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 14.4 sums it up in one sentence: the rating must be no lower than 30 °C above the highest anticipated ambient temperature and close to that value, so not raised further than necessary. Unventilated concealed spaces, skylights and glazed roofs may need 93 or 100 °C; under normal conditions in temperate climates 68 or 74 °C is suitable (14.4 Note 1). Going too high lengthens the response time and lets a small fire grow.
Glass bulb colour code
The table is EN 12845 Table 37b (colours per EN 12259-1); NFPA 13-2025 Table 7.2.4.1(a) uses the same colours, with the differences listed in the NFPA section below.
| 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 | 79 °C (68 °C only if the ambient stays at or below 38 °C) | Yellow |
| Steel-roofed warehouse, summer roof void | 55–65 °C | 93 °C (100 °C if the ambient exceeds 63 °C) | Green |
| Glazed roof, atrium | 60–70 °C | 93 °C; 100 °C if the ambient exceeds 63 °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 (260 °C if the ambient exceeds 197 °C) | Black |
Every row has been checked against the EN 12845 14.4 rule: the rating may not be lower than the highest anticipated ambient plus 30 °C.
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. Under NFPA 13-2025 7.2.5.2 and 7.2.5.3.1, sprinklers and concealed cover plates may be painted or given ornamental finishes only by the manufacturer.
One step up on a dry system
On a dry pipe system the water delay can run to 60 seconds for OH and HH and 90 seconds for LH (EN 12845 Table 18). 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. EN 12845 14.4, however, asks for a rating close to the required value, so stepping up is a design decision for the actual conditions, not a requirement of the standard.
Comparison with NFPA 13
For the NFPA side of the picture — the group names set against the °F values, the Response Time Index bands that decide how fast a head reacts, and the +30 °C rule worked through room by room — see sprinkler temperature ratings and colour codes under NFPA 13.
The colour codes largely overlap but are not identical. The differences between NFPA 13-2025 Table 7.2.4.1(a) and (b) and EN 12845 Table 37b:
- Fusible link, lowest range: NFPA says “uncolored or black” for 57–77 °C; EN 12845 says “uncoloured” only.
- Second range: NFPA 79–107 °C, EN 12845 80–107 °C (white in both).
- Highest range: at 343 °C the NFPA fusible link is orange; in EN 12845 the 320–343 °C range is black.
- Glass bulb: NFPA gives 121–149 °C and 163–191 °C as ranges (blue, purple); EN 12845 gives single values such as 121 and 141 °C (blue) and 163 and 182 °C (mauve).
- Selection rule: EN 12845 14.4 says “ambient plus at least 30 °C”. The NFPA table instead gives the maximum ceiling temperature for each rating: 57 °C → 38 °C, 68 °C → 49 °C, 79 and 93 °C → 66 °C, 121–149 °C → 107 °C, 163–191 °C → 149 °C. The NFPA margin is therefore 13–27 °C for the 57–93 °C ratings, and the two standards can lead to different ratings in the same space.
The terminology differs as well: NFPA uses temperature classifications (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 and 343 °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?
Under EN 12845 14.4, no lower than 30 °C above the highest anticipated ambient, and close to that value. 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. 93 °C is enough up to a 63 °C ambient; above that, 100 °C is needed.
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. Under NFPA 13-2025 7.2.5.3.1 only the manufacturer may finish the plate; order factory-finished plates instead.
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Download MEP Calc on the App StoreEN 12845:2015+A2:2026 14.4, Table 37b and Table 18. EN 12259-1 (sprinkler component standard). NFPA 13 (2025) Table 7.2.4.1(a) and (b), 7.2.5. The manufacturer's catalogue governs.