What is the difference between 'operability' and 'reliability' in a process safety context?

• A. Operability concerns safe and effective operation within safety limits; reliability concerns uptime and consistent performance
• B. Operability is about maintenance scheduling; reliability is about safety
• C. Both are identical
• D. Reliability disregards safety

Answer: (A)

Operability and reliability address different aspects of safe, effective operation. Operability is about being able to run the plant safely and effectively within design and safety limits—the control systems, alarms, interlocks, human factors, and procedures that let operators keep the process within its safe operating envelope and handle disturbances without violating safety margins. Reliability, on the other hand, is about how often equipment and systems perform their required function over time—the probability of staying up and operating as intended, including maintenance, failure rates, and the availability of protective features.

So the best match says operability concerns safe and effective operation within safety limits, while reliability concerns uptime and consistent performance. Maintenance scheduling and the idea that reliability is about safety are not the core definitions here, and the two terms are not identical nor is reliability about disregarding safety.