The 9 Classes of Dangerous Goods Explained

Every hazardous shipment in Canada belongs to one of nine classes. Here is what each class covers, with real examples, and how shippers legally assign a product to the right one.

The 9 classes at a glance

That table answers the what. The rest of this guide answers the questions that actually cause fines: who must classify, what the jargon means, and what to do when a product fits two classes at once.

Who is legally responsible for classifying?

Not the driver, and not the trucking company. The law puts classification on the consignor, the party shipping the goods.

And guessing is not allowed. The consignor must keep written proof of how the goods were classified, a test report, a lab report, or a document explaining the classification, and keep it available for five years from the date on the shipping document (Section 2.2.1). When an inspector asks how you decided a drum was Class 3, "the supplier told me" is not a proof of classification.

Primary class, subsidiary class, packing group

Three terms unlock everything else in Schedule 1. Here they are, straight from the Regulations.

Dangerous goods is defined in the Act itself:

Primary class is the product's main danger, the first class shown in column 3 of Schedule 1. Transport Canada describes it as the class posing the highest hazard, which takes precedence over any other class posing a lower hazard.

Subsidiary class is a second danger the same product carries, shown in parentheses in column 3. A liquid can be flammable first and corrosive second.

Packing group grades how dangerous the product is, which drives container choice:

One wrinkle worth remembering: some classes have no packing groups at all. Gases (Class 2) and radioactive materials (Class 7) skip them entirely, Class 7 by explicit rule (Section 2.39).

How to read Schedule 1

Schedule 1 is the master list of every regulated dangerous good in Canada. Four columns do the work:

• Column 1, UN Number: the four-digit ID for the shipping name
• Column 2, Shipping Name: the official name the goods must travel under
• Column 3, Class: the primary class, with any subsidiary class in parentheses under it
• Column 4, Packing Group: the danger grade, I, II, or III

Those same UN numbers end up on labels and placards, which is where classification meets the physical world. If you have not read it yet, our guide to TDG placards and labels covers exactly how each class gets displayed on containers and trucks.

The 9 classes, one by one

Class 1: Explosives

Substances and articles with an explosion hazard, split into six divisions by how they explode. Class 1.1 is a mass explosion hazard, 1.2 a projection hazard, 1.3 a fire hazard with minor blast or projection, 1.4 no significant hazard beyond the package, 1.5 very insensitive substances, and 1.6 extremely insensitive articles (Section 2.10). Examples: black powder, fireworks, detonators.

Class 2: Gases

Compressed, liquefied, or refrigerated gases and aerosols, in three divisions. Class 2.1 Flammable Gases ignite in a mixture of 13% or less by volume with air. Class 2.2 Non-flammable Non-toxic Gases travel at an absolute pressure of 280 kPa or more at 20 degrees C. Class 2.3 Toxic Gases are known to be toxic or corrosive to humans (Section 2.14). Examples: aerosol cans, helium, anhydrous ammonia.

Class 3: Flammable Liquids

No divisions. The test is the flash point:

Gasoline and acetone are the classic members. This is the class most Canadian drivers actually haul.

Class 4: Flammable Solids, Spontaneous Combustion, Water-reactive

Three divisions for three different fire tricks. Class 4.1 solids burn readily (safety matches). Class 4.2 substances ignite spontaneously in air (wet cotton waste). Class 4.3 substances release flammable gas on contact with water (lithium hydride), which is why 4.3 fires get worse when you hose them (Section 2.21).

Class 5: Oxidizers and Organic Peroxides

Class 5.1 Oxidizing Substances yield oxygen that feeds other fires, like potassium nitrate. Class 5.2 Organic Peroxides are thermally unstable compounds containing the bivalent -O-O- structure (Section 2.24). Some Type B organic peroxides need temperature control in transport, which is also why they lose the 500 kg placarding exemption.

Class 6: Toxic and Infectious Substances

Chloroform sits in 6.1. Clinical and medical waste travels as 6.2 under UN3291.

Class 7: Radioactive Materials

No divisions and no packing groups, both by explicit rule (Sections 2.38 and 2.39). Class 7 also gets special treatment everywhere else in TDG: its labels and placards can never be reduced in size, and its Category III Yellow shipments never qualify for the 500 kg placarding exemption.

Class 8: Corrosives

No divisions. The defining test is brutal and specific:

Corrosives also attack metal, which threatens the container itself mid-transport. Hydrochloric acid and sodium hydroxide are the everyday members.

Class 9: Miscellaneous

The catch-all for goods that are dangerous in transport but fit nowhere else, with no divisions (Section 2.44). Its membership list is surprisingly modern: lithium ion batteries (UN3480), dry ice (UN1845), and environmentally hazardous substances (UN3077). If your business ships electronics, Class 9 is your class.

"The classification mistakes I see are never exotic. Someone ships a cleaning concentrate as a regular parcel because the label on the retail box looks harmless. Schedule 1 does not care what the marketing says. If the chemical is listed by name, that classification is the law."

Samira AliCertified Public Health Inspector, 10+ years across Canada and the U.S.

How a product gets its class

The official process runs in three steps:

Step 1: Check the name. If the product appears by name in column 2 of Schedule 1, the decision is already made for you:

Step 2: Test against the criteria. Not listed by name? The consignor evaluates the product against the class criteria in Part 2, flash point tests, toxicity data, pressure thresholds, using lab testing where needed.

Step 3: Resolve mixed hazards. When a product meets the criteria for more than one class, the Precedence of Classes rules in Section 2.8 decide which becomes the primary class. Four classes always win primary status when present: Class 1 Explosives, Class 5.2 Organic Peroxides, Class 6.2 Infectious Substances, and Class 7 Radioactive Materials.

Every step of this lands on the training exam, and it is exactly the kind of question that trips people up. Try the free TDG practice test and see how you score on classification before the real thing.

The short version

1. Canada has 9 classes of dangerous goods, from explosives to the miscellaneous class that holds lithium batteries and dry ice.
2. The consignor (shipper) is legally responsible for classification, with written proof kept for five years.
3. Primary class = main danger. Subsidiary class = second danger, in parentheses. Packing group = danger grade I, II, or III.
4. Schedule 1 is the master list: UN number, shipping name, class, packing group.
5. Listed by name in Schedule 1? That classification is mandatory. Not listed? Test against Part 2 criteria.
6. Mixed hazards get resolved by the precedence rules, and explosives, organic peroxides, infectious substances, and radioactives always take primary.

This article is general information, not legal advice. Classification depends on the specific product, its properties, and its quantities. Always verify against the current Transportation of Dangerous Goods Act, 1992 and Regulations.