What type of system is activated in a frangible bulb sprinkler head?

In a frangible bulb sprinkler head, the system is activated by a liquid within a glass bulb. This design utilizes a glass bulb that contains a colored liquid, typically a glycol or alcohol-based fluid. When the ambient temperature increases due to a fire, the liquid inside the bulb expands. Upon reaching a specific temperature, the pressure caused by the expansion of the liquid breaks the glass, which releases water from the sprinkler system.

This method is effective because it allows for a precise and quick response to heat, ensuring that the sprinkler activates only when needed. The use of a liquid in a sealed glass bulb is a reliable and time-tested mechanism that ensures consistent performance under expected temperature conditions in fire suppression systems.