Note that on March 31 2004 the NRPB announced that its advice was now that the UK should adopt the ICNIRP exposure guidelines. This page details the previous, 1993, NRPB exposure guidelines. More on the 2004 NRPB guidance.
The legal position
There are no statutory regulations in the UK which limit the exposure of people to power-frequency electric or magnetic fields. However, the NRPB (which has statutory responsibility for advising on non-ionising radiation protection, including power-frequency fields) has published field-strength guidelines on the basis of well-established physiological effects of acute exposure (Documents of the NRPB Volume 4 number 5 1993)
The guidelines are expressed in terms of “basic restrictions” and “investigation levels”.
- The basic restriction relates directly to the effect on the body of exposure to fields.
- At power frequencies, the principal basic restriction is that the induced current in the body should not exceed 10 mA m-2 in certain specified parts of the body.
It is not possible to measure the induced current in the body directly. To aid in assessing whether the basic restriction is exceeded or not, the NRPB gives investigation levels.
- At power frequencies, for electric fields, the investigation level for human exposure is 12 kV m-1,
- for magnetic fields it is 1,600 microteslas (µT).
- If the field is less than the investigation level, the basic restriction will not be exceeded, and no further investigation is needed.
- If the field exceeds the investigation level, it does not necessarily follow that the basic restriction is exceeded, but further investigation is necessary.
more on how investigation levels are calculated and what fields are actually needed to exceed the basic restriction
All exposures in the UK produced by the electric power system should fall within those values.
Summary of the NRPB Guidance:
At power frequency:
- Basic restriction: induced current density in the central nervous system 10 mA m-2
- Investigation level for magnetic fields: 1600 µT
- Investigation level for electric fields: 12 kV m-1
What effects is the NRPB Guidance based on?
In setting their Guidance, the NRPB looks at all the evidence for all possible suggested effects of EMFs on people. The actual numbers are chosen to prevent effects of magnetic fields on the body through induced currents and indirect effects such as microshocks. The NRPB looks at the scientific evidence that EMFs may cause cancer, but does not consider this evidence strong enough to justify setting guidelines.
In 2001 the NRPB’s Advisory Group on Non-Ionising Radiation (AGNIR) produced a major report on the evidence that EMFs may be linked to cancer. In response, the NRPB stated in part:
“Guidelines for limiting exposure to electromagnetic fields are presently based on preventing established health effects, which for ELF EMFs are those related to induced currents in the tissues of the central nervous system. Epidemiological studies are also taken into account. The Board considers that the AGNIR report provides no additional scientific evidence to require a change in exposure guidelines"
Although the various reports of the NRPB Advisory Group concentrate on cancer and neurodegenerative disease, the studies which the Board take into account when setting exposure guidelines include other suggested health effects. For example, the NRPB exposure guidelines state:
“Epidemiological studies of general health and birth outcome in populations exposed to electromagnetic fields have been reviewed in a Board report. These studies do not appear to show long-term health effects from the levels of electromagnetic fields to which people are normally exposed.”