What is the difference between DANGER, WARNING and CAUTION colours on US safety signs?

At a glance

Standard

ANSI Z535.1 Safety Colors (series Z535.1–Z535.6)

Edition

2022 per secondary listings; OSHA incorporates the 2006 (R2011) edition

Signal-word ladder

DANGER red · WARNING orange · CAUTION yellow · NOTICE blue

Regulator

US OSHA, 29 CFR 1910.144 and 1910.145

Severity, not category

The ISO system asks 'what kind of message is this?' — prohibition, warning, instruction, safe condition. ANSI Z535 asks a different question: 'how severe and how likely is the harm?' That is why it needs more steps of hazard colour. Red is reserved for the top of the ladder, orange sits between, and yellow is the lowest injury-related level. Blue NOTICE is outside the injury ladder altogether, used for messages such as property damage or procedures. Because the colour is attached to a printed signal word, the system works even for someone who cannot distinguish orange from red: the word says the level, the colour lets a trained eye read it from further away.

Six books with one palette

Z535 is a series. Z535.1 defines the safety colours themselves; Z535.2 applies them to environmental and facility signs; Z535.3 sets criteria for safety symbols; Z535.4 covers product safety signs and labels; Z535.5 covers temporary tags and barricade tape; and Z535.6 covers safety information in manuals and other collateral. The series is maintained by an ANSI-accredited committee with NEMA as secretariat and is revised on a roughly five-year cycle. Colourwise could not confirm the current edition on ANSI's own catalogue, which blocks automated checks, so the 2022 year shown here comes from secondary listings and should be confirmed before it is quoted in a specification.

Why OSHA still cites a 2006 edition

Federal regulations incorporate private standards by reference at a fixed edition, and updating that reference requires rule-making. OSHA's sign and tag rule, 29 CFR 1910.145, still refers to the colour tables of ANSI Z535.1-2006 (reaffirmed 2011), alongside a 1967 predecessor. Separately, 1910.144 makes red mandatory for fire-protection equipment, danger and emergency-stop devices on hazardous machines, and yellow mandatory for caution and physical hazards such as tripping and falling. OSHA has said it accepts signs designed to later Z535 editions where they give equal or better protection, which is why modern products carry newer-format labels. None of this is compliance advice; the point is that 'the ANSI colour' can mean different editions depending on who is asking.

A tag is not a sign under OSHA's rule. Danger tags are red-based, caution tags yellow-based, and orange warning tags may be used for a hazard level between the two.

Converging with ISO

Since the 1990s the Z535 committee has aligned its symbols with ISO so that American labels can use ISO-style pictograms in the symbol panel while keeping the signal-word header. The main remaining visual differences are the orange WARNING level and the header panel itself, which ISO signs do not use. Manufacturers exporting in both directions often print one label that carries an ISO 7010 pictogram, an ANSI signal word in its colour, and text in several languages. The colours still disagree at the edges: ANSI red and ISO red are specified independently, and printed labels from different suppliers vary within each system's tolerance.

The data

What goes wrong, and what to do

How to check it yourself

1. Read the signal word first; the colour should match it (DANGER red, WARNING orange, CAUTION yellow, NOTICE blue).
2. If the label is for a US workplace, check whether a contract or regulator names a specific Z535 edition.
3. For exported equipment, check whether the destination expects ISO 7010 signs instead of or as well as ANSI labels.

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.

• StandardStrong evidence

  OSHA's rule on accident prevention signs and tags specifies danger-sign colours and caution-sign colours by reference to the tables of ANSI Z535.1-2006 (R2011), with caution signs using a yellow background and black lettering.

  Source: 29 CFR 1910.145 — Specifications for accident prevention signs and tags

• StandardStrong evidence

  US federal regulation 29 CFR 1910.144 assigns red to fire-protection equipment, danger and emergency-stop devices on hazardous machines, and yellow to caution and physical hazards.

  Source: 29 CFR 1910.144 — Safety color code for marking physical hazards

• ConventionModerate evidence

  In the ANSI Z535 signal-word system DANGER is shown on red, WARNING on orange, CAUTION on yellow and NOTICE on blue, with the levels distinguished by the severity of the potential harm.

  Caveat: Summarised from a secondary source and not yet checked against the standard itself; confirm with the standard before relying on it.

  Source: ANSI Z535 (Wikipedia); 29 CFR 1910.145 — Specifications for accident prevention signs and tags

• FactLimited evidence

  The current ANSI Z535.1 edition is listed as 2022.

  Caveat: Taken from a secondary listing; ANSI's own catalogue could not be checked. Confirm with ANSI or NEMA before citing.

  Source: ANSI Z535 (Wikipedia)

Related questions

Is orange WARNING more serious than yellow CAUTION?

Yes. In the Z535 ladder orange WARNING marks a hazard that may kill and will injure, while yellow CAUTION marks one that may injure but not kill. Red DANGER sits above both.

Does OSHA require the newest ANSI Z535 edition?

OSHA's rule text still refers to Z535.1-2006 (reaffirmed 2011) for colours. Designs to newer editions are widely used; whether they satisfy a particular obligation is a question for the regulator, not a colour page.

What is the blue NOTICE panel used for?

For safety-related information that does not involve a risk of personal injury — for example, a practice that could damage equipment. It sits outside the red–orange–yellow injury ladder.

Related topics

Go further

Sources

• 29 CFR 1910.145 — Specifications for accident prevention signs and tags — US Occupational Safety and Health Administration (Official standard or government)
• 29 CFR 1910.144 — Safety color code for marking physical hazards — US Occupational Safety and Health Administration (Official standard or government)
• ANSI Z535 (Wikipedia) — Wikipedia (Reference work)

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.