Which of the following is NOT a main category of hazardous materials?

The correct response highlights that "Psychological" is not recognized as a main category of hazardous materials. In the context of hazardous materials, the primary categories typically include chemical, biological, and radiological threats. Each of these categories involves specific types of hazards that emergency responders need to be trained to handle safely.

Chemicals can range from toxic substances to corrosive materials. Biological hazards include pathogens like viruses, bacteria, and other organisms that can cause diseases in humans. Radiological materials involve radioactive substances that can emit harmful radiation.

In contrast, "Psychological" does not fit within the standard classifications related to hazardous materials. While psychological impacts can arise in emergency scenarios—such as trauma from exposure to hazardous situations—they do not comprise a category related to physical substances or materials that pose a direct risk to health and safety. Understanding these different categories is crucial for effective response and management in hazardous materials situations.