In 49 CFR terminology, which statement best differentiates a hazardous material from a hazardous substance?

• A. Hazardous material is regulated under the Hazardous Materials Regulations (HMR); hazardous substances are not regulated at all.
• B. Hazardous materials and hazardous substances are the same in all contexts.
• C. Hazardous material is regulated under HMR; hazardous substances are materials with hazardous properties that may be regulated differently.
• D. Hazardous substances are regulated under the HMR; hazardous materials are not regulated.

Answer: (C)

In DOT terms, hazardous materials are the substances and articles that the Hazardous Materials Regulations (HMR) govern for safe transportation. Hazardous substances are materials with hazardous properties that may be regulated differently, depending on the context or supervisory authority (for example, they may fall under EPA/ CERCLA rules or have special HMR provisions like different reporting or packaging requirements). So the best choice reflects that hazardous materials are regulated under the HMR, while hazardous substances, though hazardous, are defined separately and may be regulated differently. The other options misstate the relationship or imply the terms are interchangeable.