The purpose of classification and labelling of a substance or a mixture is to ensure that the hazards of a chemical product are clearly informed to the consumers and to the workers using them. The criteria that determine the various hazard classes are defined in appendix I of the CLP regulation. They pertain to the physical properties as well as the toxicity of a product for humans and for the environment.
A series of substances already falls under an "harmonised" classification, i.e. an official classification that was agreed at the European level. In case of these substances, which are listed in appendix VI of the regulation, it is mandatory to use the official harmonised classification.
How must a classification be established?
You will find detailed information on interpreting data for each hazard category in the technical guide prepared by ECHA: "Guidance on the Application of the CLP Criteria" (only available in English).
You can also take help of the tool associated with the inventory of notifications: this system allows you to search based on name, CAS number, etc. It allows you to check the existence of harmonised classification in a consolidated database and also check whether your substance has already been notified and with what classification.
Warning! Since the classifications given in the inventory are not harmonised, they were not checked and guaranteed by the European authorities.