Variation of emergency-room electromagnetic-interference potential

The diurnal behavior of electromagnetic fields within a typical urban-hospital emergency room was measured during a 4.4-day period. The merged 24-hour field plot showed strong day-night variation of field. Such variation indicated that there were times of higher risk of electromagnetic interference (EMI) during the 24-hour cycle, peaking between 12 noon and 10 pm. Using cumulative energy to produce an equivalent effective field, the effect of multiple simultaneous transmissions was found to slightly increase EMI risk.