What event causes the sprinkler head cap to open?

The event that causes the sprinkler head cap to open is a predetermined rise in temperature. Sprinkler systems are designed to activate when the ambient temperature in a space reaches a certain threshold, typically due to a fire. Each sprinkler head has a heat-sensitive element, often either glass bulbs filled with a colored liquid or fusible links that melt at specific temperatures.

When the temperature rises due to a fire, this element reacts by breaking (in the case of glass bulbs) or melting (in the case of fusible links), allowing water to flow from the sprinkler head. This mechanism is critical for effectively controlling or extinguishing fires before they can spread, as it ensures that the sprinklers respond quickly to a fire's heat while preventing unintended activation from minor heat sources. This function is essential for the overall safety and reliability of the fire suppression system.