Power frequency or utility transmission power lines passing near or through a property can serious influence how the land might be developed for use. For instance, AC magnetic fields which are naturally emitted by power frequency lines, might cause serious interference (EMI) with sensitive equipment in a research laboratory or medical facility under consideration for construction. Growing concern exists that new schools not be sited near power lines as a precautionary measure against exposure of students to unknown health risks from power line EMF.

FMS provides land use planners, developers and lenders with the critical information about EMF from power frequency lines to make informed siting and investment decisions. The assessment of existing and future EMF conditions within the boundaries of a potential development project can provide guidance for changes in the project.

The first step in assessing EMF impact to a subject property from power lines is to conduct a survey by measuring existing AC magnetic fields present on the property from adjacent power sources such as power transmission lines. It is also important to note that EMF levels are capable of changing dramatically over very small periods of time. Indeed, AC magnetic fields from a transmission line can change as much as 100% to 300% or more from season to season – and can do so within a 24 hour period. An accurate assessment of EMF must take into consideration this potential for temporal variation and the changes in current loads that cause it.

Often, FMS constructs a computer model to calculate AC magnetic field levels from transmission and distribution lines. The computer model can predict magnetic field environments under varying conditions and loads. FMS computer models estimate AC magnetic field levels at different elevations as well as distances from the source, so decision makers can make an assessment of field values in relation to the height of the proposed building. Some relatively rare situations may require spot measurements on-site for correlation to the computer model and line loads. In some cases FMS has proposed that a potential EMF problem could be economically addressed by changes in the transmission line. In these cases, FMS has worked with the local utility to “rephase” the passing transmission lines, a process that, if properly done, will lower AC magnetic field values across the property of concern.