TDG Placards and Labels: When and How to Use Them

One rule decides almost everything: 450 litres. Get that number right and the rest of the marking rules fall into place. Get it wrong and the fine is addressed to you.

The 450 litre rule: label or placard?

The question I hear most on this topic sounds simple: are the stickers on the boxes enough, or does the truck itself need the big diamond signs? The law answers it with a single number. Everything in TDG marking starts with whether your container is a small or large means of containment, and the cutoff is 450 litres.

Transport Canada's safety marks guidance then sets the general rule: labels are displayed on small means of containment, 450 L or less, and placards are displayed on large means of containment, greater than 450 L.

In plain terms: boxes, drums, and jerry cans get labels. Tote tanks, highway tankers, and railway cars get placards. One detail people miss: capacity means the maximum volume of water the container can hold, not how much product is inside it. A half-empty 1,000 L tote is still a large means of containment.

How big they must be

Why so strict about size? Because these marks are not for you. They are for the firefighter deciding how close to get to your vehicle at 2 a.m. The sizes exist so the marks can be read from a safe distance.

Labels: 100 mm

Placards: 250 mm

When the container is too small or oddly shaped

The Regulations allow shrinking, with hard floors. A label may be reduced to the point where it fits together with the shipping name, technical name, and UN number, but never below 30 mm per side. A placard on an odd-shaped large container may be reduced, but never below 100 mm per side.

One hazard class gets no flexibility at all. Transport Canada's guidance is blunt: the Class 7 Radioactive Materials placard and label cannot be reduced under any circumstances.

Where they go

The right mark in the wrong spot is still a violation. Placement rules are short and specific.

Labels go on any side of the small container except the side it rests on or stacks on during transport. For cylinders, the label goes on or near the shoulder.

Placards follow the four-sides rule:

Each side and each end means four placards total, visible from any angle a first responder approaches. Print our free TDG safety marks wall poster and the placement rules hang right where your team loads.

The 500 kg exemption and its 9 exceptions

Here is the relief valve. If your whole load of dangerous goods is light enough, the vehicle placard can be skipped.

Two traps hide inside that sentence. First, gross mass counts the containers plus their contents, not just the product. Second, subsection (2) lists nine categories where the exemption never applies, no matter how light the load:

• Goods requiring an ERAP (Emergency Response Assistance Plan)
• Goods requiring a subsidiary class placard under Section 4.15.1
• Class 1, Explosives, with narrow exceptions for small quantities
• Class 2.1, Flammable Gases, if the vehicle will travel by vessel
• Class 2.3, Toxic Gases
• Class 4.3, Water-reactive Substances
• Class 5.2, Organic Peroxides Type B needing temperature control
• Class 6.1, Toxic Substances under Special Provision 23
• Class 7, Radioactive Materials requiring a Category III Yellow label

Notice the pattern: everything on that list is a load where a first responder cannot afford one second of guessing. If your goods sit anywhere near those classes, placard the vehicle. This exemption is a close cousin of the 150 kg training exemption, and the two get confused constantly. Our guide to the TDG 150 kg and 500 kg exemptions untangles them side by side.

"The 500 kg exemption is where I see good companies get burned. They weigh the product and forget the drums. Gross mass means everything on the deck, steel included. Twenty drums of product at 20 kg each is not 400 kg once the drums join the math."

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

Double hazards: subsidiary marks

Some products carry two dangers at once, like a liquid that is both flammable and corrosive. TDG handles this with subsidiary class marks.

On small containers, the rule is broad: one label for the primary class and one for each subsidiary class listed in column 3 of Schedule 1, for each of the dangerous goods in the container.

On large containers, subsidiary placards are required only in specific high-risk situations. Under Section 4.15.1, a subsidiary placard must be displayed next to the primary placard, on each side and each end, when the goods require an ERAP and the subsidiary class is Class 1 Explosives, Class 4.3 Water-reactive Substances, Class 6.1 Toxic Substances in Packing Group I for inhalation toxicity, or Class 8 Corrosives for UN2977 or UN2978 uranium hexafluoride.

The practical takeaway: label every hazard on boxes, but on trucks, subsidiary placards belong to a short, dangerous list. If your goods are on it, you almost certainly have an ERAP and already know it.

UN numbers

The four-digit UN number is the chemical's ID badge. Emergency crews look it up in seconds to know exactly what they are dealing with.

On small containers, the UN number goes next to the primary class label, or inside a white rectangle on the label itself, as long as it does not cover the symbol, class number, or text. The prefix UN is dropped when it sits inside the label.

On large containers, UN numbers are required when the goods need an ERAP or when a liquid or gas is in direct contact with the container. The display rule is specific:

That orange panel with black numbers you see beside placards on tankers? Now you know exactly what it is and why the numerals are 65 mm tall.

Lost a placard mid-trip? Read this

Highway wind, rain, and gravel are hard on safety marks. So who is responsible when a placard disappears somewhere past Thunder Bay? The Regulations name the carrier, and the duty is continuous:

If a mark falls off or becomes unreadable during the trip, the carrier replaces it, immediately, not at the next depot. Smart carriers keep spare placards in the cab for exactly this reason.

The short version

1. 450 L or less: label. More than 450 L: placard.
2. Labels are at least 100 mm per side, placards at least 250 mm, on all four sides of the vehicle.
3. Shrinking is allowed to 30 mm for labels and 100 mm for placards. Class 7 never shrinks.
4. Loads of 500 kg or less usually skip the vehicle placard, unless the goods hit one of the 9 high-risk exceptions.
5. UN numbers ride next to or inside the mark, 65 mm black numerals on large containers.
6. The carrier must keep every mark displayed for the whole trip and replace lost ones immediately.

This article is general information, not legal advice. Marking requirements depend on the specific dangerous goods, quantities, and mode of transport. Always verify against the current Transportation of Dangerous Goods Act, 1992 and Regulations.