A sprinkler's temperature rating is read from its colour before its label. But red in a glass bulb means 68 °C, while red on a fusible link means 163 to 191 °C. This table keeps the two systems in separate columns.
The selection rule: ambient plus 30 °C
EN 12845 sums it up in one sentence: the rating must be at least 30 °C above the highest anticipated ambient temperature, but not raised further than necessary. Going too high lengthens the response time and lets a small fire grow.
Glass bulb colour code
| Nominal temperature | Bulb liquid colour | Typical space |
|---|---|---|
| 57 °C | Orange | Cooled spaces, ambient below 27 °C |
| 68 °C | Red | Offices, hotel rooms, air-conditioned retail (the most common) |
| 79 °C | Yellow | Unconditioned corridors, warm climates |
| 93 °C | Green | Under steel roofs, glazed roofs, boiler rooms |
| 100 °C | Green | Unventilated ceiling voids |
| 121 °C | Blue | Around hot processes |
| 141 °C | Blue | Near flues, hot zones of boiler rooms |
| 163 °C | Mauve | Around drying ovens |
| 182 °C | Mauve | Paint and drying ovens |
| 204 / 227 / 260 / 286 / 343 °C | Black | Around industrial furnaces |
Fusible link colour code (yoke arms)
On a fusible link sprinkler the colour is not in a bulb but on the yoke arms, and it indicates a range rather than a single temperature.
| Temperature range | Arm colour |
|---|---|
| 57 – 77 °C | Uncoloured |
| 80 – 107 °C | White |
| 121 – 149 °C | Blue |
| 163 – 191 °C | Red |
| 204 – 246 °C | Green |
| 260 – 302 °C | Orange |
| 320 – 343 °C | Black |
The most dangerous confusion at inspection: red. It is 68 °C in a glass bulb and 163 to 191 °C on a fusible link. Where both types are mixed in one facility, correct reading is impossible without a labelling procedure.
Selection by space
| Space | Expected max ambient | Rating to select | Colour |
|---|---|---|---|
| Office, hotel room, air-conditioned shop | 30–35 °C | 68 °C | Red |
| Unconditioned school or mall corridor | 40 °C | 68–79 °C | Red / Yellow |
| Steel-roofed warehouse, summer roof void | 55–65 °C | 93 °C | Green |
| Glazed roof, atrium | 60–70 °C | 93–100 °C | Green |
| Boiler room, routine | 50–60 °C | 93 °C | Green |
| Boiler room, near the flue | 90–110 °C | 141 °C | Blue |
| Near a paint or drying oven | 140–150 °C | 182 °C | Mauve |
| Around an industrial furnace | 180–200 °C | 227 °C | Black |
Two stages in a concealed sprinkler
A concealed sprinkler works in two stages: first the cover plate releases at a typical 57 °C solder, then the main glass bulb (usually 68 or 74 °C) operates. The plate rating must always sit below the main bulb. Painting the plate on site insulates the solder and the sprinkler never opens — the most common field error there is.
One step up on a dry system
On a dry pipe system the water delay can run to 60 seconds. The field reflex is to go one step up: where 68 °C suits a wet system, 79 or 93 °C is preferred on a dry one. That reduces the risk of early activation from a neighbouring fire and lessens the burden of drying out a main once it has operated.
Comparison with NFPA 13
The physical sprinkler is the same and the colour codes overlap. The difference is terminology: NFPA uses group names (Ordinary 57–77 °C, Intermediate 79–107 °C, High 121–149 °C, Extra High 163–191 °C, Very Extra High 204–246 °C, Ultra High 260–302 °C); EN 12845 works with numerical values. Do not mix the two languages on one project; labels, drawings and the handover file should carry the same terminology.
Frequently Asked Questions
What temperature is a red sprinkler?
68 °C in a glass bulb. But on a fusible link sprinkler, red yoke arms indicate the 163 to 191 °C range. Where both types are mixed in one facility, misreading is inevitable.
How is the rating selected?
At least 30 °C above the highest anticipated ambient, but not higher than necessary. Typically 68 or 74 °C in a temperate climate; 93 to 100 °C under unventilated ceiling voids and glazed roofs.
Why is 93 °C used under a steel roof?
Roof void temperatures reach 55 to 65 °C on a summer afternoon. A 68 °C rating does not give the 30 °C margin there; a heat wave brings a false activation and discharges the system.
Can a concealed cover plate be painted?
No. An extra paint layer insulates the 57 °C solder, the plate does not fall and the sprinkler never opens. Order factory-finished plates instead.
SprinkCalc — Fire Sprinkler Design Across Three Standards
SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.
Download SprinkCalc on the App Store
MEP Calc — 86+ Engineering Calculators
MEP Calc bundles 86+ engineering modules in one iOS app: 21 fire calculations plus heating, cooling, HVAC, plumbing, steam and natural gas.
Download MEP Calc on the App StoreBS EN 12845:2015+A1:2019 colour code table and sprinkler type clauses. EN 12259-1 (sprinkler component standard). NFPA 13 (2025) temperature rating chapter. The manufacturer's catalogue governs.