Which safety device is made from a metal alloy that burns when overheated?

• A. Pressure relief valve
• B. Fusible plug
• C. Thermal fuse
• D. Safety shutoff switch

Answer: (B)

Overheating protection relies on a fusible element that melts at a specific temperature to provide automatic relief. A fusible plug is made from a metal alloy with a very low melting point. When the boiler overheats, the alloy melts and the plug opens a path for steam to escape, reducing pressure and preventing an explosion. This melting action is the defining feature of a fusible plug. In contrast, a pressure relief valve opens due to high pressure, a thermal fuse is used to open an electrical circuit when heat becomes excessive, and a safety shutoff switch stops fuel or power without melting a fusible alloy.