The product ID markings on a tank must be what?

The product ID markings on a tank must be presented as black 4-inch numbers on orange panels. This specific color combination is standard practice within the transport and identification of hazardous materials. The use of orange panels serves as a cautionary visual signal, indicating the presence of hazardous substances, while the black numbers ensure that the identification is easily readable from a distance.

This marking system is established by the Department of Transportation regulations to ensure quick recognition of hazardous materials during transport. Visibility and clarity in labeling are crucial for safety professionals, emergency responders, and transporters in recognizing the nature of the contents in the event of an accident or emergency, facilitating an appropriate response.

The other options do not adhere to the established regulations for marking hazardous materials, which is why they are less appropriate for the product ID markings on tanks.