At high levels, well above the occupational exposure limits, EMFs have effects on us as humans, which have been scientifically proven and are well understood. But what are these established effects and what can we do to prevent them?

What effects do EMFs have on humans?

When we are exposed to very high electric or magnetic fields many times above the occupational exposure limits, they can cause a current to be induced within us, although it is very small.

These induced currents, if high enough, can interact with nerves in the body. We can observe the effects that these induced currents have on nerves in laboratory experiments. These experiments have shown that the first biological effect is on the retina in the eye and causes ‘magnetophosphenes’. These are a flickering sensation in the peripheral vision and start to occur at approximately 10,000 µT. These effects in themselves are not harmful, but exposure limits have been set to prevent all effects of induced currents on the nervous system, including preventing magnetophosphenes.

Induced currents cannot be easily measured in humans, so models are used to calculate these effects, and this is called dosimetry.

What are the exposure limits to prevent induced currents?

Exposure guidelines are usually designed to prevent all effects of induced currents, on the basis that any effect in the brain or nervous system is potentially harmful.

The ICNIRP exposure guidelines used in the UK and the European Union recommend that people at work should not be exposed to current densities in the head, neck and trunk of greater than 10 mA/m² (the "basic restriction") with a lower limit of 2 mA/m² for the general population, which may include people who are more sensitive because of medical conditions.

What currents do EMFs produce?

The most accurate way to determine how much current is induced is to perform a numerical calculation. For the purposes of the calculation, the body is split into millions of small elements called “voxels”. One of the most important factors is the conductivity of each tissue. Each voxel is assigned a conductivity appropriate to the tissue type it represents. Computers are then used to calculate the current induced in each voxel.

The following results are taken from the papers by Dimbylow for magnetic and electric fields, which are those used by the UK Government.

The current induced by a field depends on the direction of the field and, for electric fields, whether the body is grounded. These results are for the most sensitive conditions, i.e., the conditions where it takes the smallest external field to induce the given current.

To induce a current of 10 mA/m² in the central nervous system requires:

• A magnetic field of 1800 µT in a man or 2000 µT in a woman (this would be aligned side-to-side of the body and is in the retina)
• An electric field of 48 kV/m in a man or 46 kV/m in a woman (this is a vertical field for a grounded person and is again in the retina)

To induce a current of 2 mA/m² in the central nervous system requires:

• A magnetic field of 360 µT for a man (the value for women is higher)
• An electric field of 9.2 kV/m for a woman (the value for men is higher)

These calculations form the basis of the public exposure levels in place in the UK.