Hazardous materials differ in the risks they present during transportation. The nine classes group materials by hazard, with divisions providing more detail where needed.
From explosives and gases to corrosives and radioactive materials, the descriptions below explain what each class covers and provide representative examples and identification numbers. U.S. domestic and international classifications may differ; qualifications are noted where relevant.
Educational overview only. Use current regulations and qualified hazardous materials guidance for shipment-specific decisions.
Class 1: Explosives
1.1 Explosives
UN0029 · UN0030 · UN0081 · UN0082 · UN0084 · UN0034
Explosives presenting a mass explosion hazard that can affect almost the entire load virtually instantaneously, such as military munitions, detonators, and commercial blasting explosives.
1.2 Explosives
UN0007 · UN0321 · UN0182 · UN0334 · UN0015
Explosives presenting a projection hazard but no mass explosion hazard, such as some ammunition, artillery shells, rockets, and certain fireworks.
1.3 Explosives
UN0161 · UN0499 · UN0186 · UN0335
Explosives that pose a fire hazard and either a minor blast hazard, a minor projection hazard, or both, but no mass explosion hazard, such as smokeless powder, solid propellants, rocket motors, and certain fireworks.
1.4 Explosives
UN0012 · UN0014 · UN0336 · UN0191 · UN0105
Explosives presenting a minor explosion hazard, with explosive effects largely confined to the package and no expected projection of fragments of appreciable size or range, such as small arms ammunition, certain fireworks, hand signal devices, and safety fuses.
1.5 Explosives
UN0331 · UN0332 · UN0482
Very insensitive explosive substances that have a mass explosion hazard but a very low probability of initiation or transition from burning to detonation under normal transport conditions, such as appropriately classified ANFO and emulsion blasting agents used in mining.
1.6 Explosives
UN0486
Extremely insensitive explosive articles with no mass explosion hazard and a negligible probability of accidental initiation or propagation, mostly specialized military munitions.
Class 2: Gases
2.1 Flammable Gas
UN1075 · UN1978 · UN1011 · UN1001 · UN1049 · UN1966 · UN1971 · UN1972 · UN1950
Gases that meet flammability criteria when mixed with air, such as propane, butane, acetylene, hydrogen, methane, and flammable aerosols. UN1950 belongs here only when the aerosol is classified as flammable.
2.2 Non-Flammable Gas
UN1066 · UN1977 · UN1013 · UN2187 · UN1046 · UN1006 · UN3159
Compressed, liquefied, or refrigerated gases that do not meet flammable-gas or poisonous-gas criteria. Hazards can include pressure, oxygen displacement, extreme cold, or oxidizing properties. Examples include nitrogen, carbon dioxide, helium, argon, and certain refrigerant gases.
2.3 Poisonous Gas — Zone A & B
UN1017 · UN1076 · UN1053 · UN1045
Highly toxic gases that are dangerous to inhale even at low concentrations, with Zones A and B representing the highest acute inhalation-toxicity categories. Examples include chlorine and hydrogen sulfide (Zone B), and phosgene and fluorine (Zone A).
2.3 Poisonous Gas — Zone C & D
UN1005 · UN1016 · UN1079 · UN1050
Toxic gases assigned to Zones C or D by acute inhalation-toxicity criteria, such as sulfur dioxide and anhydrous hydrogen chloride (Zone C), and carbon monoxide and anhydrous ammonia (Zone D). These gases can still cause serious injury or death. UN1005 has an international Division 2.3 entry and a U.S. domestic Division 2.2 entry with special inhalation-hazard communication requirements.
Class 3: Flammable Liquids
3 Flammable Liquid
UN1203 · UN1202 · UN1170 · UN1263 · UN1090 · UN1993
Liquids that meet transport flammability criteria, generally based on flash point, such as gasoline, certain diesel fuels, ethanol, flammable paints, and solvents. Qualifying liquids may be treated as combustible liquids under U.S. domestic rules; the applicable shipping description depends on the product and transport conditions.
