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      • Fields greater than 0.2 or 0.4 µT
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You are here: Home / Sources / Field levels and exposures / Fields greater than 0.2 or 0.4 µT

Fields greater than 0.2 or 0.4 µT

Why are we interested in fields greater than 0.4 microteslas?

Several epidemiology studies of magnetic fields and childhood leukaemia have used a field of 0.4 microtesla (µT) as a cutpoint in the analysis, to define the highest exposure group. Both the United Kingdom Childhood Cancer Study (UKCCS) and the Ahlbom pooled analysis used >0.4 µT as the top exposure category, and in the Ahlbom pooled analysis, it was only in this top category that a statistically significant association was found. Because of this, there is quite a bit of interest in homes with fields greater than 0.4 µT.

What exactly is the field we are interested in?

The epidemiological studies measured the background field in the home (often in the child’s bedroom). That is, they deliberately measured the field away from any domestic appliances. It is easy to find fields of greater than 0.4 µT close to appliances, we are interested here in homes where the field is greater than 0.4 µT even away from appliances.

They also measured the field for 24 hours or longer (often 48 hours). Fields vary over time. The field can go above 0.4 µT for short periods in quite a lot of homes. We are interested here only in homes where the 24 hour average is above 0.4 µT.

Finally, they measured the field in the home. Obviously we know that people spend time outside the home and are exposed to fields there as well, but it’s hard to measure that, and we often use the field in the home as a surrogate for total exposure. When people talk about “0.4 µT” they usually mean the field in the home.

How many UK homes are like this?

The largest set of measurements that we have of field in homes in the UK was done as part of the UKCCS.

They did measurements on 2226 homes of control children; just 9 (0.4%) were assessed as having fields greater than 0.4 µT.

44 (2.0%) had fields similarly assessed as greater than 0.2 µT.

Both these percentages are lower than in many other countries, particularly the USA.

Where do these fields come from?

We often assume that high magnetic fields must come from visible high-voltage power lines. Such lines certainly can produce fields greater than 0.4 µT. An average National Grid transmission line produces 0.4 µT within about 60 m (this is an average and the distance may be higher or lower for specific lines). More on fields from transmission lines and more specifically on how far from different overhead lines the field falls to 0.4 µT.

However, only some of the homes with these fields are close enough to a high-voltage power line to experience the high field from it. . The best figures we currently have (see above) are:

  • Fields greater than 0.4 µT: 43% of these homes
  • Fields greater than 0.2 µT: 23% of these homes

If the field does not come from a high-voltage power line, it probably comes from either distribution wiring outside the home or some feature of the wiring in the home. It is unusual for these sources to produce fields this high, but it is not impossible.

To find out exactly where these fields do come from, the electricity industry and the DTI jointly funded the then Leukaemia Research Fund to visit the homes. The work was done by HPA-RPD. The results were published in July 2005 as a Report and in March 2007 as a peer-reviewed paper.

They investigated 21 homes with fields (24-hour average in the general volume of the home) greater than 0.4 µT. 43% of these were due to high-voltage overhead lines. The breakdown is shown in the following diagram.

 diagram showing split of sources at 0.4 microteslas

 
They also did a similar exercise for homes with fields greater than 0.2 µT. As expected, less of these – 23% - come from power lines and more from low voltage sources, as shown in the following diagram.

 diagram showing split of sources for fields of 0.2 microteslas

 The original UKCCS paper suggested that only 1 of the 9 controls with fields greater than 0.4 µT received that exposure from a high-voltage power line. This new work shows that is more than this – slightly less than half - but it is still not all.

See also:

  • More information on field levels in homes
  • Some of the studies that have used these cutpoints - the UKCCS, CCRG and pooled analyses

 

Latest news

  • New publication on cancer incidence from the UK electricity industry Cohort Study August 27, 2019
  • How has the reported risk for childhood leukaemia changed over time? February 11, 2019
  • Media stories about microshocks in children’s playground September 10, 2018
  • New studies on leukaemia and distance from power lines June 1, 2018
older news

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To contact the electricity industry’s EMF Unit Public Information Line (UK only):
telephone 0845 7023270 or email [email protected].

