Answer reviewed 9 February 2023
Under the Globally Harmonised System of Classification and Labelling of Chemicals (GHS), chemicals are classified according to their hazard class and their hazard category.
The hazard class is assigned according to the physical, health and/or environmental hazards posed by the chemical.
The hazard category refers to the severity of the hazard within a hazard class.
A hazard class may have only one category or may be divided into several categories. The hazard categories are identified by the descriptors ‘Category’, ‘Division’, and ‘Type’ as well as more specific descriptors. The categories are designated a letter, or a number which may be further subdivided, e.g., Category 1A, 1B, etc. or Division 1.1, 1.2, etc.
The lower the number, the higher the hazard and risk which is indicated, with the category designated 1 or A being the most hazardous within a class. Where there is further subdivision, the category identified as 1A indicates a greater hazard than the one identified as 1B; similarly, the category labelled 1.1 is more hazardous than one labelled 1.2.
Each chemical classified as hazardous under the GHS will belong to at least one hazard class and one category within the class. The hazard classification of a chemical can be found in Section 2 Hazard Identification of the chemical’s Safety Data Sheet (SDS).
A useful resource:
Safe Work Australia has produced a poster of the labelling information required for chemicals in the different hazard classes and their subdivision into hazard categories.1 We recommend that you print it out for your reference.
Under the (GHS), whilst there are only 9 pictograms, there are many more hazard categories. The poster sets out:
- Classification: listing each hazard class and the categories within that class
- Labelling: noting the labelling that is required for each hazard class and category, i.e. relevant pictograms, signal words, hazard codes and statements under the GHS.
Taking the hazard class of flammable liquids as an example, it is clear that there is a progression of lessening hazard through the 4 categories, which is reflected in the labelling components:
- Pictogram: Categories 1-3 require the pictogram whereas category 4 does not.
- Signal Word: Categories 1-2 require the signal word “Danger”, which indicates a more severe hazard, whereas categories 3-4 only require the signal word “Warning”
- Hazard Code and Statements: The category 1 statement is the most hazardous with category 4 being the least hazardous
The corresponding portion of the Safe Work Australia poster1 is reproduced here:
Considering hazard identification for hydrochloric acid:
The Chem-Supply SDS for hydrochloric acid 25 - 36%2, provides the following hazard information:
- Skin Corrosion/Irritation: Category 1B
- Specific Target Organ Toxicity Single Exposure Category 3 (respiratory tract irritation)
- Corrosive to Metals: Category 1
When we look at the Safe Work Australia poster1 and focus on the hazard categories identified, we can see them in context and where they sit within the hazard class:
Skin corrosion/irritation: category 1B1: in between 1A and 1C and more hazardous than category 2
Specific Target Organ Toxicity Single Exposure: category 31: less hazardous than categories 1 and 2
Corrosive to Metals: category 11: This only has 1 category
References and further reading:
1 ‘Classification and labelling for workplace hazardous chemicals poster’. 2021. Safe Work Australia Website. Classification and labelling for workplace hazardous chemicals poster | Safe Work Australia (accessed February 2023) © Commonwealth of Australia 2014. This work is licensed under a Creative Commons Attribution 3.0 Australia Licence
2 Chem-Supply. (2022) ‘Hydrochloric acid 25 - 36%, Safety Data Sheet’. Search https://shop.chemsupply.com.au/ to source the latest Safety Data Sheet via the product information page.
ChemSafetyPro. (2016, June 1) ‘GHS Hazard Class and Hazard Category’. Retrieved from the Chemsafetypro website. http://www.chemsafetypro.com/Topics/GHS/GHS_hazard_class.html
Science ASSIST. 2023. Science ASSIST Information Sheet: Chemical Labels, Retrieved from the Science ASSIST website: https://assist.asta.edu.au/resource/2455/science-assist-information-sheet-chemical-labels
Safe Work Australia, (nd) ‘Hazardous Chemicals’, Retrieved (7 February 2023) from the Safe Work Australia website: https://www.safeworkaustralia.gov.au/safety-topic/hazards/chemicals/hazardous-chemicals
Safe Work Australia, (nd). ‘Labelling Hazardous Chemicals’, Retrieved (7 February 2023) from the Safe Work Australia website: https://www.safeworkaustralia.gov.au/safety-topic/hazards/chemicals/labelling-hazardous-chemicals
University of New South Wales. 2016. HS681: GHS Fact Sheet. Retrieved from the University of NSW website: https://www.unsw.edu.au/planning-assurance/safety