The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is an internationally agreed-upon standard managed by the United Nations that was set up to replace the assortment of hazardous material classification and labelling schemes previously used around the world. Core elements of the GHS include standardized hazard testing criteria, universal warning pictograms, and safety data sheets which provide users of dangerous goods relevant information with consistent organization. The system acts as a complement to the UN numbered system of regulated hazardous material transport. Implementation is managed through the UN Secretariat. Although adoption has taken time, as of 2017, the system has been enacted to significant extents in most major countries of the world. This includes the European Union, which has implemented the United Nations' GHS into EU law as the CLP Regulation, and United States Occupational Safety and Health Administration standards.
History Before the GHS was created and implemented, there were many different regulations on hazard classification in use in different countries, resulting in multiple standards, classifications and labels for the same hazard. Given the $1.7 trillion per year international trade in chemicals requiring hazard classification, the cost of compliance with multiple systems of classification and labeling is significant. Developing a worldwide standard accepted as an alternative to local and regional systems presented an opportunity to reduce costs and improve compliance.
The GHS development began at the 1992 Rio Conference on Environment and Development by the United Nations, also called Earth Summit (1992), when the International Labour Organization (ILO), the Organisation for Economic Co-operation and Development (OECD), various governments, and other stakeholders agreed that "A globally harmonized hazard classification and compatible labelling system, including material safety data sheets and easily understandable symbols, should be available if feasible, by the year 2000".
The universal standard for all countries was to replace all the diverse classification systems; however, it is not a compulsory provision of any treaty. The GHS provides a common infrastructure for participating countries to use when implementing a hazard classification and Hazard Communication Standard.
Hazard classification The GHS classification system defines and classifies the physical, health, and/or environmental hazards of a substance. Each category within the classifications has associated pictograms to be used when applied to a material or mixture.
Physical hazards As of the 10th revision of the GHS, substances or articles are assigned to 17 different hazard classes largely based on the United Nations Dangerous Goods System. Explosives are assigned to one of four subcategories depending on the type of hazard they present, similar to the categories used in the UN Dangerous Goods System. Category 1 includes explosives not covered by the 6 Dangerous Goods categories. Flammable gases are assigned to one of 3 categories based on reactivity: Category 1A includes extremely flammable gases ignitable at 20 °C and standard pressure of 101.3 kPa, pyrophoric gases, and chemically unstable gases that may react in the absence of oxygen. Category 1B gases meet the flammability criteria of 1A, but are not pyrophoric or chemically unstable and have a lower flammability limit in air. Category 2 includes gases which do not meet the above criteria but otherwise are flammable at 20 °C and standard pressure. Aerosols and chemicals under pressure are categorized into one of 3 categories, but may be additionally classified as explosives or flammable gases if material properties match the previous classifications. From category 1 to 3, aerosols are classified as most to least flammable. All aerosols under these categories carry a bursting hazard. Oxidizing gases are any gaseous substance which contribute to combustion of other materials more than air would. There is only one category of oxidizing gases. Gases under pressure are categorized as compressed, liquefied, refrigerated, or dissolved gases, all of which may explode when heated or (in the case of refrigerated gases) cause cryogenic injury, such as frostbite. Flammable liquids are categorized by flammability, from Category 1 with flash point < 23 °C and initial boiling point < 35 °C to Category 4 with flash point > 60 °C and < 93 °C. Flammable solids are classified as solid substances which are readily combustible or may contribute to a fire through friction, and ignitable metal powders. They are placed into Category 1 if a fire is not stopped by wetting the substance, and Category 2 if wetting stops the fire for at least 4 minutes. Self-reactive substances and mixtures are liable to detonate or combust without the participation of air and are placed into 7 categories from A to G with decreasing reactivity. Pyrophoric liquids are liable to ignite after 5 minutes of coming in contact with air. Pyrophoric solids follow the same criteria as pyrophoric liquids. Self-heating substances, which differ from self-reactive substances in that they will only ignite in large quantities (kilograms) and after a long duration of time (hours or days). Category 1 is reserved for samples which self-heat in small quantities (25 mm2), and all other self-heating substances that only heat in large quantities are listed under Category 2. Substances and mixtures which, in contact with water, emit flammable gases are categorized from 1 to 3 based on the ignitability of the gas emitted. Oxidizing liquids contribute to the combustion of other materials and are categorized from 1 to 3 in decreasing oxidizing potential. Oxidizing solids follow the same criteria as oxidizing liquids. Organic peroxides are unstable substances or mixtures and may be derivatives of hydrogen peroxide. They are categorized from A to G based on inherent ability to explode or otherwise combust. Corrosive to metals materials may damage or destroy metals, based on tests done on aluminum and steel. The corrosion rate must be greater than 6.25 mm/year on either material to qualify under this classification. Desensitized explosives are materials that would otherwise be classified as explosive, but have been stabilized, or phlegmatized, to be exempted from said class.
