Hazardous materials, often abbreviated as “hazmat,” are substances that pose a potential risk to health, safety, property, or the environment when handled, stored, or transported. These materials can be pure chemicals, mixtures, manufactured products, or articles containing hazardous components, such as certain batteries or cleaning fluids. While “hazmat” is the most common term used by the general public and emergency responders in the United States, the technical and regulatory language is much more specific. Precise terminology is used to ensure that everyone involved in the transportation chain understands the exact nature of the material’s danger.
Formal Technical Terminology
The technical name applied to these substances depends primarily on the regulatory body and the mode of transport, leading to two distinct formal terms. Within the United States, the Department of Transportation (DOT) primarily uses the term “Hazardous Materials” when regulating substances that pose an unreasonable risk during commerce. This term is codified in U.S. federal regulations and applies broadly to domestic shipments by ground, rail, air, and water.
When the material is transported internationally, particularly by air or sea, the governing technical term shifts to “Dangerous Goods.” This terminology is established by the United Nations (UN) and is adopted by international organizations like the International Air Transport Association (IATA) and the International Maritime Organization (IMO). Although they refer to the same physical substances, the difference in terminology reflects the jurisdiction regulating the transport. For example, a flammable liquid shipped domestically is a Hazardous Material, but the same liquid shipped internationally is classified as Dangerous Goods.
The UN Model Regulations provide the global framework that both the U.S. and international bodies base their rules upon, creating a standardized classification system. This harmonization ensures that a substance is recognized and handled with the same safety precautions regardless of its origin or destination.
The Nine Classes of Dangerous Goods
The international technical system categorizes all substances into nine major classes, which are based on the material’s primary hazard. This uniform system allows for a quick, recognizable assessment of the danger posed by any given item. The classes range from materials that present an immediate explosion risk to those that pose a long-term environmental threat.
The nine classes are:
- Class 1: Explosives, which are materials designed to function by explosion or deflagration, such as fireworks or military ordnance.
- Class 2: Gases, which are subdivided based on their risk, including flammable gases, non-flammable and non-toxic gases like helium, and toxic gases.
- Class 3: Flammable Liquids, defined as liquids with a flashpoint below 60 degrees Celsius (140 degrees Fahrenheit), meaning they can readily produce a flammable vapor.
- Class 4: Flammable Solids, including readily combustible solids, substances liable to spontaneous combustion, and substances that emit flammable gases when in contact with water.
- Class 5: Oxidizing Substances and Organic Peroxides. Oxidizers can cause or contribute to the combustion of other material, and organic peroxides are thermally unstable and can undergo exothermic decomposition.
- Class 6: Toxic and Infectious Substances, covering poisons and biohazardous materials like certain laboratory specimens.
- Class 7: Radioactive Material, encompassing any material containing radionuclides where both the activity concentration and total activity exceed specified values.
- Class 8: Corrosives, consisting of substances that cause severe damage upon contact with living tissue or other materials.
- Class 9: Miscellaneous Dangerous Goods, which are materials that present a hazard during transport but do not fit into the other eight categories, such as lithium batteries and certain environmentally hazardous substances.
Technical Identification and Labeling
Communicating the specific hazard of a material is achieved through a technical labeling system that uses standardized visual and numeric identifiers. For bulk shipments, such as tankers or railcars, diamond-shaped signs known as placards are displayed on all four sides of the transport vehicle. These placards are color-coded and feature the symbol and the hazard class number (1 through 9) that corresponds to the material’s primary risk.
A more precise technical identifier is the four-digit UN Number, or NA Number in North America, which is displayed prominently on the placard or the package. This number serves as a unique “fingerprint” for a specific hazardous substance, such as UN 1203 for gasoline or UN 1017 for chlorine. Emergency responders use this number to quickly look up the exact chemical composition and necessary response procedures in guides like the Emergency Response Guidebook.
The most comprehensive technical communication is contained within the required shipping papers, often called a dangerous goods declaration. This official document must list the proper shipping name, the UN number, the hazard class, the packing group (which indicates the degree of danger), and the quantity of the material being transported. This documentation ensures that every party in the supply chain has the technical data necessary for safe handling, stowage, and emergency intervention.