Enertech Consultants

Campbell, CA, United States

Enertech Consultants

Campbell, CA, United States
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Vergara X.P.,University of California at Los Angeles | Vergara X.P.,EPRI | Kheifets L.,University of California at Los Angeles | Silva M.,Enertech Consultants | And 2 more authors.
American Journal of Industrial Medicine | Year: 2012

Background: To evaluate a consistent association between jobs in "electric" occupations and amyotrophic lateral sclerosis (ALS), a comprehensive job exposure matrix (JEM) that includes electric shocks and magnetic fields (MF) is needed. Methods: We used incident electric shocks and electrocutions from two available data sources along with expert judgment to create a JEM that was integrated into an existing MF JEM. The final JEM contained ordinal electric-shock exposure assignments for 501 job titles. Results: Main occupational groups experiencing the electric shocks were precision production, craft, and repair occupations. Specific jobs with the highest proportion of shocks per 100,000 workers were: electrical apprentices (99.7), mechanic and repairer helpers (74.0), hoist and winch operators (63.3), and electrical power installers (52.4). Examples of job titles with low electric-shock exposures were administrative support occupations, data-key entry operators, and waiters and waitresses. Conclusions: Combining publicly available data with an expert panel is a viable method to construct an electric-shock MF JEM. This JEM will allow an evaluation of association between electric shocks and neurodegenerative diseases. © 2011 Wiley Periodicals, Inc.


Kavet R.,EPRI | Hooper C.,Enertech Consultants | Buffler P.,University of California at Berkeley | Does M.,University of California at Berkeley
Radiation Research | Year: 2011

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 3.661) as well as a statistically significant positive trend across magnetic-field strata (EOR of 4.2 per stratum with 95% CI 2.47.4). 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. © 2011 by Radiation Research Society.


Vergara X.P.,EPRI | Fischer H.J.,University of California at Los Angeles | Yost M.,University of Washington | Silva M.,Enertech Consultants | And 2 more authors.
International Journal of Environmental Research and Public Health | Year: 2015

We present an update to an electric shock job exposure matrix (JEM) that assigned ordinal electric shocks exposure for 501 occupational titles based on electric shocks and electrocutions from two available data sources and expert judgment. Using formal expert elicitation and starting with data on electric injury, we arrive at a consensus-based JEM. In our new JEM, we quantify exposures by adding three new dimensions: (1) the elicited median proportion; (2) the elicited 25th percentile; and (3) and the elicited 75th percentile of those experiencing occupational electric shocks in a working lifetime. We construct the relative interquartile range (rIQR) based on uncertainty interval and the median. Finally, we describe overall results, highlight examples demonstrating the impact of cut point selection on exposure assignment, and evaluate potential impacts of such selection on epidemiologic studies of the electric work environment. In conclusion, novel methods allowed for consistent exposure estimates that move from qualitative to quantitative measures in this population-based JEM. Overlapping ranges of median exposure in various categories reflect our limited knowledge about this exposure. © 2015 by the authors; licensee MDPI, Basel, Switzerland.


Kheifets L.,University of California at Los Angeles | Crespi C.M.,University of California at Los Angeles | Hooper C.,Enertech Consultants | Oksuzyan S.,University of California at Los Angeles | And 3 more authors.
Journal of Exposure Science and Environmental Epidemiology | Year: 2015

We conducted a large epidemiologic case-control study in California to examine the association between childhood cancer risk and distance from the home address at birth to the nearest high-voltage overhead transmission line as a replication of the study of Draper et al. in the United Kingdom. We present a detailed description of the study design, methods of case ascertainment, control selection, exposure assessment and data analysis plan. A total of 5788 childhood leukemia cases and 3308 childhood central nervous system cancer cases (included for comparison) and matched controls were available for analysis. Birth and diagnosis addresses of cases and birth addresses of controls were geocoded. Distance from the home to nearby overhead transmission lines was ascertained on the basis of the electric power companies' geographic information system (GIS) databases, additional Google Earth aerial evaluation and site visits to selected residences. We evaluated distances to power lines up to 2000 m and included consideration of lower voltages (60-69 kV). Distance measures based on GIS and Google Earth evaluation showed close agreement (Pearson correlation >0.99). Our three-tiered approach to exposure assessment allowed us to achieve high specificity, which is crucial for studies of rare diseases with low exposure prevalence. © 2015 Nature America, Inc. All rights reserved.


