Where can officers identify a material by finding its number?

The correct choice is based on the identification system used for hazardous materials as outlined in the Emergency Response Guidebook (ERG). The orange panel is specifically designed to provide responders with critical information about hazardous materials during emergencies.

Each hazardous material is assigned a specific identification number, which can be found on the orange panel. This panel includes guidance on the nature of the material and the necessary precautions to take, making it an essential resource for officers at the scene of a chemical incident.

In contrast, the other options include resources like the chemical aid booklet, which provides general information but does not focus specifically on the identification numbers in the same immediate context as the orange panel. The black and white panel, as well as the red panel, serve different purposes in the ERG and are not meant for the identification of materials by their numbers.