TABLE 2-16 Typical Induced Currents and Fields for a 1-µT, 60-Hz Uniform Magnetic Field

 

Current Density, µA/m2

Electric Field, µ V/m

Subject

Average

Maximum

Average

Maximum

Human, 1.7 m, 70 kg

1.3-1.9a

8 (20)b

14-17.7

161 (296)b

Rat, 0.3 kg

0.3

1.31

4.4

17.7

Mouse, 0.02 kg

0.12

0.4

1.7

5.7

a The average current density depends on the electric properties used for the muscle tissue.

b Values in parentheses obtained from the analysis with an improved resolution of 0.65 cm instead of 1.3 cm.

SOURCES: Xi et al. 1994; Xi and Stuchly 1994.

a ratio of 1:9 is obtained for humans versus rats from the modeling results and 1:6 from the weight-to-volume ratios (maximum current path).

Induced current densities have also been computed for a lineman working near power lines (Stuchly and Zhao 1996). Predictably, both average and maximum values are much greater in this case than in environmental exposures. A comparison is given in Table 2-17. A range of maximum current densities induced locally by hand-held appliances is also given in the same table (Cheng et. al. 1995).

It is interesting to compare the induced currents for human exposure to 60-Hz electric versus magnetic fields. Referring to Tables 2-15 and 2-17, approximately the same maximum current densities (of 2 µA/m2) are obtained for an exposure to a 4-V/m electric field and a 0.1-µT (1-mG) magnetic field. (These results are for equal current densities in the head for the magnetic-field exposure and in the neck for the electric-field exposure.) Another comparison can be made by considering the average and maximum induced electric fields. For the electric-field exposure, the reduction factor is about 10 -7 for the average field and 10-5 for the maximum field as compared with the external electric field. Therefore,

TABLE 2-17 Current Densities Induced in a Person by a 60-Hz Magnetic Field Under Various Exposure Conditions

 

Induced Current Density

Exposure

Average

Maximum

0.2 µT, uniform

0.56 µA/m2

4.2 µA/m2

500 kV, 1,000 A, 0.5 m away

0.4 mA/m2

2.8 mA/m2

138 kV, 500 A, 0.5 m away

0.24 mA/m2

1.7 mA/m2

25 kV, 200 A, 0.5 m away

83 µA/m2

0.6 mA/m2

Hair dryers

0.1-8 mA/m2

Electric shavers

1.5-11 mA/m2



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