Dangerous goods safety marks: labels, placards and other marks

A truck driver, a warehouse worker and a firefighter may all have only seconds to decide how to treat a package or vehicle. Dangerous goods safety marks are designed for that moment. Part 4 of the TDG Regulations uses the term safety marks for all of them: labels on packages, placards on vehicles and large containers, and other marks such as the UN number, the limited quantity mark and the marine pollutant mark. They are standardized internationally, so a trained person can read them anywhere.

Labels

A label is a diamond (a square set on one corner) at least 100 mm on each side, with a solid line inside its edge. Its top half shows a symbol, such as a flame, skull and crossbones or exploding bomb, and its bottom corner shows the class or division number. Some labels also carry words, such as FLAMMABLE LIQUID or CORROSIVE, although words are optional in many cases. The background colour helps recognition: red for flammable gases and liquids, green for non-flammable gases, yellow for oxidizers, white for toxic substances, black and white for corrosives, and white with vertical stripes for class 9.

Each package normally carries a label for its primary class and a label for each subsidiary class. Since alignment with the UN system, subsidiary labels show the class number at the bottom just like primary labels. Labels go on the same side of the package as the shipping name and UN number, near them, and must not be folded over an edge or hidden by other marks. Small containers that cannot fit a full-sized label may use smaller labels within limits set by the regulations. A package must not carry a label that does not apply to its contents.

Package marks

Besides labels, most packages must show the UN number, preceded by the letters UN, and the shipping name, next to the label. Several other marks may be required depending on the goods and the mode:

• Orientation arrows on combination packagings holding liquids, showing which way is up.
• The limited quantity mark, a diamond with black top and bottom corners and a white centre, on packages shipped under the limited quantity rules (lesson 10).
• The environmentally hazardous substance mark, a diamond showing a dead fish and a bare tree, for marine pollutants and environmentally hazardous substances.
• The elevated temperature mark, a thermometer symbol, for goods shipped hot.
• The inhalation hazard mark for toxic-by-inhalation goods, which Canada also accepts in its US form since 2026.
• The lithium battery mark, a rectangle with a red hatched border showing batteries and a flame, which since the 2026 amendments no longer needs a telephone number in Canada.
• The word OVERPACK on an outer package that holds labelled packages whose labels cannot be seen.

Placards

A placard is a large version of a label, at least 250 mm on each side, displayed on the outside of a vehicle, freight container, tank or other large means of containment. Placards must be displayed on each side and each end of the vehicle or container, so that they can be seen from any direction. They must be clearly visible, not hidden by doors, ladders or equipment, kept clean and in good condition, and removed or covered when the dangerous goods have been unloaded. A placard that does not match the contents is dangerous because it sends responders the wrong message.

When to placard is set out in sections 4.15 to 4.16.1 of the TDG Regulations. In general, a road vehicle or railway vehicle carrying dangerous goods must display placards for each primary class when the total gross mass of dangerous goods in the vehicle is more than 500 kg. The 500 kg relief does not apply to certain dangerous goods, which must be placarded in any quantity. These include goods that require an emergency response assistance plan, certain explosives, toxic gases (2.3), goods that are dangerous when wet (4.3), organic peroxides that require temperature control, certain highly toxic 6.1 goods, and radioactive materials requiring a Category III-Yellow label. Goods that need a subsidiary class placard must also show it.

Large means of containment, such as tanks and bulk containers with a capacity of more than 450 L, must also show the UN number. It can be displayed in the centre of the placard, on an orange panel next to it, or on a white rectangle, depending on the situation. UN numbers are required when the goods require an emergency response assistance plan or when a liquid or gas is in direct contact with the container. Regulations amended in 2026 also allow UN numbers to be placed inside hazard labels on some packages.

For mixed loads, the regulations allow a DANGER placard in some circumstances instead of placards for each class, but not for goods that must always be placarded or that require an ERAP. The details are in Part 4. When a load contains dangerous goods with a subsidiary class that requires a subsidiary placard, both must be displayed.

