14.0 Exposure limits
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Moreover, the significant differences of exposure limits for various groups of per-
sons are clearly visible, as well as the corresponding “maximum values“.
For EM fields at the workplace, there is a seperate prescription from the German
“Berufsgenossenschaften“ (BGV B11) which allows higher exposure for a short
time period.
Mathematical examples:
The 50Hz power supply system (mains wiring, high-voltage lines) would have a
maximum allowed electric field strength of under 250/0,050 = 5.000 V/m.
In contrast, an energy-saving lamp with an operating frequency of 5kHz, the
electric field strength may only be less than 87 V/m - a big difference.
Those low-frequency fields with the highest impact in daily life are those caused
by regular mains wiring and appliances operated very closely to the human
body, such as electrical shavers and hair dryers. Contrary to popular belief,
appliances such as TVs, computers and monitors are neglectible as they are
mostly shielded very well (TCO99) or operated at “large“ distances (TV) and
thus, exposure levels are very low.
14.2 Device limits
In contrast to limits for personal safety, the so-called device limits are often
SIGNIFICANTLY more restrictive and are subject to greater variations depen-
ding on frequency. For example, a hair dryers limit is totally different to that of a
computer monitor - values may well vary by a factor of 100. Nevertheless, all
device limits must also conform to limits for personal safety and are a sub-
set of those.
A good example for device limits are the well-known monitor labelling schemes
“MPR2“ and the more stringent “TCO99“, the latter of which will be outlined here.
TCO99 recommendations are again frequency-dependant:
Frequency E field [V/m] H field [µT]
5Hz-2kHz 10 0,200
2kHz-400kHz 1 0,010
There is a vast difference to the personal safety limits outlined previously.
However, it is noteworthy that the TCO99 recommendation also prescribes com-
plex details of the measurement setup such as specific distances, antennas,
number of measurements taken, monitor settings etc. for correct measurement.
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