Extremely low-frequency electromagnetic fields from indoor transformers: a review of occupational and residential exposure assessment studies

The widespread use of electrical and electronic devices in the 21st century has been attributed to human exposure to electromagnetic fields (EMFs), and potential public health threats. Amongst other electrical devices, indoor transformer stations have exposed both general public and workers to potentially high levels of extremely low-frequency electromagnetic fields (ELF-EMFs), resulting in acute and severe health implications. In this review, the health effects resulting from occupational and residential exposure to ELF-EMFs from indoor transformer stations were assessed by synthesizing evidence from published studies. Population, Exposure, Comparison and Outcome (PECO) framework was used as a guide in documenting the evidence, and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) to select studies that match the inclusion criteria. Following the PRISMA guide, a total of 13 studies formed part of this review. Highest magnetic field (MF) exposure level found from a residential exposure assessment study was 11.60 mu T, 0.2 m above the transformer station, with the lowest at 0.1 mu T due to household electrical appliances. Occupational exposure assessment revealed the highest exposure level of 4.67 mu T in the transformer room and lowest at >0.05 mu T. Cancer was mostly prevalent in residential studies with longer exposure period (>34 years), and with non-specific exposure symptoms (3 years and 18 months exposure period) within occupational exposure studies. This review found insufficient evidence to suggest the average exposure levels of ELF EMF from indoor transformers, which could pose significant health risks. However, these findings have a noteworthy implication for environmental health and occupational safety.