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

Z535.1-2022, approved 2 June 2022; 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. Red and orange both concern death or serious injury; what separates them is whether that outcome is expected or only possible. 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. Since its 2002 revision Z535.1 has only defined the colours, as measurable specifications, and left what each colour is used for to the other parts. The series is maintained by an ANSI-accredited committee with NEMA as secretariat and is revised every five years or so. NEMA's published extract of Z535.1 shows the 2022 edition, approved on 2 June 2022, and lists these six standards; ANSI's own catalogue could not be consulted, so confirm that no later edition has appeared before quoting one 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. When OSHA added the Z535 references in 2013 it said it believed signs meeting the Z535 series were at least as protective as the older ones, and it wrote the rule so that an employer may follow either set of colour tables. Editions later than those the rule names are not mentioned in it. 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. The rule does not mandate tag colours, but OSHA's appendix recommends red for danger tags, yellow for caution tags and orange for warning tags, which may stand for a hazard level between the two.

Converging with ISO

NEMA's forewords describe successive revisions, from 2007 onwards, as improving harmonisation with international standards, and Z535.1 now prints the ISO safety colours beside its own. 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 two sets of colours are specified separately, but NEMA states that the ISO safety colours fall inside the Z535.1 tolerances, so the difference a reader sees between two labels is more likely to be supplier variation than a disagreement between the systems.

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

• StandardStrong evidence

  In the ANSI Z535 signal-word system DANGER is white on safety red, WARNING black on safety orange, CAUTION black on safety yellow and NOTICE white on safety blue. DANGER and WARNING both concern death or serious injury, expected in the first case and possible in the second; CAUTION concerns minor or moderate injury; NOTICE is for messages not about personal injury.

  Caveat: NEMA's published foreword confirms the red, orange and yellow pairings and the role of NOTICE. The lettering colours, the blue NOTICE panel and the severity wording come from a 2013 US Army pamphlet that applies the Z535 series, so they reflect the 2011 editions; the purchased standards were not read.

  Source: ANSI Z535.2-2011 (R2017) American National Standard for Environmental and Facility Safety Signs — contents and scope; Department of the Army Pamphlet 385-11: Army Guidelines for Safety Color Codes, Signs, Tags, and Markings; 29 CFR 1910.145 Appendix A — Recommended Color Coding

• FactStrong evidence

  ANSI Z535.1, the safety colours standard, is in its 2022 edition, approved on 2 June 2022.

  Caveat: Confirmed from NEMA's published extract of the standard on 1 October 2026. ANSI's webstore could not be consulted, so a later edition listed only there would not have been seen.

  Source: ANSI Z535.1-2022 American National Standard for Safety Colors — contents and scope

• FactStrong evidence

  When OSHA added the ANSI Z535 references to its signage rules in 2013 it stated its belief that signs meeting the Z535 series are at least as protective as those meeting the older ANSI standards, and the rule accepts the colour tables of either.

  Source: Updating OSHA Standards Based on National Consensus Standards; Signage (Federal Register, 13 June 2013); 29 CFR 1910.145 — Specifications for accident prevention signs and tags

Related questions

Is orange WARNING more serious than yellow CAUTION?

Yes. In the Z535 ladder orange WARNING marks a hazard that could cause death or serious injury, while yellow CAUTION marks one that may cause minor or moderate injury. Red DANGER sits above both, for hazards where death or serious injury is expected.

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 Z535.2-2011 (R2017) American National Standard for Environmental and Facility Safety Signs — contents and scope — National Electrical Manufacturers Association (NEMA), secretariat of the Z535 Committee (Standards body)
• Department of the Army Pamphlet 385-11: Army Guidelines for Safety Color Codes, Signs, Tags, and Markings — Headquarters, US Department of the Army (Official standard or government)
• 29 CFR 1910.145 Appendix A — Recommended Color Coding — US Occupational Safety and Health Administration (Official standard or government)
• ANSI Z535.1-2022 American National Standard for Safety Colors — contents and scope — National Electrical Manufacturers Association (NEMA), secretariat of the Z535 Committee (Standards body)
• Updating OSHA Standards Based on National Consensus Standards; Signage (Federal Register, 13 June 2013) — US Occupational Safety and Health Administration (Official standard or government)

Reviewed 1 October 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.