Which type of sprinkler head uses a metal alloy that melts at a specific temperature?

• A. Glass Bulb Sprinkler Head
• B. Fusible Link
• C. Electrical Heat Sensor
• D. Thermal Cap

Answer: (B)

Sprinkler heads that activate at a set heat level by melting a metal alloy are fusible-link sprinklers. A small piece of fusible alloy holds the sprinkler’s mechanism in place; when heat reaches the alloy’s melting point, it liquefies, the link fails, and the plug is released so water can flow through the head. The melting point is chosen to match a specific temperature, giving a predictable activation in a fire. Other types rely on different methods—glass bulb heads break a glass capsule when heated, electrical heat sensors trigger via an electrical mechanism, and some designs use a cap or other release method that does not involve a melting metal alloy.