Pipe Marker Requirements: ASME A13.1 Decoded (2026 Guide)

Does OSHA require pipes to be labeled?

Short answer: Not as a general rule. Federal OSHA has no general-industry pipe-marking standard. It incorporates ANSI A13.1–1956 by reference in a short list of narrow places — welding gas piping, pulp and paper mills, and textile machinery — and OSHA's own incorporation table at 1910.6(e)(6) names exactly those three. Everywhere else, pipe marking is driven by the current ASME A13.1–2023 consensus standard, by HazCom, by fire and building codes, and by the General Duty Clause. The edition gap between what OSHA cites and what industry buys is 67 years.

Published August 27, 2026

Pipe marking is the single most misdescribed duty in facility identification. Vendor pages routinely assert that "OSHA requires pipe labeling to ANSI A13.1," which collapses two separate things: a consensus standard that most facilities do follow, and a federal regulation that almost never compels it. Getting the distinction right matters at the moment a facility has to justify a marking scheme — to an insurer, to a fire marshal, to a contractor's safety plan review, or to an OSHA compliance officer who has arrived for something else entirely.

This guide is a decode reference. It gives the two tables a specifier actually needs — the colour scheme and the size schedule — then locates the legal duty precisely, section by section. For the wider signage picture see our OSHA safety sign requirements hub, and for the chemical-communication layer that sits alongside pipe markers see GHS pictograms and HazCom labels.

Why this matters.
An unmarked pipe is a decision made by whoever cuts into it. Maintenance crews, contractors and emergency responders read pipe contents off the marker or off nothing at all — and a line that carries steam, ammonia, natural gas or a caustic reads identically to a chilled-water line from six feet away. Because there is no general federal pipe-marking rule, a facility that gets this wrong is not cited under a marking standard; it is cited under Section 5(a)(1), the General Duty Clause, after someone is hurt. The marking scheme is cheap. The absence of one is only ever priced after the incident.

Where the pipe-marking duty actually comes from

Federal OSHA incorporates the 1956 edition of ANSI A13.1 by reference. Incorporation by reference means the text of the consensus standard becomes enforceable federal law — but only inside the standards that name it, and only in the edition named. OSHA's incorporation-by-reference table at 29 CFR 1910.6(e)(6) lists the sections where A13.1–1956 applies, and the list is short.

Two consequences follow, and both are counter-intuitive enough that they are worth stating plainly.

First: if a facility is not a paper mill, a textile plant, a welding-gas installation or a flammable-liquid processing plant, no federal standard tells it to mark its pipes at all. Hospitals, schools, food plants, data centres, breweries, warehouses and ordinary manufacturing have no federal pipe-marking rule. That is not a licence to leave pipes bare — state plan states, fire codes, mechanical codes, the ammonia refrigeration process-safety rules and the General Duty Clause all reach the same place from other directions — but the honest statement is that the compulsion comes from somewhere other than a marking standard.

Second: where OSHA does compel marking, it compels the 1956 edition. A13.1–1956 predates the modern colour scheme entirely. A facility that marks to the current ASME A13.1–2023 scheme is following better practice than the regulation demands, which is the correct thing to do, but a specifier should understand that the two documents are not the same document and that "meets ANSI A13.1" on a vendor page tells you nothing about which of them.

The ASME A13.1 colour scheme

A13.1 moved from ANSI to ASME stewardship, and the standard is properly cited today as ASME A13.1–2023. The 2007 edition rebuilt the colour scheme around fluid service — what the contents do to a person — replacing the older sort by inherent hazard level. The 2023 edition carries that scheme forward — six defined combinations plus four reserved for the user — having expanded the scope and definitions, clarified the colour designations, enhanced the legend guidance and added flow-direction graphics.

The four user-defined rows are the part specifiers get wrong. They are not spare colours to be used at will by whoever is holding the label printer. A13.1 makes them available on the condition that the facility defines them — in a written scheme, communicated through training. A purple marker that means reclaimed water in Building 2 and process brine in Building 4 is worse than no marker, because it teaches people that the colour carries information when it does not.

Reading the classification, not the fluid name

The scheme sorts by what the fluid does, not by what it is called. Anhydrous ammonia is a toxic and corrosive fluid, so it sits on orange — even though it is also flammable in the right concentration band. Oxygen is not flammable in the strict sense, but it is an oxidizer, which is why the classification names the yellow band "flammable and oxidizing fluids." When a fluid could plausibly land in two bands, A13.1 expects the more severe classification, with the additional hazard carried by supplementary wording on the marker rather than by inventing a colour.

