49 CFR 172.101 Hazardous Materials Table: Columns, Placards, Stowage

The Hazardous Materials Table at 49 CFR 172.101 is the federal master list that assigns every regulated substance a proper shipping name, identification number, hazard class, packing group, label set, packaging authorization, and quantity and stowage limits across ten columns. Maintained by the Pipeline and Hazardous Materials Safety Administration, it is the starting point for almost every shipping decision that follows.¹ Read the entry wrong and every downstream choice — label, package, paperwork, placard, vehicle — inherits the mistake. Read the row correctly and the rest of Parts 172, 173, and 177 tell you exactly what to do.

Column 1 Symbols and What They Change

The first column carries six symbols that override or narrow how the rest of the row applies. Miss one and you can apply the wrong rules or skip a requirement that only kicks in for a specific mode.

A plus sign (+) locks in the proper shipping name, hazard class, and packing group. Even if the material does not technically meet the definition of that class, the assigned classification governs.
A means the material is regulated only when shipped by aircraft.
W means the material is regulated only when shipped by vessel.
D means the proper shipping name is appropriate for domestic transportation only.
I means the proper shipping name is appropriate for international transportation.
G means the shipper must add a technical name in parentheses next to the proper shipping name on shipping papers, following 49 CFR 172.203(k).

The G designation is the one shippers miss most often. When the proper shipping name is generic, such as “Corrosive liquid, n.o.s.,” the technical name of the actual chemical belongs in parentheses so emergency responders know what they’re dealing with.² For mixtures, the technical names of the two most hazardous components must be listed.³

Columns 2 and 4: Proper Shipping Name and Identification Number

Column 2 holds the legally recognized description of the material. It has to appear on shipping papers and package markings exactly as listed. If the substance isn’t in the table by its specific chemical name, pick the closest generic or “not otherwise specified” (n.o.s.) entry that matches its chemical family and hazard characteristics.²

Column 4 pairs each name with a four-digit identification number. A UN prefix means the number follows international standards and is recognized worldwide. An NA prefix means the number is valid only within the United States and cannot be used on international shipments.² Those numbers feed straight into the Emergency Response Guidebook, which responders use for isolation distances and firefighting procedures at a scene.⁴

On the shipping paper, the identification number, proper shipping name, hazard class, and packing group must appear in that order with nothing else interspersed. For example: “UN2744, Cyclobutyl chloroformate, 6.1, (8, 3), PG II.”⁵

Column 3: Hazard Class or Division

Column 3 places each material in one of nine hazard classes describing its primary danger, with several classes broken into divisions for precision. The word “Forbidden” in this column means the material cannot be offered for transportation at all under that entry.²

Class 1: Explosives, Divisions 1.1 through 1.6, ranging from mass explosion hazards to extremely insensitive articles.
Class 2: Gases. Division 2.1 flammable, 2.2 non-flammable, 2.3 poisonous.
Class 3: Flammable liquids.
Class 4: Flammable solids (4.1), spontaneously combustible materials (4.2), materials dangerous when wet (4.3).
Class 5: Oxidizers (5.1) and organic peroxides (5.2).
Class 6: Toxic substances (6.1) and infectious substances (6.2).
Class 7: Radioactive materials.
Class 8: Corrosives.
Class 9: Miscellaneous hazardous materials.

The class in Column 3 drives most of what follows in the row: which labels the package needs, which packaging section applies, how much can go on a passenger aircraft, and where the material can sit on a vessel.

Precedence When a Material Fits More Than One Class

Some materials meet the definition of more than one class. When that happens and the material isn’t specifically listed in the table by name, the hierarchy in 49 CFR 173.2a decides which class controls. Radioactive materials (other than limited quantities) rank highest, followed by poisonous gases, then flammable gases, and down through Class 9.⁶

The packing group follows the same most-dangerous-wins logic. A Class 3 Packing Group II flammable liquid that also meets the Division 6.1 Packing Group I threshold for oral toxicity ships as Class 3, Packing Group I. The more stringent packing group governs even when the primary class stays the same.⁶

Column 5: Packing Group

Column 5 grades danger within a hazard class. Packing Group I is the greatest danger, II is moderate, and III is the least severe.² Not every material gets one. Gases, explosives, radioactive materials, infectious substances, and some other entries have their own packaging regimes and skip packing groups entirely.

