Hazard Classes and Pictograms
This domain tests the 31 hazard classes, the difference between a class and a category, and the mapping from hazard to pictogram and signal word. Most exam items ask you to classify a product from a short property list and then select the correct symbol.
The 31 classes
WHMIS 2015 has 19 physical hazard classes and 12 health hazard classes. Physical classes include flammable gases, flammable aerosols, oxidizing gases, gases under pressure, flammable liquids, flammable solids, self-reactive substances, pyrophoric liquids and solids, self-heating substances, water-reactive substances, oxidizing liquids and solids, organic peroxides, corrosive to metals, combustible dusts, simple asphyxiants, pyrophoric gases, and physical hazards not otherwise classified. Health classes include acute toxicity, skin corrosion/irritation, serious eye damage/eye irritation, respiratory or skin sensitization, germ cell mutagenicity, carcinogenicity, reproductive toxicity, STOT-single exposure, STOT-repeated exposure, aspiration hazard, biohazardous infectious materials, and health hazards not otherwise classified.
Class and category
A class names the type of hazard; a category ranks severity. Category 1 is usually the most severe, but some classes use types (gases under pressure: compressed, liquefied, refrigerated liquefied, dissolved) or letters (self-reactive substances A to G). A product can carry several classifications, and the label and SDS must reflect all of them.
Pictogram mapping
- Flame: flammable gases, aerosols, liquids and solids; pyrophoric, self-heating, water-reactive and self-reactive substances; organic peroxides.
- Flame over circle: oxidizing gases, liquids and solids.
- Exploding bomb: self-reactive substances and organic peroxides.
- Gas cylinder: gases under pressure.
- Corrosion: skin corrosion, serious eye damage, corrosive to metals.
- Skull and crossbones: acute toxicity categories 1 to 3.
- Health hazard: carcinogenicity, germ cell mutagenicity, reproductive toxicity, STOT, aspiration hazard, respiratory sensitization.
- Exclamation mark: acute toxicity category 4, skin/eye irritation, skin sensitization, STOT category 3, respiratory irritation and narcotic effects.
- Biohazard symbol: biohazardous infectious materials; this is not a GHS pictogram.
Worked example
A liquid has a flash point of 18 degrees C and an initial boiling point of 40 degrees C. Flammable liquid category 1 requires flash point below 23 degrees C and initial boiling point at or below 35 degrees C. Category 2 requires flash point below 23 degrees C and initial boiling point above 35 degrees C. Because 40 degrees C is above 35 degrees C, the product is category 2: signal word Danger, flame pictogram, hazard statement Highly flammable liquid and vapour. If the boiling point were 34 degrees C, it would be category 1. If the flash point were 45 degrees C, it would be category 3.
Traps that cost marks
- Confusing category 1 and category 2 because both have a flash point below 23 degrees C; check the boiling point.
- Using skull and crossbones for acute toxicity category 4; that category uses the exclamation mark.
- Forgetting that the corrosion pictogram also covers corrosive to metals, not just skin and eyes.
- Counting the environment pictogram as a WHMIS pictogram.
- Assuming every hazard class carries a pictogram.