The minimum acceptable value of the shielding efficiency
depends on the maximum field strength likely to be
encountered, and the field strength that is acceptable to the
worker. During live work, a worker in the electric field
perturbs the field, i.e., the field strength is enhanced at some
parts of the worker's body and reduced at others, in
comparison with the unperturbed field which would have
existed without the worker. The greatest measured electric
field enhancement on a grounded person standing in a vertical
field is that at the forehead, where the local field strength is of
the order of 20 times the unperturbed field strength [4]. At the
end of an Outstretched arm, the enhancement factor is about
9.3.
Skin hair exposed to electric field becomes charged and
vibrates, which can produce unpleasant sensation. Hair
stimulation is a function of the electric field strength and the
wearer's body posture. One can conservatively adopt the 2%
annoyance threshold level (15 kV1m) as the acceptable
unperturbed field strength for head hair stimulation [5]. For
the enhancement factor of 20, this translates to a maximum
allowable field strength of 300 kVlm at the head within the
hood of the conductive suit. At the same time, it is reasonable
to assume than the actual maximum field strength at the outer
surface of the hood during live work is approximately 3000
kVIm, which corresponds to the corona onset field strength in
air. Consequently, a reduction factor of at least 10, or
shielding efficiency of at least 90% is needed in order to
reduce the external field of 3000 kV1m outside the hood to
the allowable value of 300 kV1m inside the hood. As pointed
out earlier, this value of shielding efficiency is achievable
relatively easily for modern conductive suits
The minimum acceptable value of the shielding efficiencydepends on the maximum field strength likely to beencountered, and the field strength that is acceptable to theworker. During live work, a worker in the electric fieldperturbs the field, i.e., the field strength is enhanced at someparts of the worker's body and reduced at others, incomparison with the unperturbed field which would haveexisted without the worker. The greatest measured electricfield enhancement on a grounded person standing in a verticalfield is that at the forehead, where the local field strength is ofthe order of 20 times the unperturbed field strength [4]. At theend of an Outstretched arm, the enhancement factor is about9.3.Skin hair exposed to electric field becomes charged andvibrates, which can produce unpleasant sensation. Hairstimulation is a function of the electric field strength and thewearer's body posture. One can conservatively adopt the 2%annoyance threshold level (15 kV1m) as the acceptableunperturbed field strength for head hair stimulation [5]. Forthe enhancement factor of 20, this translates to a maximumallowable field strength of 300 kVlm at the head within thehood of the conductive suit. At the same time, it is reasonableto assume than the actual maximum field strength at the outersurface of the hood during live work is approximately 3000kVIm, which corresponds to the corona onset field strength inair. Consequently, a reduction factor of at least 10, orshielding efficiency of at least 90% is needed in order toreduce the external field of 3000 kV1m outside the hood tothe allowable value of 300 kV1m inside the hood. As pointedout earlier, this value of shielding efficiency is achievablerelatively easily for modern conductive suits
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