Going underground: Electrical substations and health

Concerned citizens and municipal authorities contacted their public health region about a proposal by an electrical utility company to build an underground electrical substation in an urban area, near to an elementary school and playground.

1. Background – substations and electromagnetic fields
2. Literature search
3. What are the health implications of exposure to ELF magnetic fields?
4. What is the potential for public exposure to ELF magnetic fields at substations?
5. Are there regulations on exposure to ELF magnetic fields for the public?
6. Should the precautionary principle be applied?
7. Conclusion

Authors
Acknowledgements
References

1. Background – substations and electromagnetic fields

Substations are used for the transmission and distribution of electricity, and are typically built above ground. To meet growing electricity demands in high density urban areas, and due to the limited availability and expense in acquiring land, an option is to place substations underground.

Placing substations underground or in basements of buildings has precedent, but is not a common practice. In Canada, the first underground substation became operational in 1984 in Cathedral Square, downtown Vancouver, above which is a fountain, walking paths and a grassy area. In Toronto, Copeland Station, is being built downtown beneath an existing machine shop.¹ In 2011, the first US underground substation was installed below a two acre park in Anaheim.² Other underground substations are operational or planned for Tokyo³  and Singapore.⁴ The existing underground substation in Frankfurt, Germany, has a green space and garden atop the installation.⁵

At distribution substations, a transformer decreases voltage (a step down process) and increases current before electricity is distributed to consumers.⁶ At a frequency of 60 Hz, the electricity flow from the power grid, including power lines and substations, emits non-ionizing radiation in the form of Extremely Low Frequency (ELF) electromagnetic fields, classified as below 300 Hz in the electromagnetic spectrum.⁷

An electromagnetic field is a wave of energy created when electrically charged particles move through space. An electric charge must be moving in order to create a magnetic field. Thus, in alternating currents at 60 Hz (cycles per second) in the power supply, the charges move back and forth, producing time-varying magnetic fields. The larger the charge and the faster its motion, the stronger the magnetic field created. The strength of a magnetic field is usually measured in tesla (T) or more commonly, microtesla (µT), which is one millionth of a tesla.⁸

Power frequency electric and magnetic fields can induce small circulating electrical currents within the human body, raising concerns about the impacts of electromagnetic fields on human health.⁹ Unlike electric fields, magnetic fields pass easily through barriers, such as walls, buildings or the ground, and are thus the main focus of concern about exposure and potential health risks.

2. Literature search

A rapid literature search was undertaken regarding exposure and health effects from ELF magnetic fields produced by electrical substations, as well as information on related guidelines and regulations. Databases accessed included Medline, CINAHL (EBSCO), Web of Science, Google, and Google Scholar. Keywords included “substation” “power line” or “transmission” AND “electromagnetic”, “magnetic” or “extremely low frequency” AND (“health” “cancer” “leukemia” “children” or “exposure”). Inclusion criteria: academic reviews published post-2014; reports on measurement of ELF magnetic fields; and national and international guidelines. Exclusion criteria: studies that examined radiofrequency or other non-ELF radiation effects, studies/reviews in a language other than English, and primary research conducted using animals or human cell lines.

3. What are the health implications of exposure to ELF magnetic fields?

Due to the limited number of underground substations existing in North America, few public concerns have been raised specifically about underground substations. However, a consideration is that children may be exposed to ELF magnetic fields when playing in greenspaces created above substations or attending daycares or schools situated nearby. In general, children are regarded as being more vulnerable to the effects of environmental exposures, including electromagnetic fields. Because ELF magnetic fields can pass through most materials, exposure to this type of non-ionizing radiation is of particular concern. Additional environmental health risks that are not considered here, but may be pertinent to underground substations, are the potential for noise, fire hazards,¹⁰ and vulnerability to seismic events.¹¹

In general, scientific studies differ as to whether they conclude that chronic exposure to low-level ELF magnetic fields may have health implications. Key findings of selected reports and reviews are summarized below.

