Protection from electromagnetic fields

Protection from electromagnetic fields

Technology News |
By Jean-Pierre Joosting

The deadline is approaching. All EU member states must implement Directive 2013/35/EU, known as the EMF Directive, in their national laws by 1st July 2016. This means that employers face new challenges: They must make a risk assessment for every place of work and document the results. There was thus keen anticipation for the supplementary guidelines from the EU Commission that has come into force by the end of 2015. However, the “minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields)” – as in the original title of the Directive – have been in force since it was published, so employers need to get busy with this.

Directive 2013/35/EU, published on 29th June 2013, is not just a replacement for the previous Directive 2004/40/EC. It also replaces national regulations, because one aim of the EU is to unify workplace health and safety practices in order to minimize distortion of competition between the member states. In Germany, for example, the EMF Directive will be implemented through a new health and safety regulation, which will abolish the old familiar accident prevention regulation BGV B11, now known as DGUV 15. The contents of the Guidelines are incorporated into a technical regulation that replaces the performance regulations BGR B11, currently DGUV Rule 103-013.


Exposure level values and action levels

Among the new points in the EMF Directive are the exposure level values in the lower frequency range up to 10 MHz, which are primarily based on the recommendations of ICNIRP (International Commission on Non-Ionizing Radiation Protection) from 2010, whereas the previous Directive 2004/40EC was based on the ICNIRP recommendations of 1998. The limits for electric field strengths have also been tightened to some extent. In contrast, the permissible values for magnetic fields in the low frequency range are much more generous. The latest research and scientific knowledge has led the ICNIRP to adjust its limit value recommendations.

The EMF Directive takes two types of direct biophysical effect caused by electromagnetic fields into account. Firstly, these are thermal effects such as tissue heating caused by energy absorption, which occur with high frequencies. Strong high frequency fields can cause internal burns, leading to blindness in extreme cases, for example. Secondly, the EMF Directive considers effects such as muscle, nerve and sensory organ stimulation that can be caused by low frequencies. Such effects can cause optical illusions, for example.

In addition to this, the EMF Directive takes indirect effects into account, such as spark discharges and contact currents that can be induced by electromagnetic fields, interference with heart pacemakers or metallic implants, and the projectile risk from ferromagnetic objects – even a paperclip can become a dangerous missile in a strong static magnetic field.

Figure 1: Robot welding equipment.

The exposure level values (ELV), which are based on the actual field strengths within the human body, are mandatory for protection against biophysical effects. They cannot, however, be measured in practice. For this reason, the EMF Directive specifies so-called action levels (AL), which can be measured outside the human body. Human safety is adequately demonstrated as long as these action levels are not exceeded. This then automatically ensures compliance with the exposure level values.

Action levels – how to measure, when to act?

The EMF Directive makes a distinction here between thermal and non-thermal effects. Thermal effects are not only dependent on the field strength, but also on the frequency. For this reason, the Directive defines frequency dependent action levels in the range from 100 kHz to 300 GHz. Protective measures are needed if they are exceeded. Any measuring equipment used must therefore evaluate the field strengths correctly for frequency and accurately sum the individual effects, since there are usually lots of frequencies “on air” in the high frequency range – e.g., close to transmitter equipment. Personal field monitors worn on the person can warn staff of excessive field strengths in such situations.

Non-thermal effects are also frequency dependent. The EMF Directive therefore defines frequency dependent action levels for the range from 1 Hz to 10 MHz: Low action levels, above which sensory effects – transient changes in sensory perception – may occur, and high action levels, above which effects detrimental to health are to be expected. Protective measures are already required if the low action levels are exceeded. Preventive measures must be implemented to ensure that the high action levels are not exceeded.

Typical low frequency fields are primarily present in the industrial environment and are often pulsed fields. For this reason, the EMF Directive specifies the use of the weighted peak method, which weights the peak values in the time domain, as the reference method for non sine wave fields. Measuring instruments specifically designed for safety applications already implement this measurement method, also known as Shaped Time Domain (STD).

Figure 2: Person in transformer station.

Employers obliged to act

A new requirement of the EMF Directive is that employers must carry out a risk assessment for every workplace. This does not mean that measurements always have to be made everywhere, though. In many cases, such as in offices or laboratories where only low current devices are used, the compliance statements (CE marks) of the equipment manufacturers are sufficient. However, the sum of the exposure levels must be considered and calculated here where necessary.

In other cases, measurements must be made. If the action levels are exceeded, the employer must take action: Technically, by making use of alternative procedures, adding screening, providing protective equipment; or organizationally, by controlling access, limiting length of stay, operational instructions, etc.

The EMF Directive does not specify particular protective measures or any details of implementation. The guidelines to facilitate implementation of the Directive that the EU Commission cover calculation methods, describe the weighted peak method for the low frequency range, explain how to sum multi-frequency fields in the high frequency range, and give simplified procedures for small and medium-sized businesses as well as the formal requirements that have to be met by employers. This does not mean that there will need to be any changes in the measurement technology itself, however.

Narda Safety Test Solutions provide a comprehensive program of test equipment for verifying that workplaces comply with 2013/35/EU. Measurements are simplified and incorrect measurements avoided by means of wideband measuring sets that automatically allow for the frequency-dependent action levels, use of the Weighted Peak method, and direct display of the results as a percentage of the action level. Selective measuring equipment allows analysis of individual field sources, while at the same time providing an assessment of the overall field exposure that complies with the Directive. Personal monitors worn on the body give warning even before entering an area where the field strength is above the permitted level. Narda also provides suitable software for further evaluation, documentation, and management of the results.

Figure 3: Person near transmitter.

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