🔥 Free Monthly Webinars (30 minutes): Check out the schedule! Extremely Popular (Don't miss out) 🔥Learn More

How does a automatic fire sprinkler head work?

An automatic fire sprinkler system head is a valve, that when the temperature sensitive bulb reaches its predetermined fixed temperature, expands, breaks and then allows the free flow flow of water.

CEO, Firewize
26 Jul, 2019
Sprinkler Head Operation Animation Slowmo

An automatic fire sprinkler system head is a valve, in broad terms there are two types of sprinkler heads. All valve type sprinkler heads contain a heat-sensitive element and plug to control the flow of water;

  1. glass bulb type; A glass bulb sprinkler heads include a temperature sensitive glass bulb. The liquid in the glass bulb is colour coded to indicate its operating temperature.  When the liquid in the glass bulb expands and reaches its predetermined fixed temperature, the glass bulb breaks and then allows the free flow flow of water on to the source of heat that caused it to operate.
  2. fusible link type; A fusible link fire sprinkler head includes a two-part metal element that is fused by a heat-sensitive alloy that holds the valve plug in place. The heat-sensitive alloy acts as the heat-sensitive element of a fusible link sprinkler. When it reaches its' designated temperature, it melts, and the two metal plates detach from each other.

There is a third type of sprinkler head that strictly speaking is not a valve. These fire sprinkler heads are the open type. An open type sprinkler head does not contain a temperature sensitive element or plug. This type of sprinkler head is associated with deluge fire sprinkler systems. The purpose of these sprinkler head is to distribute water according to the water spray pattern of the head.

Fire Sprinkler Head Components

Fire Sprinkler Head Components

The glass bulb for an automatic fire sprinkler head is the active component that breaks when it reaches its nominal operating temperature.  There are generally two sizes of the glass bulb;

  • 3mm - Quick Response
  • 5mm - Standard Response

Due to thermal conductivity, the thinner (3mm) quick response will respond more quickly to a rise in temperature and operate more quickly than the 5mm standard response.

Sprinkler Head Operating Temperatures

The glass bulb or fusible link in an automatic fire sprinkler system is calibrated to operate at a designated temperature. Sprinkler heads are selected and installed taking into consideration the use, location and typical ambient operating temperatures.

The Australian Standard AS 2118.1 states that the temperature rating chosen shall be not less than 30ºC above the highest anticipated temperature conditions except under specific conditions;

  1. Under glazing, translucent plastics and uninsulated metal roofs, in unventilated concealed spaces and show windows on external walls, and in other locations that are directly exposed to the sun, it may be necessary to install sprinklers with a temperature rating between 79°C and 100°C.
  2. n High Hazard systems protecting high piled storage, sprinklers having a nominal temperature rating of 141°C shall be used at the roof or ceiling roof or ceiling, except where in the case of special sprinklers, the listing, manufacturers published data sheets and codes and standards referenced herein, recommend an alternative temperature rating.
  3. Where high-temperature sprinklers are installed within drying ovens or hoods over papermaking machines and the like (see Clauses 5.6.14 and 5.7.6), sprinklers at the ceiling or roof immediately over and to a distance of 3 m beyond the boundary of such structures shall be of the same temperature rating, subject to a maximum of 141°C.
Sprinkler Head Operating Temperatures
ºC ºF Colour
Automatic Fire Sprinkler Bulb Operating Temperatures
57ºC 135ºF Orange
68ºC 155ºF Red
79ºC 175ºF Yellow
93ºC 200ºF Green
141ºC 286ºF Blue
182ºC 360ºF Purple
260ºC 500ºF Black


Firewize policy is one of continuous improvement, details of products, procedures or methods described within this document are subject to change without notice. All information provided here is believed to be correct at the time of publication.

Every effort has been made to ensure the accuracy of information which is provided in good faith nothing contained herein is intended to incorporate any representation or warranty, either express or implied or to form the basis of any legal relations between the parties hereto, additional to or in lieu of such as may be applicable to a contract of sale or purchase.

This guide is provided solely on the basis that users will be responsible for making their own assessment of the matters discussed herein and are advised to verify all relevant representations, statements and information. Firewize does not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.

👋🏼 Howdy, got a suggestion? Please complete this 30 second survey to let us know what you think of our website.