Radiation Symbol (1948)

International ionising radiation trefoil symbol
Yellow and magenta ionising radiation trefoil used in the US

In 1946, the ionising radiation trefoil started as a ‘doodle’ produced by a group of people at the Berkeley Radiation Laboratory, University of California, who were keen to develop a warning symbol for this new kind of dangerous material. The trefoil represents the activity of an atom.

It was first rendered as magenta on a blue background. However, the blue proved to be unpopular and, in 1948, Bill Ray and George Warlick, at the Oak Ridge National Laboratory in Tennessee, cut out the magenta symbol and stapled them on to cards of different colours. To get a sense of what stood out the most they put the cards outdoors and found that, from a distance, magenta on yellow best conveyed the idea of danger, which became the standard design in early 1948.

The trefoil is black in the international version, which is also used in America.

The symbol is drawn with a central circle of radius R, an internal radius of 1.5R and an external radius of 5R for the blades, which are separated from each other by 60°.

International ionising radiation trefoil symbol

The sign is commonly referred to as a radioactivity warning sign, but it is actually a warning sign of ionising radiation.

ISO 21482 high-level sealed-source ionising radiation symbol

On February 15, 2007, two groups — the International Atomic Energy Agency (IAEA) and the International Organisation for Standardisation (ISO) — jointly announced the adoption of a new ionising radiation warning symbol to supplement the traditional trefoil symbol.

Since then, the use of a yellow background has come to be a general indication of ‘hazard’, as defined by the ISO, which decides on criteria for worldwide signs; outside the United States, the magenta trefoil is often printed on black.

In 2001, when it was learned that, in certain parts of the world, people who did not understand the meaning of trefoil were touching and disassembling lethal material, the IAEA announced its intention to create a new radiation symbol.

The new symbol, to be used on sealed radiation sources, is aimed at alerting anyone, anywhere to the danger of being close to a strong source of ionising radiation.

It depicts, on a red background, a black trefoil with waves of radiation streaming from it, along with a black skull and crossbones, and a running figure with an arrow pointing away from the scene. The radiating trefoil suggests the presence of radiation, while the red background and the skull and crossbones warn of the danger. The figure running away from the scene is meant to suggest taking action to avoid the labeled material.

The new symbol is not intended to be generally visible, but rather to appear on internal components of devices that house radiation sources so that if anybody attempts to disassemble such devices they will see an explicit warning not to proceed any further.

Hazardous Waste Management

The calculated and structured design of the radiation symbol — with the use of a whole number radii and the same percentage of separation for the blades — makes this design easy to recreate and display on various different objects. The clean design is easily recognisable, with the yellow hazard colour being an important indicator of potential danger.