New ISO Standard - Supplementary Ionizing-Radiation Warning Symbol

A new radiation warning symbol, to supplement the existing trefoil symbol has been published by ISO as Standard #21482- Ionizing-Radiation Warning –Supplementary symbol. The trefoil symbol has no inherent meaning and only those people that have been educated in its meaning have knowledge that it represents the presence of ionizing radiation. The new symbol is the completion of a multi-year effort by the IAEA to develop a universal radiation warning symbol that anyone anywhere will understand the message of “Danger- Stay Away”. The new symbol was developed with human factor experts, graphic artists, and radiation protection experts. Many possible symbols were initially tested in international children, and then those symbols that were most successful in conveying the desired message were tested further by the Gallup Institute in both people with limited education and those educated in 11 countries around the world. The new symbol universally conveyed the intended message regardless of the person’s age, education or cultural background.

The symbol is intended for IAEA Category 1, 2 and 3 sources defined as dangerous sources capable of causing death or serious injury. The symbol should be placed on the device housing the source, as a warning not to dismantle the device or to get any closer. Where practical, it should be placed under the device cover such that it is not visible under normal use but would be visible if anyone attempts to disassemble the device. The symbol is not intended for doors or shipping containers.

In the near future, many source manufactures have agreed to use the symbol on newly manufactured large sources such as irradiators, teletherapy heads and industrial radiography units. Strategies to place the symbol on existing large sources are being developed by the IAEA. The standard can be obtained at

Information: Carolyn Mac Kenzie,