Fire Sprinkler

The sprinkler head is the component of a fire sprinkler system that discharges water when the effects of the fire have been detected, such as when the predetermined temperature has been exceeded. In buildings protected by properly maintained, and designed fire sprinklers, over 99% of fires are controlled by fire sprinklers alone.

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Detailed Description for Fire Sprinkler

A fire sprinkler or sprinkler head is the component of a fire sprinkler system that discharges water when the effects of a fire have been detected, such as when a predetermined temperature has been exceeded. In buildings protected by properly designed, and maintained fire sprinklers, over 99% of fires were controlled by fire sprinklers alone. 



A sprinkler with a green bulb indicating a liquid alcohol and intermediate temperature classification.

Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb (see below) or a two-part metal link held together with fusible alloy such as Wood's metal[12] and other alloys with similar compositions. The glass bulb or link applies pressure to a pipe cap which acts as a plug which prevents water from flowing until the ambient temperature around the sprinkler reaches the design activation temperature of the individual sprinkler. Because each sprinkler activates independently when the predetermined heat level is reached, the number of sprinklers that operate is limited to only those near the fire, thereby maximizing the available water pressure over the point of fire origin.


The bulb breaks as a result of the thermal expansion of the liquid inside the bulb. The time it takes before a bulb breaks is dependent on the temperature. Below the design temperature, it does not break, and above the design temperature it breaks, taking less time to break as temperature increases above the design threshold. The response time is expressed as a response time index (RTI), which typically has values between 35 and 250 m½s½, where a low value indicates a fast response. Under standard testing procedures (135 °C air at a velocity of 2.5 m/s), a 68 °C sprinkler bulb will break within 7 to 33 seconds, depending on the RTI. The RTI can also be specified in imperial units, where 1 ft½s½ is equivalent to 0.55 m½s½. The sensitivity of a sprinkler can be negatively affected if the thermal element has been painted.


Maximum Ceiling TemperatureTemperature RatingTemperature ClassificationColor Code (with Fusible Link)Liquid Alcohol in Glass Bulb Color
100 °F / 38 °C 135-170 °F / 57-77 °C Ordinary Uncolored or Black Orange (135 °F / 57 °C) or Red (155 °F / 68 °C)
150 °F / 66 °C 175-225 °F / 79-107 °C Intermediate White Yellow (175 °F / 79 °C) or Green (200 °F / 93 °C)
225 °F / 107 °C 250-300 °F / 121-149 °C High Blue Blue
300 °F / 149 °C 325-375 °F / 163-191 °C Extra High Red Purple
375 °F / 191 °C 400-475 °F / 204-246 °C Very Extra High Green Black
475 °F / 246 °C 500-575 °F / 260-302 °C Ultra High Orange Black
625 °F / 329 °C 650 °F / 343 °C Ultra High Orange Black


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