Pneumatic or electric power supplies should not be isolated or disconnected from operating positions unless the technician understands the ---- beforehand.

The correct choice emphasizes the importance of understanding failure modes before isolating or disconnecting pneumatic or electric power supplies. Failure modes refer to the various ways in which a system or component can fail to operate as intended. By comprehensively understanding these potential failures, a technician is better equipped to anticipate the consequences of isolating power supplies. This knowledge helps in assessing risks and minimizing hazards that can arise when systems are taken offline unexpectedly.

For instance, if a technician is aware that isolating a particular power supply might lead to an uncontrolled energy release or failure of downstream equipment, they can take appropriate precautions to mitigate those risks before proceeding with the disconnection. Having a grasp of the failure modes ensures that the technician can plan for safe operations, maintaining the integrity of the system and protecting personnel.

In the context of the other choices, while operating procedures, hazard assessments, and safety protocols are all essential aspects of safe operations in a technical environment, they do not specifically address the critical understanding of how systems might fail as a result of disconnection. Hence, the awareness of failure modes directly relates to the technician's ability to safely manage the power supply disconnection process.