What does the letter "W" specify for certain materials?

The letter "W" is used in the context of hazardous materials to indicate that certain materials are specifically regulated only when they are transported by water or vessel. This designation is important for ensuring that regulations are appropriately applied based on the mode of transport, as different transportation methods may present different risks and require distinct safety measures.

For those materials marked with "W," it means that while they may not be subjected to the same regulations when transported by land or air, they still pose specific risks when transported over water. The guidelines ensure the safety of marine environments and the prevention of hazardous spills or incidents that could occur during maritime transportation.

Understanding this designation helps in compliance with environmental regulations and ensures proper handling of materials that may pose a risk when placed in aquatic environments, which is a crucial aspect of hazardous materials management.