Hazard classification is the identification of the intrinsic potential of a substance or mixture to cause adverse effects to humans or the environment. It is used to communicate potential hazards during transport, handling, storage and disposal. Unlike a risk assessment, the classification process is intended to be based solely on “intrinsic properties” of the material, and does not include the determination of safe thresholds or take into account exposure levels or the extent of any exceedance of effect thresholds during handling and use.

A classification can either be self-imposed by industry (self-classification) or officially set by a regulatory authority (harmonised classification). Under laws of certain jurisdictions such as the EU, Industry may be required to ‘self-classify’ substances as new knowledge uncovers adverse properties of the chemical.

Many chemical substances are classified (by self- or harmonised classification) as “hazardous” physico-chemically, to human health or to the environment, and there are different degrees (categories) of hazard, such as carcinogenicity and aquatic water toxicity. There are also special calculations for the classification of mixtures containing hazardous substances. The physical form, solid (Powder or massive metal), liquid or gas, may also influence the hazardous properties of the substance or mixture.

Once the hazard category is determined, the information is communicated accordingly via a label and a (Material) Safety Data Sheet (MSDS or SDS), for the purposes of handling, transport, use and disposal. There are specific symbols associated with each hazard category which are internationally recognised.