How can subsidiary placards be identified in relation to primary placards?

Subsidiary placards are used to communicate additional hazards associated with a shipment of hazardous materials, complementing the primary placard that indicates the main hazard. The correct answer highlights that subsidiary placards do not carry the class or UN number, distinguishing them from primary placards.

Primary placards are designed to convey the most significant hazard of a shipment and typically feature a specific color scheme and the relevant UN number, which identifies the material. In contrast, subsidiary placards provide information about secondary hazards but skip the class or UN number to focus on that secondary risk. This helps responders identify all potential hazards without cluttering the primary safety message.

The other options present characteristics that do not accurately define subsidiary placards in relation to primary placards. For example, color schemes and shapes can vary widely between different types of hazardous materials, and subsidiary placards can actually share color schemes and shapes with some primary placards. Similarly, subsidiary placards do not indicate a higher hazard level; instead, they clarify additional hazards associated with a material that may not be evident from the primary placard alone. Recognizing this distinction is crucial for effective hazard communication and response planning in the handling of hazardous materials.