What is a key indicator of a material's hazard class?

The specific UN (United Nations) number is a key indicator of a material's hazard class because it provides a standardized reference that categorizes hazardous materials based on their properties and associated risks. Each UN number corresponds to a specific substance or group of substances and is part of the Globally Harmonized System (GHS), which helps ensure consistency and safety in the transport and handling of hazardous materials across different countries.

By using the UN number, handlers and transporters can quickly identify the nature of the hazard associated with the material, including whether it poses risks such as flammability, toxicity, or environmental hazards. This information is crucial for implementing the correct safety measures and regulatory compliance during shipping and handling.

Other choices, such as the color of the container, the size of the shipment, and the shape of the packaging, can vary widely and do not provide a reliable or consistent means of identifying the hazard class of a material. Those aspects may assist in visual identification or packaging standards but lack the specificity and comprehensive information that the UN number offers.