The isolation distance in the numbered guides is to be used:

• A. Before identifying the hazardous material
• B. Once the 3-digit guide number has been obtained
• C. Only during large-scale evacuations
• D. When the emergency response team arrives

Answer: (B)

The isolation distance in the numbered guides is meant to be used once the 3-digit guide number has been obtained. This guide number corresponds to specific hazardous materials and dictates the protocols, including necessary isolation distances, to ensure safety during an incident. By consulting the guide after identifying the material, responders can effectively determine the appropriate measures to take, including how far people should be from the hazard to minimize exposure or risk.

Implementing isolation distances prior to identifying the material or during large-scale evacuations would not provide the necessary context that the guide offers regarding specific hazards. The isolation distance is a critical component derived from the characteristics of the material as noted in the guide, emphasizing the importance of proper identification before any evacuation or distancing action is taken.