Every hazmat placard on the road belongs to one of nine DOT hazard classes defined under 49 CFR — identified by class number, color, and symbol. This page is a plain-language reference to the classes, how UN numbers and ERG guide numbers fit in, and how DOT placards differ from the GHS pictograms you'll see on a shipping label.
| Class | Name | Divisions |
|---|---|---|
| 1 | Explosives | 1.1–1.6, by hazard severity |
| 2 | Gases | 2.1 Flammable · 2.2 Non-Flammable/Non-Toxic · 2.3 Toxic |
| 3 | Flammable Liquid | — |
| 4 | Flammable Solid | 4.1 Flammable Solid · 4.2 Spontaneously Combustible · 4.3 Dangerous When Wet |
| 5 | Oxidizer / Organic Peroxide | 5.1 Oxidizer · 5.2 Organic Peroxide |
| 6 | Toxic / Infectious Substance | 6.1 Toxic · 6.2 Infectious Substance |
| 7 | Radioactive | — |
| 8 | Corrosive | — |
| 9 | Miscellaneous Dangerous Goods | — |
HazMat Pro covers all 19 placard divisions across these nine classes, each with color, symbol, common UN numbers, and handling notes.
A UN number identifies the specific material inside — not just its hazard class. Two shipments can carry the same placard but different UN numbers, and the UN number is what a first responder or dispatcher actually looks up.
| UN Number | Material | Class |
|---|---|---|
| UN1075 | Liquefied Petroleum Gas (LPG) | 2.1 |
| UN1203 | Gasoline | 3 |
| UN1830 | Sulfuric Acid | 8 |
| UN3480 / UN3481 | Lithium Ion Batteries | 9 |
Each UN number also maps to an ERG guide number — a two- or three-digit page reference in the Emergency Response Guidebook covering potential hazards, safety distances, and initial response steps for that material.
Required under 49 CFR on vehicles and bulk containers in transport. Identifies hazard class for responders, carriers, and inspectors on the road.
Required under OSHA's Hazard Communication Standard on product labels and Safety Data Sheets. Warns workers handling the container at the workplace.
The same material can carry both at once — a transport placard on the tanker and a GHS pictogram on the drum inside it. They're answering different questions for different audiences, which is why HazMat Pro keeps a glossary for both alongside the placard and UN number data.
HazMat Pro puts all 19 DOT placard divisions, 55+ UN numbers with ERG guide numbers, and the GHS/DOT glossary in one offline-first reference — plus a voice-powered Identify tool for when you'd rather ask than search.
DOT placards, UN numbers, ERG guide numbers, and GHS pictograms — searchable and fully offline.
Open HazMat ProNine hazard classes, several split into numbered divisions — like 2.1 Flammable Gas or 4.3 Dangerous When Wet — for 19 placard divisions in total.
A four-digit code identifying the specific material being shipped, such as UN1203 for gasoline. It's what shipping papers and lookups actually key off of, not just the hazard class.
A page reference in the Emergency Response Guidebook that a UN number maps to, covering hazards, safety distances, and initial response steps for that material.
Placards mark transport vehicles under DOT rules; GHS pictograms mark product labels and SDS sheets under OSHA rules. The same material can carry both at the same time.
Placards, UN numbers, ERG guide numbers, and Identify — offline.
Search 100+ UN numbers for class, packing group, and ERG guide.
Type a UN number or material, get the guide number.
What's tested, key facts, and practice questions.