BBEMG - Belgian BioElectroMagnetics Group

Belgian BioElectroMagnetics Group

FAQ on other sources of EMF

FAQ on other sources of EMF

1. Could electricity in the human body set off an alarm in a supermarket? This has recently happened and I have not been able to explain the triggering of the alarm on my passage near the cashier.

No, electricity in the human body cannot set off this kind of alarm.

Antitheft systems in supermarkets are most of the time made up of a smart label with a coil stuck onto the product and when it goes off, a security gate reacts to the signal sent onto.

In your case, an it has already happened to me, perhaps you have on you or in your handbag a little object of which the label have not been removed or inactivated (it can be quite tiny). The typical example is that of make-up items (lipstick, for example).

2. In your website, you give magnetic field values for domestic electrical devices, as for example electric alarm clocks or bedside lamps. Measurement distances are the most often 30 cm. Could you provide me with field values at a larger distance, e.g. 1 meter? How does magnetic field intensity decrease with the distance.

In the surroundings of an electrical cable (e.g. a cable from a high voltage powerline), the field intensity is inversely proportional to the distance (in our jargon, we use the notation 1/r). In the surroundings of domestic cables ("round-trip" conductors), the field intensity decreases with the square of the distance (1/r²) and near a coil, as for example an industrial induction furnace, with the cube of the distance (1/r³).

To answer your question, electric alarm clocks, bedside lamps and most household appliances can be considered as sources from which magnetic field intensity decreases with the square of the distance. In concrete terms, this means that when the distance doubles, field intensity decreases by a factor of 4. For example, if the magnetic field intensity is 1 microTesla at 30 cm from an electric alarm clock, the intensity will become 0.25 µT at 60 cm, 0.0625 at 120 cm, and so on.

3. I would like to know to how strong an electromagnetic field intensity I am subjected when close to an induction stove top. The resulting field must be quite high since the metal heats up so quickly. Is this field dispersed in every directions or only upwards (to the saucepan)?

Before consulting the exposure values below, you must keep in mind that the frequency range is not limited to 50 Hz: components of higher frequencies also exist (see question 3 in FAQ on calculations and technical questions).

In 2006 we performed measurements around an induction stove top with an ESM-100 Maschek measuring device, which gives components of an induction field at 50 Hz, but also in the range of 5 Hz to 400 kHz. This apparatus can therefore give various values: an overall value on the whole range of frequency ('all'), an overall value in the lower part of the frequency range from 5 Hz to 2 kHz ('low') and an overall value in the higher part of the frequency range from 2 to 400 kHz ('high').

Below you will find the results of the measurements (µT means microTesla i.e. a millionth of Tesla).

Initial ambiant atmosphere:

  • everything off, during the day : +/- 0,03 µT in the whole frequency range (a little less in 'high')
  • everything off, in the evening : more or less 0,3 µT
   

One position 'On' (max value) without hood

Idem with hood in 'normal' functioning

Four positions 'On' + hood

Low frequencies
'low'

10 cm

0,2 µT

0,4 µT

0,5 µT

 

60 cm

0,06 µT

1 µT

1,3 µT

High frequencies
'high'

10 cm

5 µT

2 µT

6 µT

 

60 cm

0,3 µT

0,3 µT

5 µT

Overall value
'all'

10 cm

n.a.

2 µT

8 µT

 

60 cm

0,3 µT

1 µT

n.a.

50 Hz

10 cm

0,15 µT

0,4 µT

0,5 µT

 

60 cm

0,04 µT

0,9 µT

1 µT

In front of a stove top, at around 50 cm or even 1 m, the field is always reduced at around 0,3 µT (four positions 'On' + hood) (value at 50 Hz).

So, an induction stove top in use generates a 50 Hz field of 0,3 µT just in front of the stove top (for the cook) and up to 1 µT above the positions in use if the hood is functioning (field mainly coming from the hood). High frequency components generate fields higher than those at 50 Hz.

4. Could you inform me about the electric and magnetic fields generated by a photovoltaic system:

a) From 2 assemblies (assembled in parallel) of 10 collectors (6A direct current at 30V) connected in series (editor's note: see X for an explanation of the connections of the collectors).
b) From the inverter.

In direct (non time-varying) current, the health effects of magnetic fields are negligible. (They reach several teslas, such as in NMR in hospitals). If you want an approximate idea of the value of the magnetic induction field, estimate the distance from the panels and apply the following formula:

B (en Tesla) = µ . i / (2 . pi . r)

where

µ is the permeability of free space (see Glossary - Magnetic permeability)

i (in A) = the current through the panels

pi = 3.14

r = the distance from the panels

Thus using your data, it is around 0.5 microtesla 2m away from the panels. It is constant (not time-varying). As a comparison, the earth's magnetic field, also constant in time, is around 40 microteslas at our latitudes (50° north).

For the inverter a measurement will be required, but the increase in the field is clearly very localised (a few tens of cm). There remains the supply line, which like any line generates a nearby field, which rapidly falls to 0.4 microtesla beyond a few tens of cm (let's say 20 cm).

Likewise, the electric field only has a potential impact on health if it is variable (fortunately other than for thunderstorms...), but there is of course a constant electric field. This field depends on the configuration and the radius of the live conductors. It decreases very quickly with the distance from the conductor. Given the orders of magnitude here, it is of the order of a few V/m in the immediate proximity, much less than the earth's natural field.

