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How are bismuth alloys used in fire-detection equipment?

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A labeled periodic table element box for bismuth shows atomic number 83, symbol Bi, atomic weight 208.9804, electron configuration, and properties including solid state, rhombohedral crystal structure, and weakly acidic oxides. — bismuth Properties of bismuth.

Bismuth is a key component in a group of materials known as fusible alloys, which are characterized by their low melting points. These alloys are utilized in fire-detection equipment, such as automatic safety sprinklers, because they are engineered to melt at specific, relatively low temperatures.12

When a fire occurs, the heat causes the bismuth-containing alloy to melt, which triggers the sprinkler system to automatically release water. By incorporating bismuth, these alloys benefit from the element's unique properties, specifically its low melting point and its tendency to expand upon solidification, which makes it an essential ingredient for these safety applications.12