Worst case

In validation, the condition, product or location chosen because it is the hardest to control, so that success there covers the easier cases. In cleaning validation it is usually the least soluble or most toxic product, the largest batch or the hardest-to-clean part of the equipment; in qualification and process validation, operating limits that challenge the system. A validation plan should explain why each worst case was chosen. Revisit the choice when a new product joins a shared line, because the new product may become the worst case.