Sprinkler Colour Code and Temperature Ratings: NFPA 13 Chart

Look closely at a sprinkler head and you'll see one of two thermal mechanisms: a colored glass bulb or a fusible link between two metal plates. This thermal element determines when the sprinkler activates — wrong temperature selection degrades fire performance and increases maintenance costs. NFPA 13's thermal classification system exists to make this choice simple in the field.

Glass Bulb Color Codes

The liquid color inside the glass bulb tells you the sprinkler's operating temperature. The code per NFPA 13-2025 Table 7.2.4.1(a):

European catalogues carry a few intermediate steps this table does not — 100°C and 121°C, and a mauve 163°C alongside the 182°C — together with typical spaces for each rating; those are listed in our complete sprinkler temperature and colour code table.

NFPA 13 ties each colour to a classification, so blue and purple bulbs stand for a range, not a single value. TS EN 12845+A2 Table 37b lists the nominal ratings one by one: blue 121 and 141°C, mauve 163 and 182°C, green 93 and 100°C. On site the exact rating is read from the marking on the sprinkler; the colour only tells you the group.

Response Time Index (RTI)

How fast a sprinkler responds is a separate measure: Response Time Index (RTI). Unit: (m·s)^0.5. Lower RTI = faster response.

The advantage of quick response is clear: it catches the fire in its early stage and reduces the number of people exposed to smoke and heat. On the other hand, its higher sensitivity makes it more reactive to hot air collecting under the ceiling in summer or to temporary heat sources; in the field a slightly higher false-activation risk is seen than with standard types. NFPA 13-2025 9.4.3.1 requires sprinklers in light hazard occupancies to be quick-response (or residential, quick-response CMSA or ESFR).

Temperature Selection Logic

NFPA 13-2025 Table 7.2.4.1 gives the maximum ceiling temperature permitted for each class: 38°C for a 57°C orange bulb and 49°C for a 68°C red bulb (Ordinary), 66°C for Intermediate (79-107°C), 107°C for High (121-149°C). EN 12845 14.4 states a simpler rule: the operating temperature should be close to, but at least 30°C (54°F) above, the highest anticipated ambient temperature. This margin minimizes false discharge risk. Examples:

• Office (ceiling 27°C): 68°C red bulb   (27 + 30 = 57 < 68 ✓)
• Attic (summer 48°C): 93°C green   (48 + 30 = 78 < 93 ✓)
• Boiler room (steady 80°C): 141°C blue   (80 + 30 = 110 < 141 ✓)
• Industrial oven vicinity (100°C): 141°C blue   (100 + 30 = 130 < 141 ✓; the NFPA High class ceiling limit is 107°C). A 182°C purple rating would needlessly delay response.

Temperature Selection in Turkey

Turkish attic temperatures can reach 55-60°C in summer. Putting a standard 68°C red bulb in such an attic both violates NFPA 13 Table 7.2.4.1(a) (maximum ceiling temperature 49°C for that bulb) and sharply increases summer accidental activation risk. In Turkey's southern cities, attic sprinklers need the Intermediate class (79°C yellow or 93°C green), and NFPA 13-2025 9.4.2.5(5) requires attic sprinklers (peaked or flat) to be of the Intermediate class in any case; with the ambient + 30°C rule, 93°C green is the right choice for 55-60°C.

Fusible Link

An older sprinkler type but still current. Instead of a glass bulb, two metal pieces held by low-melting-point solder. As heat rises, the solder melts, the pieces separate, and the sprinkler opens. Advantage: more tolerant of mechanical shock than a glass bulb. Disadvantage: it cannot carry high pressure loads at low temperatures with the same confidence.

The colour code moves with it. On a fusible link sprinkler there is no coloured liquid to read, so the code sits on the yoke arms instead, and each colour stands for a temperature range rather than one nominal value. The ranges below follow NFPA 13-2025 Table 7.2.4.1(b) and our sprinkler temperature and colour code table:

NFPA 13 and EN 12845: Same Colours, Different Language

The sprinkler itself does not change when you cross standards, and the colour codes overlap. What changes is the vocabulary used to describe a rating, which is where drawings and handover files go wrong on multi-standard projects.

• NFPA 13 names groups. A specification written to NFPA calls out Ordinary, Intermediate, High, Extra High or Very Extra High, and the glass bulb table above shows which colour falls in which group. Per our temperature and colour code comparison, the full NFPA group bands run Ordinary 57–77 °C, Intermediate 79–107 °C, High 121–149 °C, Extra High 163–191 °C, Very Extra High 204–246 °C and Ultra High 260–302 °C.
• EN 12845 states numbers. The European standard works with the nominal value — 68 °C, 93 °C, 141 °C — and does not use the group names at all. Its selection rule is the same one applied throughout this article: at least 30 °C above the highest anticipated ambient temperature, and no higher than necessary, because an unnecessarily high rating lengthens the response time and lets a small fire grow.
• Do not mix the two languages on one project. Labels, drawings, the equipment schedule and the handover file should all speak either group names or numerical values. A schedule that says "Extra High" next to a bulb marked 182 °C is readable to the designer and ambiguous to everyone who maintains the system afterwards.

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Three Common Mistakes

1. Single temperature throughout the building: When the same 68°C bulb is fitted in the office, kitchen and boiler room, false activation in the kitchen during the summer months is only a matter of time.
2. Low temperature in holiday properties: In a resort hotel on the southern coast, moving from 68°C to a 79°C yellow bulb is much sounder.
3. Ignoring hot locations: Attics, skylights exposed to direct sun and enclosed show windows need the Intermediate class, commercial cooking equipment the High or Extra High class (NFPA 13-2025 9.4.2.5(4)-(7)).
4. Confusing body colour with bulb colour: The sprinkler body finish (chrome, brass, white epoxy) and the glass bulb colour are entirely separate things; mixing them up causes serious errors in counts and schedules.

Conclusion

Sprinkler thermal characteristics look simple, but they lie at the root of about 70% of false discharge events; a wrong rating either delays operation or invites false discharge. Reading the space correctly, measuring the maximum ceiling temperature, and applying the ceiling temperature limits of NFPA 13 Table 7.2.4.1 together with the EN 12845 ambient + 30°C rule is critical. If 4-5 different temperature classes are used in a building, the spare cabinet must cover this diversity.