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Two three-fold black-on-yellow warnings that are mixed up constantly and share no controls at all.
Count what is around the centre. Three solid blades radiating from a small disc is ionising radiation; three broken rings overlapping a central circle is biological hazard. They are the same size, the same colours and the same three-fold arrangement, which is why signage catalogues themselves get them wrong — and the responses could not be less alike. One calls for distance, shielding and time; the other for containment, disinfection and a disposal route.
Three blades around a disc is radiation; three interlocking broken rings is biological hazard.
Drawn from the visual attributes recorded for each symbol. Only traits the two records disagree about are listed.
| Trait | Radiation warning symbol | Biohazard symbol |
|---|---|---|
| Built from | abstract and triangles | circles and abstract |
| Enclosing border | No enclosing border | Sits inside a border |
| Colour | black and yellow | Not colour-specific |
| Radiation warning symbol | Biohazard symbol | |
|---|---|---|
| Shape at the centre | Three solid blades around a small filled disc | Three broken rings overlapping a central circle |
| Sign standard reference | ISO 7010 W003 | ISO 7010 W009 |
| Where you meet it | Sealed sources, radiography and radiotherapy rooms, isotope stores, transport packages | Sharps bins, clinical waste, containment laboratories, specimen transport |
| What reduces the risk | Distance, shielding and time | Containment, disinfection and the correct disposal route |
| Relationship (from Symbolwise's records) | Commonly confused with Biohazard symbol — Three blades around a disc is radiation; three interlocking broken rings is biological hazard.; Part of the same system as Biohazard symbol — Both belong to the ISO safety symbols system. | Commonly confused with Radiation warning symbol — Three broken rings around a circle is biological; three solid blades around a disc is radiation.; Part of the same system as Radiation warning symbol — Both are internationally recognised hazard-warning trefoils, though for different hazard types and standards bodies. |
ISO 7010, Graphical symbols — Safety colours and safety signs
International Organization for Standardization · retrieved 2026-08-02
Paywalled and NOT READ in full. Registered so records can state that a sign has a standard reference and a defined shape and colour — E003 for first aid, E010 for a defibrillator. The catalogue of registered signs and their reference numbers is public even where the standard text is not. See docs/paywalled-standards.md.
Hazard symbol (radiation trefoil origin and 1963 ISO standardisation)
Wikipedia / HandWiki mirror · retrieved 2026-07-26
Retrieved via a Wikipedia mirror rather than en.wikipedia.org directly; the 1946 Berkeley origin and 1963 ISO date should be treated as widely reported rather than independently primary-verified.
Science History Institute · retrieved 2026-07-26
A building's assembly point is a safe place to stand once you are outside. A ship's muster station is a staffed step in a procedure: you are counted against a roll, briefed, and if necessary allocated to a survival craft, which is why it has a letter or a number and appears on your cabin door card. Both are green, both show grouped figures, and both are called an assembly point in ordinary speech — and treating a muster station as somewhere merely to wait is the misunderstanding drills exist to correct.
The becquerel counts nuclear decays — one per second — and says nothing about harm. The sievert weights absorbed energy by the kind of radiation delivering it, and so estimates biological effect. A becquerel of one isotope and a becquerel of another can carry very different risk, which is exactly why exposure limits and medical doses are stated in sieverts and never in becquerels.
The plain black flag excludes the competitor: their race is over. The black flag with an orange disc reports a mechanical problem that endangers others and sends the driver to the pits to have it fixed, after which they may rejoin. Both are shown with a number board, both are black, and confusing them costs a competitor a race they could have finished.
They are alternatives, not a pair. The double square means the appliance is protected by double or reinforced insulation and needs no earth connection, which is why it can legitimately have a two-pin plug. The earth symbol marks a terminal that must be connected, because that appliance relies on earthing instead.