On a placard, the number at the bottom of the diamond indicates the

• A. UN number
• B. numeric hazard rating
• C. hazard class
• D. page number

Answer: (C)

The bottom number on a hazmat placard identifies the hazard class. That tells you the general type of danger the material poses (for example, a 3 means flammable liquids, a 6 means toxic substances, a 8 means corrosives). Knowing the hazard class helps responders decide on the appropriate approach, PPE, and procedures for containment, firefighting, or spill control.

The UN number is a separate identifier for the specific substance, usually found on shipping papers or labels, not the bottom placard number. The numeric hazard rating you might see in other systems (like the NFPA 704 diamond) comes from a different labeling scheme, not the bottom of the placard. And a page number isn’t part of what the placard conveys.