Which boundary is defined by the arc fault on the surface of the skin requiring PPE?

The boundary defined by the arc fault on the surface of the skin requiring personal protective equipment (PPE) is indeed the flash protection boundary. This boundary is critical in electrical safety, specifically concerning arc flash hazards. When an arc flash occurs, it releases an enormous amount of thermal energy which can cause severe burns and injuries. The flash protection boundary is established at a distance from the arc source that is determined to be safe for unprotected personnel. Within this boundary, individuals must wear appropriate PPE to protect against potential exposure to heat and energy produced by an arc flash. The requirement for PPE is crucial in order to minimize the risk of injury in environments where electrical equipment is exposed to potential arcing faults.

The other options relate to different safety considerations. The shock boundary pertains to the distance where a person could potentially receive an electrical shock from live parts, while hazardous boundary refers to areas that pose various dangers but are not specifically tied to arc flash conditions. Limited access boundaries are intended to restrict access to areas where work is being done, primarily for safety and organizational purposes. Therefore, the flash protection boundary is specifically aligned with the need for PPE in situations where arc faults could occur, making it the correct answer.