The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) has been developed through cooperation between the International Labour Office (ILO), the Organization for Economic Co-operation and Development (OECD) and the United Nations on the basis of a mandate given in Agenda 21 by the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro. The GHS addresses classification of chemicals by types of hazard and proposes harmonized hazard communication elements, including labels and safety data sheets. It aims at ensuring that information on physical hazards and toxicity from chemicals be available in order to enhance the protection of human health and the environment during the handling, transport and use of these chemicals. It provides a basis for harmonization of rules and regulations on chemicals at national, regional and worldwide level. This fourth revised edition of the GHS contains various new or revised provisions concerning, inter alia, new hazard categories for chemically unstable gases and non-flammable aerosols.