The packing group sets the performance standards a container has to meet. A Packing Group I material demands packaging tested to survive more severe drops, stacking loads, and internal pressure than Packing Group III. It also controls which limited quantity exceptions are available and how large an inner packaging can be.

Column 6: Labels and Placards

Column 6 lists the hazard warning labels that must appear on the outside of each package. These are the standardized diamond-shaped labels with color coding and symbols — a flame for flammables, a skull and crossbones for toxic materials, a trefoil for radioactive goods. They must be durable, weather-resistant, and placed near the proper shipping name marking.²

Many materials carry subsidiary hazards in addition to their primary risk. A corrosive liquid that is also flammable needs a corrosive label and a flammable liquid label. Column 6 lists the required subsidiary labels for each entry, and 49 CFR 172.402 adds rules for materials not addressed directly in the table. A Division 2.3 poisonous gas that also meets the definition of a flammable gas, for example, must carry a flammable gas label in addition to its poison gas label.⁷

Vehicle Placarding Thresholds

Placards are the larger diamond signs on trucks, railcars, and freight containers. They do the same job as package labels but at vehicle scale, so responders can identify the hazard from a distance. For materials listed in Table 2 of 49 CFR 172.504, placarding is required when the total gross weight of hazardous materials in the vehicle reaches 454 kg (1,001 pounds). Below that threshold, Table 2 materials don’t need placards. Any quantity in a bulk packaging, though, requires placarding regardless of weight.⁸

High-hazard materials in Table 1 of the same section — including explosives, poisonous gases, and radioactive materials — require placarding at any quantity. No weight exception applies to those.

Column 7: Special Provisions

Column 7 lists alphanumeric codes that point to special provisions in 49 CFR 172.102. These layer on top of the general rules and can impose unique packaging requirements, testing mandates, temperature controls, or handling restrictions for a specific material. A code might restrict the type of metal allowed in a container or require a particular certification before shipment.² Skipping the cross-reference is an easy mistake, because every code has to be looked up individually.

Marine Pollutant Designations

Some substances carry a marine pollutant designation under Appendix B to the table. If a marine pollutant isn’t listed by name and doesn’t fit any hazard class from 1 through 8, it ships under one of two Class 9 entries: “Environmentally hazardous substances, liquid, n.o.s.” (UN3082) or “Environmentally hazardous substances, solid, n.o.s.” (UN3077). If it does meet the definition of a hazard class from 1 through 8, the shipper classifies it under that class using the precedence rules and picks the best matching proper shipping name.⁹

Column 8: Packaging Authorizations

Column 8 splits into three sub-columns. Column 8A cites the section covering packaging exceptions, where lighter-duty packaging is allowed. Column 8B identifies the required non-bulk packaging specification. Column 8C covers bulk packaging for larger quantities, such as cargo tanks and rail tank cars.²

Each code points to a specific section in Part 173. A “202” in Column 8B for gasoline, for example, sends you to 49 CFR 173.202, which sets the performance standards for drums, jerricans, and other non-bulk containers. Bulk containers face more demanding structural requirements because a failure releases far more material.²

Columns 9 and 10: Quantity Limits and Stowage

Columns 9A and 9B cap the maximum net quantity per package on passenger-carrying aircraft or railcars (9A) and on cargo-only aircraft (9B). For many high-risk materials, Column 9A simply reads “Forbidden,” which means the substance cannot travel on any passenger conveyance. Less dangerous materials may be permitted in small quantities, with the cargo-only limit set higher.²

