Effects function simulation of residential appliance field exposures

This paper demonstrates the application of effects function analysis to residential magnetic field exposure, focusing on appliance sources and mitigation choices. Residential field exposure time series were synthesized by using a sample of background household field measurements, a model of average daily appliance use, and a small sample of EMDEX data of field exposure from 12 household appliances. Four alternative effects functions (average field strength with or without a threshold, field strength window, sudden field changes) were simulated by using the synthesized time series data for different exposure situations, such as high and low levels of appliance use, simple avoidance, and use of a set of hypothetical “low field” appliances (50% lower fields). In particular, field exposure from the use of bedside clocks and electric blankets was examined. Results demonstrate that the choice of effects function is critical for the ranks of field sources and exposure reduction choices. For the effects function of average field strength with or without a threshold, exposure from background fields dominated exposure from all appliances except for bedside clocks and electric blankets. In the case of the field strength window effects function, the dominant field sources changed with the width of the window. For the effects function based on rapid field changes, appliance use was the major source of exposure. Because of the small sample size of our data set and other simplifications, specific results should be viewed as illustrative. Bioelectromagnetics 18:116–124, 1997. © 1997 Wiley-Liss, Inc.     

Comparison of residential power-frequency magnetic fields away from appliances in different countries

The purpose of this paper is to review measurements of residential power-frequency magnetic fields made in different countries and to determine whether average magnetic fields away from appliances are higher in some countries than in others. The paper includes 27 studies reporting measurements of residential magnetic fields in samples of homes: 14 from North America, 5 from the United Kingdom, and 8 from other European countries. Various factors that might make the results from individual studies unrepresentative of average fields in the relevant country are identified and discussed. Because distributions of magnetic fields generally are approximately log-normal, they are summarised by their geometric means. The best estimate of the geometric means of long-term average background fields in the United States is 60-70 nT and in the United Kingdom approximately 36-39 nT. In other countries, there are insufficient studies to draw firm conclusions on average fields. Measurements of personal exposure are higher than measurements of background fields, perhaps because they include exposures from appliances and other sources in the home. The ratio of personal exposure to background field seems, on average, to be approximately 1.4.     

Magnetic-field flux density and spectral characteristics of motor-driven personal appliances

Flux density and spectral measurements were carried out on magnetic fields generated by several types of motor-driven personal appliances used near the body. Among the units tested were several for which the average flux densities, as determined at the surfaces of the appliance, exceeded 0.4 mT. Time-rates-of-change (dB/dt) for several units exceeded 1000 T/s, and several units exhibited high-frequency components in the low-MHz range. Use of such appliances, although normally of short duration, can represent exposure to magnetic fields of relatively high flux density, which may also have high-frequency components. Compared to other household and commercial sources of magnetic fields, those generated by certain motor-driven personal appliances may represent a significant contribution to time-weighted average exposure and may represent an important source of local induced currents in the body. Furthermore, high-frequency transients that represent only a minor contribution to time-weighted average exposure may generate significant instantaneous induced currents. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

The possible role of contact current in cancer risk associated with residential magnetic fields

Residential electrical wiring safety practices in the US result in the possibility of a small voltage (up to a few tenths of a volt) on appliance surfaces with respect to water pipes or other grounded surfaces. This "open circuit voltage" (V(OC)) will cause "contact current" to flow in a person who touches the appliance and completes an electrical circuit to ground. This paper presents data suggesting that contact current due to V(OC) is an exposure that may explain the reported associations of residential magnetic fields with childhood leukemia. Our analysis is based on a computer model of a 40 house (single-unit, detached dwelling) neighborhood with electrical service that is representative of US grounding practices. The analysis was motivated by recent research suggesting that the physical location of power lines in the backyard, in contrast to the street, may be relevant to a relationship of power lines with childhood leukemia. In the model, the highest magnetic field levels and V(OC)s were both associated with backyard lines, and the highest V(OC)s were also associated with long ground paths in the residence. Across the entire neighborhood, magnetic field exposure was highly correlated with V(OC) (r = 0.93). Dosimetric modeling indicates that, compared to a very high residential level of a uniform horizontal magnetic field (10 mu T) or a vertical electric field (100 V/m), a modest level of contact current (approximately 18 mu A) leads to considerably greater induced electric fields (> 1 mV/m) averaged across tissue, such as bone marrow and heart. The correlation of V(OC) with magnetic fields in the model, combined with the dose estimates, lead us to conclude that V(OC) is a potentially important exposure with respect to childhood leukemia risks associated with residential magnetic fields. These findings, nonetheless, may not apply to residential service used in several European countries or to the Scandinavian studies concerned with populations exposed to magnetic fields from overhead transmission lines.     

