What type of control is characterized by a trained operator monitoring reactor temperature and pressure to stop a process if conditions become too extreme?

The correct answer is characterized by employing a human operator, who continuously observes and adjusts the operating conditions of a process, such as a reactor's temperature and pressure. This system relies on the operator's training and decision-making abilities to intervene when conditions become extreme, emphasizing an active role in managing safety.

In this context, procedural controls outline specific actions and processes that must be followed, often including operator interventions in response to anomalies. The monitoring by a trained operator is a classic example of relying on procedures to maintain safety and operational integrity, thus identifying it correctly as the procedural control approach.

Other control types, such as inherent, do not rely on human intervention but rather on the design features that minimize hazards from the outset. Active controls usually imply some form of machinery or automated systems coming into play, while passive controls would inherently work without any action taken, serving to automatically mitigate risks without operator involvement. Understanding these distinctions clarifies why the procedural approach accurately describes the scenario presented in the question.