Close to your inverter, there is also a field that can be variable as you have a 50 Hz output. It is inevitably of the same order of magnitude as the rest of your electrical installation as the voltage is the same and the conductors used have the same diameter. Again there may be an effect close to the inverter depending on its design (coils or electronic), but it is very localised.

Note:

There are different ways to connect photovoltaic collectors together: in series, in parallel, or combined series/parallel.

  • The serial system delivers high voltages as the voltages of each collector are added together: the 10 x 6A and 30V collectors connected in series will always supply 6A direct current (insofar the collectors are all exposed to sunlight in the same way), but at a voltage of 300V.
  • The parallel system delivers high currents: the 10 x 6A and 30V collectors connected in parallel will supply 60A direct current, at a voltage of 30V
  • The combined systems: this is the connection described in this question. We have a system with 2 x 10 collectors in series. The 2 assemblies of 10 collectors are assembled in parallel. The system can thus supply 12A and 300V.

5. We installed photovoltaic panels on the roof of our house. The inverter is placed on the outside wall of our daughter’s bedroom (7-year-old). We assume that a magnetic field is generated by this equipment, and we are especially worried about her health as she is going to sleep just beside it.

It is true that a magnetic field is generated by the inverter. Its intensity directly depends on the current intensity that is flowing through the equipment. Thus magnetic field values will depend on the outdoor brightness. In the evening and at night, panels are not working and no magnetic field will be generated.

You will find values measured around an inverter on the following page: Photovoltaic panels.

With these measurements, we can state that at around 1 m of the inverter when the panels are delivering their maximum capacity, magnetic field intensities fall to low values.

6. Do energy saving bulbs expose us to high electromagnetic fields ?

Energy saving bulbs (or compact fluorescent lamps, CFL) are composed of a fluorescent tube turned up on itself. In a fluorescent tube, light is produced in 2 steps: (1) the passage of electric current leads to excitation of atoms of gas in the tube, which primarily generates ultraviolet radiation, (2) this radiation is then absorbed by the fluorescent material that covers the inner tube and is converted into light.

The principle of functioning is described in the following page : Uses of electricity and electromagnetic properties.

These lamps generate both low frequency fields and higher frequencies fields (due to the electronic ballast). The waveform and the harmonic contents of a 11 W economic lamp are shown in the two figures below.

Waveform of a 11 W economic lamp

The harmonic contents of a 11 W economic lamp

Source : Decat et al, 2007 (1)

The team of Gilbert Decat (BBEMG 2005-2009) performed measurements at different distances from eight energy saving bulbs, a halogen lamp and an incandescent lamp (see a summary table in the file LampPoster.pdf). The values measured are within the exposure limits recommended by ICNIRP (1998) and the Council of Europe (1999/515/EC). However, at a distance of 5 cm from the lamps, some higher frequencies components of the electric field may exceed the reference values of ICNIRP. As a precaution, it is advisable to place energy saving lamps at 20 cm from people. This recommendation is also based on the fact that interferences between electric field and old pacemakers (produced before 1990) could occur when holders of these cardiac implants are too close to the lamps.

For further information on exposure values, we suggest to consult documents available at: http://www.gd-emf-consulting.be/?p=6 ou http://www.gd-emf-consulting.be/?p=7. Please feel free to contact Gilbert Decat if you do not find the documents needed.

(1) Decat, G., Meynen, G., & Van Tichelen, P. (2007). Evaluatie van het elektrisch en magnetisch veld van spaarlampen. Eindverslag, Studie uitgevoerd in opdracht van LNE, 2007/IMS/R/.

7. I sleep near the electrical meter and panel of my house.  Given the large amounts of electric and magnetic fields, is there a risk for my health? Are there any shields that would reduce the fields?

The intensity of the magnetic field depends on the current intensity. Usually at night, we consume little energy and intensity of the magnetic field around the meter and the panel is very low.

Also the magnetic field strength decreases rapidly with distance: at 1 m, the field strength is already much lower than against the facilities.

A measurement would be useful to know exact field levels, but the placement of your bed on the opposite wall of the meter should already be sufficient to reach low levels.

There are special materials that allow shielding magnetic field, but they are very expensive and require a very careful placement. They are rarely used. You will find further information in the following thematic file: Magnetic field attenuation.

8. In the cities, electric cables often run along the facades. Sometimes, public lighting is even hung to houses, at bedroom height. Is there no electromagnetic pollution in homes related to these cables?

Magnetic field intensity depends on the intensity of the current flowing through the cable.

We made measurements in a house. The probe has been located against the inside wall, at the height of the electrical cables. The distance between the probe and the cables was 36 cm. The following figure shows the magnetic field values recorded. Values range from 1 to 5 µT.

Public lighting 

We also made spot measurements when we place the probe (around 11 am) and when we remove it (around 9 am). At 1 m from the wall, measured values were always below 0.3 – 0.4 µT.

Public lighting was switched on at 9:16 pm. Measurements do not allow us to distinguish magnetic fields generated by public lighting from those generated by distribution cable, however values should vary according to electrical consumption and public lighting should not make a difference.

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Latest update on 23/04/2015

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