Residential exposure to magnetic fields generated by 110-400 kV power lines in Finland

In a specific case, the magnetic field generated in a building by a nearby power line is usually easy to calculate, although the accuracy of these calculations is sensitive to the quality of source information. To be able to study public health dimensions of magnetic field exposure (e.g., risk of cancer), it is necessary to evaluate the size and exposure of the population at risk. Relatively little quantitative information on public exposure to power-frequency magnetic fields of high-voltage power lines is available. This report describes residential exposure to magnetic fields from 110 kV, 220 kV, and 400 kV power lines in Finland at the national level, including 90% of the total line length in 1989. A geographical information system (GIS) was used to identify the buildings located near the power lines. After determining the distances between the lines and the buildings, historical data on load currents of these lines were used to calculate the magnetic fields. The residential magnetic field histories were then linked to the residents by means of a computerized central population register. The data obtained on personal exposure have also been utilized in a nationwide epidemiological study on magnetic field exposure of power lines and risk of cancer. The methods of exposure assessment and results of the number of buildings near 110 kV, 220 kV, and 400 kV power lines, their average annual magnetic fields, and personal exposure to magnetic fields from these lines are described. We found that 15,600 residents lived in an average residential magnetic field ≥0.1 μT caused by power lines in 1989. The number of these residents increased fivefold during 1970-1989. We estimated that 0.3% of the population was exposed in their residences to an annual average magnetic flux density from 110 kV, 220 kV, and 400 kV power lines higher than 0.1 μT, the level that the background magnetic flux density in general does not exceed in Finnish homes. Thus, the problem of magnetic field exposure generated by high-voltage lines concerns only a relatively small fraction of the total population in Finland. However, the size and exposure of the population at risk remain somewhat arbitrary in practical multisource situations, as the biological interaction mechanism, the concept of harmful dose, and, in particular, the significance of the duration of exposure are unknown. © 1995 Wiley-Liss, Inc.     

Comparison between personal exposure to 60 Hz magnetic fields and stationary home measurements for people living near and away from a 735 kV power line.

This study compares stationary home measurements with a personal exposure monitor of 60 Hz magnetic fields in a group of 18 people living near a 735 kV line and 17 people living far away from the line. Most of them were white collar workers who worked during the day. They wore a personal Positron meter for 24 h, while a similar meter was left in their home, away from any appliances. For people living away from the line, the impact of residential activities appeared rather weak when considering the average intensity of the field during the awake period (at home): 0.22 microT for personal exposure versus 0.18 microT for stationary measurements (P = 0.09). The impact of residential activities during the awake period was more detectable when using the percentage of time with exposure above 0.78 microT: median 0.4 for personal vs. 0.0 for stationary measurements (P =.01). The temporal variability of the exposure during the awake period was also significantly higher for personal exposure than for stationary measurements. For people living near the line, the intensity of the magnetic field from the line dominated the personal exposure when considering the mean of measurements and the percentage of time above a threshold. However, the temporal variability was greater for the personal exposure during the awake period. Although limited due to its small sample size, the present study seems to demonstrate the usefulness of considering different indexes of exposure when assessing residential exposure to 60 Hz magnetic fields.     

