What should responders do when they encounter an unknown substance?

When responders encounter an unknown substance, it is crucial to treat it as hazardous until proven otherwise. This approach is grounded in safety protocols designed to protect both the responders and the public from potential harm. Unknown substances can pose a variety of risks, including toxicity, flammability, or reactivity, and assuming a non-hazardous status could lead to serious consequences including exposure or contamination.

By treating the substance as hazardous, responders ensure that they take appropriate precautions, such as maintaining a safe distance, using personal protective equipment (PPE), and establishing a secure perimeter. This response aligns with the principles of risk management in hazardous materials operations, where erring on the side of caution is paramount.

Addressing the other options, immediate testing may not be feasible or safe due to the variability in the substances and the potential danger they pose. Ignoring the substance altogether could lead to a catastrophic situation if it happens to be harmful, and documenting it without taking appropriate safety measures does not address the immediate risks that may be present. Thus, treating the substance as hazardous is the most prudent and responsible action in hazardous materials operations.