Some items can be manually removed from the waste before mechanical processing. They are reserved for small operations and also applicable to the contaminants from source-separated materials. To start the separation, sorting belt or table is needed and workers and hoppers or other receptacles have to be positioned. The process rely on the separation requires a good understanding of basic principles of time and motion, of the composition of the waste, and of the comfort and safety requirements of the sorters. The most important thing is safety.