An analysis of associations between social class and ambient magnetic fields in metropolitan Melbourne.

In the course of a study on residential magnetic-field exposure, some incidental data were obtained that bear on the issue of confounding of magnetic field exposure by social class. We have explored the possibility that the magnetic flux density of 50 Hz fields measured in Melbourne streets is correlated with a number of variables that index the socio-economic status of the neighborhood. We have examined also for a correlation between field-intensity levels and sums of some or all of the indicators, which were weighted to provide an overall score on socio-economic status. Although some of the indexes were weakly, but significantly, correlated with environmental levels of magnetic fields, the combined indices were not. These results indicate that socio-economic status is not likely to be a confounder in epidemiological studies of residential exposure to ELF magnetic fields in Melbourne.     

Residential magnetic fields predicted from wiring configurations: II. Relationships To childhood leukemia.

Case-control data on childhood leukemia in Los Angeles County were reanalyzed with residential magnetic fields predicted from the wiring configurations of nearby transmission and distribution lines. As described in a companion paper, the 24-h means of the magnetic field's magnitude in subjects' homes were predicted by a physically based regression model that had been fitted to 24-h measurements and wiring data. In addition, magnetic field exposures were adjusted for the most likely form of exposure assessment errors: classic errors for the 24-h measurements and Berkson errors for the predictions from wire configurations. Although the measured fields had no association with childhood leukemia (P for trend=.88), the risks were significant for predicted magnetic fields above 1.25 mG (odds ratio=2.00, 95% confidence interval=1.03-3.89), and a significant dose-response was seen (P for trend=.02). When exposures were determined by a combination of predictions and measurements that corrects for errors, the odds ratio (odd ratio=2.19, 95% confidence interval=1.12-4.31) and the trend (p =.007) showed somewhat greater significance. These findings support the hypothesis that magnetic fields from electrical lines are causally related to childhood leukemia but that this association has been inconsistent among epidemiologic studies due to different types of exposure assessment error. In these data, the leukemia risks from a child's residential magnetic field exposure appears to be better assessed by wire configurations than by 24-h area measurements. However, the predicted fields only partially account for the effect of the Wertheimer-Leeper wire code in a multivariate analysis and do not completely explain why these wire codes have been so often associated with childhood leukemia. The most plausible explanation for our findings is that the causal factor is another magnetic field exposure metric correlated to both wire code and the field's time-averaged magnitude.     

Residential magnetic fields predicted from wiring configurations: I. Exposure model.

A physically based model for residential magnetic fields from electric transmission and distribution wiring was developed to reanalyze the Los Angeles study of childhood leukemia by London et al. For this exposure model, magnetic field measurements were fitted to a function of wire configuration attributes that was derived from a multipole expansion of the Law of Biot and Savart. The model parameters were determined by nonlinear regression techniques, using wiring data, distances, and the geometric mean of the ELF magnetic field magnitude from 24-h bedroom measurements taken at 288 homes during the epidemiologic study. The best fit to the measurement data was obtained with separate models for the two major utilities serving Los Angeles County. This model's predictions produced a correlation of 0.40 with the measured fields, an improvement on the 0.27 correlation obtained with the Wertheimer-Leeper (WL) wire code. For the leukemia risk analysis in a companion paper, the regression model predicts exposures to the 24-h geometric mean of the ELF magnetic fields in Los Angeles homes where only wiring data and distances have been obtained. Since these input parameters for the exposure model usually do not change for many years, the predicted magnetic fields will be stable over long time periods, just like the WL code. If the geometric mean is not the exposure metric associated with cancer, this regression technique could be used to estimate long-term exposures to temporal variability metrics and other characteristics of the ELF magnetic field which may be cancer risk factors.     

