How are cylinders used for returning used refrigerant to suppliers marked?

Cylinders used for returning used refrigerant to suppliers are indeed marked with a yellow band 12 inches from the top. This specific marking is crucial for safety and identification purposes. It helps to distinguish these cylinders from others that might contain different substances, ensuring that they are handled appropriately during transport and return to suppliers.

The yellow band serves as a visual cue that alerts technicians and handlers of the contents inside, which are used refrigerants that require special attention and processing for safe disposal or recycling. This marking helps streamline the process for suppliers who receive these cylinders, as they can quickly assess the contents without confusion.

The other options do not conform to the recognized standards for marking these cylinders. While other bands signify different types of gases or materials, the yellow band is specifically aimed at ensuring the safe return and management of used refrigerants.