Hazmat Placards: What They Are, Classes, UN IDs, DOT Rules

Hazmat placards are the diamond-shaped signs you see on trucks, railcars, containers, and bulk packages that communicate, at a glance, what kind of hazardous materials are inside. Using color, symbols, a hazard class number (1–9), and often a four-digit UN/NA ID, they alert drivers, the public, and first responders to key risks and response actions. In the U.S., placarding is required by the Department of Transportation (49 CFR Part 172, Subpart F), and getting it right is essential for safety, compliance, and avoiding costly delays or fines.

This guide explains exactly how placards work and when you need them. You’ll learn the meaning of each component, see the DOT hazard classes and divisions, understand UN and NA identification numbers, and know the difference between placards, labels, and markings. We’ll cover Table 1 vs. Table 2 requirements, mixed loads and the DANGEROUS placard, bulk package rules, size and placement, responsibilities and training, material choices that last, and common mistakes to avoid—with a quick decision guide and options to source compliant, customizable placards.

How hazmat placards communicate hazards (components, colors, numbers)

Every hazmat placard encodes risk the same way: standardized colors, pictograms, and numbers instantly signal what’s inside and how to respond. Under DOT Chart 17, layouts are consistent so drivers and responders can read them in seconds. Here are the pieces:

Hazard class number: 1–9 shown at the bottom.
Division number: In the center where applicable (e.g., 1.1–1.6, 2.1–2.3).
UN/NA ID: Four-digit number in the center when required.
Compatibility letter: A–S on Class 1 (explosives) indicates loading compatibility.
Colors, symbols, words: Orange=explosives; red=flammable; green=nonflammable gas; yellow=oxidizer; white=toxic/infectious; blue=dangerous when wet; black/white=corrosive; striped/split designs flag Class 4, 5, 7, 9 traits.

DOT hazard classes and divisions at a glance

DOT hazard classes define the primary risk your hazmat placards must communicate. There are nine classes; several include divisions that refine the hazard. Use this quick reference to validate your shipping descriptions, labels, and placards before a load moves.

Class 1 — Explosives: 1.1–1.6
Class 2 — Gases: 2.1 Flammable; 2.2 Nonflammable; 2.3 Toxic
Class 3 — Flammable/combustible liquids
Class 4 — Flammable solids: 4.1 Flammable solid; 4.2 Spontaneously combustible; 4.3 Dangerous when wet
Class 5 — Oxidizer/peroxide: 5.1 Oxidizer; 5.2 Organic peroxide
Class 6 — Toxic/infectious: 6.1 Toxic; 6.2 Infectious
Class 7 — Radioactive
Class 8 — Corrosive
Class 9 — Miscellaneous

UN and NA ID numbers and how they’re used

UN and NA ID numbers are the four-digit codes that precisely identify the hazardous material behind a placard. UN numbers (0004–3534), assigned by the United Nations Committee of Experts, cover internationally regulated dangerous goods. NA numbers (8000–9279), assigned by DOT, identify materials not classified by the UN. When required, the ID appears in the center of hazmat placards so drivers and responders can match the load to the correct hazard information, class/division, and compatibility group.

Select the right description: Use the ID to choose the proper shipping name, packing group, and compliant placards.
Apply safe loading rules: Verify segregation limits and Class 1 compatibility (A–S) when applicable.
Stay consistent: Align ID numbers across markings, labels, and placards.

Placards, labels, and markings: what’s the difference?

One common compliance gap is mixing up placards, labels, and markings. They’re related but not interchangeable. Placards are for vehicles, containers, and bulk packages; labels are for individual packages; markings identify what’s inside. PHMSA’s DOT Chart 17 groups all three because they must tell the same story: the hazard class, the proper shipping description, and the UN/NA ID. If any element conflicts, responders and inspectors lose trust—and you risk violations.

Placards: Vehicle/bulk warnings that signal primary hazards to the public and responders.
Labels: Package-level hazard diamonds that mirror the class/division for handlers.
Markings: UN/NA ID and proper shipping name that identify the contents.