• At the ELF range (≤ 300 Hz), electric and magnetic fields, when considered separately, do not cause photochemical reactions or tissue heating and therefore have been considered not capable of causing adverse health effects.¹²
• In 2002, the International Agency for Research on Cancer (IARC) classified ELF magnetic fields as “possibly carcinogen to humans” (Group 2B) primarily based on limited epidemiological evidence of their association with childhood leukemia, which is the most common malignancy overall in children and youth.¹³
• A 2016 review article¹⁴ supported the IARC 2B classification, citing recent studies showing an association between daily mean exposure levels exceeding 0.3 – 0.4µT with development of childhood leukemia. However, a causal relationship cannot be inferred as controversy remains about underlying biases, including selection bias, and there is a lack of convincing data on mechanisms, based on experimental studies using animal models.¹⁴
• A UK study¹⁵ also found an association between exposure to high voltage power-lines and childhood leukemia, even for distances of up to 600 m away. This finding was suspect as a magnetic field is usually not detected at a distance greater than 100 m from the power line center.¹⁶ As well, no relationship with leukemia was observed from exposure to underground cables and there were diminished effects observed from exposure in later study periods.¹⁵
• A pooled analysis of ten studies on the association of magnetic field exposure with childhood brain tumors concluded there was no consistent evidence of an increased risk.¹⁷
• A review on risks of infertility and adverse pregnancy outcomes associated with exposure to ELF magnetic fields emphasized study design limitations and conflicting results, with some studies (not all) showing positive associations with spontaneous abortions.¹⁸
• According to the Scientific Committee on Emerging and Newly Identified Health Risks there is no convincing evidence for a causal relationship between ELF magnetic fields and self-reported symptoms.¹⁹
• Apart from a cross-sectional study from Iran,²⁰ no publications specifically related adverse health outcomes to magnetic field exposure from substations. The Iranian study assessed cognitive effects in children related to the proximity of their school to a substation. Students from two schools in Tehran located near a high voltage electricity substation (distances of 30m and 50m, with an average magnetic flux destiny of 0.245 μT for both schools) had poorer working memory than those in control schools (magnetic field of 0.164 μT, at distances of 610m and 1390m). The relevance of this finding is unclear as cognitive function is affected by many factors not considered here, including socioeconomic variables.

4. What is the potential for public exposure to ELF magnetic fields at substations?

Magnetic field strength varies depending on voltage and current, type of transformer and substation, and distance from the source, with increasing distance corresponding to decreasing magnetic field strength. Spot measurements in public areas in European cities were conducted to summarize outdoor averages of ELF magnetic fields, where magnetic field strength ranged from 0.05 – 0.2 µT.²¹ Higher values occurred directly beneath high voltage power lines, while maximum fields at boundary fences of above ground substations were up to 20-80 µT.²¹ Measured values at a perimeter fence surrounding an above ground 275-400kV substation averaged 10 µT.²² In comparison, magnetic field measurements at UK substations had a mean value of 1.1 µT at the substation boundary and 0.2 µT up to 1.5 m from the boundary.²¹ The highest magnetic field is usually produced by the lines and cables supplying the substation and not by the equipment inside the substation itself.¹⁶

Repeated measurements of magnetic fields taken 1.5 m above ground level at two underground substations in Belgium (which transform 11000 V to voltages of 220 V and 400 V), averaged 0.2 µT and 0.35 µT (range 0.037 – 0.5 µT). These values were lower than that found in two detached substations (averaging 0.51 and 2.6µT). Maximum field values for underground substations were obtained when taken at ground level.²³ A wide range of magnetic field measurements were obtained from the existing Vancouver underground substation (0.2 – 10 µT).²⁴

