Writing risk assessments for chemical classes

In brief

This is a complex question. In considering safety aspects of any substance it is important to consider both what is being used and how it is being used. Conducting a risk assessment of a broad category such as a chemical group or class may limit the scope of the assessment; for a specific use of an individual chemical, a further risk assessment may be necessary. For example, a general risk assessment for handling/storing flammable solids might not include the precautions necessary for activities involving the burning of magnesium.

Jurisdictional legislation and policies: It is essential to consult the policies and procedures of your school or school sector to determine what they require regarding risk assessments for chemicals. Note that in some jurisdictions (e.g. WA), a risk assessment is required for each hazardous substance used in the workplace¹.

GHS and ADG: It is important to have a good understanding of both the GHS and the ADG Code.

The ADG Code relates to physical hazards such as flammability, corrosivity and oxidising properties, which are important considerations in the segregation of chemicals to ensure their safe transport.
The GHS is a system of classification and labelling of workplace hazardous chemicals. The GHS classifies substances for the purpose of their safe handling in the workplace and includes health hazard classifications such as chronic toxicity or sensitising properties, which are not covered by the ADG Code as they not so relevant for the transport of chemicals. The GHS does not replace the ADG Code for the transport of chemicals.

Chemical categories: In general, the DG classes translate to GHS classifications. If conducting risk assessments according to chemical categories, either the DG classes or the GHS classifications could be used as a starting point, with further subgrouping where appropriate. The more narrow the chemical category, the more specific the risk assessment can be. Some suggestions to consider:

An individual risk assessment may be necessary for a chemical which has more than one hazard class.
Corrosive chemicals might be further subdivided according to whether the substance is an acid or a base, and dilute or concentrated.
Flammable and oxidising chemicals could be assessed according to their hazard class subdivisions.
Inorganic solids could be grouped according to the cation, where the cation is hazardous (e.g. nickel salts, copper salts) or according to the anion where this is hazardous (dichromates, sulfides).
Organic substances could be treated according to functional group (e.g. alcohols, alkanes, esters)
Toxic chemicals are a more complex hazard class. The following categories or groups could be considered for risk assessment purposes:

Acute toxicity: In general, Dangerous Goods Class 6.1 Toxic substances corresponds to the GHS hazard class Acute toxicity, Categories 1,2 or 3. These substances are identified with the GHS06 pictogram (skull and crossbones). Substances with Specific Target Organ Toxicity - single exposure, identified by the GHS08 pictogram (health hazard), could be included here.
Chronic toxicity: Substances of chronic, rather than acute, toxicity, such as Carcinogenicity, Mutagenicity and Reproductive toxicity, identified with the GHS08 pictogram (health hazard). Substances with Specific Target Organ Toxicity - repeated exposure, identified by the GHS08 pictogram (health hazard), could be included here.
Dyes/stains/indicators: many of these have an associated chronic toxicity hazard.
Enzymes: many of these are respiratory sensitisers or have a chronic toxicity hazard.

Additional Information

The GHS:

Under the model work health and safety laws, Australia has adopted the 3rd revised edition of the GHS. In the GHS there are 9 hazard pictograms and some of these may identify more than one hazard category. For more information see:

http://www.safeworkaustralia.gov.au/sites/swa/whs-information/hazardous-chemicals/pages/hazardous-chemicals-other-substances
http://www.safeworkaustralia.gov.au/sites/SWA/about/Publications/Documen... , a poster which gives a good overview of the GHS classification for each hazard class.
http://cwm.unitar.org/publications/publications/cw/ghs/GHS_Companion_Gui... (Last accessed December 2016). See page 3 for a useful table showing the hazard classes corresponding to each pictogram.

The Australian Dangerous Goods (ADG) Code:

The ADG classification provides a good basis for the organisation of chemical storage according to the physical hazards presented by the various dangerous good classes. The DG classification can be found in Section 14 of the safety data sheet. Note that there can still be incompatibilities within a Dangerous Goods class and where a chemical belongs to more than one class.

For more information see:

https://infrastructure.gov.au/transport/australia/dangerous/dg_code_7e.aspx Chapter 9 has good guidance for the segregation of incompatible goods
http://www.safeworkaustralia.gov.au/sites/SWA/about/Publications/Documen... especially see Appendix G: Comparison of GHS Pictograms with the ADG Code class labels.
http://www.education.vic.gov.au/Documents/school/principals/management/g... is a good summary and includes examples of chemicals used in schools (Link updated October 2017)

Risk Assessments:

Guidance material for conducting risk assessments can be found in Section 3 of the model code of practice "Managing risks of hazardous chemicals in the workplace". See: https://www.safeworkaustralia.gov.au/doc/model-code-practice-managing-ri...

References

¹WA Occupational Safety and Health Regulations 1996, Regulation 5.15

'An introduction to the GHS Fact Sheet' Queensland Department of Education and Training website. http://cwm.unitar.org/publications/publications/cw/ghs/GHS_Companion_Gui... (Accessed December 2016)

'Chemicals and hazardous substances' Queensland Department of Education and Training website. https://education.qld.gov.au/initiatives-and-strategies/health-and-wellbeing/workplaces/safety/hazards (Link updated June 2019)

'Chemical management' Victoria Department of Education and Training website. http://www.education.vic.gov.au/school/teachers/management/Pages/chemica...(Updated 15 June 2017)

Guidance on the classification of hazardous chemicals under the WHS regulations. 2012 http://www.safeworkaustralia.gov.au/sites/SWA/about/Publications/Documen...

'Hazardous chemicals including Globally Harmonised System of Classification and Labelling of Chemicals (GHS)' Safe Work Australia Website. http://www.safeworkaustralia.gov.au/sites/swa/whs-information/hazardous-chemicals/pages/hazardous-chemicals-other-substances (Accessed July 2016)

Labelling or workplace hazardous chemicals Code of Practice. 2015. http://www.safeworkaustralia.gov.au/sites/SWA/about/Publications/Documen...

Managing risks of hazardous chemicals in the workplace Code of practice. 2012. "Managing risks of hazardous chemicals in the workplace" See: https://www.safeworkaustralia.gov.au/doc/model-code-practice-managing-ri... (Link updated: 25 June 2018)

Standards Australia. AS/NZS 2243.10-2004 Safety in Laboratories – Storage of chemicals. Sydney Australia.

'The Australian Dangerous Goods Code Edition 7.4' The Department of Infrastructure and Regional Development website https://infrastructure.gov.au/transport/australia/dangerous/dg_code_7e.aspx (Accessed June 2016)

'The Globally Harmonised System of Classification and Labelling of Chemicals' Safe Work Australia Website. www.safeworkaustralia.gov.au/sites/SWA/whs-information/hazardous-chemicals/classifying-chemicals/Documents/GHS-Training-Part-1-Introduction.pptx (Accessed July 2016)