Workers in Many Sectors
Workers Must Understand WHMIS Labelling not Classification

Written by: Rob Hallsworth

Published on: 13 September 2021

WHMIS exists to protect workers from hazardous chemicals. It is based on the Globally Harmonized System of Classification and Labelling of Chemicals commonly referred to as GHS. GHS focuses on 2 items:

  • Classification – the arrangement of hazards into groups based on specific criteria
  • Labelling – the use of  symbols and descriptions of the hazards based on their classification

Classification is at the Heart of WHMIS but of Little Relevance to Workers

Classification of a hazardous products is performed by the Supplier. It is based on a very specific set of criteria for each of the Classes and Categories used in GHS. The detail describing how to classify products comprises 80% of the content of the GHS.

While this information is critical to Suppliers in preparing an SDS it is of little use to Employers and Workers because the descriptions and criteria have little in common with the day-to-day activities of the users of the chemical products.

Here are 2 examples of how a product is classified to illustrate this point:

Class – Acute Toxicity (Inhalation)

Criteria – Lethal Concentration 50 (LC50)

LC50 is the concentration of a substance in air that causes the death of 50.0% of a group of test animals

Range Category 2

  • Gases (ppm) > 100 and ≤500
  • Vapours (mg/l) > 0.5 and ≤2
  • Dusts and Mists (mg/l)  > 0.05 and ≤ 0.5

Class – Flammable Liquids

Criteria – Flash Point & Boiling Point

Flash point is the lowest temperature at which the application of an ignition source causes the vapours of a liquid to ignite.

Initial boiling point is the temperature at which the first gas bubble appears

Range Category 1

  • Flash point < 23°C
  • Initial boiling point ≤ 35°C

The Value of WHMIS to Workers is in Labelling

Once a hazardous product has been classified, the product is labelled according to GHS. This process is so simple that only 10% of the content of GHS describes how to do it.

Here are the required labels for the 2 examples illustrated above

Acute Toxicity (Inhalation) – Category 2


Fatal if Inhaled – Signal Word Danger


Flammable Liquids – Category 1 


Extremely flammable liquid and vapour – Signal Word Danger


This is much easier to understand.

Don’t Focus on Classification, Focus on Labelling

Many organizations and WHMIS education sessions focus on how WHMIS works and the process of classifying hazards. In one WHMIS training session, we evaluated that background information accounted for 2/3 of the content and 3/4 of the questions in the quiz.

But that is not what employers and workers need to worry about. They need to understand labelling – the description of the hazards.

Why? Because understanding the hazards is the first step in preventing workplace injury and illness.

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