Class 4: Flammable Solids
4.1 Flammable Solids
UN1944 · UN1945 · UN1331 · UN1350 · UN1869 · UN2555 · UN2556 · UN2557 · UN1325
Includes readily combustible solids, self-reactive materials, solid desensitized explosives, and qualifying polymerizing materials. Examples include matches, magnesium turnings, and nitrocellulose formulations meeting the specified water, alcohol, nitrogen, or plasticizer conditions. UN1350 sulfur is the international Division 4.1 entry; the U.S. domestic entry is NA1350, Class 9, with exceptions based on form and packaging.
4.2 Spontaneously Combustible
UN1381 · UN1362 · UN1856 · UN1383
Pyrophoric or self-heating materials that can ignite or heat up in contact with air without an external ignition source. Examples include white phosphorus, appropriately classified activated carbon, oily rags, and certain pyrophoric metals. UN1856 oily rags carries air and vessel indicators in the DOT table and is not automatically regulated for highway transport solely under that entry.
4.3 Dangerous When Wet
UN1428 · UN2257 · UN1402 · UN1415 · UN1418
Materials that, on contact with water, can become spontaneously flammable or release flammable or toxic gases at rates meeting transport classification criteria. Examples include sodium, potassium, calcium carbide, lithium metal, and magnesium powder.
Class 5: Oxidizers and Organic Peroxides
5.1 Oxidizers
UN1942 · UN2067 · UN2014 · UN2015 · UN2984 · UN1748 · UN2880 · UN2468 · UN1490
Substances that can cause or enhance the combustion of other materials, generally by yielding oxygen. Examples include appropriately classified ammonium nitrate and fertilizer, hydrogen peroxide solutions, certain pool chlorination chemicals, and potassium permanganate. Hydrogen peroxide entries depend on concentration: UN2984 covers 8% to less than 20%; UN2014 covers 20% to 60%; and UN2015 covers stabilized hydrogen peroxide or aqueous solutions above 60%. UN2014 and UN2015 also carry corrosive hazards.
5.2 Organic Peroxide-Type B
UN3101 · UN3102 · UN3111 · UN3112
Organic peroxides that, as packaged for transport, neither detonate nor deflagrate rapidly but can undergo a thermal explosion. UN3111 and UN3112 are temperature-controlled entries. Examples include certain concentrated benzoyl peroxide and other peroxide formulations used in plastics and resin production.
5.2 Organic Peroxide-Type C/D
UN3103 · UN3104 · UN3105 · UN3106 · UN3113 · UN3114 · UN3115 · UN3116
Organic peroxides classified as Type C or D under prescribed tests. Type C does not detonate, deflagrate rapidly, or undergo a thermal explosion as packaged; Type D meets separate limits on detonation, deflagration, and heating under confinement. These materials may still burn or decompose dangerously. Examples include certain MEKP hardeners, benzoyl peroxide pastes, and curing agents, depending on concentration and formulation. UN3113 through UN3116 require temperature control.
5.2 Organic Peroxide-Type E/F
UN3107 · UN3108 · UN3109 · UN3110 · UN3117 · UN3118 · UN3119 · UN3120
Organic peroxides classified as Type E or F, with lower explosive potential under prescribed tests, which may still undergo hazardous decomposition. UN3117 through UN3120 require temperature control. Examples include certain dicumyl peroxide, cumene hydroperoxide, and diluted peroxide formulations used in rubber and plastics manufacturing. Type G is a separate classification with no corresponding UN number in this list and is exempt from Division 5.2 requirements when the regulatory criteria are met.
Class 6: Toxic and Infectious Substances
6.1 Poison /Toxic — Inhalation Hazards Zone A & B
UN1092 · UN1098 · UN1051 · UN2480 · UN3381 · UN3382 · UN3383 · UN3384 · UN3385 · UN3386 · UN3387 · UN3388 · UN3389 · UN3390
Toxic liquids assigned to poisonous-by-inhalation Zones A or B based on acute vapor toxicity and volatility, such as stabilized acrolein (Zone A) and allyl alcohol (Zone B). These entries may also have flammable, corrosive, oxidizing, or water-reactive subsidiary hazards.
