Sources of EMFs
EMFs come from a wide range of sources and vary enormously in the
strength of the fields.
See also:
electric fields ,
magnetic fields ,
units used for EMFs,
instruments available for measuring fields.
The diagram
(right) shows how the magnetic field varies over a typical
house. The peaks come from the various appliances, and they
are superimposed on a low background field, which varies only
slightly across the house.
Appliances are present in every home and fields come
from everything from your kettle to your TV - even a mobile phone. A minority of
homes in the UK are close enough to an overhead
power line, an
underground cable or a
substation for that to be the main source of the background
field. But in most homes, the background field comes from
low-voltage
distribution wiring . House wiring can sometimes contribute too.
Outside the home, we can experience
EMFs in schools , when using electrified transport , and at
work . |
Distribution of magnetic field over the ground floor of
a typical house.
|
Fields from any source fall with distance: more
Did you know that…? Some
facts and figures
- The sort of home we live in can affect the level of fields we
are exposed to.
more
- It’s not just where you live that matters. As you move
about, you experience fields from many other sources (such as
appliances) as well as the background fields in the home. This
means your personal exposure is higher than the background field
in the home. more
- Magnetic fields vary
over time. They vary over the course of a day as loads vary.
They also vary over the year.
- The average magnetic field in a home in the UK is about 50 nT.
This is lower than in many other countries.
more
- The great majority of homes in the UK have fields less than
0.4 µT. About 1.5% of UK homes have average fields greater
than 0.2 µT and about 0.4% greater than 0.4 µT. These
percentages of homes with higher fields are smaller than in many
other countries, particularly America, as shown in this table:
| Country |
% exposed to long-term average
fields greater than: |
| |
0.2 µT |
0.4 µT |
| USA |
9.2 |
0.9 |
| Canada |
11.8 |
3.3 |
| UK |
1.5 |
0.4 |
| Germany |
1.4 |
0.2 |
- Only about a half of homes in the UK with fields above 0.4 µT
get that exposure from high-voltage power lines – in the
rest, the field probably comes from the distribution system or
house wiring. more
- Fields have also changed over longer periods
of time – perhaps four-fold over the last forty years, though
this is hard to quantify. more
back |
