Which monitored condition indicates a loss of system integrity that may require a shutdown?

The best choice for indicating a loss of system integrity that may require a shutdown is the loss of lubricating oil. Lubricating oil is essential for reducing friction and wear in machinery, especially in engines and turbines. If there is a loss of lubricating oil, it can lead to severe damage due to increased friction, overheating, and eventual mechanical failure. This condition poses a significant risk to the overall safety and functionality of the system, making it critical to respond immediately, potentially requiring a shutdown to prevent catastrophic failure.

While high temperature can also indicate serious issues and may require attention, it often results from other underlying problems, such as insufficient lubrication. Low flow can lead to decreased efficiency but does not always constitute an immediate risk to system integrity. High level in tanks or reservoirs can indicate overflow or flooding risks, but is generally less critical than the direct impact a loss of lubrication would have on the machinery's operation and safety. Thus, the loss of lubricating oil stands out as a condition that directly threatens the system's integrity and necessitates urgent action.