Final answer:
The DOT Hazard Class chart uses a classification system to label different types of hazards, with each class indicating a unique category of risk. There is no class that represents the highest hazard ranking as all classes signify various kinds of hazards.
Step-by-step explanation:
The Department of Transportation (DOT) ranks hazards of materials using a classification system where different classes correspond to different types of hazards. According to the DOT Hazard Class chart, the highest hazard ranking does not necessarily correspond to the lowest number. Each class represents a different type of hazard rather than a hierarchy of danger levels. Therefore, none of the hazard classes are ranked higher or lower than others in terms of hazards; they are simply indicative of different categories of risks. For example, Class 2 refers to gases, Class 5 to oxidizing substances and organic peroxides, Class 7 to radioactive materials, and Class 9 to miscellaneous dangerous substances and articles.