When placards are required under 49 CFR 172 (Table 1 vs Table 2)

Under 49 CFR Part 172, Subpart F (as summarized in PHMSA’s DOT Chart 17), placarding hinges on two lists. Table 1 covers certain high‑hazard materials that must be placarded for any quantity. Table 2 covers most other hazardous materials; for these, placards are required based on the total amount loaded (and other conditions). Carriers may also display placards even when not required, provided they otherwise meet Subpart F specifications.

Start with classification: Confirm the correct hazard class/division.
Check the right table: If it’s on Table 1, placard for any amount; if Table 2, determine whether the quantity/conditions trigger placarding.
Match everything: Ensure placards align with your shipping description, labels, and UN/NA IDs.

Mixed loads, subsidiary hazards, and the DANGEROUS placard

Moving different hazardous materials together complicates placarding and segregation. Each hazard class on the vehicle may drive a placard, and some materials carry a subsidiary hazard that must be reflected in package labels and the shipping description, even while the vehicle placard communicates the primary risk. Compatibility matters too: Class 1 explosives use letters A–S to control what can ride together, and many restrictions apply when commingling different dangerous goods. Under DOT rules summarized in Chart 17, a DANGEROUS placard is permitted in limited cases for mixed loads of multiple Table 2 hazard classes; carriers may also display placards even when not required if they otherwise conform to 49 CFR Part 172, Subpart F.

Map the hazards: Identify primary and any subsidiary hazards for every line item.
Check the tables: Verify if class‑specific placards are required or if DANGEROUS is allowed for the mix.
Confirm compatibility: Apply Class 1 letters and other segregation limits before loading.
Keep it consistent: Align placards with markings, labels, and shipping papers on all sides and ends.

Bulk packages and ID number display rules

For bulk packages—think tank trucks, rail tank cars, and loaded freight containers—the vehicle itself communicates the hazard. Under DOT Chart 17 and 49 CFR Part 172, Subpart F, these shipments must display hazmat placards on each side and each end. When ID numbers are required, the four‑digit UN/NA ID is shown in the placard’s center so inspectors and responders can immediately tie the load to the correct class/division and response actions. Carriers may also display placards voluntarily if they otherwise conform to Subpart F.

Match IDs everywhere: The same UN/NA number must align with markings, labels, and shipping papers.
Audit before departure: Confirm the hazard class placard and any required ID appear on all four sides.

Placard size, placement, and visibility requirements

DOT Chart 17 summarizes the core rule: display hazmat placards on each side and each end of the transport vehicle, railcar, or bulk container, and ensure they’re clearly visible from the direction they face. Use the standardized, square-on-point design and keep them legible. If a placard is obscured because units are coupled, the other sides must still present unobstructed placards.

Keep unobstructed: Avoid ladders, hoses, tarps, doors, or equipment.
Maintain legibility: Clean, unfaded, not peeling; replace when damaged.
Use correct design: Proper color, symbol, wording for the class.
Match IDs: If required, show the same UN/NA number in the center on all sides.

Responsibilities, training, and documentation you need to have

Placard compliance isn’t just a diamond on the door—it’s people and paperwork working together. FMCSA requires safety inspections before and during hazmat trips, and DOT Chart 17 provides the shared “language” your team must recognize instantly. Your job is to train for that language, verify consistency, and document what’s moving so responders and inspectors can trust what they see.

Verify the description: Match the classification, proper shipping name, and UN/NA ID across shipping papers, markings, labels, and hazmat placards.
Train for recognition: Teach staff to read Chart 17 components—colors, class/division, compatibility letters—and to perform pre‑trip/en‑route checks.
Audit before departure: Confirm size, placement on each side and end, visibility, legibility, and correct IDs; replace damaged/faded placards.
Plan the move: Follow FMCSA routing and parking rules and keep placards unobstructed during loading, tarping, or coupling.
Keep records handy: Ensure drivers carry up‑to‑date documentation and that placards are updated when mixtures or quantities change.

Materials and durability: choosing placards that last

Sun, weather, and wash cycles can ruin a placard mid‑route. Choose durable materials so your hazmat placards stay legible and compliant.

