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CAS Number - Chemical Abstracts Service Registry Number

Definition

• A CAS (Chemical Abstracts Service) Registry Number is a unique identifier that tells you, for example, that acetone and dimethyl ketone are actually the same substance. From a safety and inventory perspective, this is a terrific idea. As of September 2009, there were 53,000,000 unique substances indexed by CAS. See http://www.cas.org/aboutcas/faq.html for more info.

The Chemical Abstracts Service, http://www.cas.org/, is a division of the American Chemical Society, http://www.acs.org/.

Further Information

Currently, OSHA only requires certain items on an MSDS and a CAS number is not one of them. The US is now moving to adopt the Globally Harmonized System of Classification and Labeling of Chemicals, and under the pending legislation CAS numbers will become required content. We strongly recommend adding CAS numbers to MSDS's in the interim (one can add additional items to MSDS's beyond those that are required). Key point: CAS numbers identify the chemical, but not its concentration or specific mixture. For example, hydrogen chloride (HCl) has the CAS number 7647-01-0. That CAS number will appear on containers of anhydrous hydrogen chloride, a 20% solution of HCl in water, and a 2.0 molar solution of HCl in diethyl ether. The numbers you see on trucks on the highway are not CAS Numbers, but U.S. Department of Transportation (DOT) mandated UN/NA codes which are not necessarily specific to each chemical. Their aim is to assist emergency responders. To find out what's in that tanker truck, check out the interactive version of the Emergency Response Guidebook at http://wwwapps.tc.gc.ca/saf-sec-sur/3/erg-gmu/erg/ergmenu.aspxm. Once you know what chemical it is, you can look up the MSDS. You can order a printed copy of the guidebook by following the appropriate link on http://phmsa.dot.gov/hazmat/library/erg. Great fun for the kids on those long trips!

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MSDS Relevance

Filing chemicals by CAS number is one way to avoid the problem of finding an MSDS by name ("did I file that under dichloromethane or methylene chloride??"). Even if you have a computerized system you should include a field for CAS number because chemical names are often misspelled by non-chemists and spelling checkers do not handle technical terms very well. For more on chemical naming, see the IUPAC entry.

Remember: CAS numbers uniquely identify a chemical, but not necessarily the manufacturer or concentration. Other identifying systems are discussed in their own MSDS FAQ entry.

Further Reading

• CAS Registry Overview at the CAS web site.
• Visit our MSDS Software or MSDS Suppliers pages for systems that include the CAS Number as a searchable category.
• The National Institute of Standards (NIST) Chemistry WebBook is searchable by CAS number, but has only thermodynamic and spectroscopic data rather than safety data.
• WebElements has a page that explains how to use checksums to determine if a CAS number is valid.

See also: DOT, EINECS number, NSN and NIIN's, UN/NA numbers.

Additional definitions from Google and OneLook.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.