Which materials must always be placarded regardless of quantity?

The correct answer is that Table 1 materials must always be placarded regardless of quantity. Table 1 includes hazardous materials that are deemed highly dangerous and pose significant risks to public safety and the environment. These materials are identified in the context of emergency response and transportation regulations, and they trigger stringent requirements for labeling and placarding to ensure proper handling and communication about the dangers associated with them.

In contrast, common household chemicals may not need placarding depending on their quantities and overall hazardous classification. Flammable liquids do require placarding, but this is often quantity-dependent, meaning smaller amounts might not trigger such requirements. Radioactive waste does have specific regulations regarding placarding, but the requirements can vary based on the amount and type of radioactive material, rather than being a blanket requirement for all quantities. Therefore, the unyielding requirement for placarding of Table 1 materials emphasizes their high-risk designation, ensuring that they are consistently recognized and managed appropriately during transport and in emergency situations.