Health hazards Acute toxicity includes five GHS categories from which the appropriate elements relevant to transport, consumer, worker and environment protection can be selected. Substances are assigned to one of the five toxicity categories on the basis of LD50 (oral, dermal) or LC50 (inhalation). Skin corrosion means the production of irreversible damage to the skin following the application of a test substance for up to 4 hours. Substances and mixtures in this hazard class are assigned to a single harmonized corrosion category. Skin irritation means the production of reversible damage to the skin following the application of a test substance for up to 4 hours. Substances and mixtures in this hazard class are assigned to a single irritant category. For those authorities, such as pesticide regulators, wanting more than one designation for skin irritation, an additional mild irritant category is provided. Serious eye damage means the production of tissue damage in the eye, or serious physical decay of vision, following application of a test substance to the front surface of the eye, which is not fully reversible within 21 days of application. Substances and mixtures in this hazard class are assigned to a single harmonized category. Eye irritation means changes in the eye following the application of a test substance to the front surface of the eye, which are fully reversible within 21 days of application. Substances and mixtures in this hazard class are assigned to a single harmonized hazard category. For authorities, such as pesticide regulators, wanting more than one designation for eye irritation, one of two subcategories can be selected, depending on whether the effects are reversible in 21 or 7 days. Respiratory sensitizer means a substance that induces hypersensitivity of the airways following inhalation of the substance. Substances and mixtures in this hazard class are assigned to one hazard category. Skin sensitizer means a substance that will induce an allergic response following skin contact. The definition for "skin sensitizer" is equivalent to "contact sensitizer". Substances and mixtures in this hazard class are assigned to one hazard category. Germ cell mutagenicity means an agent giving rise to an increased occurrence of mutations in populations of cells and/or organisms. Substances and mixtures in this hazard class are assigned to one of two hazard categories. Category 1 has two subcategories. Carcinogenicity means a chemical substance or a mixture of chemical substances that induce cancer or increase its incidence. Substances and mixtures in this hazard class are assigned to one of two hazard categories. Category 1 has two subcategories. Reproductive toxicity includes adverse effects on sexual function and fertility in adult males and females, as well as developmental toxicity in offspring. Substances and mixtures with reproductive and/or developmental effects are assigned to one of two hazard categories, 'known or presumed' and 'suspected'. Category 1 has two subcategories for reproductive and developmental effects. Materials which cause concern for the health of breastfed children have a separate category: effects on or via Lactation. Specific target organ toxicity (STOT) category distinguishes between single and repeated exposure for Target Organ Effects. All significant health effects, not otherwise specifically included in the GHS, that can impair function, both reversible and irreversible, immediate and/or delayed are included in the non-lethal target organ/systemic toxicity class (TOST). Narcotic effects and respiratory tract irritation are considered to be target organ systemic effects following a single exposure. Substances and mixtures of the single exposure target organ toxicity hazard class are assigned to one of three hazard categories. Substances and mixtures of the repeated exposure target organ toxicity hazard class are assigned to one of two hazard categories. Aspiration hazard includes severe acute effects such as chemical pneumonia, varying degrees of pulmonary injury or death following aspiration. Aspiration is the entry of a liquid or solid directly through the oral or nasal cavity, or indirectly from vomiting, into the trachea and lower respiratory system. Substances and mixtures of this hazard class are assigned to one of two hazard categories this hazard class on the basis of viscosity.
Environmental hazards Acute aquatic toxicity indicates the intrinsic property of a material of causing injury to an aquatic organism in a short-term exposure. Substances and mixtures of this hazard class are assigned to one of three toxicity categories on the basis of acute toxicity data: LC50 (fish) or EC50 (crustacean) or ErC50 (for algae or other aquatic plants). These acute toxicity categories may be subdivided or extended for certain sectors. Chronic aquatic toxicity indicates the potential or actual properties of a material to cause adverse effects to aquatic organisms during exposures that are determined in relation to the lifecycle of the organism. Substances and mixtures in this hazard class are assigned to one of four toxicity categories on the basis of acute data and environmental fate data: LC50 (fish), EC50 (crustacea) ErC50 (for algae or other aquatic plants), and degradation or bioaccumulation. Ozone Depleting Potential indicates the ability of the materials to damage the Ozone Layer, determined by the Montreal Protocol. Substances and mixtures bearing this quality have the Hazard Statement H420.