CAS Numbers and UN Numbers - Identifications Systems for Materials and Chemicals


Various methods are used to identify materials. Two of the more common methods are CAS Numbers and UN Numbers. These systems are explained below.

CAS Numbers

CAS Numbers are unique identifiers assigned by the Chemical Abstracts Service (CAS), a division of the American Chemical Society. They are the most widely recognized identification system and a CAS number is assigned to all chemical compounds, materials, alloys, minerals, proteins etc referred to in printed media. The assigned number has no significance to the chemical/material it refers to.

CAS numbers are made up of up to 9 digits, divided into 3 sections by hyphens.

UN Numbers

UN Numbers are 4 digit identifiers assigned by the United Nations (UN). They are used to identify potentially hazardous materials and are commonly used in international commerce (e.g. on shipping containers) and by fire fighters to identify harmful substances. They are typically applied poisonous and explosive materials.


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  1. jose matos jose matos United States says:

    Are CAS Number required on shipping papers like UN numbers?

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