The legacy scheme, and when you may keep it

Before the 2007 rebuild, A13.1 sorted pipe contents by inherent hazard rather than by fluid service. Materials inherently hazardous took a safety yellow field with black legend; materials of inherently low hazard took safety green with white legend; fire-quenching materials sat on red. A great many facilities in the United States are still labelled that way, and the labels are still on the pipe.

A13.1 addresses this directly and sensibly. An existing identification scheme can be treated as meeting the current requirements if the scheme is described in writing, or employees are trained to the operation and hazards of the piping systems. A facility already marked to the pre-2007 scheme may continue to extend it rather than being forced into a full re-label.

That provision is the single most useful sentence in A13.1 for a maintenance manager, and it is almost never quoted by vendors, because it removes the urgency from a re-labelling quote. The practical reading: consistency plus documentation beats edition currency. A building uniformly marked to the older scheme with a written legend posted in the mechanical room is in better shape than a building half-converted to the current scheme with no document at all.

Marker length and text height by pipe diameter

Size is set by the outside diameter of the pipe including any covering or insulation — not by nominal pipe size. This trips up specifiers on insulated chilled-water lines, where a 2-inch pipe inside 1.5 inches of insulation is a 5-inch outside diameter for marking purposes and jumps two rows in the table.

A note on the second row: the standard prints the metric value as 19 mm and the imperial as 0.7 in, and 19 mm is 0.748 in, so the two are not exact conversions of each other. Several vendor summaries resolve this by printing 0.75 in. If a specification has to survive a dispute, cite 19 mm — it is the value the table actually carries, and it is the larger of the two readings.

Pipes too small to carry a marker

A13.1 contemplates pipes below the smallest table row. On very small lines — instrument tubing, sample lines, small-bore drains — the practical answer is a permanently attached tag rather than a wrapped marker. The information duty does not disappear because the pipe is narrow; the delivery method changes.

What has to be on the marker besides the colour

Colour alone identifies a hazard class, not a fluid. A13.1 expects the marker to carry three things.

1. The legend. The name of the contents, spelled out well enough that a person who does not work in that building can read it. "STEAM 125 PSIG" beats "HPS." Abbreviations that live only in the plant's drawings do not belong on a marker that a fire crew may read at 3 a.m.
2. Directional arrows. Arrows show flow direction. Where flow can run either way, the standard expects arrows in both directions rather than a guess. Arrows are what make a marker useful during isolation — they tell the person at the valve which side of it goes dead.
3. Supplementary hazard information where it exists. Pressure, temperature and hazard wording ride on the marker. A line that will scald and a line that will freeze skin need that stated, because the colour band alone does not distinguish them.

Where markers go, and how far apart

Placement is where a well-specified marker set fails in practice: the labels get bought, then installed wherever the ladder happened to be. A13.1 asks for markers at the points where a person makes a decision about the pipe.

• Adjacent to every valve and flange. These are the points where the system is opened.
• Adjacent to every change of direction. A pipe that turns is a pipe a reader can lose track of.
• On both sides of wall, floor and ceiling penetrations. Each side is a different room with a different set of people in it.
• At intervals along straight runs sufficient for identification. The standard sets a functional test rather than a fixed dimension. In practice, specifying a maximum interval — many facilities write 25 or 50 feet into their own scheme, and shorten it in congested overhead racks — is what makes the requirement auditable.

Orientation follows the reader. Markers should be visible from the normal point of approach: below the centreline for pipe running above eye level, above the centreline for pipe running below eye level. A marker rotated onto the top of an overhead pipe has been installed but not delivered.

Where A13.1 stops and HazCom takes over

A13.1 identifies contents. It does not communicate chemical hazards in the sense the Hazard Communication Standard means, and OSHA's HazCom rule at 1910.1200 does not require labels on pipes — it imposes its container-labelling duty on containers, while still requiring that employees be informed of the hazards of chemicals in unlabelled pipes through the information and training provisions.

A13.1 bridges the two. Where piping connects to containers labelled under GHS, a corresponding label may be applied to the piping carrying at least the product name or identifier, the pictogram, the signal word, and the physical, health and environmental hazard statements. That is a genuinely useful option in a plant where the tank farm is GHS-labelled and the transfer lines were not.

The practical division of labour, for a written programme: the pipe marker answers what is in this line and which way is it going; the safety data sheet and the HazCom written programme answer what will it do to me and what do I do about it. Neither substitutes for the other, and an inspector who finds a well-marked pipe system and no HazCom programme has found two findings, not one.

