CAS number

A unique numeric identifier for a chemical substance, used to match inventories against regulatory lists.

A CAS Registry Number uniquely identifies a chemical substance, written as up to ten digits in three hyphenated parts, such as 67-64-1 for acetone.

It is the practical key for compliance work, because trade names vary between suppliers and over time while the CAS number does not. Matching an inventory against EPA's List of Lists is done on CAS number.

The final digit is a check digit, so a mistyped CAS number can usually be detected rather than silently matching the wrong substance.

Related terms

• List of ListsEPA's consolidated table of chemicals regulated under EPCRA and CERCLA, with their thresholds.
• SDS Section 3Composition: the ingredients, their CAS numbers, and concentration ranges.
• Safety Data SheetThe 16-section document a manufacturer must supply describing a hazardous chemical's hazards, handling and properties.

A plain-English explanation, not legal advice. Figures are the federal baseline; your state may differ, so see the state-by-state requirements.