Non-ionizing radiation symbol

How to read it

In Great Britain the sign is a warning triangle, Non-ionizing radiation: a black pictogram of waves spreading from the tip of a mast, on a yellow triangle with black edging. The Health and Safety Executive (HSE) uses “non-ionising radiation” for optical radiation and for electromagnetic fields (EMFs). Its guide to the Control of Electromagnetic Fields at Work Regulations 2016 describes EMFs as static electric, static magnetic and time-varying electric, magnetic and electromagnetic (radio wave) fields with frequencies up to 300 GHz. Among the sources of high-frequency fields it lists broadcasting and TV antennas, radar and radio transmitters, diathermy and dielectric heating, such as plastics welding and microwave drying. A strong static magnetic field has a sign of its own, Strong magnetic field.

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Not the radiation trefoil

The radiation trefoil warns of ionising radiation and radioactive material. The British regulations keep the two apart: Radioactive material and Non-ionizing radiation are separate warning signs. Lasers come under optical radiation in HSE’s pages on non-ionising radiation, but the regulations give the laser beam its own triangle too.

The US radio-frequency sign

OSHA’s standard on nonionizing radiation, 29 CFR 1910.97, has its own warning symbol for radio-frequency radiation, which it defines to include microwaves. It is a red isosceles triangle above an upside-down black one, separated and outlined by an aluminium-coloured border, with the words “Warning—Radio-Frequency Radiation Hazard” in the upper triangle; any further warning information goes in the lower one. OSHA says the standard’s exposure limit is written in voluntary language and has been ruled unenforceable, but the sign design still stands, and newer designs are also acceptable.

Where you’ll see it

The EU’s directive on electromagnetic fields at work, 2013/35/EU, says workplaces where workers are likely to be exposed to fields above its action levels are marked with signs under the safety signs directive, 92/58/EEC. Signs specific to electromagnetic fields are not required where access is already suitably restricted for other reasons and workers are informed of the risks. Around phone masts, the US Federal Communications Commission says a person at a rooftop antenna site could meet radio-frequency levels higher than on the ground, though levels near the safety guidelines are only likely very close to and directly in front of the antennas.