Final answer:
Closed-system vial-transfer devices should be used within an ISO Class III environment of a Biological Safety Cabinet (BSC) as per USP 797.
Step-by-step explanation:
Per USP 797, when closed-system vial-transfer devices (CSTDs) are used, they shall be used within an ISO Class III environment of a BSC (Biological Safety Cabinet).
A Biological Safety Cabinet (BSC) is a ventilated enclosure designed for safely working with hazardous agents, including biological agents. It provides personnel, environmental, and product protection. There are different classes of BSCs based on the level of containment they offer.
In the context of the question, ISO Class III BSCs are recommended for use with closed-system vial-transfer devices to ensure maximum safety and containment of highly infectious agents.