Column 10 handles vessel stowage. Column 10A assigns a stowage category (letters A through E) that dictates whether the material can ride on deck, must stay below deck, or is handled under other restrictions. Column 10B adds codes for separation from heat sources or incompatible cargo.²

Segregation Rules for Highway Transport

Vessel stowage isn’t the only compatibility rule. For trucks and storage facilities, 49 CFR 177.848 contains a segregation table that controls which hazard classes can share space. An “X” in the table means the two classes are flatly prohibited from loading together. An “O” means they can share a vehicle only if separated well enough that a leak from one package could not allow the materials to mix.¹⁰

Some combinations are singled out because the consequences of mixing are catastrophic. Cyanides cannot share a vehicle with acids if the combination could generate hydrogen cyanide gas. Division 6.1 Packing Group I, Hazard Zone A poisons cannot travel with flammable liquids, corrosive liquids, or oxidizers. When a package carries a subsidiary hazard label, the segregation rules for that subsidiary hazard apply if they are more restrictive than the rules for the primary hazard.¹⁰

Limited Quantity Relief

Small, consumer-sized packages of certain hazardous materials qualify for limited quantity exceptions that relax several requirements. For Class 3 flammable liquids in combination packaging, the inner container limit depends on the packing group: 0.5 liters for Packing Group I, 1.0 liter for Packing Group II, and 5.0 liters for Packing Group III. Total package weight cannot exceed 30 kg (66 pounds).¹¹

Packages that qualify are generally exempt from hazard labeling (except on aircraft), specification packaging, shipping paper requirements, and placarding. The relief does not apply if the material is a hazardous waste, hazardous substance, or marine pollutant, or if it travels by air or vessel.¹¹

What the Table Alone Doesn’t Tell You

Reading the row correctly is the first compliance step, not the last. A complete shipment still requires a properly prepared shipping paper retained by both shipper and carrier (two years for most hazardous materials, three for hazardous waste), documented hazmat employee training every three years, PHMSA annual registration for higher-risk shipments, immediate telephone notice to the National Response Center at 800-424-8802 for serious incidents, and a written incident report within 30 days of discovering a reportable release. Miss those obligations and civil penalties can reach $102,348 per violation, or $238,809 where death, serious injury, or major property damage results, with criminal exposure under 49 U.S.C. 5124 of up to five years — ten if a release causes death or bodily injury.¹²¹³¹⁴¹⁵¹⁶¹⁷ The table tells you what the material is and how to package it. The rest of Subchapter C tells you how to move it lawfully.

1
Pipeline and Hazardous Materials Safety Administration. Office of Hazardous Materials Safety
2
eCFR. 49 CFR 172.101 – Purpose and Use of Hazardous Materials Table
3
eCFR. 49 CFR 172.203 – Additional Description Requirements
4
Pipeline and Hazardous Materials Safety Administration (PHMSA). 2024 Emergency Response Guidebook
5
eCFR. 49 CFR 172.202 – Description of Hazardous Material on Shipping Papers
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eCFR. 49 CFR 173.2a – Classification of a Material Having More Than One Hazard
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eCFR. 49 CFR 172.402 – Additional Labeling Requirements
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eCFR. 49 CFR 172.504 – General Placarding Requirements
9
FindLaw. Code of Federal Regulations Title 49 Transportation 49.172.101 – List of Marine Pollutants
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eCFR. 49 CFR 177.848 – Segregation of Hazardous Materials
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eCFR. 49 CFR 173.150 – Exceptions for Class 3 (Flammable and Combustible Liquids)
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eCFR. 49 CFR 172.201 – Preparation and Retention of Shipping Papers
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eCFR. 49 CFR 172.704 – Training Requirements
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eCFR. 49 CFR 171.15 – Immediate Notice of Certain Hazardous Materials Incidents
15
eCFR. 49 CFR 171.16 – Detailed Hazardous Materials Incident Reports
16
eCFR. 49 CFR 107.329 – Maximum Penalties
17
Office of the Law Revision Counsel. 49 USC 5124 – Criminal Penalty