Fire Protection Deep Dive
True or False: The color of the liquid inside a fire sprinkler glass bulb tells you the temperature at which that sprinkler will activate.
TRUE
Answer & Explanation:
Answer: True. Each color is calibrated to a specific temperature range so the bulb bursts only when the surrounding air reaches that temperature.
Inside each bulb, a tiny air bubble sits in a heat-sensitive liquid. As heat rises, the liquid expands, forcing the bubble to disappear. The resulting pressure shatters the glass, releasing the water seal.
A: In short: bulb size matters, but temperature determines the color! The colored liquid inside the glass bulb is a chemical solvent (alcohol or glycerin) mixed with dye. The color indicates the activation temperature, ranging from orange/red (135°F–170°F) for offices, to black (400°F+) for industrial ovens. When a fire breaks out, the liquid expands much faster than the glass. It compresses a tiny air bubble inside until the bubble vanishes, creating an immense outward pressure that shatters the glass and releases the water.
Learn more:
- Orange/Red (135–170°F, homes/offices), Yellow/Green (175–225°F, kitchens/warehouses), Blue/Purple/Black (250°F+ industrial/boiler areas).