Hazard Classification

Hazard classification is the foundation of WHMIS 2015. Before a product can be properly labeled or documented in a safety data sheet, it must first be classified according to standardized criteria. Classification involves evaluating the intrinsic properties of a material to determine what types of hazards it presents and how severe those hazards are.

Under WHMIS 2015, hazards are organized into two main groups: physical hazards and health hazards. Physical hazards relate to the chemical or physical properties of a product, such as flammability or reactivity. Health hazards relate to the adverse health effects that can occur when a person is exposed to the product. Some products present only physical hazards, some only health hazards, and many present both types.

Each hazard type is further divided into specific hazard classes, and most classes are subdivided into categories that indicate the severity of the hazard. Category 1 generally represents the most severe hazard, while higher category numbers indicate less severe hazards. However, not all hazard classes use the same numbering system, so it is important to understand the specific classification criteria for each hazard type.

The responsibility for classifying products rests primarily with suppliers. Suppliers must evaluate test data, scientific studies, and other relevant information to determine how their products should be classified. However, employers may also need to classify products in certain situations, such as when they produce hazardous materials for use in their own workplace or when they receive unclassified materials.

Physical hazards encompass a wide range of properties related to how a material behaves chemically or physically. These hazards can lead to fires, explosions, violent reactions, or other dangerous situations if materials are not handled properly. WHMIS 2015 includes numerous physical hazard classes, each with specific classification criteria.

Flammable materials are among the most common physical hazards encountered in workplaces. This category includes flammable gases (such as propane), flammable aerosols (like spray paints), flammable liquids (including gasoline and solvents), and flammable solids (such as certain metal powders). The classification considers factors like flash point, boiling point, and the material's ability to sustain combustion. Materials that ignite easily and burn rapidly are classified in more severe categories.

Oxidizing materials pose a different type of fire hazard. Rather than burning themselves, oxidizers supply oxygen that allows other materials to burn more intensely. Oxidizing gases, liquids, and solids can cause or intensify fires and can make fire-fighting extremely difficult. Common examples include oxygen cylinders, hydrogen peroxide, and certain chlorine compounds used in pool maintenance and cleaning products.

Other significant physical hazard classes include gases under pressure, which can burst containers if mishandled; corrosive to metals, which can damage equipment and containers; explosives and self-reactive substances, which can detonate or violently decompose; pyrophoric materials, which can spontaneously ignite when exposed to air; and substances that emit flammable gases on contact with water. Some materials also present hazards not covered by other classes and are classified as "physical hazards not otherwise classified."

Health hazards describe the potential adverse health effects that can result from exposure to a hazardous product. These effects can range from mild irritation to life-threatening conditions, and they may occur immediately after exposure (acute effects) or develop over time with repeated exposure (chronic effects). Understanding health hazard classifications helps workers recognize the potential health risks they face and take appropriate protective measures.

Acute toxicity refers to harmful effects that occur after a single exposure or multiple exposures within a short period (usually 24 hours or less). Materials with acute toxicity can cause effects ranging from skin or eye irritation to serious illness or death, depending on the category and exposure route. Exposure can occur through swallowing (oral), skin contact (dermal), or breathing (inhalation). Highly toxic substances, such as cyanide compounds, are classified in Category 1 or 2, while less toxic substances fall into higher category numbers.

Chronic or long-term health hazards include some of the most serious classifications under WHMIS 2015. Carcinogenicity refers to materials that can cause cancer. Germ cell mutagenicity describes substances that can cause genetic mutations that may be passed to offspring. Reproductive toxicity includes effects on sexual function and fertility as well as developmental effects on unborn children. Specific target organ toxicity identifies materials that damage particular organs such as the liver, kidneys, nervous system, or respiratory system after single or repeated exposure.

Other important health hazard classes include respiratory and skin sensitization, which can cause allergic reactions that may worsen with repeated exposure; aspiration hazard, which applies to materials that can enter the lungs and cause chemical pneumonia; and skin corrosion or irritation and serious eye damage or irritation. Biohazardous infectious materials represent a unique category covering organisms that can cause disease. Like physical hazards, materials may also present "health hazards not otherwise classified" when they pose risks not adequately addressed by the standard categories.

The hazard classification assigned to a product directly determines what information appears on its label and safety data sheet. Each hazard class and category is associated with specific pictograms, signal words, hazard statements, and precautionary statements. This standardized approach ensures that similar hazards are communicated consistently across all products and all suppliers.

When a product is classified into multiple hazard classes, all relevant pictograms must appear on the label (though WHMIS allows certain exceptions when one pictogram would be redundant with another more severe hazard pictogram). The most severe classification determines the signal word: "Danger" is used for more severe hazards, while "Warning" is used for less severe hazards. Only one signal word appears on a label, even if the product has multiple hazards.

Hazard statements are standardized phrases that describe the nature and severity of each hazard. For example, "Highly flammable liquid and vapor" or "Causes serious eye damage." These statements are precisely worded according to international GHS standards to ensure global consistency. Similarly, precautionary statements provide standardized information about prevention, response, storage, and disposal measures appropriate for each hazard.

Understanding hazard classification helps workers make sense of the information they see on labels and safety data sheets. When workers know that a skull and crossbones pictogram indicates acute toxicity, or that the health hazard pictogram may signal a carcinogen, they can better assess the risks they face and take appropriate precautions. This understanding is fundamental to working safely with hazardous materials.