What is a fake EMF

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Some call it casually "electrosmog", others scientifically "EMF": What is meant in both cases are the physical fields that arise in connection with the diverse use of electrical energy and which we cannot perceive predominantly with our "five senses". Their effects on the human organism have been scientifically controversial for a long time. Every company has to decide for itself how to deal with this inconsistent assessment situation.

ibu - engineering office for building biology

Dr.-Ing. Martin H. Virnich

Although the official side always points out the validity of the existing limit values, even the Federal Office for Radiation Protection (BfS) recommends that the minimization requirement as far as possible be observed again and again under precautionary aspects: "ALARA" (As Low As Reasonably Achievable).

The terminology alone is a confusing and difficult to understand topic. The colloquial and ostensibly descriptive term "electrosmog" actually obscures more than it illuminates. For what appears to be a phenomenon in common parlance, in physical reality encompasses several different types of electrical, magnetic and electromagnetic fields.

Misleading abbreviation

The abbreviation “EMF” stands for the scientifically correct, but linguistically extremely cumbersome word aggregate “electrical, magnetic and electromagnetic fields”, but it is not easy to understand this abbreviation. Because the letters E and M are used twice: once separately (E for electrical and M for magnetic) and once combined as EM for electromagnetic fields. So it should actually be called E ‑ M-EM-F, but this abbreviation will be shortened again to EMF.

If one also takes into account the possible different time behavior of these fields, there are five different EM “field types”

  • Static electric fields (constant electrical fields)
  • Static or stationary magnetic fields (M constant fields)
  • Low-frequency alternating electrical fields (E ‑ NF)
  • Low-frequency alternating magnetic fields (M ‑ NF)
  • High-frequency electromagnetic fields (EM-HF, EM waves)

While static electric and magnetic fields also occur naturally on earth and we have been used to them since the ages of evolution, there are low and high frequency EMFs in nature only in extremely low intensities. In the civilized living and working environment, the technically created fields dominate by far in a very broad spectrum - here technology has significantly changed the natural electromagnetic spectrum.

These five field types have different sources or causes and, as a result, different physical properties and different spreading behavior.

Accordingly, separate measuring devices must be used for each field type for the professional measurement of immissions or emissions (there is no universal standard measuring device for all field types!), And long-term recordings are often required for fields with fluctuating intensity over time, for example. The different properties of the different field types also result in completely different requirements for effective field reduction measures. Shields, which are highly effective for low-frequency and static electric fields, for example, have no effect on magnetic fields, and the "Faraday cage" that is so often cited (and often in the wrong place) has only a very limited area of ​​action. Effective field reduction measures require specialist know-how.

Office workplaces

Office technology has been revolutionized in recent years and decades by electronics and communications technology. From the very beginning, the VDU workstation was the focus of critical consideration with regard to possible health complaints. As a result, the Swedish TCO guideline was created at a very early stage and test procedures were established for monitors that are allowed to carry the label “low-radiation according to TCO”.

In the meantime, this label has become almost a matter of course for screens, and for some years it has also been awarded for printers, scanners, copiers and fax machines. With a holistic view, one should of course take into account that it does not make much sense to work on a low-radiation screen in accordance with TCO if the workplace is exposed to significantly higher EMF emissions from other devices. The TCO guide values ​​have proven to be a good benchmark for assessing the overall situation at the workplace with regard to low-frequency fields. (see section "International Limits and Guideline Values").

The main causes of magnetic fields at office workplaces are typically the transformers of the power supply units in the office equipment and plug-in transformers that are outsourced from the equipment. Many desks have special storage trays for these plug-in transformers, for external power packs and power strips below the desk top - so these components are very close to the person working. The stray magnetic field reduces very quickly with increasing distance, but it should be at least one meter.

The clutter of device connection cables, extension cables and power strips under the desk often contributes to the fact that electrical 50Hz alternating fields are coupled to the desk and spread over the entire desk top; the strongest fields are then to be measured at the edge of the desk, immediately in front of the person working. The desks with electrical height adjustment, which are particularly favorable from an ergonomic point of view, are unfortunately noticeable in many cases due to this "desk electrics" due to particularly strong fields. This does not have to be, and there is another way, this is just a sign of the separate work of "specialists" in different areas, without a holistic approach.

In the private sector, for example, products such as water beds (with electric heating), electric blankets and baby monitors show that there is another way: Here there are the purest “field slings” and intelligent solutions with the declared and achieved goal of field poverty to almost zero emissions .

There is now a rich arsenal of shielded components available on the market for office workplaces, such as device connection cables, connector strips and cable ducts that do not emit any electrical fields [1].

In addition, you should make sure that the devices used are equipped with a mains plug with earthing contact, if possible. As a rule, these have significantly lower electrical fields than devices with the Euro flat plug. This also applies in particular to notebooks [2].

More and more cordless mice and keyboards are used as peripheral devices for notebooks and PCs. Even if the transmission power is not very high, this can lead to considerable pollution at the workplace, as the distance to the "radio device" is very short. And while the transmission power for Bluetooth applications for the office area was initially limited to the power classes 1 mW and 2.5 mW, today you usually find devices with 100 mW transmission power.

These short-range exposures can be avoided through the consistent use of corded keyboards and mice: a real mouse simply has a tail!

