8 Main WHMIS Symbols And Their Classes

As a Safety Consultant, I am often asked: Which are the main WHMIS symbols, and what hazard classes do they represent? In this article, I demystify each pictogram, link it to actual hazard classes, illustrate workplace scenarios, and explain how understanding these symbols helps ensure regulatory compliance and worker safety. This guide aligns with the “Main WHMIS Symbols And Their Classes” and includes “WHMIS pictogram classes,” “Hazardous Materials Information System symbols.”

What is the WHMIS Symbol

WHMIS symbols are standardized pictograms used in the Workplace Hazardous Materials Information System (WHMIS) to quickly identify the type of hazard a chemical or product presents. These symbols are part of Canada’s national system for hazard communication and are designed to keep workers safe by providing visual warnings on labels and safety data sheets (SDS).

What They Represent:

Each symbol represents a specific class or category of hazard, such as:

• Fire hazard

• Toxic exposure

• Health damage

• Environmental risks

• Corrosive substances

• Explosive or reactive materials

• Compressed gases

These symbols are typically shown inside a red diamond-shaped border, aligning with the Globally Harmonized System (GHS) adopted under WHMIS 2015.

Purpose of WHMIS Symbols:

• Alert workers about the type of danger associated with the product.

• Promote safe handling, storage, and disposal of hazardous materials.

• Reduce workplace accidents by making hazard communication clear and consistent.

Example:

A container with a Flame symbol means the contents are flammable or combustible, while a Skull and Crossbones symbol means the substance is acutely toxic and can cause serious harm or death.

Understanding these symbols is crucial for workplace safety and is a key part of WHMIS training in Canada.

WHMIS Symbols And Their Classes

1. Flame – Flammable hazards and self‑reactive risks

Symbol and Class Overview

The Flame pictogram—a stylized red flame in a diamond border—alerts workers to flammable and combustible materials. It’s linked to these classes and categories under WHMIS 2015:

• Flammable gases, liquids (Categories 1–3), solids (1–2)

• Aerosols (1–2)

• Self‑reactive substances (Types B–F), organic peroxides (Types B–F)

• Pyrophoric liquids/solids (1), self‑heating substances (1–2), water‑reactive compounds.

Real‑World Scenario

In a paint shop, flammable solvents like acetone and toluene are in 20‑litre drums. These carry a Flame pictogram. Workers learn through WHMIS training that using non‑spark tools and storing these drums in ventilated, fire‑rated cabinets prevents ignition risks.

Why It Matters

A glance at this symbol signals high fire risk, prompting engineers to install explosion‑proof pumps and prohibit hot work nearby. Safety signage, periodic inspections, and updated SDS align with WHMIS compliance and reduce injury risk.

2. Flame Over Circle – Oxidizing hazards

Symbol and Class Overview

The Flame over Circle pictogram shows a flame atop a circle, warning of oxidizing substances that can intensify fire:

• Oxidizing gases (1), liquids (1–3), solids (1–3) 

Real‑World Scenario

In a laboratory, bottles of 30 % hydrogen peroxide sport this symbol. Staff know to separate them from organic solvents and store them upright, in cool cabinets with airflow. Gloves and eye protection are mandatory to prevent contact burns.

Safety Impact

Understanding this pictogram prevents serious incidents—like wildfires triggered when oxidizers contact flammable materials. It fosters smart inventory control and emergency readiness in labs, hospitals, and manufacturing.

3. Gas Cylinder – Gases under pressure

Symbol and Class Overview

This symbol—a compressed gas cylinder—signals a pressurized gas hazard:

• Gases under pressure: compressed, liquefied, refrigerated, dissolved

• Also applies to chemicals under pressure (Categories 1–3) 

Real‑World Scenario

At an auto‑repair garage, compressed air and oxygen tanks are chained securely. Technicians inspect cylinder valves monthly. If a cylinder tips or overheats, it may become a rocket—a literal projectile—so stable storage and safety rails are enforced.

Safety Impact

Training stresses never tampering with valves, recognizing cylinder codes, and replacing worn regulators. The Gas Cylinder symbol prevents mechanical injuries and ensures safe gas usage.

4. Corrosion – Corrosives to skin, eyes, and metals

Symbol and Class Overview

The Corrosion pictogram—showing a test tube pouring liquid on metal and skin—means:

• Corrosive to metals (1)

• Skin corrosion/irritation (Categories 1–1C)

• Serious eye damage (Category 1) 

Real‑World Scenario

In manufacturing, sulphuric acid in battery production bears this symbol. Workers wearing acid‑resistant gloves and chemical splash goggles follow spill‑neutralization procedures immediately to avoid severe burns and equipment damage.

Safety Impact

This pictogram raises awareness about implementing fume hoods, using sealed transfer systems, and maintaining eye‑wash stations. Regular training reinforces protocols for handling caustic materials.

