Final answer:
In certain circumstances, two tiers of containment can be used to enhance safety.
Step-by-step explanation:
In certain circumstances, it is acceptable to use two tiers of containment to enhance safety when working with infectious agents. For example, a Class II Biological Safety Cabinet (BSC) can be placed within a negative pressure room to provide an extra layer of protection. This combination ensures that any potential contaminants are effectively contained and filtered before being exhausted to the environment.