The LWF Blog
Fire Safety Engineering for Design – Sprinkler Heads – Part 228
March 31, 2025 10:16 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 227, LWF discussed high hazard risks. In part 228, we will talk about sprinkler heads.
The choice of sprinkler head for a sprinkler system is crucially important. The head is usually responsible for detecting a fire, as well as the release of water spray in appropriate quantities and spray characteristics to suppress the fire.
Many sprinkler heads have a heat-sensitive element – a glass bulb or fusible metallic link (or a combination of the two), which seal the head until it is activated by the heat from a fire. It is not always the case, however, as sometimes the sprinkler design calls for both detection and water-release to be activated in other ways. Such sprinkler heads do not have a heat-sensitive element and are known as ‘open’ sprinklers. The water supply for this type of system is activated by other means, such as a ‘deluge’ valve, which may be activated electrically or pneumatically.
Sprinklers with a heat-sensitive element are colour-coded relative to the operating temperature of the glass bulb or fusible link.
The operating temperature of sprinkler heads is normally not less than 30 °C above the highest expected ambient temperature. For most conditions, this suggests a sprinkler head rating of 68 °C and the bulb required will be red.
BS EN 12845 contains tables laying out the relevant colour codes for sprinklers, as follows:
| Glass bulb sprinklers | Fusible link sprinklers | ||
| Nominal operating temperature in °C | Liquid colour code | Nominal operating temperature within range/ °C | Yoke arms colour code |
| 57 | Orange | 57-77 | Uncoloured |
| 68 | Red | 80 – 107 | White |
| 79 | Yellow | 121 – 149 | Blue |
| 93 | Green | 163 – 191 | Red |
| 100 | Green | 204 – 246 | Green |
| 141 | Blue | 320-343 | Black |
| 163 | Mauve | ||
| 182 | Mauve | ||
| 204 | Black | ||
| 227 | Black | ||
| 260 | Black | ||
| 286 | Black | ||
| 343 | Black | ||
Three sizes of sprinkler are commonly available to suit the various applications, i.e. nominal orifice sizes of 10, 15 and 20 mm. It is usual to see 10 mm sprinklers used on light hazard installations, 15 mm on ordinary hazard installations and 20 mm on high hazard installations. ESFR sprinklers may have sizes of 20 mm or more, however the K-factors (coefficient of discharge) is key and for storage protection, larger is more effective.
In part 229 of LWF’s series on fire engineering we will resume talking about sprinkler heads with the five key attributes of a sprinkler head that are important to sprinkler design. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.