Radiation
Warns of radioactive material or ionizing radiation.
Understanding this sign
Yellow triangular signs draw attention to a hazard, such as electricity, moving machinery, or a hot surface.
A warning pictogram does not state the severity, safe distance, or protective measures. Read the accompanying instructions.
What ISO 7010 W003 Warns About
W003 warns of ionising radiation. It shows the radiation trefoil — a central circle with three blades radiating outward — in black inside the ISO 3864-1 warning triangle on a yellow field. The sign indicates that radioactive material, a radiation source, or radiation-generating equipment such as an x-ray set may be present, and that exposure could occur. It is a prompt to observe access controls, dose limits, and shielding arrangements before entering, because ionising radiation is invisible and its harm is cumulative.
The trefoil tells the reader that ionising radiation is the hazard, but it does not describe the dose rate, the type of radiation, or whether a source is currently exposed. A low-activity sealed source and a high-output irradiator can display the same symbol. For that reason W003 is used with supplementary information — the nature of the source, the controlled or supervised area designation, dose-rate data, and contact details — so that people can judge the actual risk rather than react to the symbol alone.
Radiation Posting Rules in the United States
In the United States the wording and colour of radiation postings are prescribed rather than left to a generic symbol. Under the Nuclear Regulatory Commission's standards for protection against radiation, 10 CFR Part 20, areas are posted with specific legends such as "Caution, Radiation Area", "Caution, High Radiation Area", or "Caution, Radioactive Material(s)", using the conventional radiation symbol — a magenta or purple-black trefoil on a yellow background — together with the required text. The exact wording depends on the dose rate that could be received in the area.
This means the ISO 7010 W003 sign and a US NRC posting are related but not identical. W003 uses a black trefoil in a triangle and communicates the hazard internationally; NRC-regulated facilities must use the mandated legend and symbol format to meet 10 CFR 20 posting requirements. Where a facility falls under NRC or an Agreement State programme, the regulatory posting governs, and a generic W003 symbol does not by itself satisfy the specific wording the rule requires. Agreement States apply equivalent requirements under their own regulations.
Where the Radiation Warning Belongs
Post W003 at the boundaries of areas where ionising radiation may be encountered: x-ray and radiography rooms, radioactive source stores, isotope and radiochemistry laboratories, nuclear medicine and radiotherapy areas, industrial radiography exclusion zones, irradiator control points, and shielded equipment enclosures. On sealed-source devices and transport packages it identifies the radioactive contents so that handlers and responders recognise them immediately. The sign belongs at the point where a person could cross into a zone of elevated dose, not only at the source itself.
For radiography and irradiator work, signage is normally combined with active controls: warning lights or beacons that indicate when a source is exposed or a beam is energised, interlocks, barriers, and audible alarms. A static W003 sign warns of the potential hazard; the dynamic controls tell people when it is actually present. Postings should also carry the responsible person and emergency contact, because radiation incidents require specialist response and the people who find a problem may not be radiation workers.
Understanding and Distinguishing the Trefoil
The radiation trefoil warns specifically of ionising radiation — the energetic radiation from radioactive decay and x-ray equipment that can damage living tissue. It is not the symbol for non-ionising sources such as radiofrequency fields, microwaves, or lasers, which have their own warnings; conflating them can lead to the wrong protective measures. W003 should also not be confused with the separate ionising-radiation and radioactivity hazard markings used on transport packages under dangerous-goods rules, which carry additional classification detail.
There is also a distinct supplementary symbol for high-activity sealed sources, introduced by the IAEA and ISO, showing the trefoil with radiating waves, a skull, and a running figure. It is intended to be placed near the source inside a device housing to deter dismantling, not as a general area sign, and it does not replace W003. Understanding which symbol applies — area warning, transport marking, or the sealed-source deterrent — keeps radiation signage accurate and avoids sending a stronger or weaker message than the situation warrants.
Where you will see W003
Installed at x-ray rooms, radiography exclusion zones, radioactive source stores, isotope laboratories, nuclear medicine areas, industrial inspection cells, irradiator controls, and shielded equipment rooms.
Common questions about W003
What does the radiation trefoil sign mean?
The black three-bladed trefoil in a yellow triangle is ISO 7010 W003, warning of ionising radiation. It indicates that radioactive material, a radiation source, or radiation-generating equipment such as an x-ray machine may be present and that exposure is possible. It is a prompt to follow access controls, shielding, and dose limits before entering the area.
Does the ISO W003 sign meet US radiation posting requirements?
Not on its own. In the US, the NRC's 10 CFR Part 20 requires specific legends such as "Caution, Radiation Area" using the conventional magenta-on-yellow radiation symbol and mandated wording that depends on the dose rate. NRC-regulated and Agreement State facilities must use those prescribed postings; a generic W003 symbol does not by itself satisfy the required text.
Does W003 cover lasers or radio-frequency radiation?
No. W003 warns of ionising radiation only — the kind from radioactive materials and x-ray equipment. Lasers, radiofrequency fields, and microwaves are non-ionising and have their own separate warning signs. Using the radiation trefoil for a non-ionising source would misidentify the hazard and could lead to the wrong protective measures being applied.
What is the trefoil symbol with a skull and running person?
That is the IAEA/ISO supplementary warning for high-activity sealed radioactive sources, showing the trefoil with radiating waves, a skull, and a person running away. It is designed to sit near the source inside a device to deter people from dismantling it, not as a general area sign, and it does not replace the standard W003 warning triangle.
Reference details
| Symbol code | W003 |
|---|---|
| Sign family | ISO Warning Signs |
| Standard reference | ISO 7010:2019 / ISO 3864-1 ISO Online Browsing Platform: W003 |
| Screen color reference | #FFCC00. Screen colors are not a production color specification. |
| Download formats | SVG reference artwork; a 1024 × 1024 pixel PNG conversion on a white canvas. |
| Record date | · How to interpret our dates |
| Page updated |
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Sources and artwork credits
- Artwork source
- Wikimedia Commons file page
- Creator credited by source
- MaxxL
- License
- Public domain
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