Three numbers identify a chemical in the safety data sheet: the CAS and EC numbers say what the substance is, the UN number says how it is transported. What each format means and where it appears in the SDS.
Author: Maximilián Pálffy, chemical engineer General information, not legal or professional advice. Always check identifiers against the official lists and the consolidated texts on EUR-Lex.A CAS Registry Number is a unique identifier that Chemical Abstracts Service assigns to a substance when it enters the CAS REGISTRY database. It is numeric, has up to 10 digits divided by hyphens into three parts, and the right-most digit is a check digit – ethanol, for example, is 64-17-5.
Under the CLP Regulation, a substance without a harmonised entry in Annex VI and without an entry in the classification and labelling inventory is identified on the label and in the SDS by its CAS number together with the IUPAC name or another international chemical name.
Source: CAS – CAS REGISTRY · CLP, Article 18(2)Section 14 of the SDS gives the UN number or ID number – the four-figure identification number of the substance, mixture or article preceded by the letters “UN” or “ID” – from the UN Model Regulations, IMDG, ADR, RID, ADN or ICAO TI.
For road transport the rules come from the ADR, which Directive 2008/68/EC makes binding for inland transport in the EU. The international agreements are updated every two years; the current versions apply from 1 January 2025.
Source: Regulation (EU) 2020/878, Annex II, Section 14 · Directive (EU) 2025/149The 16 sections of the SDS use the identifiers in three places:
We check identifiers, classification and transport data in every safety data sheet we author or translate.
