A detailed AC ELF magnetic field site survey of unoccupied
tenant space located on the "sub-cellar" level in a building
was performed on August 10th, 2005. Data recorded inside the tenant
space revealed magnetic flux density levels exceeding 422 milligauss
(mG) at the 1-meter level and as high as 4400 mG right underneath the
busways. Subsequently, a 6,004 ft AC ELF magnetic shielding solution
was recommended to attenuate levels to 10 mG and less under all normal
operating conditions.
Shielding installation began on 24 November 2005, and
was completed on 18 November 2005. During the shielding installation,
preliminary data was collected verify shielding performance. During
this data collection, it was noted that circulating ground currents
on the adjacent conduits (not originally intended for shielding) effected
the overall shielding performance.
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