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High magnetic field levels sufficient to cause excessive computer monitor distortion and concern about uncertain health effects, caused this high school in the midwest to abandon use of a large classroom and attached offices located immediately above the school’s basement transformer vault and main switchpanels.
This superimposed view of the classroom floor plan over the basement electrical facilities show that the utility transformer vault and distribution panels are immediately beneath the classroom. Peak magnetic fields of 112 mG are present in the classroom above. The entire classroom area has very sizable fields, averaging 26 mG..
Exposed copper bus bars mounted to the ceiling of the transformer vault (immediately beneath classroom floor) are the most significant source of magnetic fields.
As a first mitigation measure, FMS designed a custom manufactured multi-layer magnetic shield for installation around the exposed transformer vault ceiling mounted bus-bars.
This is a view of the custom manufactured multi-layer magnetic field shield for the bus-bars, just prior to shipment to the high school installation site.
This is a photo of the custom bus bar shield, being hoisted into an external entrance well, for installation around the ceiling mounted bus-bars.
This view shows the completed installation of the custom multi-layer shield around the exposed ceiling mounted copper bus bars.
As a second mitigation measure intended to further reduce elevated magnetic fields in the entire area of the classroom and attached office, FMS installed a continuous plane of shielding material on the floor of the classroom and offices.
This photo shows the completed installation of shielding material on the floor of the classroom and attached offices.
This is a 3D plot of magnetic field conditions at one meter from the floor, in the classroom area prior to the installation of the custom bus-bar shield and shielding of the classroom and office floors. Peak fields of 112 mG and an average of 26 mg were present throughout the classroom and offices. The second plot of magnetic field conditions at one meter from the floor in the classroom, shows the dramatic results after the FMS shielding installation. Peak conditions were reduced to less than 10 mG and the average throughout the classroom and offices was comfortably below 5 mG.
Over its 20 years, FMS has successfully completed hundreds of EMI projects which included a diverse range of consulting and mitigation services.