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What do pipe colour codes mean?
Short answer
Pipe colours tell you what is inside, but the UK and US systems ask different questions. BS 1710 gives each broad class of contents a basic colour — green for water, silver-grey for steam, brown for oils, yellow ochre for gases, violet for acids and alkalis, light blue for air — and adds safety colours for hazards; ASME A13.1 colours the label by the hazard if the contents escape, such as yellow for flammables, orange for toxic or corrosive fluids and red for fire-fighting. In both, the text legend and flow arrow carry the real information.
At a glance
UK
BS 1710:2014 — basic identification colour bands by content
US
ASME A13.1-2026 — label colours grouped by hazard
Common ground
Red for fire-fighting; green for water
Biggest difference
BS 1710 codes the substance, A13.1 codes the hazard
The 3 standards
BS 1710: Specification for identification of pipelines and services
Issued by
BSI
Edition
2014 (2014)
Status
Current
Applies to
United Kingdom
Identifies pipe contents with a basic identification colour band, adding safety colours and text where the contents are hazardous.
Colour meanings in BS 1710
Colour
Meaning
Paired with
Green
Water
—
Silver-grey
Steam
—
Brown
Oils
—
Yellow ochre
Gases (other than air)
—
Violet
Acids and alkalis
—
Light blue
Air
—
Black
Other liquids
—
Orange
Electrical services and ventilation ducts
—
Red (safety colour)
Fire-fighting services
—
Status checked 29 September 2026. Summary only, from secondary sources. BS 1710 is sold by BSI; its colour references and banding layouts are not reproduced.
ASME A13.1: Scheme for the Identification of Piping Systems
Issued by
American Society of Mechanical Engineers
Edition
2026 (2026)
Status
Current
Applies to
United States
Identifies above-ground pipe contents with a coloured label, legend and flow arrow, grouped by the hazard the contents pose if released.
Colour meanings in ASME A13.1
Colour
Meaning
Paired with
Red
Fire-quenching fluids
White text
Orange
Toxic and corrosive fluids
—
Yellow
Flammable fluids and oxidisers
Black text
Brown
Combustible fluids
White text
Green
Water
White text
Blue
Compressed air
White text
Purple, white, grey, black
Reserved for user-defined fluids
—
Status checked 29 September 2026. Summary only. ASME sells the standard; the edition is confirmed from ASME's catalogue and the colour groups from secondary sources describing the 2007 and later editions. Check the 2026 text for changes.
ASME A13.1-2023: Scheme for the Identification of Piping Systems (2023 edition)
Issued by
American Society of Mechanical Engineers
Edition
2023 (2023)
Status
Superseded by asme-a13-1
Applies to
United States
The previous edition, still on sale from ASME and still referenced by some site specifications.
Colour meanings in ASME A13.1-2023
Colour
Meaning
Paired with
Same colour groups as the current edition
Hazard-based colour groups for pipe labels
—
Status checked 29 September 2026. Kept for the audit trail: a specification that names the 2023 edition is not automatically updated by the 2026 one.
Summarised in Colourwise’s own words; not the text of any standard and not compliance advice. Always work from the current edition obtained from the issuing body.
Coding the substance versus coding the hazard
BS 1710 starts from the question 'what kind of fluid is this?' Water is green whatever its temperature or use; steam is silver-grey; oils are brown; gases are yellow ochre. A safety colour and text are then added where needed, so a pipe carrying a hazardous gas shows both the gas colour and a warning band. ASME A13.1 starts from 'what happens if it leaks?' so a flammable gas and a flammable liquid share a yellow label, and anything toxic or corrosive shares orange. Neither approach is better in the abstract: the substance approach helps maintenance staff trace services, the hazard approach helps someone decide how fast to leave. They produce different colours for the same pipe, which matters on multinational sites.
Bands, labels and legends
In the British scheme colour is usually applied as bands at intervals, near valves, junctions and wall penetrations, with the pipe itself left in its natural or painted finish; some installations paint the whole pipe. The American scheme uses labels with a coloured background, a legend naming the contents, and an arrow for direction of flow, placed at similar points. Both assume people will read the text: colour gets attention and narrows the possibilities, the legend says exactly what is inside. A colour band alone on a pipe that could carry two different gases is not identification.