# Placarding decision for a mixed load (simplified; always check the regulations for exceptions).
load = [  # (description, class, gross mass kg, always-placard group?)
    ("Propane cylinders", "2.1", 210, False),
    ("Paint, PG II",      "3",   180, False),
    ("Corrosive cleaner", "8",   160, False),
]
always = [item for item in load if item[3]]
total = sum(item[2] for item in load)

# Canada: placard each primary class if total gross mass of dangerous goods exceeds 500 kg,
# or in any quantity for goods outside the 500 kg relief.
ca_classes = sorted({c for _, c, _, _ in load}) if total > 500 else sorted({c for _, c, _, a in always})
print(f"total dangerous goods: {total} kg")
print("Canada placards:", ca_classes or "none required")

# US: Table 2 materials need placards at 1,001 lb (454 kg) aggregate gross weight or more.
total_lb = total * 2.20462
us_classes = sorted({c for _, c, _, _ in load}) if total_lb >= 1001 else []
print(f"total in pounds: {total_lb:.0f} lb")
print("US placards (Table 2):", us_classes or "none required", "| DANGEROUS placard option for mixed Table 2 loads")

total dangerous goods: 550 kg
Canada placards: ['2.1', '3', '8']
total in pounds: 1213 lb
US placards (Table 2): ['2.1', '3', '8'] | DANGEROUS placard option for mixed Table 2 loads

In this example the total of 550 kg crosses the Canadian 500 kg line, and at about 1,213 pounds it crosses the US 1,001-pound line, so placards for classes 2.1, 3 and 8 are needed in both countries (or a DANGEROUS placard for this mixed Table 2 load in the United States, if no single class reaches 1,000 kg from one facility). Remove one 160 kg item and the load drops below both lines, but every other requirement, such as documents and training, still applies.

Segregation

Some dangerous goods react violently with each other. An oxidizer next to a flammable liquid feeds a fire; an acid next to a cyanide can release toxic gas; water-reactive goods next to aqueous liquids can produce flammable gas if packages leak. Keeping incompatible goods apart is called segregation. The TDG Regulations contain specific segregation requirements for some goods, such as explosives and for marine transport through the IMDG Code, and the general requirement that goods be loaded so there is no release that could endanger public safety. Shippers and carriers should follow the segregation guidance on safety data sheets and keep incompatible classes apart, using separate vehicles or physical distance where needed.

Placards on the road: practical points

Many carriers use placard holders with flip panels, so the driver can show the right class for each load. Flip placards are convenient but easy to leave on the wrong setting, so drivers should check every placard against the shipping document before each trip and after every drop-off on a multi-stop route. When a delivery removes the last of a class from the vehicle, its placard must come off or be covered.

Placards must stay readable. A placard caked in road grime or faded by the sun until its colour and symbol cannot be recognized does not meet the rules. Placards must not be placed where doors, ladders or equipment hide them, and they must be at least 75 mm away from other markings that could reduce their effectiveness. On a trailer, the front placard can go on the front of the trailer or on the front of the tractor.

Empty means of containment are not always free of the rules. A tank that has carried dangerous goods and has not been cleaned, purged or filled with a non-dangerous product still contains residue, and the TDG Regulations generally treat it as carrying those dangerous goods, so it keeps its placards and UN numbers until it has been cleaned. Small empty containers with residue are also regulated unless an exemption applies.

Rail cars and freight containers follow the same idea at a larger scale: four placards, identification numbers for bulk loads and placards that match the contents. Intermodal containers carried by ship also follow the IMDG Code, so they may arrive with marks such as the marine pollutant mark that road-only shipments rarely show.

Drivers should also check placards after any event that could dislodge or damage them, such as a car wash, a collision with a loading dock or a long run through snow and salt, and carry spare placards for the classes they regularly haul.