Hazmat Placards

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What to do if you see a hazmat placard on the road

hazmat placard meaning

What each hazmat placard means

A hazmat placard communicates a cargo's primary hazard through color and shape alone, before you even read the text: orange means explosives, solid red means flammable, yellow means oxidizer, and two-color diamonds (like corrosive's white-and-black) signal a combined hazard. Here's what each one means, and why a few color combinations are so easy to remember backwards.

The logic behind each class's color

The system has nine hazard classes (1 through 9), fixed by 49 CFR Part 172, Subpart F in the US and harmonized with the UN Recommendations. Solid-color placards signal a single, direct hazard: orange is explosives (Class 1), red is flammable (Class 2.1 gas, Class 3 liquid), green is non-flammable gas (Class 2.2), blue is "dangerous when wet" (Class 4.3), and yellow is oxidizer (Class 5.1). Plain white, meanwhile, shows up on three different classes, toxic gas (2.3), toxic (6.1) and infectious (6.2), distinguished by the pictogram (a skull or the biohazard symbol), not the color.
When two colors split the diamond in half, it's because the substance combines two hazards. Three of those combinations are frequently remembered backwards: Class 8 (corrosive) is white on top and black on the bottom, not the reverse,, Class 4.2 (spontaneous combustion) is white on top and red on the bottom, and Class 5.2 (organic peroxide) flips that logic: red on top and yellow on the bottom. Class 7 (radioactive) is the easiest to recall correctly: yellow on top, white on the bottom, with a black trefoil. Class 9 breaks the halves pattern entirely: seven black stripes cover only the upper half, with the numeral '9' underlined at the bottom point, the only class with that underline rule.

Examples

Solid red diamond

Input: Vermelho, sem divisão de cor
Expected output: Classe 3, Líquido inflamável (ou 2.1 se for gás)

Gasoline and ethanol are common examples shipped under Class 3.

White-on-top, black-on-bottom diamond

Input: Metade branca / metade preta
Expected output: Classe 8, Corrosivo

Sulfuric acid and sodium hydroxide (lye) are common examples.

Full tool FAQ

Who needs to be able to recognize hazmat placards?

Drivers and carriers of hazardous cargo, first responders (firefighters, EMS, highway patrol), dispatchers and roadside inspectors, plus students of logistics, safety engineering and dangerous-goods transport. Recognizing the color and class from a distance is the first step in deciding how to react safely near a placarded truck or railcar.

What should I do if I see a hazmat placard on the road, especially at an accident scene?

Why are placard colors and shapes standardized worldwide?

Is the Class 8 (corrosive) placard black on top or on the bottom?

Does Brazil use the same placard system?

Does every infectious substance (Class 6.2) shipment display a vehicle placard?

Frequently asked questions

What does the number at the bottom point of the placard represent?

It's the hazard class (or subdivision) number, from 1 through 9, for example "3" for flammable liquid or "4.2" for spontaneous combustion. It is not the specific product's UN identification number; that, when required, appears separately on a rectangular orange panel.

Why do some placards have two colors and others just one?

A single color signals one direct, isolated hazard (solid red for flammable, for example). Two colors, split in half, signal that the substance combines two regulated hazards together, such as corrosive plus a secondary risk, or radioactive with its pictogram sitting on a specific yellow band.

Where is the exact legal definition of each color?

In 49 CFR Part 172, Subpart F (sections 172.521 through 172.560), which describes, placard by placard, the background color, the symbol/text/border color and, where applicable, which half gets which color. That is the source used to build this tool's table.

Next steps

Class	Category	Examples
1.1	Explosives with a mass explosion hazard	TNT · Dynamite
1.2	Explosives with a projection hazard	Detonating fuzes · Some types of military ammunition
1.3	Explosives with a fire hazard	Smokeless powder · Display fireworks
1.4	Explosives with no significant blast hazard	Consumer fireworks · Small-arms ammunition
1.5	Very insensitive substances with a mass explosion hazard	Blasting agents (ANFO) · Type B mining blasting agents
1.6	Extremely insensitive articles with no mass explosion hazard	Certified extremely insensitive detonating articles (EIDS) · Certain modern military ordnance
2.1	Flammable gas	Propane · Butane
2.2	Non-flammable, non-toxic gas	Compressed nitrogen · Helium
2.3	Toxic gas	Chlorine · Phosgene
3	Flammable liquid	Gasoline · Ethanol
4.1	Flammable solid	Sulfur · Nitrocellulose
4.2	Substance liable to spontaneous combustion	White phosphorus · Activated carbon (self-heating)
4.3	Substance dangerous when wet	Sodium metal · Calcium carbide
5.1	Oxidizing substance	Ammonium nitrate · Concentrated hydrogen peroxide
5.2	Organic peroxide	Methyl ethyl ketone peroxide (MEKP) · Benzoyl peroxide
6.1	Toxic substance	Potassium cyanide · Certain organophosphate pesticides
6.2	Infectious substance	Regulated medical waste · Diagnostic specimens
7	Radioactive material	Cobalt-60 (medical/industrial use) · Uranium ore
8	Corrosive substance	Sulfuric acid · Sodium hydroxide (lye)
9	Miscellaneous dangerous substances and articles	Lithium-ion batteries · Dry ice (solid carbon dioxide)

Placard

Class

What each hazmat placard means

The logic behind each class's color

The system has nine hazard classes (1 through 9), fixed by 49 CFR Part 172, Subpart F in the US and harmonized with the UN Recommendations. Solid-color placards signal a single, direct hazard: orange is explosives (Class 1), red is flammable (Class 2.1 gas, Class 3 liquid), green is non-flammable gas (Class 2.2), blue is "dangerous when wet" (Class 4.3), and yellow is oxidizer (Class 5.1). Plain white, meanwhile, shows up on three different classes, toxic gas (2.3), toxic (6.1) and infectious (6.2), distinguished by the pictogram (a skull or the biohazard symbol), not the color.

When two colors split the diamond in half, it's because the substance combines two hazards. Three of those combinations are frequently remembered backwards: Class 8 (corrosive) is white on top and black on the bottom, not the reverse,, Class 4.2 (spontaneous combustion) is white on top and red on the bottom, and Class 5.2 (organic peroxide) flips that logic: red on top and yellow on the bottom. Class 7 (radioactive) is the easiest to recall correctly: yellow on top, white on the bottom, with a black trefoil. Class 9 breaks the halves pattern entirely: seven black stripes cover only the upper half, with the numeral '9' underlined at the bottom point, the only class with that underline rule.

Examples

Solid red diamond

Input: Vermelho, sem divisão de cor
Expected output: Classe 3, Líquido inflamável (ou 2.1 se for gás)

Gasoline and ethanol are common examples shipped under Class 3.

White-on-top, black-on-bottom diamond

Input: Metade branca / metade preta
Expected output: Classe 8, Corrosivo

Sulfuric acid and sodium hydroxide (lye) are common examples.

Full tool FAQ

Who needs to be able to recognize hazmat placards?

What should I do if I see a hazmat placard on the road, especially at an accident scene?

Why are placard colors and shapes standardized worldwide?

Is the Class 8 (corrosive) placard black on top or on the bottom?

Does Brazil use the same placard system?

Does every infectious substance (Class 6.2) shipment display a vehicle placard?

Frequently asked questions