Worked example: specifying markers for a mixed mechanical room

A distribution centre's mechanical room carries four services overhead: a 6-inch insulated chilled-water supply measuring 8.5 inches over the insulation, a 2-inch bare compressed-air header, a 1-inch natural-gas line to the rooftop units, and a 4-inch sprinkler main. The facility has no written marking scheme. Here is the sequence that produces a defensible one.

1. Classify each line by fluid service before pricing anything. Chilled water is other water, so safety green with white legend. Compressed air is its own class, so safety blue with white legend. Natural gas is a flammable fluid, so safety yellow with black legend. The sprinkler main is a fire-quenching fluid, so safety red with white legend.
2. Measure outside diameter including insulation, not nominal pipe size. The chilled-water line measures 8.5 inches over the insulation, which puts it in the 6.8-to-10-inch row: a 24-inch colour field with 2.5-inch letters, not the 12-inch marker its nominal 6-inch size would have suggested.
3. Size the remaining three from the table. The 2-inch air header falls in the 1.4-to-2.4-inch row: 8-inch field, 19 mm letters. The 1-inch gas line falls in the 0.7-to-1.3-inch row: 8-inch field, 0.5-inch letters. The 4-inch sprinkler main falls in the 2.5-to-6.7-inch row: 12-inch field, 1.3-inch letters.
4. Write the legends in plain language with the operating condition. "CHILLED WATER SUPPLY," "COMPRESSED AIR 110 PSIG," "NATURAL GAS," "SPRINKLER MAIN." Resist the site abbreviations; the audience includes people who have never been in the building.
5. Set arrow direction at each marker from the actual flow, verified at the pump or the meter. Where a line can reverse — a loop return, a bypass — specify bidirectional arrows rather than picking one.
6. Fix the placement schedule before ordering quantities. Count valves, flanges, direction changes and wall penetrations, then add straight-run markers at the interval the written scheme adopts. Quantity falls out of the count; ordering by guesswork always under-buys the congested runs.
7. Write the scheme down and post the legend. A one-page sheet naming each colour, each classification and any user-defined colours the site has adopted, posted in the mechanical room and included in new-hire and contractor orientation. This is what converts a set of labels into a compliant identification scheme, and it is the document that satisfies A13.1's provision for existing schemes.
8. Fold the scheme into the isolation procedures. Pipe markers and lockout/tagout are the same conversation at different moments: the marker tells the technician which line to isolate, the energy-control procedure tells them how. If the markers and the LOTO procedure name the lines differently, the markers lose.

Frequently asked questions about pipe marker requirements

Does OSHA require pipe markers in general industry?

No. There is no general-industry OSHA standard requiring pipes to be labelled, marked or coloured. OSHA incorporates ANSI A13.1–1956 in a narrow set of standards — welding gas piping at 1910.253(d)(4)(ii), pulp and paper mills at 1910.261(a)(3), and textiles at 1910.262(c)(7) — and imposes a separate piping-identification duty on flammable-liquid processing plants at 1910.106(h)(4)(ii)(c). Outside those, the duty arises from the General Duty Clause, from fire and mechanical codes, from state plan requirements, and from process-safety rules.

What is the current edition of ASME A13.1?

ASME A13.1–2023 is the current edition, succeeding the 2020, 2015, 2007 and 1996 editions. The 2023 revision expanded the scope and definitions, clarified the colour designation system, enhanced the legend guidance and added flow-direction graphics. Note the publisher: the standard is maintained by ASME, so "ASME A13.1–2023" is the correct citation even though it is often still written as ANSI A13.1. OSHA's incorporations still name the 1956 edition, a 67-year gap.

What are the six ASME A13.1 pipe marking colours?

Fire-quenching fluids are white on safety red; toxic and corrosive fluids are black on safety orange; flammable and oxidizing fluids are black on safety yellow; combustible fluids are white on safety brown; potable, cooling, boiler feed and other water is white on safety green; and compressed air is white on safety blue. Four further combinations — white on purple, black on white, white on grey and white on black — are reserved for the user to define in writing.

What letter height does a pipe marker need?

Letter height scales with the outside diameter of the pipe including its covering: 0.5 in (13 mm) up to 1.3 in diameter, 0.7 in (19 mm) to 2.4 in, 1.3 in (32 mm) to 6.7 in, 2.5 in (64 mm) to 10 in, and 3.5 in (89 mm) above 10 in. Where the imperial and metric values disagree slightly, the metric figure is the one printed in the standard.