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Navigation
  • What are EMFs
    • Terminology – an introduction
    • Electric fields
    • Magnetic fields
    • Units for measuring EMFs
    • Measuring and calculating EMFs
      • “EMF Commercial”
    • Adding fields together
    • Radiofrequencies
    • Screening EMFs
  • Sources
    • Overhead power lines
      • Fields from specific power lines
        • 400 kV
        • 400 kV – specific cases
        • 275 kV
        • 132 kV
        • 66 kV
        • 33 kV
        • 11 kV
        • 400 V/230 V
        • Replacing a 132 kV line with a 400 kV line
      • Summaries of fields from all power lines
      • Factors affecting the field from a power line
        • Voltage
        • Current
        • Clearance
        • Height above ground
        • Conductor bundle
        • Phasing
        • Balance between circuits
        • Balance within circuit
        • Ground resistivity
        • Two parallel lines
      • Calculating and measuring fields from power lines
        • Geometries of power lines
        • Raw data
        • On-line calculator
      • Fields from power lines – more detail on the physics
        • Field lines from a power line
        • The direction of the field from a power line
        • Power law variations in the field from a power line
      • Statistics of power line fields
    • Underground power cables
      • Different types of underground cable
      • Fields from cables in tunnels
      • Gas Insulated Lines (GIL)
      • Underground cables with multiple conductors
      • Effect of height on fields from underground cables
      • Screening fields from underground cables
    • Low-voltage distribution
      • UK distribution wiring
      • USA distribution wiring
    • House wiring
    • Substations
      • National Grid substations
        • Static Var Compensators
      • Sealing-end compounds
      • Distribution substations
      • Final distribution substations
        • Indoor substations
    • Transport
      • EMFs from electric trains (UK)
      • EMFs from cars
    • Appliances
    • Electricity meters
      • Smart meters
      • Traditional meters
    • Occupational exposures
      • Live-line work
      • Static Var Compensators
      • Occupational exposures on pylons
    • Field levels and exposures
      • Personal exposure
      • Other factors that vary with magnetic fields
      • Fields greater than 0.2 or 0.4 µT
    • Screening EMFs
      • Screening fields from underground cables
      • EMF Reduction Devices
  • Known effects
    • Induced currents and fields
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
      • Bees and microshocks
    • EMFs and medical devices
      • Standards relating to pacemakers and other AIMDs
    • Effects of EMFs on equipment
  • Research
    • Types of research
    • Epidemiology
    • Animal and laboratory experiments
    • Mechanisms
    • Specific studies
      • UKCCS
      • CCRG
      • French Geocap study
      • CEGB cohort
      • Imperial College study
  • Current evidence on health
    • Childhood leukaemia
      • Survival from childhood leukaemia
      • Childhood leukaemia and Downs
      • Childhood leukaemia and night-time exposure
      • The “contact current” hypothesis
    • Other health effects
    • Scientific review bodies
      • WHO
      • IARC
    • Electric fields and ions
    • Comparing EMFs to other issues
  • Exposure limits for people
    • Limits in the UK
    • Limits in the EU
    • Limits in the USA
    • Limits in the rest of the world
    • Limits from specific organisations
      • ICNIRP 1998
      • ICNIRP 2010
      • NRPB 1993
      • NRPB 2004
      • EU 2004
      • EU 2013
  • Policy
    • UK policy
      • Power lines and property – UK
    • Compliance with exposure limits
    • European EMF policy
    • Precaution
    • SAGE
      • SAGE First Interim Assessment
        • Government response to SAGE First Interim Assessment
      • SAGE Second Interim Assessment
        • Government response to SAGE Second Interim Assessment
        • SAGE Second Interim Assessment – the full list of recommendations
  • Finding out more
    • EMF measurement and commercial services
    • Links
    • Literature
    • Contact us
  • Static fields
    • Static fields – the expert view