The Radiation Symbol  – Behind Every Hazard Label There’s an Awesome Backstory! 

For hundreds of years, the symbol of a skull and crossbones was all we needed to communicate the concept of poison. That is, until we started using radioactive compounds.  

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.  

At the time, it was rendered as magenta, and was set on a blue background. The shade of magenta used (Roman Violet) was chosen because it was distinctive and more expensive than other pigments, so less likely to be used on other signs. However, the blue background colour tended to fade with weathering and was difficult to see in poor light which resulted in the background being changed to yellow.  The trefoil is now black in the international version, which is also used in America along with the magenta version.

The radioactive symbol itself 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°.  The calculated and structured design of the 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 simple, readily identifiable and discernible at a large distance.

The symbol is commonly referred to as a ‘radioactivity warning symbol’, but it is actually a warning against the potential presence of ionising radiation.  Ionising radiation is a much broader category than radioactivity alone, as many non-radioactive sources also emit potentially dangerous levels of ionizing radiation.  This includes x-ray apparatus, radiotherapy linear accelerators, and particle accelerators.  Ionising radiation is extremely dangerous because of the way it acts on materials like air, water, and living tissue – removing electrons from atoms and molecules.  Non-ionising radiation exists all around us from many sources and is a form of radiation with less energy than ionizing radiation and can be used to heat substances, for example, the microwave oven.

An International Standard

In 1974, after approval by national standards bodies, the symbol became an international standard as ‘ISO 361-Basic Ionising Radiation Symbol’.  The standard specifies the shape, proportions, application and restrictions on the use of the symbol – it may be used to signify the actual, or potential, presence of ionising radiation and should not be used for non-ionising electromagnetic waves or sound waves.  The standard does not specify the radiation levels at which it is to be used.

After almost 70 years of use, the trefoil symbol has become an iconic emblem, both inside and outside of science, but what about a person who has no learned knowledge of its meaning?  In February, 2007, two groups—the International Atomic Energy Agency (IAEA) and the International Organization for Standardisation (ISO)—jointly announced the adoption of a new ionising radiation warning symbol to supplement the traditional trefoil symbol.

The new symbol, to be used on sealed radiation sources, is aimed at alerting everyone to the danger of being close to a strong source of ionising radiation.  It depicts a black trefoil (on a red background) 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 danger.  The figure running away from the scene is meant to suggest taking action to avoid the labelled material.  This 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.  This updated pictogram provides a more intuitive depiction of the hazards and consequences of ionising radiation, which can be universally understood.

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