Association of residential magnetic fields with contact voltage

The US National Electrical Code's (NEC) requirement to ground a home's electrical service to the residential water line results in a voltage between the water line and earth, V W-E. The voltage may result from ground return current that flows into the earth via the water line or from inductive effects from other sources of magnetic fields, such as transmission lines. This voltage can, in turn, serve as a source for Vbath, the voltage between the water fixtures and conductive drain pipes sunk into the earth beneath a residence. Vbath can be a source of contact current exposure to a child touching a water fixture while bathing. Previous research has suggested that exposure to these currents could be the basis for the association between power-frequency magnetic fields and childhood leukemia. In this study, we assessed the association between measured Vbath and VW-E with the average spot-measured magnetic field, Bavg, in a sample of 191 single-family residences in the Denver metropolitan area. This area was the source of cases and controls for previous studies of electric and magnetic field (EMF) and childhood cancer. The association of both Vbath and VW-E with Bavg had upward trends across magnetic field strata (<0.1 microT (reference); 0.1-<0.3 microT; and > or = 0.3 microT). In addition, VW-E was associated with Vbath. Without further study, these results cannot be applied to multi-dwelling residences or to electrical systems prevalent in other nations. Nonetheless, when combined with the finding that contact current is a far more plausible candidate than the residential magnetic field for mediating biological effects on the basis of comparative dose to bone marrow, these associations indicate that contact current exposure deserves further study.     

Spectral analysis of magnetic fields from domestic appliances and corresponding induced current densities in an anatomically based model of the human head

Magnetic fields emitted by electric appliances such as razors, hair dryers, and drills were measured in the frequency domain. Results show the presence of high-frequency components (up to 96 kHz for razors, up to 3.4 kHz for hair dryers, and up to 8.6 kHz for drills) in the harmonic content of the fields. The measured fields were used to calculate the induced current densities in an anatomically based model of the human head (resolution 1.31 cm) by using the impedance method. The harmonic field contribution to the current density was higher than that from the carrier frequency for all the tested appliances. © 1995 Wiley-Liss, Inc.     

The relationship between residential magnetic fields and contact voltage: a pooled analysis

It has been suggested that residential exposure to contact currents may be more directly associated with the potential for an increased risk of leukemia in childhood than magnetic fields. Contact current exposure occurs when a child contacts a bathtub's water fixtures, which are usually contiguous with a residence's electrical ground, and when the drainpipe is conductive. The Northern California Childhood Leukemia Study (NCCLS) is the only epidemiological study known to address whether contact current may confound the reported association between residential magnetic fields and childhood leukemia. The study contributed contact voltage and magnetic-field data for over 500 residences of leukemia cases and control children. We combined these data with the results of previous measurement studies of contact voltage in other communities to conduct an analysis of the relationship of magnetic fields with contact voltage for a total sample of 702 residences. The Spearman correlation of magnetic field with contact voltage was 0.29 (Spearman, P < 0.0001). Magnetic-field and contact voltage data were both divided into tertiles, with an upper magnetic-field cutpoint of 0.3 μT suggested by values used in epidemiological results and an upper contact voltage cutpoint of 60 mV based on dosimetric considerations. Expressed as an exposure odds ratios (EOR), we report an association of contact voltage with magnetic fields of 15.1 (95% CI 3.6-61) as well as a statistically significant positive trend across magnetic-field strata (EOR of 4.2 per stratum with 95% CI 2.4-7.4). The associations appear to be large enough to support the possibility that contact current could be responsible for the association of childhood leukemia with magnetic fields.     

