Extremely-Low Frequency Fields

Extremely-low frequency (ELF) electric and magnetic fields (EMF) have frequencies between 1 Hz up to 3 kHz. ELF EMF are produced whenever electricity is generated (i.e. power stations), transmitted and distributed (i.e. power lines) or used (i.e. electric appliances). The frequency used in Ireland and throughout Europe is 50 Hz. Low frequency energies are considered fields rather than radiation, since they have long wavelengths (around 5,000 km at 50 Hz). This means that the electric and magnetic fields have independent characteristics and therefore need to be measured separately.

ELF fields

Electric fields are easily blocked by solid materials, including buildings and trees. Therefore, the levels of ELF electric fields at which the public may be exposed are very low, and generally are not a concern. ELF magnetic fields are not as easily shielded.  However, the magnetic field falls off rapidly with distance from the source.  The table below summarises the levels of magnetic fields around common ELF sources.

 ELF B-field (microTesla, μT)
Source Distance 1 (near) Distance 2 (far)
Overhead (AC) 110-400 kV transmission line 0.5-4.9 μT at 10 m <0.01 μT at 100 m
Overhead (AC) 10-60 kV distribution line 1.1-1.4 μT at ≤5 m ≈0.8 μT at 10 m
Underground (AC) power line 0.1-0.9 μT at ≤5 m ≈0.03 μT at 10 m
Hair dryer ≈30 μT at 15 cm ≈0.1 μT at 30 cm
Electric stove ≈3 μT at 15 cm ≈0.2 μT at 60 cm
Television set ≈0.7 μT at 30 cm ≈0.2 μT at 60 cm
Fluorescent bulb ≈0.1 μT at 15 cm ≈0.1 μT at 30 cm

Note: Magnetic field estimates from EirGrid and HydroQuebec. The current recommended reference level for public exposure to ELF magnetic fields (at 50 Hz) is 100 µT (1999/519/EC).