How do United Nations (UN) placards identify general hazards?

The identification of general hazards by United Nations (UN) placards is achieved through the use of hazard class numbers. These numbers are part of a standardized system that categorizes and communicates the specific types of hazards associated with various materials. Each hazard class is designated by a unique number that corresponds to a general category of risk, such as flammable substances, explosive materials, or toxic substances.

The use of these hazard class numbers allows emergency responders and transportation personnel to quickly identify the type of hazard present and take the necessary precautions when dealing with the materials. This method of labeling is essential for ensuring safety during transportation and in emergency situations.

Other options, while related to hazard communication, do not serve the primary purpose that hazard class numbers do. For example, using a numerical scale from 0 to 4 indicates relative risk in a different context, but it is not a standard feature of UN placards. Similarly, while product names may provide additional context, they are not a requirement on placards, hence relying solely on them for hazard identification wouldn't be effective. Changing the shape of placards is also not part of the UN placarding system, which primarily uses colors and numbers for immediate hazard recognition.