Under which circumstance may repair party personnel omit wearing life jackets and carrying a protective mask?

The correct choice relates to specific operational procedures that prioritize safety while enabling effective emergency response. In scenarios where repair party personnel are engaged in rescue or repair operations, they typically are required to wear certain protective gear, including life jackets and protective masks. However, the use of an oxygen breathing apparatus (OBA) creates a unique situation.

When personnel are wearing an OBA, it is designed to provide breathable air in environments that are hazardous, such as areas with smoke or potential toxins. The nature of the OBA affects the physical space and ergonomics, making it impractical or potentially ineffective to also wear a life jacket simultaneously. Therefore, under these specific circumstances, personnel may omit the life jacket and protective mask to ensure their OBA operates effectively and allows them to perform their duties safely without additional cumbersome equipment.

By focusing on this operational context, the rationale for omitting the life jacket and mask becomes clear: priority is given to the necessity of maintaining breathable air in a hazardous environment, while still adhering to safety measures as much as possible under the circumstances.