What is the only exception to certification by a shipper?

The correct answer highlights a specific situation where a shipper may be exempt from the usual certification requirements in hazardous materials transportation regulations. When the shipper is a private carrier of his own product, he is not required to go through the formal certification process. This exemption acknowledges that individuals transporting their own materials may have a direct understanding and handle of what they are transporting, reducing the need for the extensive procedural checks that apply to commercial shippers who deal with third-party logistics.

The regulations are designed to ensure safety and compliance for hazardous materials in the shipping process, emphasizing that shippers must be certified to confirm their knowledge of the materials and regulations. This exception reflects a recognition of specific circumstances, where the individual being the private carrier may have a vested interest and personal responsibility for the materials being transported.

The other scenarios presented do not qualify as exceptions to the certification requirements according to hazardous materials regulations. For example, proper placarding is essential for hazardous materials transport but does not exempt the shipper from certification. Similarly, a shipper's health issues or improper packing of cargo do not provide valid grounds for bypassing certification. Each of these situations still falls under the regulatory requirements designed to promote safety and accountability in the transportation of hazardous materials.