Which type of failure corresponds to warning signs but the system is still operating?

• A. Functional Failure
• B. Hidden Failure
• C. Potential Failure
• D. Post-Failure

Answer: (C)

Warning signs while the system is still operating point to potential failure. This means a fault is developing and indicators (such as alarms, diagnostic readings, or trending deviations) show something is drifting toward failure, but the equipment continues to run within its current limits. The key idea is to act before the issue becomes an actual outage or functional loss. For example, a sensor may drift and show readings moving toward the limit, or a component may exhibit rising vibration that hasn’t yet caused a shutdown. If these signs are monitored and addressed, the system can be kept reliable; otherwise the next step could be a real, functional failure. This differs from a functional failure, where the system no longer performs its intended function; a hidden failure, where faults exist without any evident warning, and a post-failure state, which occurs after a failure has already happened.