In order to save the "laborious and arduous" charging of the built-in batteries or the "complicated" battery change, charging mats (power mats) are offered, sometimes also directly as mousepads, on which, for example, wireless data transmission does not take place, but wireless energy transmission in Frequency range of several tens of kilohertz. The more energy is transferred, the stronger the fields are. And with the power mousepad, the user's hand lies directly on the field source!

Cordless telephones based on the DECT standard and WLAN for PC networking have become almost a matter of course in today's offices. Apart from the repeatedly noted security gaps due to the lack of encryption in WLAN, it should be noted that the access points are continuous transmitters. Even if there is no data to be "shoveled", the access point sends a permanent ready signal, 10 times per second: WLAN - always on! And in the delivery state, the WLAN is usually activated on PCs and notebooks. If you want to do without it, you have to deactivate it. Instead of WLAN, the wired network is not only the emission-minimized, but also the faster and more secure alternative in terms of data technology. The data transmission via the electrical network using in-house PLC (PowerLine Communication), e.g. known as dLAN.

The base stations of DECT cordless telephones are also classic permanent transmitters. Even if there is no phone call, they send out a ready signal that is periodically pulsed at 100 Hertz. For about three years now, variants with the feature “Eco Mode” or with similar-sounding names that contain the syllable “Eco” have been offered. Here the base station stops sending the otherwise permanent ready signal if only a single handset is registered with the base and this handset is in the base's charging cradle. Apart from the fact that this ruins the battery in the long run, the feature in this form is also not very user-friendly. The models with the “Eco Mode plus” or “fulleco” feature, in which the base station only transmits as long as the telephone is being used, represent a significant step forward. A list of DECT telephones with this feature can be found under [3].

Finally, wireless headsets are also very popular in offices. These often work according to the DECT standard - with a constantly transmitting base station. The corded headset is the alternative of choice here. But be careful: there are also corded headsets that also have a built-in DECT permanent transmitter. As well as telephones and fax combos with corded handset and integrated DECT base station or beamer with permanently active WLAN module. On the other hand, industry today offers many opportunities to create low-field jobs without having to forego comfort and performance. Prerequisite: The declared will to do so, the correct information about the market offer and areas of application and the skilful professional implementation.

Production jobs

In production, you often work with significantly greater electrical power than in the office area. Accordingly, very high EMFs can occur in the immediate vicinity of machines, systems, drives, transformers, motors, welding systems, induction furnaces, etc. Here, too, there are often options for field reduction through shielding, active compensation or new installation.

Non-linear consumers such as electronic controls, regulators, frequency converters, inverters and electronic ballasts of fluorescent lamps are a particular problem. The harmonics generated by these devices as a “dirty effect” have coined the phrase “dirty power”. Apart from possible interference with other devices, there may even be safety problems due to the 3rd harmonic (150 Hz) if an older electrical system with a reduced neutral conductor cross-section was installed. Since at 150 Hz, three times the fundamental oscillation, the currents do not compensate each other in the three-phase system, but add up, there can be considerable currents on the N conductor - up to the risk of fire.

External sources

In addition to the “home-made” immissions from their own devices and installations, workplaces can also be exposed to immissions from external sources. These are radio, television and mobile radio transmitters in the high-frequency range - the latter are the dominant source nowadays with four-fold area-wide mobile radio coverage by four network operators in three frequency bands (GSM 900 / D network, GSM 1800 / E network, UMTS) The new broadband service WiMAX (Worldwide Interoperability for Microwave Access) and LTE (Long Term Evolution), the fourth generation of mobile communications, the successor to GSM and UMTS, are in the starting blocks. Contrary to often read assurances, immission measurements show again and again that one is not protected from strong immission under an antenna on the roof of one's own office building.

In the low-frequency range, high-voltage lines, underground cables, risers, cable routes, transformers, railway systems and stray (false) currents are to be mentioned as field sources. Fault currents due to an unfavorable supply network (TN-C orTN-C ‑ S) can also develop on metallic pipe systems (water, gas, heating) and the shields of data lines.

Advice on reducing EMF

Here, as with many other sources, e.g. chemical sources, the basic principle is that "emission control takes precedence over immission control": It is better and easier to avoid the emission of fields centrally at the point of origin than to reduce immission locally in many places.

Operating principles:

  • Avoid the creation of fields: E.g. wired wire / fiber optic solutions instead of wireless / radio; Switch off devices or installations that are not required; Install electrical systems that cannot lead to the formation of stray (faulty) currents (pure TN-S network, TT network)
  • Keep distance from the field source or remove the field source from the location (e.g. power supply units, plug-in transformers, radio devices)
  • Shielding: shielded components (emission protection) or surface shielding (immission protection)
  • Use compensation effects through out-of-phase fields (passive, active, spatial, phase shift in three-phase networks)

In all measures to reduce EMF, the DIN VDE regulations must be observed, particularly with regard to compliance with and continued protection of people and property!

International limit and guide values

As already mentioned at the beginning, the biological effects and thus the health effects of EMF on the human organism are very controversial in science and society. Accordingly, there is a very wide range of limit values ​​and precautionary recommendations. Some examples of this are compiled in Table 1. This clearly shows the extremely different evaluation and risk assessment, because it is not about factors of two, five or ten, but two to three powers of ten! There are similarly large and even greater differences in the area of ​​high frequency.

Further reading and internet links

Safety engineer 12 | 2009

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