Development of a protocol for assessing time-weighted-average exposures of young children to power-frequency magnetic fields

A study was carried out in 1990 to guide the development of a protocol for assessing residential exposures of children to time-weighted-average (TWA) power-frequency magnetic fields. The principal goal of this dosimetry study was to determine whether area (i.e., spot and/or 24 h) measurements of power-frequency magnetic fields in the residences and in the schools and daycare centers of 29 children (4 months through 8 years of age) could be used to predict their measured personal 24-h exposures. TWA personal exposures, measured with AMEX-3D meters worn by subjects, were approximately log-normally distributed with both residential and nonresidential geometric means of 0.10 μT (1.0 mG). Between-subjects variability in residential personal exposure levels (geometric standard deviation of 2.4) was substantially greater than that observed for nonresidential personal exposure levels (1.4). The correlation between log-transformed residential and total personal exposure levels was 0.97. Time-weighted averages of the magnetic fields measured in children's bedrooms, family rooms, living rooms, and kitchens were highly correlated with residential personal exposure levels (r = 0.90). In general, magnetic field levels measured in schools and daycare centers attended by subjects were smaller and less variable than measured residential fields and were only weakly correlated with measured nonresidential personal exposures. The final measurement protocol, which will be used in a large US study examining the relationship between childhood leukemia and exposure to magnetic fields, contains the following elements: normal- and low-power spot magnetic field measurements in bedrooms occupied by subjects during the 5 years prior to the date of diagnosis for cases or the corresponding date for controls; spot measurements under normal and low power-usage conditions at the centers of the kitchen and the family room; 24-h magnetic-field recordings near subjects' beds; and wire coding using the Wertheimer-Leeper method. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Early pregnancy loss and exposure to 50-Hz magnetic fields

The possibility of an association of early pregnancy loss (EPL) with residential exposure to ELF magnetic fields was investigated in a case-control study. Eighty-nine cases and 102 controls were obtained from the data of an earlier study aimed at investigating the occurrence of EPL in a group of women attempting to get pregnant. Magnetic-field exposure was characterized by measurements in residences. Strong magnetic fields were measured more often in case than in control residences. In an analysis based on fields measured at the front door, a cutoff score of 0.5 A/m (0.63 μT) resulted in an odds ratio of 5.1 (95% confidence interval 1.0–25). The results should be interpreted cautiously due to the small number of highly exposed subjects and other limitations of the data. © 1993 Wiley-Liss. Inc.     

Power frequency magnetic fields and risk of childhood leukaemia: Misclassification of exposure from the use of the ‘distance from power line’ exposure surrogate

A recent study examining the relationship between distance to nearby power lines and childhood cancer risk re‐opened the debate about which exposure metrics are appropriate for power frequency magnetic field investigations. Using data from two large population‐based UK and German studies we demonstrate that distance to power lines is a comparatively poor predictor of measured residential magnetic fields. Even at proximities of 50 m or less, the positive predictive value of having a household measurement over 0.2 µT was only 19.4%. Clearly using distance from power lines, without taking account of other variables such as load, results in a poor proxy of residential magnetic field exposure. We conclude that such high levels of exposure misclassification render the findings from studies that rely on distance alone uninterpretable. Bioelectromagnetics 30:183–188, 2009. © 2008 Wiley‐Liss, Inc.     

A model for characterizing residential ground current and magnetic field fluctuations

The current through the residential grounding circuit is an important source for magnetic fields; field variations near the grounding circuit accurately track fluctuations in this ground current. In this paper, a model is presented which permits calculation of the range of these fluctuations. A discrete network model is used to simulate a local distribution system for a single street, and a statistical model to simulate unbalanced currents in the system. Simulations of three-house and ten-house networks show that random appliance operation leads to ground current fluctuations which can be quite large, on the order of 600%. This is consistent with measured fluctuations in an actual house. © 1994 Wiley-Liss, Inc.     

