The colour of the liquid in a fire sprinkler's glass bulb shows the temperature at which that sprinkler opens. An orange bulb operates at about 57°C, red at 68°C, yellow at 79°C and green at 93°C. Higher ratings use blue, purple and black bulbs for hot spaces such as plant rooms. NFPA 13 links each colour to a temperature classification and a maximum ceiling temperature.

Reading the colour correctly helps owners spot wrong replacements and heads installed in the wrong place. This guide explains what each bulb colour means and how NFPA 13 groups the ratings. It covers which ratings suit typical UAE ceilings and roof spaces. It also explains when a sprinkler head must be replaced under NFPA 25.

What do sprinkler bulb colours mean?

Each sprinkler bulb is a sealed glass tube filled with a coloured liquid and a small air bubble. When fire heats the liquid, it expands until the glass shatters and the sprinkler opens. The liquid colour identifies the temperature at which that bulb is designed to break.

The colour code lets inspectors confirm ratings without removing heads or reading tiny markings. It also helps technicians choose the correct spare during a replacement. On concealed or factory-painted sprinklers, the rating is usually stamped on the deflector, not shown by a bulb.

Quick Answer

A sprinkler bulb's liquid colour shows the temperature at which the glass bursts and the sprinkler opens. Inspectors can use the colour to confirm each head's rating without removing it.

What temperature is each sprinkler bulb colour?

Orange glass bulbs operate at about 57°C, and red bulbs at about 68°C. Yellow bulbs are rated about 79°C, green about 93°C and blue about 141°C. Purple bulbs are rated about 182°C, while black bulbs cover ratings of 204°C and above.

NFPA 13 groups these ratings into classes, starting with ordinary at 57 to 77°C with orange or red bulbs. Intermediate covers 79 to 107°C with yellow or green bulbs, and high covers 121 to 149°C with blue. Extra high uses purple, and the very hottest classes use black bulbs.

Quick Answer

An orange sprinkler bulb is about 57°C, red 68°C, yellow 79°C, green 93°C and blue 141°C. Purple bulbs are about 182°C, and black bulbs cover ratings of 204°C and above.

Which sprinkler temperature rating suits UAE buildings?

NFPA 13 matches each temperature class to the highest temperature normally expected at the ceiling. Ordinary rated sprinklers suit ceilings up to 38°C, and intermediate ratings suit ceilings up to 66°C. High ratings suit hotter ceilings reaching up to 107°C.

Most air-conditioned offices, apartments and shops in the UAE use ordinary red or orange bulbs. Unventilated roof voids, plant rooms, kitchens near cooking equipment and spaces under skylights may need intermediate or high ratings. Summer heat in Dubai makes checking actual ceiling temperatures in these spaces essential rather than optional.

Quick Answer

Under NFPA 13, ordinary ratings suit ceilings up to 38°C, intermediate up to 66°C and high up to 107°C. Hot UAE roof voids and plant rooms may need higher ratings.

Can you replace a sprinkler with a different bulb colour?

A replacement sprinkler should normally match the original's temperature rating, response type, orifice size and deflector style. Fitting a different colour changes when the head operates and can upset the design. NFPA 25 requires replacements to match the characteristics of the sprinklers being replaced.

A different rating is acceptable only when a designer confirms the change suits the space and the system. For example, a room converted into a hot plant area may need higher rated heads. Our sprinkler head replacement service explains how matching spares are selected and recorded.

Quick Answer

Replacement sprinklers should match the original temperature rating, response type, orifice size and deflector style. Changing the bulb colour needs a designer's confirmation that the new rating suits the space.

When should a sprinkler bulb be replaced?

Replace a sprinkler when its bulb is cracked, leaking, empty or missing its air bubble. Replace it when damaged, or when corrosion, loading or site-applied paint affects its performance. Any sprinkler that has operated must also be replaced, never reused or reset.

NFPA 25 also sets age-based testing, requiring representative samples of standard sprinklers after 50 years in service. Under the 2023 edition, most fast response sprinkler heads need testing or replacement at 25 years. Our guide to fire sprinkler system maintenance explains where these checks fit in routine inspections.

Quick Answer

Replace sprinklers with damaged bulbs or frames, or corrosion, loading or site paint affecting performance. NFPA 25 samples standard heads at 50 years and most fast response heads at 25.

Frequently Asked Questions

What is the most common sprinkler bulb colour?
Red bulbs rated about 68°C are among the most common in air-conditioned offices, shops and homes. Orange bulbs rated about 57°C are also widely used where ceiling temperatures stay low.
What does a green sprinkler bulb mean?
A green sprinkler bulb indicates an intermediate temperature rating of about 93°C. It is used where ceiling temperatures run higher than normal, such as some plant rooms or equipment spaces.
What does a blue sprinkler bulb mean?
A blue sprinkler bulb indicates a high temperature rating of about 141°C. It suits hot areas such as boiler rooms, spaces near ovens or unventilated voids under a metal roof.
Why do some sprinklers have thinner bulbs?
Thinner bulbs, often about 3 mm, usually indicate fast response sprinklers that heat up and operate more quickly. The sprinkler's listing, not bulb size alone, confirms its actual response classification.
Do sprinkler frame colours matter?
Yes, fusible link sprinklers and some bulb sprinklers also use frame colour to show the temperature class. Under NFPA 13, intermediate frames are white, high blue and extra high red.
Can I paint over a sprinkler head?
No, paint can coat the heat-sensitive element, insulating it and delaying operation during a fire. Under NFPA 25, site-painted sprinklers generally need assessment and replacement, not cleaning by building staff.
What happens if the wrong temperature sprinkler is installed?
A rating that is too low may operate accidentally in a hot space, causing water damage. A rating that is too high may open late and let a fire grow.
How long do fire sprinklers last?
Many sprinklers stay in service for decades if they are kept clean and undamaged. NFPA 25 requires sample testing of standard sprinklers after 50 years to confirm they still work.
Do sprinkler bulbs break in hot weather?
Correctly rated bulbs should not break from normal summer heat inside an air-conditioned building. Bulbs installed in unexpectedly hot roof spaces, or rated too low, can operate without any fire.
Who can replace sprinkler heads in Dubai?
Sprinkler heads should be replaced by a fire contractor approved by Dubai Civil Defence. The contractor should record each replacement's temperature rating, model, location and date in the maintenance file.

Main Takeaways

Sprinkler bulb colour shows operating temperature: orange about 57°C, red 68°C, yellow 79°C, green 93°C and blue 141°C. NFPA 13 matches ordinary ratings to ceilings up to 38°C and intermediate ratings to 66°C. Replacements should match the original temperature rating, response, orifice and deflector. Damaged, operated or site-painted sprinklers, or those affected by corrosion, need replacement by an approved contractor.

Checking your sprinkler colours

Bulb colours give building owners a quick way to check that sprinklers suit their spaces. Look for mismatched colours in the same room, which often point to careless past replacements. Check hot areas such as roof voids and plant rooms, where ordinary heads may be wrong. Record any concerns and photographs before your next maintenance visit so they are checked.

If you find damaged bulbs, painted heads or unexpected colours, arrange an inspection rather than guessing. A qualified contractor can confirm each rating against the approved design drawings and replace faulty heads correctly. QSERV inspects and maintains sprinkler systems for commercial and residential buildings across the UAE. Contact us to book a sprinkler condition survey and a written defect report.

Sources & References

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