No studies have assessed personal exposures to magnetic fields for children in residences, schools, or playgrounds in close proximity to substations. Personal monitoring for ELF magnetic fields from power lines was conducted in a study from Taiwan involving children at schools located close to high voltage transmission lines.²⁵ For selected classrooms and playgrounds within 30 m of the transmission lines, 27% of exposed children had a personal mean exposure greater than 0.4 µT during school hours.²⁵

5. Are there regulations on exposure to ELF magnetic fields for the public?

Guidelines and regulations for public exposure to power frequency magnetic fields vary widely. Canada and the US do not have federal guidelines or regulations regarding public exposure to power frequency magnetic fields. Health Canada (2016) states that there is “no conclusive evidence of harm caused by exposures at levels found in Canadian homes and schools, including those located just outside the boundaries of power line corridors… and …does not consider that any precautionary measures are needed regarding daily exposures to EMFs [electromagnetic fields] at ELFs…”.⁷

A 2008 statement from the Federal Provincial Territorial Radiation Protection Committee (FPTRPC) noted “Given the lack of convincing scientific evidence…there are no national guidelines in Canada limiting exposure to power-frequency EMFs”.²⁶

The majority of countries for which information was available tend to abide by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) 1998 guidelines for limiting exposure to time-varying electromagnetic fields, of 100 µT.²⁷ This guideline was changed to 200 µT in 2010.⁸ Many countries apply special limits in consideration of exposure to children, including Croatia, Finland, France (all 0.4 µT), while Sweden has some of the lowest limits (0.2 µT) (Table 1). It is not known if any of the guidelines are actually enforced.

Table 1: World-wide guidelines for extremely low frequency magnetic field exposure.

EU – European Union; WHO – World Health Organization; ALARA – as low as reasonably possible
* Special provision made for children
^ǂ When two values are given for a country, the second refers to children/day cares/schools 

6. Should the precautionary principle be applied?

The WHO Environmental Health Criteria Monograph on ELF fields⁴¹ concluded that because of uncertainties about the existence of chronic effects, and the limited evidence associating exposure to ELF magnetic fields with childhood leukemia, prudent avoidance is recommended to decrease exposure under the proviso that health, societal, and economic benefits of electric power are not compromised.⁴¹ Recommended precautionary measures that may reduce exposure to ELF magnetic fields, such as from substations, include engineering effective electrical configurations in the design stage; increasing the distance of the substations and cables away from public areas; and exploring the use of specialized shielding materials in major power cables and transformers.

According to the 2008 response statement by the FPTRPC, any precautionary measures applied to power lines should favour low cost or no cost options.²⁶ In 2008, Toronto city council adopted a product avoidance policy to minimise exposure to electromagnetic fields, particularly for young children near power line corridors. Any recreation or parkland, residential, school or day nurseries newly planned or amended, which are adjacent to power line corridors, must adopt low or no cost measures to minimize exposures to electromagnetic fields. Furthermore, a health impact assessment is required to minimise any increase to yearly average exposures when new or upgraded high-voltage transmission lines are proposed within the city.⁴²

7. Conclusion

There are no Canadian federal or provincial limits on public exposure to power frequency magnetic fields. Health Canada has taken the approach that evidence of harm from ELF electromagnetic exposure is inconclusive.

Some countries have proposed exposure limits of 0.4 µT, or less for children based on studies showing an association of childhood leukemia with exposure to power frequency magnetic fields exceeding 0.4 µT. However, the findings remain controversial due to potential biases in epidemiological studies to date.

The proposal to build an underground substation near to a school and playground was withdrawn by the electrical utility.

Authors

Helen Ward^1, Aroha Miller^1,2, Lydia Ma¹ and Tom Kosatsky^1,2

^1. National Collaborating Centre for Environmental Health, Vancouver, BC
^2. BC Centre for Disease Control, Vancouver, BC

Acknowledgements

The author wishes to acknowledge Michele Wiens of the National Collaborating Centre for Environmental Health who conducted the literature search and referencing.

References