What type of materials must be separated from regular mail as per USPS guidelines?

Hazardous materials must be separated from regular mail according to USPS guidelines because they pose a safety risk to postal workers, facilities, and the public. The USPS has strict regulations regarding the handling and transportation of hazardous materials, which include items that can be flammable, explosive, or toxic. These items require special handling, labeling, and packaging to ensure compliance with safety standards and regulations.

In contrast, general merchandise, domestic packages, and priority items do not carry the same level of inherent risk and can be processed together with regular mail. The segregation of hazardous materials is essential to maintaining safety and operational efficiency within the postal system.