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Glossary
Hazardous materials, as discussed in this course, may be defined as:
A substance or material that the Secretary of Transportation has determined is capable of posing an unreasonable risk to health, safety, and property when transported in commerce. The term includes hazardous substances, hazardous wastes, marine pollutants, elevated temperature materials, materials designated as hazardous in the Hazardous Materials Table (see 49 CFR 172.101), and materials that meet the defining criteria for hazard classes and divisions in the standard.
Definition of Hazardous Materials

Substances or materials, which because of their chemical, physical, or biological nature, pose a potential risk to life, health, or property if they are released.

A “release” may occur by spilling, leaking, emitting toxic vapors, or any other process that enables the material to escape its container, enter the environment, and create a potential hazard. Hazards are classified in many different ways. The following introduces several common terms:

  1. Explosive substances release pressure, gas, and heat suddenly when they are subjected to shock, heat, or high pressure. Fourth of July celebrations use many types of explosive substances that require careful storage and handling to avoid injury.
  2. Flammable and combustible substances are easy to ignite. Paint thinners, charcoal lighter fluid, and silver polish are all highly flammable. Oxidizers, which will lend oxygen readily to support a fire, and reactive materials, which are unstable and may react violently if mishandled, pose related hazards.
  3. Poisons (or toxic materials) can cause injury or death when they enter the bodies of living things. Such substances can be classified by chemical nature (for example, heavy metals and cyanides) or by toxic action (such as irritants, which inflame living tissue, and corrosives, which destroy or irreversibly change it). One special group of poisons includes etiological (biological) agents. These are live microorganisms, or toxins produced by these microorganisms, that are capable of producing a disease.
  4. Radioactive materials are a category of hazardous materials that release harmful radiation. They are not addressed specifically in this course.
These categories are not mutually exclusive. For example, acids and bases are listed as corrosive materials, but can also act as poisons.