Extremely low-frequency magnetic fields of transformers and possible biological and health effects

Physiological processes in organisms can be influenced by extremely low-frequency (ELF) electromagnetic energy. Biological effect studies have great importance; as well as measurement studies since they provide information on the real exposure situations. In this study, the leakage magnetic fields around a transformer were measured in an apartment building in Küçükçekmece, Istanbul, and the measurement results were evaluated with respect to the international exposure standards. The transformer station was on the bottom floor of a three-floor building. It was found that people living and working in the building were exposed to ELF magnetic fields higher than the threshold magnetic field value of the International Agency for Research on Cancer (IARC). Many people living in this building reported health complaints such as immunological problems of their children. There were child-workers working in the textile factories located in the building. Safe distances or areas for these people should be recommended. Protective measures could be implemented to minimize these exposures. Further residential exposure studies are needed to demonstrate the exposure levels of ELF magnetic fields. Precautions should, therefore, be taken either to reduce leakage or minimize the exposed fields. Shielding techniques should be used to minimize the leakage magnetic fields in such cases.     

50 Hz sinusoidal magnetic fields do not affect human lymphocyte activation and proliferation in vitro

In the last 30 years, an increasing public concern about the possible harmful effects of electromagnetic fields generated by power lines and domestic appliances has pushed the scientific community to search for a correct and comprehensive answer to this problem. In this work the effects of exposure to 50 Hz sinusoidal magnetic fields, with a magnetic flux density of 0.05 mT and 2.5 mT (peak values), were studied on human peripheral blood mononuclear cells (PBMCs) collected from healthy young and elderly donors. Cell activation and proliferation were investigated by using flow cytometry techniques and 3H-TdR incorporation assays, respectively. The results obtained indicated that exposure to the fields altered neither DNA synthesis nor the capacity of lymphocytes to enter the activation phase and progress into the cell cycle. Thus, the conclusions are that two important functional phases of human lymphocytes, such as activation and proliferation, are not affected by exposures to 50 Hz magnetic fields similar to those found under power lines.     

Extremely low frequency electric fields and cancer: Assessing the evidence

Much of the research and reviews on extremely low frequency (ELF) electric and magnetic fields (EMFs) have focused on magnetic rather than electric fields. Some have considered such focus to be inappropriate and have argued that electric fields should be part of both epidemiologic and laboratory work. This paper fills the gap by systematically and critically reviewing electric‐fields literature and by comparing overall strength of evidence for electric versus magnetic fields. The review of possible mechanisms does not provide any specific basis for focusing on electric fields. While laboratory studies of electric fields are few, they do not indicate that electric fields should be the exposure of interest. The existing epidemiology on residential electric‐field exposures and appliance use does not support the conclusion of adverse health effects from electric‐field exposure. Workers in close proximity to high‐voltage transmission lines or substation equipment can be exposed to high electric fields. While there are sporadic reports of increase in cancer in some occupational studies, these are inconsistent and fraught with methodologic problems. Overall, there seems little basis to suppose there might be a risk for electric fields, and, in contrast to magnetic fields, and with a possible exception of occupational epidemiology, there seems little basis for continued research into electric fields. Bioelectromagnetics 31:89–101, 2010. © 2009 Wiley‐Liss, Inc.     

Importance of addressing National Electrical Code violations that result in unusual exposure to 60 Hz magnetic fields

We evaluated wiring in multifamily developments containing National Electrical Code(R) (NEC(R)) violations as a source of unusual exposure to 60 Hz magnetic fields. Two methods were used in this evaluation: measurement and modeling. We measured the building wiring as a source of magnetic fields in six multifamily developments in Michigan. In this small sample, building wiring proved to be an important source of exposure in four of the six cases. In all four cases with exposure from building wiring, one or more NEC violations were involved. To supplement our measurement efforts, we used computer modeling to compare magnetic field exposure due to building wiring with magnetic field exposure from external power lines. Our calculations showed that where the building wiring has a NEC violation leading to net current loops, the exposure due to wiring is likely to be more important than that from external power lines. Our results support the results obtained in a recent study of the exposure of Californian K-12 students to magnetic fields, where building wiring with one or more NEC violation was found to be the single most important exposure source. If 60 Hz magnetic fields are important to avoid, then improved enforcement of the NEC, as required by law, is perhaps the single most important mitigation policy to adopt. Bioelectromagnetics 25:102-106, 2004.