Hazard Identification: Placards, Labels, and Markings

Why Hazard Identification Matters

When a vehicle or container is involved in an incident, firefighters must identify what hazardous material may be present before they take any action. A wrong assumption can put crews inside a lethal zone without proper protection. The U.S. Department of Transportation (DOT) requires shippers and carriers to mark packages, vehicles, and containers with standardized placards, labels, and markings so that first responders can quickly determine the hazard class and look up appropriate protective actions.

The Nine DOT Hazard Classes

DOT organizes hazardous materials into nine primary hazard classes. Every firefighter must recognize each class on sight:

1. Class 1 – Explosives: Substances or articles capable of mass explosion, projection, fire, or minor blast. Subclasses 1.1 through 1.6 describe the type of hazard. Placard is orange with the class number and a bomb graphic.

2. Class 2 – Gases: Includes flammable gas (red), non-flammable/non-toxic gas (green), and toxic/poison gas (white). Examples: propane, oxygen, chlorine.

3. Class 3 – Flammable Liquids: Liquids with a flash point below 60 °C (140 °F). Placard is red with a flame. Examples: gasoline, ethanol.

4. Class 4 – Flammable Solids; Spontaneously Combustible; Dangerous When Wet: Three divisions cover solids that burn easily, materials that self-ignite, and materials that react violently with water.

5. Class 5 – Oxidizers and Organic Peroxides: Oxidizers support combustion; organic peroxides can burn and explode. Placard is yellow with a flame-over-circle symbol.

6. Class 6 – Toxic and Infectious Substances: Division 6.1 covers poisons; Division 6.2 covers biohazardous material. Skull-and-crossbones symbol on the 6.1 placard.

7. Class 7 – Radioactive Materials: Three transport categories based on radiation levels. The distinctive trefoil (propeller) symbol appears on a white/yellow label.

8. Class 8 – Corrosives: Acids and bases that destroy living tissue and metals. Placard shows a liquid dripping onto a hand and a metal surface.

9. Class 9 – Miscellaneous Hazardous Materials: Materials posing a hazard during transport not covered by other classes. Black-and-white striped placard.

Placards vs. Labels

Placards are large diamond-shaped signs (at least 250 mm / approximately 10.8 inches per side) placed on the four sides of vehicles, rail cars, and freight containers. They are required when a vehicle carries materials meeting specified quantity thresholds, or always for certain high-hazard classes regardless of quantity.

Labels are smaller diamonds affixed directly to individual packages. They use the same color coding and symbols as placards but are sized for package application.

Both display the hazard class number at the bottom of the diamond and, for most classes, a graphic symbol at the top.

UN/NA Numbers

Every regulated hazardous material is assigned a four-digit identification number:

• UN numbers (United Nations) are internationally recognized.
• NA numbers (North America) are used in the U.S. and Canada, sometimes for materials not covered by UN numbering.

These numbers appear on placards in an orange panel, on the placard itself (for some materials), or on shipping papers. A UN/NA number is the fastest direct link to the specific material identity.

Markings on Containers and Vehicles

Beyond placards and labels, look for:

• Proper shipping name: The official DOT name of the material, on the package or shipping document.
• Cargo tank specification markings: On tank trucks, a specification plate gives construction details and the material carried.
• CHEMTREC and emergency contact numbers: Often stenciled on cargo tanks.

Always check four sides of any vehicle or container. Placards on only one or two sides may be obscured by fire, smoke, or crash damage.

Using the Emergency Response Guidebook (ERG)

The ERG is the primary field reference for initial hazmat response. It is published by the U.S. DOT, Transport Canada, and the Secretariat of Communications and Transport of Mexico.

Three ways to find the correct guide page:

1. Yellow-bordered pages – Look up the UN/NA number to find the guide number.

2. Blue-bordered pages – Look up the proper shipping name to find the guide number.

3. Orange-bordered pages – Turn to the numbered guide page for initial response information, including initial isolation distances and protective actions.

The green-bordered pages at the back of the ERG provide specific initial isolation and protective action distances for certain toxic-inhalation-hazard (TIH) materials during the first 30 minutes of an incident.

60-second rule: In your competency drill, you must locate the correct guide page and read initial isolation distances within 60 seconds. Practice flipping directly to the yellow or blue section, reading the guide number, and opening the orange guide page in one smooth motion.

Safety Considerations

• Never enter the hazard zone to read a placard. Use binoculars from a safe upwind, uphill distance.
• Establish and maintain isolation perimeters using the ERG initial isolation distances until more specific information is available.
• Placards may be missing, damaged, or wrong. Cross-check with shipping papers, the driver, and CHEMTREC.
• Treat an unknown placard or missing information as the worst-case hazard until confirmed otherwise.
• PPE must match the confirmed or suspected hazard class before any closer approach. Structural firefighting gear alone is not sufficient for most chemical hazards.
• Follow your department's incident command and hazmat SOG: operations-level responders support, contain, and isolate — they do not enter the hot zone.