Substances with a vapor pressure of 300 kPa or greater at 50 degrees Celsius and those that are completely gaseous at standard atomic pressure at 20 degrees Celsius fall into the gases category. Items containing these substances are also categorized as class 2 hazardous materials. The classification is broken down into three sub-divisions that include several common items like aerosols, compressed cases, fire extinguishers, gas cartridges, natural gas and propane.

Division 2.1 Flammable gases

Division 2.2 Non-flammable, non-toxic* gases

Division 2.3 Toxic* gases

Flammable liquids have flashpoints of 60 to 65 degrees Celsius or lower. They are defined as liquids, liquids containing solids in solution or mixtures of liquids. Liquids transported at temperatures at or above their flashpoints are also classified as flammable liquids. Common examples include many adhesives, paints, alcohol, diesel fuel, gasoline, acetone and kerosene.

This class includes materials that are readily combustible under conditions that are common during transport. Self-reactive substances that may undergo strong exothermic reactions or solid desensitized explosions are also included in this category. This category is broken down into three sub-divisions. Commonly transported flammable solids include matches, metal powders, sodium batteries and activated carbon.

Division 4.1 Flammable solids, self-reactive substances and solid desensitized explosives

Division 4.2 Substances liable to spontaneous combustion

Division 4.3 Substances which in contact with water emit flammable gases

Oxidizers are substances that may contribute to or cause combustion by yielding oxygen as the result of a chemical reaction. Organic peroxides are substances that may qualify as hydrogen peroxide where organic radicals have replaced one or both of the hydrogen atoms in the chemical structure. Chemical oxygen generators, nitrates, nitrites, ammonium nitrate fertilizers and sodium nitrate are a few common examples of this type of hazardous material.

Division 5.1 Oxidizing substances

Division 5.2 Organic peroxides

Toxic substances include any substances that could cause serious injury, harm or death to a human if inhaled, swallowed or allowed to come into contact with skin. Infectious substances are materials that are known to or likely to contain pathogens such as viruses, bacteria, parasites, fungi and other microorganisms that can cause disease in humans and animals. Examples include medical and biomedical waste, biological cultures, tear gas, dyes, acids, cyanides, arsenic, nicotine and chloroform.

Division 6.1 Toxic* substances

Division 6.2 Infectious substances

This class includes materials that contain radionuclides — atoms that are subject to radioactive decay due to an unstable nucleus — where both the total activity and activity concentration exceed predefined values. These materials emit ionizing radiation, which is extremely dangerous to human health. Medical isotopes, radioactive ores, depleted uranium and density gauges are a few of the most commonly transported radioactive materials.

Corrosives include substances that disintegrate or degrade other materials on contact by way of chemical action. They will damage surrounding materials if they leak while in transit, and they can cause severe damage to living tissue. Examples include acids and acid solutions, batteries, dyes, paints and flux.

Some hazardous materials do not fall into any of the first eight categories. In these situations, they are classified as “miscellaneous hazardous materials,” a class that includes environmentally hazardous substances, genetically modified organisms, substances that are transported at high temperatures and magnetized materials. A few common examples include dry ice, lithium-ion batteries, vehicles, first-aid kits, life-saving appliances and fuel cell engines.