Vergara X.P.,EPRI | Kavet R.,EPRI | Crespi C.M.,University of California at Los Angeles | Hooper C.,Enertech Consultants | And 2 more authors.
Environmental Research | Year: 2015

The California Power Line Study is a case-control study investigating the relation between residences near transmission lines and risk of childhood leukemia. It includes 5788 childhood leukemia cases and 5788 matched primary controls born between 1986 and 2007. We describe the methodology for estimating magnetic fields at study residences as well as for characterizing sources of uncertainty in these estimates. Birth residences of study subjects were geocoded and their distances to transmission lines were ascertained. 302 residences were deemed sufficiently close to transmission lines to have non-zero magnetic fields attributable to the lines. These residences were visited and detailed data, describing the physical configuration and dimensions of the lines contributing to the magnetic field at the residence, were collected. Phasing, loading, and directional load flow data for years of birth and diagnosis for each subject as well as for the day of site visit were obtained from utilities when available; when yearly average load for a particular year was not available, extrapolated values based on expert knowledge and prediction models were obtained. These data were used to estimate the magnetic fields at the center, closest and farthest point of each residence. We found good correlation between calculated fields and spot measurements of fields taken on site during visits. Our modeling strategies yielded similar calculated field estimates, and they were in high agreement with utility extrapolations. Phasing was known for over 90% of the lines. Important sources of uncertainty included a lack of information on the precise location of residences located within apartment buildings or other complexes. Our findings suggest that we were able to achieve high specificity in exposure assessment, which is essential for examining the association between distance to or magnetic fields from power lines and childhood leukemia risk. © 2015 Elsevier Inc.


PubMed | EPRI, University of Southern California, University of California at Los Angeles and Enertech Consultants
Type: Journal Article | Journal: British journal of cancer | Year: 2016

Studies have reported an increased risk of childhood leukaemia associated with living near high-voltage electric power transmission lines that extend to distances at which magnetic fields from lines are negligible. We conducted a large records-based case-control study of childhood leukaemia risk in the population living near power lines in California.The study included 5788 childhood leukaemia and 3308 central nervous system (CNS) cancer cases (for comparison) born in and diagnosed in California (1986-2008), and matched to population-based controls by age and sex. We geocoded birth address and estimated the distance from residence to transmission lines using geographic information systems, aerial imagery, and, for some residences, site visits.For leukaemia, there was a slight excess of cases within 50m of a transmission line over 200kV (odds ratio 1.4, 95% confidence interval 0.7-2.7). There was no evidence of increased risk for distances beyond 50m, for lower-voltage lines, or for CNS cancers.Our findings did not clearly support an increased childhood leukaemia risk associated with close proximity (<50m) to higher voltage lines, but could be consistent with a small increased risk. Reports of increased risk for distances beyond 50m were not replicated.


PubMed | EPRI, University of California at Los Angeles and Enertech Consultants
Type: | Journal: Environmental research | Year: 2015

The California Power Line Study is a case-control study investigating the relation between residences near transmission lines and risk of childhood leukemia. It includes 5788 childhood leukemia cases and 5788 matched primary controls born between 1986 and 2007. We describe the methodology for estimating magnetic fields at study residences as well as for characterizing sources of uncertainty in these estimates. Birth residences of study subjects were geocoded and their distances to transmission lines were ascertained. 302 residences were deemed sufficiently close to transmission lines to have non-zero magnetic fields attributable to the lines. These residences were visited and detailed data, describing the physical configuration and dimensions of the lines contributing to the magnetic field at the residence, were collected. Phasing, loading, and directional load flow data for years of birth and diagnosis for each subject as well as for the day of site visit were obtained from utilities when available; when yearly average load for a particular year was not available, extrapolated values based on expert knowledge and prediction models were obtained. These data were used to estimate the magnetic fields at the center, closest and farthest point of each residence. We found good correlation between calculated fields and spot measurements of fields taken on site during visits. Our modeling strategies yielded similar calculated field estimates, and they were in high agreement with utility extrapolations. Phasing was known for over 90% of the lines. Important sources of uncertainty included a lack of information on the precise location of residences located within apartment buildings or other complexes. Our findings suggest that we were able to achieve high specificity in exposure assessment, which is essential for examining the association between distance to or magnetic fields from power lines and childhood leukemia risk.


