Emergency relief for uncontrolled reactions often involves ______ the relief device.

• A. two-phase flow through
• B. the flow of water through
• C. meltdown of
• D. plugging of

Answer: (A)

During an uncontrolled reaction, venting must handle a mixture of vapor and liquid, so relief devices routinely deal with two-phase flow. The generation of gas combined with liquid present in the reactor means the emergency relief stream is not single-phase gas, which changes how the device behaves, its capacity, pressure drop, and potential for liquid entrainment or flashing. Designing and operating relief systems with this two-phase flow in mind ensures the device can relieve pressure safely without clogging or failing. Other options describe unrelated actions (like water flowing through the device or a meltdown) or failure modes (plugging) rather than the actual relief mechanism.