Classification
WHMIS 2015 introduces a new system for classifying hazardous products. There are at least three possible levels of classification for an individual product. Moving from the most general classification to more specific ones, these levels are:
hazard “group” → hazard “class” → hazard “category” →
and, in some cases, hazard “subcategory.”
There are two broad hazard groups: physical hazards and health hazards.
Products in the physical hazards group are classified based on characteristics such as flammability or reactivity. Health hazards are grouped based on their ability to cause a health effect, such as cancer or skin irritation. Both groups are divided into classes of
materials with similar properties.

There are 19 distinct classes in the physical hazards group and 12 classes in the health hazards group.
Classes in the Physical Hazards Group are:
1. Flammable gases
2. Flammable aerosols
3. Oxidizing gases
4. Gases under pressure
5. Flammable liquids
6. Flammable solids
7. Self-reactive substances and mixtures
8. Pyrophoric liquids
9. Pyrophoric solids
10. Self-heating substances and mixtures
11. Substances and mixtures which, in contact with water, emit flammable gases
12. Oxidizing liquids
13. Oxidizing solids
14. Organic peroxides
15. Corrosive to metals
16. Combustible dusts*
17. Simple asphyxiants*

18. Pyrophoric gases*
19. Physical hazards not otherwise classified*

Classes in the Health Hazard Group are:
1. Acute toxicity
2. Skin corrosion/irritation
3. Serious eye damage/eye irritation
4. Respiratory or skin sensitization
5. Germ cell mutagenicity
6. Carcinogenicity
7. Reproductive toxicity
8. Specific target organ toxicity – single exposure
9. Specific target organ toxicity – repeated exposure
10. Aspiration hazard
11. Biohazardous infectious materials*
12. Health hazards not otherwise classified*
* These hazard classes are part of WHMIS 2015 (Canada) but are not part of the GHS(International).
Most hazard classes are further subdivided into categories and subcategories based on the severity of the hazard. Most categories are identified by a number and subcategories by a number and letter. The lower the category number, the more severe the hazard, for example, a product classified as a
Flammable Liquid-Category 1 is more hazardous than a Flammable Liquid Category 2.