Name an example of a physical barrier in HAZMAT containment.

A physical barrier in HAZMAT containment is specifically designed to prevent the spread of hazardous materials and control their movement in the event of a spill. Dikes or berms serve this purpose effectively by creating a physical obstruction that captures and holds the hazardous material, allowing for containment and cleanup efforts to be more manageable. This helps to protect the surrounding environment and prevent contamination beyond the immediate spill area.

The other options do not function as physical barriers. Emergency response teams provide the necessary personnel and skills to manage hazardous situations but do not physically contain spills. Warning signs play an important role in communication and safety but do not offer any physical containment. Pit stops for vehicle refueling are operational areas that do not provide any physical barrier to hazards. Thus, the most accurate example of a physical barrier among the options given is indeed the dikes or berms used to prevent spill spread.