Capsule Core

The liquid inside a fire sprinkler bulb is typically a mixture of alcohol, water, and organic dyes, designed to expand predictably at specific temperatures.

The dye color corresponds to the activation temperature: orange (135°F/57°C), red (155°F/68°C), yellow (175°F/79°C), green (200°F/93°C), blue (286°F/141°C), and black (360°F/182°C).

When the surrounding heat reaches the bulb's rated temperature, the liquid expands until the thin-walled glass bulb fractures, triggering water flow.

The fluid’s high coefficient of thermal expansion ensures accurate and rapid activation, making it a critical component in automatic fire suppression systems.