Groups
The pictograms are used to help identify the many classes of specific hazards.
There are two major hazard groups used in WHMIS:
- Physical
- Health
Each group is made up of several classes and categories.
Physical
The WHMIS "physical hazard group" includes the following physical hazard classes:
- Combustible dusts
- Corrosive to metals
- Flammable aerosols
- Flammable gases
- Flammable liquids
- Flammable solids
- Gases under pressure
- Organic peroxides
- Oxidizing gases
- Oxidizing liquids
- Oxidizing solids
- Physical hazards not otherwise classified (PHNOC)
- Pyrophoric gases
- Pyrophoric liquids
- Pyrophoric solids
- Self-heating substances and mixtures
- Self-reactive substances and mixtures
- Simple asphyxiants
- Substances and mixtures which, in contact with water, emit flammable gases
Health
The WHMIS "health hazard group" includes the following health hazard classes:
- Acute toxicity
- Aspiration hazard
- Biohazardous infectious materials
- Carcinogenicity
- Germ cell mutagenicity
- Health hazards not otherwise classified (HHNOC)
- Reproductive toxicity
- Respiratory or skin sensitization
- Serious eye damage/eye irritation
- Skin corrosion/irritation
- Specific target organ toxicity – Repeated exposure
- Specific target organ toxicity – Single exposure
Categories
Hazard classes consist of categories and sometimes subcategories. The category identifies the degree of the hazard. Category 1 is always more hazardous than Category 2 or 3. Similarly, subcategory 1A is always more hazardous than subcategory 1B or 1C.
For example, "Flammable liquids" is a hazard class. Within this class, there are four divisions or categories, each with different flash point and/or initial boiling point cut-off values:
- Category 1: Flash point less than 23°C and initial boiling point less than or equal to 35°C (most flammable)
- Category 2: Flash point less than 23°C and initial boiling point greater than 35°C
- Category 3: Flash point greater than or equal to 23°C and less than or equal to 60°C
- Category 4: Flash point greater than 60°C and less than or equal to 93°C
As a worker, it is important to remember that Category 1 is always more hazardous than Category 2. Category 2 is more hazardous than Category 3, and so on if there are multiple categories.