Provided that the oil is non-flammable at both the initial and final temperatures, it is suitable for use since the system is enclosed.

• A. True
• B. False
• C. Not sure
• D. It depends on other factors

Answer: (D)

Flammability depends on more than just how the oil behaves at the two endpoint temperatures. In service, the oil can experience a wide operating range, including hot spots near compressors or during start-up and shut-down, where temperatures can exceed the initial and final points. If the oil or its vapors reach temperatures high enough to form ignitable mixtures, an ignition source could spark a flame, especially in an enclosed space where vapors can accumulate.

Other factors matter too: the actual operating temperature range, pressure, presence of air or oxygen entering the enclosure, impurities or moisture that can lower flash points, the specific refrigerant–oil mixture, and the potential for overheating or oil decomposition that might generate flammable gases. Even if the oil appears non-flammable at the stated temperatures, these additional considerations could create conditions that are not safe.

That’s why the best answer is that it depends on other factors—you can’t conclude suitability from those two temperatures alone.