When discarding an oily rag, when is it safe to throw it in the trash?

The safest time to discard an oily rag is when it is dry. Oily rags can spontaneously combust if they're not handled properly due to the heat generated by the oxidation of the oils. By ensuring that the rag is completely dry before disposal, you significantly reduce the risk of a fire hazard.

Additionally, allowing the rag to dry can also help eliminate any residual odor associated with the oil. Therefore, while avoiding throwing the rag in the trash when it's still wet or stinky is important, the key factor for safety is that it should be allowed to dry thoroughly. This ensures that any potential ignition risk is minimized.