There are two types of hazards: physical hazards and health hazards. Physical hazards will result in immediate injury to the body. The effects of health hazards may be felt within moments or over a prolonged period from initial exposure and are primarily concerned with illness or disease.
There are four ways hazardous materials can enter the body:
- Ingestion: Inadvertently swallowing hazardous materials.
- Absorption: Occurs when hazardous material enters the body through the skin or an open wound.
- Inhalation: Breathing in hazardous fumes.
- Injection: Occurs when a needle containing hazardous material pierces the skin.
Understanding WHMIS Hazard Groups, Classes & Categories for Workplace Safety
Workplace safety is a top priority in Canada, and understanding Workplace Hazardous Materials Information Systems is essential for handling hazardous materials safely. By learning these classifications, workers can better identify risks and take appropriate precautions.
What Are WHMIS Hazard Classes?
Hazard classes group products with similar hazardous properties. Most classes align with GHS standards, but some are specific to WHMIS.
Physical Hazard Classes
| Hazard Class | Key Risks |
| Flammable gases, liquids, solids | Fire or explosion hazards |
| Oxidizing gases, liquids, solids | Intensify fires or cause explosions |
| Gases under pressure | Explosion risk if heated; cryogenic burns |
| Self-reactive substances | May ignite or explode spontaneously |
| Pyrophoric liquids/solids | Ignite instantly when exposed to air |
| Corrosive to metals | Can chemically damage metals |
| Combustible dusts | Fire or explosion risk when airborne |
| Organic peroxides | Fire or explosion risk if heated |
Health Hazard Classes
| Hazard Class | Key Risks |
| Acute toxicity | Fatal, toxic, or harmful if inhaled/swallowed |
| Skin corrosion/irritation | Severe burns or reversible damage |
| Respiratory sensitization | May cause asthma or allergic reactions |
| Carcinogenicity | May cause cancer |
| Reproductive toxicity | Harms fertility or unborn children |
| Biohazardous materials | Infectious microorganisms causing disease |
Note: WHMIS does not currently include the Explosives hazard class, as it’s regulated under other Canadian laws.
What Are WHMIS Hazard Categories?
Each hazard class is further divided into categories, ranked by severity:
- Category 1 = Most hazardous
- Category 2, 3, etc. = Decreasing hazard level
For example:
- Flammable liquids (Category 1) are more dangerous than Flammable liquids (Category 3).
- Carcinogenicity (Category 1A) poses a higher cancer risk than Carcinogenicity (Category 1B).
- Some exceptions exist (e.g., Gases under pressure categories describe physical state, not hazard level).
How to Identify Hazard Classes & Categories
All hazardous products must have:
- Labels with hazard pictograms
- Safety Data Sheets (SDS) with hazard details
By reviewing these, workers can:
- Recognize hazards
- Follow proper handling procedures
- Prevent accidents
Stay Safe with WHMIS Training!
Understanding WHMIS hazard groups, classes, and categories is crucial for workplace safety. If you work with hazardous materials, proper training ensures compliance and reduces risks. Enroll in our WHMIS online course today and get certified!