What should responders do if they encounter an unknown hazardous substance?

Answer: B — Consult the Emergency Response Guidebook for guidance

Consulting the Emergency Response Guidebook for guidance is the best course of action when responders encounter an unknown hazardous substance. This comprehensive resource provides critical information on how to assess the situation safely and effectively. It includes details on recognizing hazardous materials, the appropriate protective measures, and steps to contain or mitigate the incident based on the material's properties and potential risks. Using the Emergency Response Guidebook allows responders to make informed decisions while prioritizing their safety and the safety of the public. This approach emphasizes the importance of established protocols and systematic approaches in hazardous material incidents, rather than relying on assumptions or unverified actions. By following the guidelines in this resource, responders can determine how to proceed appropriately, whether that involves evacuation, containment, or calling for specialized support.