What is imperative when checking a watertight closure for pressure/vacuum?

When checking a watertight closure for pressure or vacuum, maintaining control of the closure or fitting is critical. This is because any sudden movement or loss of grip can result in an uncontrolled release of pressure or vacuum, which can lead to potential hazards, including breaches in watertight integrity and serious safety risks for personnel.

Being in control ensures that you can manage the closure safely and respond promptly should there be any fluctuations in pressure or vacuum. This also allows for better management of the closure's functionality, ensuring it operates as intended under various conditions.

Although ensuring proper lubrication, checking for balance, and maintaining visual supervision are all important aspects of closure maintenance and operation, the most vital aspect in the context of pressure or vacuum is the immediate management of the closure itself to prevent accidents. This highlights the importance of control in ensuring the effectiveness and safety of watertight closures.