The four-digit number appearing on a placard or orange panel of a tank car is the:

• A. capacity of the tank car.
• B. United Nations product identification number.
• C. last date the tank car was pressure tested.
• D. tank car registration number.

Answer: (B)

The four-digit code on a tank car placard or orange panel is the UN product identification number. This number is assigned to hazardous materials to pinpoint exactly what substance or product is involved, so responders can quickly reference the correct hazard information and safety procedures in guides like the Emergency Response Guidebook. It’s what lets you know the specific product you’re dealing with, not the tank’s capacity, not the date of a pressure test, and not the car’s registration number. Those other identifiers are separate and not used in the placard’s four-digit UN code.