What is a UN number and why is it important for HazMat responders?

• A. A five-digit code used for labeling only.
• B. The manufacturer's phone number.
• C. A code that indicates the shipping date.
• D. A four-digit identifier assigned to a HazMat for universal recognition; it helps responders look up precautions and emergency actions.

Answer: (D)

A UN number is a four-digit identifier assigned to hazardous materials to identify them in transport systems worldwide. This code is used across countries and languages so responders can quickly recognize the material and look up the specific precautions, PPE, and emergency actions in standard reference guides like the Emergency Response Guidebook. That quick access to verified response steps helps responders isolate the area, control the release, and protect people and the environment. It’s the universal recognition and linked safety actions that make this four-digit code so essential. The other options don’t fit because they describe labels, dates, or contact info, none of which identify the hazard or guide emergency actions.