6.1 Poisonous/Toxic Materials Other Than the PIH Category
UN2588 · UN2902 · UN1561 · UN1689 · UN1680 · UN2810 · UN2811
Toxic materials not classified as poisonous by inhalation under the applicable transport criteria. Exposure hazards may include swallowing, skin contact, or inhalation of dusts, mists, or vapors. Examples include appropriately classified pesticides, arsenic trioxide, cyanide salts, and organic toxic liquids and solids.
6.2 Infectious Substances
UN2814 · UN2900 · UN3373 · UN3291
Materials known or reasonably expected to contain pathogens and meeting the transport classification criteria. UN2814 covers Category A substances affecting humans; UN2900 covers Category A substances affecting animals only; UN3373 covers Category B biological substances; and UN3291 covers regulated medical waste. Patient specimens and medical waste are not automatically regulated infectious substances.
Class 7: Radioactive Materials
Excepted Packages LSA Materials SCO and Type A Packages
UN2908 · UN2909 · UN2910 · UN2911 · UN2912 · UN2913 · UN2915 · UN3321 · UN3322 · UN3332
This group includes excepted packages (UN2908–UN2911), low-specific-activity materials (UN2912, UN3321 and UN3322), surface-contaminated objects (UN2913), and non-fissile or fissile-excepted Type A packages (UN2915 and UN3332). Examples may include medical isotopes, industrial instruments, uranium ore, and contaminated equipment, depending on their classification. The UN number alone does not establish a low external radiation level or safe handling conditions.
Type B Packages Fissile Materials and Other Specialized Entries
UN2916 · UN2917 · UN2919 · UN2977 · UN2978 · UN3327 · UN3328 · UN3329 · UN3331 · UN3333
This group includes Type B packages, special-arrangement shipments, uranium hexafluoride, and fissile Type A or Type B packages. Controls depend on radioactive contents, activity, fissile status, package design, shielding, measured radiation levels, and applicable approvals. The group is not uniformly highly radioactive or dangerous at a distance. Examples may include spent nuclear fuel, uranium hexafluoride for fuel production, and industrial radiation sources when the applicable shipping entry is met.
Class 8: Corrosives
8 Corrosives
UN1830 · UN1789 · UN1823 · UN1824 · UN2031 · UN2794 · UN2795 · UN1760
Liquids or solids that cause irreversible skin damage, or materials meeting the severe metal-corrosion criteria. Examples include sulfuric acid above 51% (UN1830), hydrochloric acid, solid or dissolved sodium hydroxide, nitric acid other than red fuming, and wet storage batteries filled with acid (UN2794) or alkali (UN2795). Some nitric acid entries also have an oxidizing subsidiary hazard.
Class 9: Miscellaneous Hazardous Materials
9 Miscellaneous Hazardous Materials
UN3480 · UN3481 · UN3090 · UN3091 · UN1845 · NA2448 · UN3077 · UN3082 · UN3257
Materials presenting transport hazards covered by Class 9, such as lithium ion and lithium metal batteries, dry ice, molten sulfur under the U.S. domestic NA2448 entry, environmentally hazardous substances, and elevated-temperature liquids. UN1845 dry ice carries air and vessel indicators in the DOT table and is not automatically regulated for highway transport solely under that entry.
Important Information
This page provides a general educational overview of hazardous materials transportation classifications. It is not a complete classification guide, shipment approval, or substitute for current regulations, required training, or qualified hazardous materials advice. Classification and transportation requirements vary by material, formulation, quantity, packaging, transport mode, and jurisdiction. Do not rely on this page alone to classify, package, label, document, or offer a shipment for transportation. All hazardous materials shipments are subject to review and acceptance by Gwynn Logistics and the applicable carrier.
Sources
U.S. DOT Hazardous Materials Table — 49 CFR §172.101
Hazard classification definitions and shipment requirements — 49 CFR Part 173
NOAA CAMEO Chemicals — chemical hazards and transport reference information
Last reviewed: October 5, 2026