What do fusible-link sprinkler heads use to release the cap and flow water?

Fusible-link sprinkler heads operate using a metal alloy that is designed to melt at a specific temperature, effectively functioning as a heat-sensitive mechanism. When the temperature around the sprinkler head rises to a predetermined level due to a fire, the alloy melts, allowing the cap of the sprinkler to release and initiate the flow of water to control the flames. This system is sensitive and reliable, ensuring that water is only discharged when needed, thus minimizing water damage in areas not affected by fire.

The other options, such as a chemical pellet or a glass bulb, pertain to different types of sprinkler mechanisms that operate based on alternatives to temperature sensitivity. For example, glass bulbs contain a liquid that expands and breaks the bulb when heated, while electrically triggered mechanisms rely on an electrical signal rather than a physical change in material properties to activate. However, fusible-link sprinkler heads are specifically designed around the melting point of a metal alloy, making option C the accurate choice for understanding their operation.