PubMed | EPRI, University of Southern California, University of California at Los Angeles and Enertech Consultants
Type: Journal Article | Journal: Journal of exposure science & environmental epidemiology | Year: 2014

We conducted a large epidemiologic case-control study in California to examine the association between childhood cancer risk and distance from the home address at birth to the nearest high-voltage overhead transmission line as a replication of the study of Draper et al. in the United Kingdom. We present a detailed description of the study design, methods of case ascertainment, control selection, exposure assessment and data analysis plan. A total of 5788 childhood leukemia cases and 3308 childhood central nervous system cancer cases (included for comparison) and matched controls were available for analysis. Birth and diagnosis addresses of cases and birth addresses of controls were geocoded. Distance from the home to nearby overhead transmission lines was ascertained on the basis of the electric power companies geographic information system (GIS) databases, additional Google Earth aerial evaluation and site visits to selected residences. We evaluated distances to power lines up to 2000m and included consideration of lower voltages (60-69kV). Distance measures based on GIS and Google Earth evaluation showed close agreement (Pearson correlation >0.99). Our three-tiered approach to exposure assessment allowed us to achieve high specificity, which is crucial for studies of rare diseases with low exposure prevalence.


PubMed | EPRI, Liberty Mutual Research Institute for Safety, University of Washington, University of California at Los Angeles and Enertech Consultants
Type: Journal Article | Journal: International journal of environmental research and public health | Year: 2015

We present an update to an electric shock job exposure matrix (JEM) that assigned ordinal electric shocks exposure for 501 occupational titles based on electric shocks and electrocutions from two available data sources and expert judgment. Using formal expert elicitation and starting with data on electric injury, we arrive at a consensus-based JEM. In our new JEM, we quantify exposures by adding three new dimensions: (1) the elicited median proportion; (2) the elicited 25th percentile; and (3) and the elicited 75th percentile of those experiencing occupational electric shocks in a working lifetime. We construct the relative interquartile range (rIQR) based on uncertainty interval and the median. Finally, we describe overall results, highlight examples demonstrating the impact of cut point selection on exposure assignment, and evaluate potential impacts of such selection on epidemiologic studies of the electric work environment. In conclusion, novel methods allowed for consistent exposure estimates that move from qualitative to quantitative measures in this population-based JEM. Overlapping ranges of median exposure in various categories reflect our limited knowledge about this exposure.


Hoburg J.F.,Carnegie Mellon University | Bain J.A.,Carnegie Mellon University | Silva J.M.,Enertech Consultants
IEEE Electromagnetic Compatibility Magazine | Year: 2013

The potential for loss of magnetically stored information in the presence of power frequency magnetic fields is described in terms of fundamental physical mechanisms. Three important mechanisms are identified: (1) short term erasure when external fields are high enough to be a significant fraction of the demagnetizing field, (2) long term thermal degradation when external fields exceed a magnetic field associated with the acceleration of the natural thermal degradation process to an unacceptable level, and (3) concentration of magnetic flux by recording equipment, leading to erasure, augmented thermal degradation or corruption of the recording process. Quantitative expressions are developed for evaluation of the first two mechanisms in terms of fundamental magnetic properties of the recording medium, and a 3-D finite element simulation is used to quantitatively assess the third mechanism for a modern recording head. The first two mechanisms typically require field levels much larger than ordinary power frequency fields, but the third mechanism can lead to local fields large enough to bring the prior mechanisms into play. Results are put in the context of prior published standards and descriptions. © 2013 IEEE Electromagnetic Compatibility Magazine.

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