Final answer:
Dual control is the best personnel control to prevent independent access to an organization's secure vault.
Step-by-step explanation:
The personnel control that is best suited to ensuring that a single person cannot independently access an organization's secure vault is Dual control. Dual control refers to the practice of requiring two or more people to work together to complete a task, such as accessing the secure vault. This ensures that no single person has complete access or control over the vault.