Under the Globally Harmonised System (GHS) of classification and labelling of chemicals, the classification of chemicals is by hazard class and category. These will be found in Section 2 Hazard Identification of the chemical’s Safety Data Sheet (SDS).
The GHS hazard class provides details on the physical, health and environmental hazards of the chemical.
The GHS hazard category refers to the severity of the hazard within the hazard class.
Each chemical will have a hazard class and at least one hazard category within that class. Some hazard classes may have 2 or more categories. A number is usually assigned to identify the hazard category. Sometimes a sub-category is also identified and this will be indicated with a letter e.g. 1A and 1B. A few hazard classes have other descriptors for the categories.
The lower the number, the higher the hazard and risk. Category 1 is the most hazardous within a class. If the category is further divided then 1A will have a greater hazard then 1B.
A useful resource:
Safe Work Australia has produced a poster with different hazard classes and their subdivision into hazard categories entitled ‘Work Health & Safety Regulations: Classification and labelling for workplace hazardous chemicals’. We recommend it is printed out for your reference see: https://www.safeworkaustralia.gov.au/doc/classification-and-labelling-wo...
Under the (GHS), whilst there are only 9 pictograms, there are many more hazard categories. This poster sets out:
- Classification: itemising 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.
Comparing categories (in flammable liquids):
If you consider the hazard class of flammable liquids, you can clearly see the progression of reducing 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
Here is that portion of the poster (with the relevant headings copied here)1:
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
Therefore, when we look at the poster and look for 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’. 2012. Safe Work Australia Website. https://www.safeworkaustralia.gov.au/doc/classification-and-labelling-wo... (Accessed April 2018) © Commonwealth of Australia 2014. This work is licensed under a Creative Commons Attribution 3.0 Australia Licence
2 ‘Hydrochloric acid 25 - 36%, Safety Data Sheet’. 2017. Chem-Supply website. https://www.chemsupply.com.au/documents/HL0201CH34.pdf
‘GHS Hazard Class and Hazard Category’. ChemSafetyPro website. http://www.chemsafetypro.com/Topics/GHS/GHS_hazard_class.html (Accessed October 2017)
‘Globally Harmonised System of Classification and Labelling of Chemicals (GHS) information sheet’ 20.16. Safe Work Australia Website. https://www.safeworkaustralia.gov.au/doc/globally-harmonised-system-clas...
‘Hazard communication under the GHS’. Safe Work Australia Website. https://www.safeworkaustralia.gov.au/classifying-chemicals#hazard-commun... (Accessed October 2017)
University of New South Wales. 2013. Fact_Sheet_on_the_GHS. https://safety.unsw.edu.au/hs681-fact-sheet-ghs (Link update May 2019)