SYM·0027 · Trefoil
Radiation
ionising radiation hazard
- Unicode
- U+2622 radioactive sign
- Meaning
- Activity radiating outward from a central source — three blades about a circle.
- History
- Doodled in 1946 at the Radiation Laboratory of the University of California, Berkeley, by a small group around Nels Garden, who wrote up the reasoning two years later. The first version was magenta on blue.
- Variants
- Magenta or black on yellow is the standard field today. ISO 21482 (2007) adds a second, blunter symbol for high-activity sealed sources — trefoil, skull, and a running figure — because testing showed the trefoil alone means nothing to someone who has not been taught it.
- Related
- ☣ ⚠ Biohazard; the ISO 7010 warning grammar (→ Visual Grammar).
- Appears
- Laboratory doors, transport packaging, waste drums, and video-game shorthand for a place you should not be.
- Evolution
- Lab doodle → international standard → generic emblem of danger.
Sources · 3
- documented Nels Garden’s 1948 correspondence from the Berkeley Radiation Laboratory, describing the design and the original magenta-on-blue colourway.
- documented ISO 361, the basic ionising radiation symbol.
- documented ISO 21482 (2007) — the supplementary symbol adopted by the IAEA after multi-country comprehension testing. A rare case of a symbol formally measured, found wanting, and supplemented.