Placards showing without the un class number testing mock visually app drill checks
A hazard diamond with no class number at the bottom is usually a subsidiary risk label, flagging a secondary hazard a material has in addition to its primary class. The number is omitted because it belongs to the primary placard. So a numberless diamond means a secondary hazard; you read its color and symbol, while the class number lives on the main placard.
No number usually means subsidiary
A hazard diamond is normally read by color, symbol, and class number, so a diamond with no number at the bottom point stands out. The usual reason is that it is a subsidiary risk label, marking a secondary hazard the material carries in addition to its primary class. The missing number is the signal that it is secondary, not primary.
Why the number is omitted
On a subsidiary label the class number is typically left off because that number identifies the primary classification, which is already shown on the main placard. Repeating it on the subsidiary label would be misleading. So you still get the color and the symbol, which tell you the type of secondary hazard, just without the number.
Reading a numberless diamond
What the cues tell you:
| Primary placard | Subsidiary label | |
|---|---|---|
| Color and symbol | Yes | Yes |
| Class number | Yes | Often omitted |
| Meaning | The main hazard | An extra hazard it also has |
A symbol and color with no class number points to a secondary hazard. Verify in your official materials.
What it means in practice
Seeing a numberless hazard diamond, read it as a subsidiary risk: the material has this hazard in addition to its primary one. For example a material might be primarily one class but also corrosive or toxic as a secondary risk, shown by a corresponding numberless label. The primary placard, with its number, sits alongside it.
How to study and verify
Learn the rule rather than memorizing cases: a hazard diamond with a symbol and color but no class number is a subsidiary risk, an extra hazard layered on the primary. Because the exact conventions for subsidiary labels are set in the regulations and can change, confirm the specifics in your official manual and the current rules.
Frequently asked questions
- What does a placard with no class number mean?
- It is usually a subsidiary risk label, flagging a secondary hazard a material has in addition to its primary class. The number is omitted because it belongs to the primary placard. Color and symbol present, number absent, means secondary hazard. Verify in your official materials.
- Why would a hazard diamond have no number?
- Because it is a subsidiary label. The class number identifies the primary classification, already shown on the main placard, so the secondary label usually leaves it off to avoid confusion.
- Can a material have a numberless and a numbered diamond?
- Yes. The primary placard carries the class number; a subsidiary label for an additional hazard usually omits it. Together they show the material's full hazard profile.