR 302.4 with a Chemical Abstract Service (CAS) Registry Number. What are CAS Registry Numbers? When determining whether to report a release of a chemical or substance, how should a facility proceed if it appears that there is a discrepancy between the hazardous substance name and the listed CAS Registry Number?

CAS Registry Numbers (often referred to simply as CAS numbers) are provided for the convenience of the regulated community and the public to aid in the identification of the designated hazardous substances. In some cases, a chemical name may have more than one CAS Registry Number associated with it due to the chemical’s various forms; however, each CAS Registry Number is a unique numeric identifier and designates only one substance. That is, two substances, or two forms of a substance, do not have the same CAS Registry Number.

If there is a discrepancy between the hazardous substance name and the listed CAS Registry Number, the hazardous substance names appearing in table 302.4 should be used as the official means to determine if a given chemical or substance is reportable. EPA strongly suggests reporting when there is doubt.

EPA appreciates learning of the CAS Registry Number discrepancies and has periodically promulgated rulemakings to correct identified discrepancies. Individuals can report possible discrepancies to the Superfund, TRI, EPCRA, RMP & Oil Information Center at (800) 424-9346. (April 4, 1985 (50 FR 13456, 13460-1) and September 8, 2001 (76 FR 55583, 55583-4) final rules)