Hazard classes refer to the classification of dangerous goods based on their hazardous characteristics for transport. The classification was issued by the United Nations.

Basics of Classification by Hazard Classes

In the "Model Regulations" of the "UN Recommendations on the Transport of Dangerous Goods," the handling of hazardous materials was established by the United Nations. The structure of the hazard classes was also defined in this context.

A division into 9 hazard classes is made, with further subdivision through the classification code. The division is as follows:

• Class 1 – Subdivision into subclasses and compatibility groups
• Classes 2 to 9 – Division through codes indicating the degree of danger or by material property

Packaging groups must also be considered.

The hazard classes are regulated in international agreements such as the European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR), on inland waterways (ADN – with ADN-D and ADN-R), in the international regulations on the carriage of dangerous goods by rail (RID), and "for the Safety of Life at Sea" (SOLAS). The hazard classifications are also applied in the road transport sector of the USA.

Hazard Class 1 – Explosive Substances

Hazard class 1 includes explosive substances and articles containing explosive substances.

Hazard class 1 is divided into the following subclasses:

1.1 Substances and articles with the ability to cause a mass explosion (mass explosion = explosion in which the entire load is almost simultaneously affected)

1.2 Substances or articles that may produce fragments, projections, and blast effects, but do not cause mass explosions

1.3 Substances and articles with a fire hazard and a minor hazard from air pressure and fragments, projections, and blast effects; substances and articles are not mass-explosive, but considerable radiant heat is generated during burning, and minor air pressure, fragment, projection, and blast effects may occur

1.4 Substances and articles with a minor explosion hazard, effects are limited to the package

1.5 Extremely insensitive but mass-explosive substances, which must not explode in an external fire test (minimum requirement)

1.6 Substances that are extremely insensitive and not mass-explosive – under normal transport conditions, the likelihood of accidental ignition or propagation of the explosion is negligible

Further division is made into the following compatibility groups:

A Initiating substances

B Articles containing initiating substances and less than two effective protective devices

C Propellants and other explosive, deflagrating substances

D Black powder, other detonating explosive substances

E Articles containing detonating explosive substances without initiating devices with propelling charge

F Articles containing detonating and explosive substances with their own initiating devices, propelling charge, or without propelling charge

G Pyrotechnic substances or articles containing pyrotechnic substances

H Articles containing explosive substances and white phosphorus

J Articles containing both explosive substances and flammable liquid or flammable gel

K Articles containing explosive substances and toxic chemical agents

L Explosive substances or articles with an explosive substance considered particularly hazardous, requiring separation of each type

N Articles containing extremely insensitive detonating substances

S Substances and articles packaged or designed so that any effects from unintended reactions are limited to the package

Hazard Class 2 – Gases and Gaseous Substances

Hazardous goods of class 2 include pure gases, gas mixtures, mixtures of one or more gases with one or more substances. Articles containing such substances also fall under hazard class 2.

Gases are substances with a vapor pressure exceeding 20 bar at 50 °C or that are completely gaseous at 20 °C and a pressure of 1013 mbar. Compressed (condensed), dissolved, and liquefied gases also belong to this hazard class. Division is made into hazard degrees A (asphyxiant), O (oxidizing), F (flammable), T (toxic), and C (corrosive). Examples of gases include hydrogen, propane gas, or even hairspray.

Hazard Class 3 – Flammable Liquids

Hazard class 3 includes substances and articles that are liquid or not completely gaseous at 20 °C and 1013 mbar, have a maximum pressure of 3 bar at 50 °C, and a flash point not exceeding 60 °C. Class 3 also includes flammable liquid substances and solid melted substances with a flash point above 60 °C. Examples of hazard class 3 include alcohol and gasoline, as well as certain liquefied metals.

There is also a subdivision into classification codes:

• F (flammable, liquid, without subsidiary risk)
• F1 (flammable, liquid, flash point maximum 60 °C)
• F2 (flammable, liquid, flash point above 60 °C)
• FT (flammable, liquid, toxic)
• FT1 (flammable, liquid, toxic)
• FT2 (pesticides)
• FC (flammable, liquid, corrosive)
• D (desensitized explosive liquid substances)

Additionally, there is a subdivision into packaging groups:

• PG I – high danger, boiling point below 35 °C
• PG II – medium danger, flash point below 23 °C, boiling point above 35 °C)
• PG III – low danger, flash point between 23 and 60 °C, boiling point above 35 °C)

Hazard Class 4 – Flammable Solids

In hazard class 4, the following division is made:

• Class 4.1 – Flammable solids, desensitized substances, self-reactive substances
(e.g., matches, sulfur, rubber waste)

• Class 4.2 – Substances liable to spontaneous combustion
(e.g., coal of vegetable origin, white phosphorus, varnishes, fish meal)

• Class 4.3 – Substances that emit flammable gases when in contact with water
(e.g., carbide, sodium, zinc dust)

Hazard Class 5 – Oxidizing Substances

Hazard class 5 includes:

• Class 5.1 – Oxidizing substances
(e.g., sodium chlorate, hydrogen peroxide)

• Class 5.2 – Organic peroxides
(e.g., methyl ethyl ketone peroxide – hardener for two-component paints)

Hazard Class 6 – Toxic Substances

A subdivision of hazard class 6 is made as follows:

• Class 6.1 – Toxic substances
(e.g., arsenic, hydrocyanic acid, pesticides)

• Class 6.2 – Infectious substances
(e.g., medical samples, clinical waste)

Hazard Class 7 – Radioactive Substances

Hazard class 7 includes all radioactive substances and articles containing radioactive substances. This includes, for example, plutonium, uranium, as well as certain medical instruments or technical testing facilities for product control.

Hazard Class 8 – Corrosive Substances

Hazard class 8 includes all substances that cause corrosion through chemical action when in contact with skin and mucous membranes. Substances that cause damage or destruction to goods or transport means when released also belong to hazard class 8. Substances that form corrosive liquid substances or corrosive vapors and mists when in contact with water or humidity also fall into this category. Hazard class 8 includes, among others, hydrochloric acid, caustic soda, and sulfuric acid.

Hazard Class 9 – Miscellaneous Dangerous Substances and Articles

Hazard class 9 includes all substances and articles that pose a danger during transport but cannot be classified into the other eight classes. This includes, for example, liquid nitrogen, asbestos, dry ice, or lithium batteries.