Exposure limits from organisations
A number of organisations have published specific EMF exposure limits, some of which have been adopted by various countries and authorities to form their national or local guidance on EMFs.
Some organisations producing guidelines are:
- International Commission on Non-Ionizing Radiation Protection (ICNIRP).
- International Commission on Electromagnetic Safety (ICES) from the IEEE.
- American Conference of Government Industrial Hygienists (ACGIH) – Occupational.
The guidelines in force in the UK are those of ICNIRP which are described below.
ICNIRP
ICNIRP has developed exposure limits covering low frequency EMFs. Importantly, its guidelines are not intended to be a complete system for protecting the public that should be applied as it stands. ICNIRP says that its guidance considers only the science, and governments will need to consider other factors before deciding whether, and how, to implement the guidelines. Thus, for example, the EU Recommendation references the ICNIRP exposure limits but expects them to be applied only where the time of exposure is significant.
For direct current fields, the guideline limits that apply to public exposures come from the 1994 ICNIRP guidelines for static magnetic fields. The 1994 ICNIRP limits for static fields, included in the EU Recommendation, are:
| Guideline level | |
|---|---|
| Magnetic fields | 40,000 µT |
| Electric fields | No limit but suggestion >25 kV/m should be avoided |
The ICNIRP 1998 guidelines are those adopted in the UK and many other European countries for public exposures.
The structure of the guidelines is to prevent established effects of EMFs in both occupational and public exposure situations. This webpage will concentrate on the public limits as these are what apply in the UK, but it is important to note that the public exposure limits are derived from the occupational limits with an additional safety factor of 5 built in.
The actual limit is the called the basic restriction, which limits the amount of induced current occurring within the central nervous system. You cannot measure this easily, so ICNIRP provide investigation levels for electric and magnetic fields that you can measure. The Health Protection Agency (now UK Health Security Agency) provide advice on how to apply the ICNIRP exposure guidelines for 50 Hz fields (those that the UK electricity system produces).
Ensuring compliance with the electric and magnetic field limits ensures compliance with the basic restriction in the table below.
| Basic restriction | Field corresponding to the basic restriction | |
|---|---|---|
| Magnetic fields | 2 mA/m2 | 360 µT |
| Electric fields | 2 mA/m2 | 9 kV/m |
These limits guarantee compliance with the basic restriction using perfect conditions. In most situations, the field required to exceed the basic restriction is much higher and can be calculated for specific situations using a technique called ‘dosimetry calculations’. Induced currents cannot be easily measured in humans, so dosimetry models are used to calculate these effects.
In 2010, ICNIRP reviewed the guidelines that apply to 50 Hz fields. One of the main changes from the ICNIRP 1998 guidelines is the distinction between central nervous system (CNS) effects (the head) and peripheral nervous system (PNS) effects (the rest of the body). ICNIRP gave different basic restrictions for each (the explanation for this is given further on). The basic restrictions are based on limiting the induced voltage within the body.
The ICNIRP 2010 guidelines include limits for both occupational and public exposures. The public limits are based on the occupational limits with an additional safety factor of 5 built in for the CNS limits, and a factor of 2 built in for the PNS limits. Again, induced voltage levels within the body cannot be easily measured, so external field strengths are given to enable demonstration of compliance.
The ICNIRP 2010 guidelines are the basis of the statutory occupational limits in force in the UK.
Occupational limits
The occupational basic restrictions which apply are:
- 100 mV/m in head
- 800 mV/m for whole body
The external electric and magnetic field values these would equate to are:
| Field corresponding to the basic restriction | |
|---|---|
| Magnetic fields | 3030 µT |
| Electric fields | 24.2 kV/m |
Public limits
The public basic restrictions which apply are:
- 20 mV/m in head
- 400 mV/m for whole body
The external electric and magnetic field values these would equate to are:
| Field corresponding to the basic restriction | |
|---|---|
| Magnetic fields | 606 µT |
| Electric fields | 9.9 kV/m |
Why are the basic restriction values different between 1998 and 2010?
In the 1998 guidelines the basic restriction is set to limit the induced current, measured in mA/m, but in ICNIRP 2010 they are set to limit the induced voltage, measured in mV/m. Both units essentially limit the same thing and have been set to prevent effects on nerves from occurring.
Why do the ICNIRP 1998 guidelines still apply to public exposures?
Although the ICNIRP 2010 guidelines are the most recent guidelines to be published covering 50 Hz, the Government advice and policy is to apply the 1998 guidance.
The new guidelines will not apply in the UK unless the Government make a specific decision to introduce them. The ICNIRP 2010 limits allow for higher public exposures, so continuing to follow the ICNIRP 1998 guidelines ensures lower public limits are applied.