An unpredicted change in a plant process is referred to as a:

A change in a plant process that occurs unexpectedly is referred to as a disturbance. This term is widely used in engineering and process control to describe variations or fluctuations in system parameters that can affect the normal operation of a process. Disturbances can arise from various factors, including changes in raw materials, environmental conditions, equipment performance, or external influences.

Understanding disturbances is crucial for operators and engineers because they need to recognize and respond to these changes to maintain the stability and efficiency of the plant operations. By identifying disturbances, operators can take corrective action or implement control measures to mitigate their impact on the process.

In the context of process control, a disturbance might be caused by something like a sudden increase in temperature or pressure due to an external factor, which would necessitate immediate responses to ensure safety and proper functioning of the system.