Do pipe markers have to include arrows?

Yes. Arrows indicate the direction of flow, and where the contents can flow in both directions the standard expects arrows in both directions rather than a single assumed direction. Arrows are what make a marker usable during isolation and emergency response, which is the main reason the marker exists.

How far apart should pipe markers be placed?

A13.1 requires markers adjacent to valves and flanges, adjacent to changes of direction, on both sides of wall and floor penetrations, and at intervals on straight runs sufficient for identification. It sets a functional test rather than a fixed distance, so facilities typically write a maximum interval — commonly 25 to 50 feet — into their own scheme to make the requirement auditable.

Is insulation included when sizing a pipe marker?

Yes, and this is the most common sizing error. The table is keyed to the outside diameter of the pipe including any covering. A nominal 6-inch chilled-water line inside insulation can easily measure 8 to 9 inches, which moves it into a larger marker row than its pipe size alone would suggest.

Can we keep using the old yellow-and-green pipe marking scheme?

In an already-marked facility, generally yes. The current edition allows an existing identification scheme to be considered as meeting the requirements where the scheme is described in writing or employees are trained to the operation and hazards of the piping systems. A consistent legacy scheme backed by a written legend is a stronger position than a half-converted building with no documentation.

What colour is anhydrous ammonia piping under A13.1?

Safety orange with black legend, because ammonia is classified as a toxic and corrosive fluid, not as a flammable one. Facilities frequently mark it yellow by analogy to its flammability, which is the wrong band. Ammonia refrigeration systems are also subject to their own identification conventions under IIAR practice, which many operators apply alongside A13.1.

What colour is a sprinkler pipe?

Safety red with white lettering, as a fire-quenching fluid. Red is reserved for fire-quenching service under A13.1, which is consistent with OSHA's own colour code at 1910.144(a)(1), where red is the basic colour for identifying fire protection equipment and apparatus.

Does HazCom require chemical pipes to be labelled?

The Hazard Communication Standard at 1910.1200 imposes its labelling duty on containers rather than on piping, but it still requires that employees be informed of the hazards of chemicals contained in unlabelled pipes through the information and training provisions. The current edition of A13.1 offers a bridge: where piping connects to GHS-labelled containers, a corresponding label carrying the product identifier, pictogram, signal word and hazard statements may be applied to the pipe.

Who is responsible for marking pipes on a construction project?

The duty usually lands on whoever owns the completed system, but it is settled contractually long before that. Mechanical specifications should name the edition, the colour scheme, the size schedule and the placement rules, and closeout should include the written legend. Projects that leave marking to "per applicable standards" reliably arrive at occupancy with unmarked pipe.

What about buried and outdoor pipe?

A13.1 addresses above-ground identification. For buried lines the relevant conventions are locating tape and the APWA uniform colour code used for utility marking, which is a different scheme with different colours. Do not import the APWA street-marking colours into a mechanical room; they mean different things.

Are pipe markers required to be a specific material?

No material is mandated. The practical test is service life in the actual environment: adhesive markers fail on hot, sweating or oily pipe, and snap-on or strap-on carriers hold up better. Outdoor and UV-exposed runs need materials rated for it. A marker that has faded to unreadable is, for every purpose that matters, an unmarked pipe.

Do valves need to be labelled as well as pipes?

A13.1 addresses piping, and marker placement adjacent to valves is one of its explicit requirements. Separate valve tagging — a unique number tied to a valve schedule and to the isolation procedures — is a distinct practice driven by maintenance and energy-control needs rather than by A13.1, and the two should use the same names for the same lines.

Further reading on this site

• OSHA safety sign requirements — the hub for facility signage: the three sign classes, the colours OSHA specifies, and the ANSI edition table.
• GHS pictograms and HazCom labels explained — the container-labelling layer that sits alongside pipe identification.
• OSHA HazCom program requirements — what the written programme has to cover, including chemicals in unlabelled pipes.
• Incompatible chemical storage and segregation — the storage side of the same identification problem.
• How to perform lockout/tagout — why marker legends and energy-control procedures must use identical line names.
• Permit-required confined space requirements — where unidentified piping into a space becomes an entry hazard.
• Danger vs warning vs caution signs — assigning the right signal word to the hazards a marked pipe reveals.
• Best lockout/tagout kits — valve and line isolation hardware for the systems these markers identify.