The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is an internationally agreed-upon hazard communication system developed by the United Nations. It was mainly developed to replace all of the different hazardous materials classification and labelling systems previously used around the world. One of the benefits of a harmonised system is that it facilitates international trade as it reduces the expenses and costs for companies associated with the need to comply with many different systems, e.g. printing out of labels, external consultants and education costs etc. Additionally, it has also helped workers better understand the chemical hazards and, consequently, work more safely while also removing the language barrier. Its symbols and phrases have the same meaning around the world. GHS prescribes standardised hazard testing criteria and safety data sheets with universal warning pictograms, which provide users of hazardous materials with plenty of useful information. It’s also important to note that the GHS system is complementary to the UN Recommendations for transporting dangerous goods.
It is a quite complex system that has the classification of chemical hazards at its core. The GHS classification is based on data obtained from tests, scientific literature, and practical experience.
Having the correct classification is not something that should be looked at only from the legal point of view. While being compliant is important, having the correct classification also ensures that personnel that handles the hazardous chemicals is aware of potential risks associated with the said chemicals. This further helps them to develop and use suitable protective and precautionary measures. Having under-classified products causes health and safety risks and can lead to penalties and fines set by the authorities. On the other hand, having over-classified products can cause an increase in transport and equipment costs and not only that, but it can also lead to lost sales, especially for the consumers’ products markets.
When classifying hazardous chemicals, one must know and understand the full composition of chemical products and then apply guidelines from the GHS to determine all relevant hazard classes and categories.
GHS Hazard Classes and Categories
GHS establishes two major standardised elements:
- classification rules for hazards of chemical products (hazard classes and categories), and
- hazard communication tools:
- Safety Data Sheet (SDS) - its requirements for format and content
- Labels - including precautionary and hazard statements, pictograms and signal words and other labelling requirements
All GHS hazards can be divided into three major groups:
- Physical hazards,
- Health hazards, and
- Environmental hazards.
Each of these groups consists of several different hazard classes, and each hazard class consist of one or more hazard categories. There could be up to seven different categories depending on the hazard class.
Hazard class is the term used to describe the different types of hazards. For example, Flammable liquid is an example of a physical hazard class. Physical hazards are based on the intrinsic properties of the chemical. Physical hazards are divided into five hazard classes: Explosive, Flammable, Oxidising, Gases under Pressure and Corrosive to metals which are then sub-divided into different categories depending on the degree of danger.
Health hazards are chemical hazards that can potentially cause harm to human health. Health hazards are divided into four main classes: corrosive, toxic, harmful and irritant. Similarly to physical hazards, health hazard classes are also sub-divided into different categories depending on the degree of danger.
Environmental hazards present chemical hazards that can potentially cause harm to the living organisms in the environment. Environmental hazards are divided into two classes: hazardous to the aquatic environment or the ozone layer. Aquatic environmental hazards are divided into acute and chronic classes and are also sub-divided into different categories depending on the degree of danger.
Hazard category is a term used to describe the sub-sections of hazard classes. Hazard categories are assigned numbers, or in the case of some hazard classes letters, with category 1 (or A) being the most hazardous. Each category has its criteria, which would mean that the chemical should be assigned to that category if fulfilled. For example, environmentally toxic substances can be assigned to four different categories (1-4) for chronic aquatic toxicity hazard class.
The first step is to determine which class or classes the chemical falls into when classifying chemicals. Once this is determined, you should assign the correct hazard category for each of the hazards classes.
Classification of mixtures according to the GHS
For the classification of mixtures, GHS uses a tiered approach. If and when available, testing data for the chemical mixture should be used for the classification together with the GHS classification guidelines. An exception to this is if your mixture is a carcinogen, a mutagen, or a reproductive toxin, where classification may be based on the strength of evidence and modified on a case-by-case basis.
Though most of the chemical mixtures are still untested and, in this case, the GHS suggests applying bridging principles with similar tested mixtures (dilutions, batching, aerosols, etc.). In case that the bridging principles are not applicable, there is no similar tested mixture available for comparison, then estimation should be made based on the ingredient’s chemical hazards information.
GHS Hazard communication
Once the chemicals have been classified, this information should be shared with other users by applying the correct hazard and precautionary statements, pictograms and a signal word to the product’s SDS. Each hazard statement has a dedicated, unique hazard code. Still, SDSs and labels must include the entire statement and not just the code to eliminate the risk of any potential misunderstanding.
Depending on the hazard class and category, labels and SDS’ need to be supplemented with the specific GHS pictogram or pictograms. Usually, hazard classes with picograms are also accompanied by one of the two signal words, ‘’Warning’’ or ‘’Danger,’’ which emphasise the severity of the hazards.
GHS does leave room for identification of other hazards such as ‘’Combustible dust’’ or hazards not otherwise classified (HNOC). At the same time, these hazards may not be classified under GHS that doesn’t mean that they should be ignored. These hazards have their unique requirements and usually don’t have any specific GHS pictograms associated with them. Still, they should be included under section 2 of the SDS and on the label.
Communication of hazards through the SDS and labels does not stop there. Both SDS and the label need to be reviewed whenever new information becomes available or legal texts and requirements change. It is continued work in progress to make sure that the product is compliant at all times.
GHS Classification & Hazard Communication jurisdictional differences
While in theory, GHS was meant to fully harmonise chemical hazard communication – classification and labelling, in reality, that is not the case. The GHS is a 'non-binding' system of hazard communication, which means that countries that want to implement it do not need to implement every chapter or the latest revision of the GHS. The first GHS edition was published in 2003, and since then, it has been revised every two years. Currently, there are nine published GHS revisions and countries which have or want to implement the GHS can choose to follow one of these revisions. The country’s authorities decide how the GHS will be adopted into their legislation, and they have the freedom to choose which hazard classes and the categories they want to implement.
This is why it is extremely important to know which GHS revision and which chapters (hazards) the country has implemented before you start checking the criteria for classification or labelling.