What word replaces the hazard class or division for materials that are too dangerous to be transported?

The correct answer is "forbidden," which is used to designate materials that are deemed too dangerous for any form of transportation. This term is critical in the context of hazmat transport because it indicates that certain substances pose such a high level of risk that their transportation is not allowed under any circumstances.

Materials labeled as forbidden typically include substances that have an extreme likelihood of causing severe damage to health, safety, or property if released. This classification helps ensure that hazardous materials that pose severe threats are adequately managed and not transported in ways that could endanger the public or the environment.

In contrast, while "prohibited," "restricted," and "hazardous" may reflect certain limitations or classifications, they do not convey the absolute ban on transporting materials that "forbidden" communicates. These terms might refer to various regulations or standards applied to materials with potential risks but do not capture the same level of danger where transportation is completely disallowed.