5. Exploding Bomb – Explosives and self‑reactive

Symbol and Class Overview

The Exploding bomb icon signifies reactive and explosive hazards:

• Self‑reactive substances and organic peroxides (Types A–B*) 

Real‑World Scenario

A chemical lab researcher handling benzoyl peroxide—used in polymerization—notes the symbol. The protocol requires storage in cool areas and the use of minimal quantities. Any heat exposure may trigger decomposition and explosion.

Safety Impact

Designing storage like a “blow‑out” secure cabinet and maintaining PPE prevents catastrophic reactions. Properly responding to the symbol is crucial for researcher and facility safety.

6. Skull and Crossbones – Acute toxicity

Symbol and Class Overview

This unmistakable Skull and Crossbones alerts to substances causing acute toxicity (Categories 1–3) via ingestion, inhalation, or skin contact.

Real‑World Scenario

An agriculture worker handling an organophosphate pesticide sees this symbol. They are trained to avoid skin contact, use gloves and respirators, wash their hands after use, and understand Poison Centre protocols. First‑aid training includes atropine injection procedures.

Safety Impact

Recognizing this symbol saves lives. It triggers immediate actions—securing areas, reporting exposure, and using antidotes. Workers also learn to read SDS for treatment steps.

7. Health Hazard – Chronic health effects

Symbol and Class Overview

The Health Hazard pictogram—human silhouette with starburst chest—indicates:

• Respiratory or skin sensitizers, mutagens, carcinogens

• Reproductive toxicity

• Specific organ toxicity (single/repeat exposures), aspiration hazards

Real‑World Scenario

In an aerospace plant, hexavalent chromium plating tanks show this pictogram. Workers understand the risk of lung cancer and reproductive harm. A full medical surveillance program, respiratory protection, and fixed local exhaust ventilation systems are installed to limit exposure.

Safety Impact

This symbol shifts focus from short‑term safety to long‑term health preservation. It ensures safety professionals design controls and health monitoring for at-risk workers.

8. Exclamation Mark – Irritants and lower‑level toxicity

Symbol and Class Overview

The Exclamation Mark warning applies to:

• Acute toxicity (Category 4)

• Skin or eye irritation (Category 2/2A)

• Respiratory/skin sensitization (Category 1)

• Specific target organ toxicity (single exposure Category 3)

Real‑World Scenario

Cleaning staff handling spray cleaners containing ammonia or bleach see this symbol. They learn to ensure adequate ventilation, wear nitrile gloves, avoid mixing chemicals (chlorine + ammonia = toxic chloramine gas), and complete spill cleanup training.

Safety Impact

This allows moderate hazard identification. Safety managers can mandate basic PPE—gloves, goggles—and SOPs to prevent eye irritation or mild respiratory effects.

Integrating WHMIS Training and Compliance

Understanding these 8 Main WHMIS Symbols goes beyond workshops. A best‑in‑class WHMIS program involves:

1. Classification using Canadian GHS rules and referencing CCOHS tools.

2. Labeling every product with appropriate symbols listed in HPR’s Schedule II.

3. SDS review, where Section 2 matches labels, including hazard classes.

4. Worker education includes classroom, on‑the‑job training, and scenario drills.

5. Site audits ensure pictograms are visible, containers are intact, and PPE is used.

6. Incident investigation uses pictogram knowledge to trace handling failures.

People Also Ask

Which WHMIS symbol indicates a carcinogen?

The Health Hazard pictogram (human silhouette with starburst) includes carcinogens, mutagens, and reproductive toxins.

How many symbols are on WHMIS labels?

WHMIS 2015 uses nine GHS-aligned pictograms, including biohazardous infectious materials. The eight main WHMIS symbols exclude the environmental symbol, focused on Canada’s core classes.

Why is the exclamation mark used on WHMIS labels?

It flags irritants, mild toxins, and sensitizers—issues like skin/eye irritation or moderate respiratory effects .

Real‑Life Example: Laboratory Chemical Spill

Last year, a spill involving sodium hypochlorite (Bleach) at a university chemistry lab was traced to misread labeling: the container bore both the Exclamation Mark and Corrosion symbols. During training, staff emphasized single-symbol containers, preventing confusion. Spill drills ensured the correct acid neutralizer was used—avoiding chlorine gas release. This scenario highlights how knowing pictograms and SDS details intimately can avert disasters.

Summary Table of 8 Main Symbols

Final Takeaways for Safety Professionals

• Train consistently using up‑to‑date pictograms and SDS.

• Audit actively for missing or mixed hazard symbols.

• Engineer controls tailored to hazard level—chronic or acute.

• Update SOPs when new chemicals enter the workplace.

• Communicate tools like posters with these 8 symbols to build hazard awareness.

By deeply understanding the Main WHMIS Symbols And Their Classes, safety teams not only comply with legislation but also cultivate a proactive, hazard-aware culture that protects health, reduces incidents, and builds trust in safety systems.

Download the PDF copy of the WHMIS regulation here – Download

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