Substrate: Rigid aluminum or high‑impact plastic for permanent mounts; heavy‑duty adhesive vinyl or magnetic panels for changeouts.
Inks/laminates: Long‑life UV inks and protective topcoats help resist peeling, chipping, and fading.
Visibility and service: Retroreflective sheeting (ORALITE) for night visibility; edge‑sealed films and clean installs better withstand road splash, fuels/de‑icers, and heat/cold cycles. Replace at the first sign of fading or cracks. Quality ORAFOL films improve durability.

Special words and marks you might see on placards

Beyond colors and numbers, certain words and pictograms on hazmat placards add quick context that matters in an emergency. DOT Chart 17 standardizes these clues—flame, gas cylinder, skull and crossbones, radiation trefoil, and the corrosion icon—so responders can decide fast. Train drivers and loaders to spot the qualifiers below and confirm they match the class/division on shipping papers.

DANGEROUS: Mixed Table 2 loads placard option.
INHALATION HAZARD: Toxic gas/vapor risk (2, 6).
SPONTANEOUSLY COMBUSTIBLE: Class 4.2 may ignite in air.
DANGEROUS WHEN WET: Class 4.3 reacts with water.
OXYGEN (O over flame): Oxidizer; intensifies fire.

Quick decision guide to determine your required placards

Use this short flow to confirm the right hazmat placards before a unit moves. It follows PHMSA’s DOT Chart 17 and 49 CFR Subpart F so what’s on the vehicle matches what’s on your shipping papers. Keep it handy for pre‑trip checks and mixed‑load decisions.

Classify and ID: Confirm hazard class/division, proper shipping name, and UN/NA ID.
Bulk or non‑bulk: Bulk packages display placards on each side and end; show the ID if required.
Table check: Look up Table 1 vs Table 2—Table 1 placards for any amount; Table 2 depends on quantity/conditions.
Mixed loads: If multiple Table 2 classes, verify when a DANGEROUS placard is allowed; confirm Class 1 compatibility letters.
Final verification: Ensure placement, visibility, legibility, and matching IDs across papers, markings, labels, and placards; voluntary placards are allowed if they conform to Subpart F.

Common mistakes to avoid and practical tips

Most placarding violations start with small misses—IDs that don’t match papers, placards hidden by tarps, or the wrong class on a mixed load. Tighten your process before the wheels turn. Use this quick, field-ready set of fixes to keep hazmat placards accurate, visible, and compliant.

Match the story: Align class/division and UN/NA ID across papers, markings, labels, and placards.
Placard the right table: Table 1 for any amount; Table 2 by quantity/conditions; voluntary placarding allowed if it conforms.
Cover all four sides: Each side and end; keep unobstructed, clean, and legible; replace damaged/faded.
Use the correct device: Placards for vehicles/bulk; display the UN/NA ID in the center when required.
Control mixed loads: DANGEROUS only when permitted; check Class 1 A–S compatibility and segregation limits.
Train and re-check: Teach Chart 17 recognition; perform FMCSA pre‑trip/en‑route checks; re‑verify after loading, tarping, or coupling.

Where to buy DOT-compliant placards and custom options

Buy DOT-compliant hazmat placards from a vendor that understands 49 CFR 172 Subpart F and uses durable materials. Safety Decals builds custom placards and hazard labels with long‑life UV inks, rugged substrates, and ORAFOL/ORALITE options for visibility. Need the UN/NA number printed or blanks for changeouts? We’ll match DOT Chart 17 designs, assist with regulatory alignment, and deliver the size, color, and mounting you need—via our Sticker Builder or by working directly with our specialists.

Key takeaways

Hazmat placards are a shared language for risk: colors, symbols, class/division numbers, and UN/NA IDs that must align across shipping papers, markings, and labels. Compliance rests on accurate classification, correct table checks (Table 1 vs. Table 2), proper size and placement on each side and end, and disciplined inspection, training, and documentation.

Keep it consistent: Class/division and UN/NA ID must match everywhere.
Check the tables: Table 1 = placard any amount; Table 2 = quantity/conditions.
Cover all sides: Use the correct design; show the ID in the center when required.
Mixed loads: Use DANGEROUS only when permitted; honor Class 1 compatibility.
Durability matters: Replace damaged/faded placards; choose UV‑resistant materials.
Train and verify: Pre‑trip and en‑route checks prevent violations.

Need compliant, long‑lasting placards or custom options? Get them made right at Safety Decals.