Orange means electrical services and ventilation in BS 1710 but toxic or corrosive contents under ASME A13.1 — the clearest example of the same colour meaning different things on either side of the Atlantic.
Editions and user-defined colours
ASME A13.1 has been revised several times, with editions in 2007, 2015, 2020, 2023 and 2026. The 2007 revision replaced a simpler four-colour scheme with the hazard groups used today and set aside four colours — purple, white, grey and black, each with a defined text colour — for users to assign to fluids the standard does not cover. BS 1710's current edition is from 2014. Sites often add their own conventions, such as a colour for chilled water or a stripe for recycled water, which is allowed where the standard leaves room but means a site key is essential. Medical gas pipelines in hospitals follow their own separate schemes.
Colour matching on pipes
BS 1710 historically referenced colours in the BS 4800 building colour system, and US labels are printed to safety colour specifications; neither is meant for eyeballing against a swatch. Paint on pipes yellows, chalks and collects dirt, and heat can darken it. In plant rooms lit by cool-white fluorescent or older discharge lamps, brown and orange, or violet and blue, can be hard to separate. The practical rule is that colour is a first filter and the legend is the identification. This page explains the codes; it is not a substitute for the standard or for a site's own identification schedule.
The data
The same contents under the UK and US schemes
Contents
BS 1710 basic colour
ASME A13.1 label colour
Drinking or cooling water
Green
Green
Compressed air
Light blue
Blue
Fire sprinkler water
Green with red safety colour
Red
Lubricating oil
Brown
Brown (combustible)
Flammable gas
Yellow ochre with warning band
Yellow
Acid or alkali
Violet
Orange (corrosive)
Electrical services / ventilation
Orange
Not covered (electrical conduit excluded)
Colourwise analysis based on Pipe marking (Wikipedia); ASME A13.1 — Scheme for the Identification of Piping Systems. Colourwise's comparison of the two schemes' published colour groups. Real installations add legends, flow arrows and site-specific colours.
What goes wrong, and what to do
A US contractor labels a UK ventilation duct as hazardous
Why: Orange means ventilation and electrical services in BS 1710 but toxic or corrosive contents under ASME A13.1.
Fix: State which standard a site uses in its identification schedule, and never rely on colour without the legend.
Two gas lines share the same yellow ochre band
Why: The basic colour identifies the class (gas), not the specific gas.
Fix: Add the gas name to the legend at each marking point, as both standards expect.
How to check it yourself
Find out whether the site follows BS 1710, ASME A13.1 or its own schedule.
Read the legend and flow arrow at the nearest valve or junction.
Treat colour as a first filter only; confirm hazardous contents from drawings or the site key.
What the evidence says
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
ASME A13.1, the Scheme for the Identification of Piping Systems, is listed by ASME in 2007, 2015, 2020, 2023 and 2026 editions, the 2026 edition being current.
BS 1710 basic identification colours assign green to water, silver-grey to steam, brown to oils, yellow ochre to gases, violet to acids and alkalis, light blue to air, black to other liquids and orange to electrical services and ventilation, with red as the safety colour for fire-fighting.
Caveat: Summarised from a secondary source; confirm against the purchased standard.
Since its 2007 revision ASME A13.1 groups fluids by hazard: yellow for flammables and oxidisers, brown for combustibles, orange for toxic and corrosive fluids, green for water, blue for compressed air, red for fire-fighting, and purple, white, grey and black for user-defined fluids.
Caveat: Summarised from a secondary source and not yet checked against the standard itself; confirm with the standard before relying on it.
Green in both BS 1710 and ASME A13.1 for ordinary water. Fire-fighting water is marked with red, and sites often add their own variations for hot, chilled or recycled water.
Why is orange used differently for pipes in the UK and US?
BS 1710 assigns orange to electrical services and ventilation, while ASME A13.1 uses orange for toxic and corrosive contents. The schemes were developed separately around different questions.
Which ASME A13.1 edition is current?
ASME lists a 2026 edition as the newest, following editions in 2023, 2020, 2015 and 2007. A contract may still name an older edition, which then governs that contract.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.