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Campbell, CA, United States

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. Source

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. Source

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. Source

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. Source

Tell R.A.,Richard Tell Assoc. Inc. | Hooper H.C.,Enertech Consultants | Sias G.G.,Southern California Edison | Mezei G.,Exponent, Inc. | And 2 more authors.
Journal of Occupational and Environmental Hygiene | Year: 2015

The southwest region of the United States is expected to experience an expansion of commercial solar photovoltaic generation facilities over the next 25 years. A solar facility converts direct current generated by the solar panels to three-phase 60-Hz power that is fed to the grid. This conversion involves sequential processing of the direct current through an inverter that produces low-voltage three-phase power, which is stepped up to distribution voltage (∼12 kV) through a transformer. This study characterized magnetic and electric fields between the frequencies of 0 Hz and 3 GHz at two facilities operated by the Southern California Edison Company in Porterville, CA and San Bernardino, CA. Static magnetic fields were very small compared to exposure limits established by IEEE and ICNIRP. The highest 60-Hz magnetic fields were measured adjacent to transformers and inverters, and radiofrequency fields from 5-100 kHz were associated with the inverters. The fields measured complied in every case with IEEE controlled and ICNIRP occupational exposure limits. In all cases, electric fields were negligible compared to IEEE and ICNIRP limits across the spectrum measured and when compared to the FCC limits (≥0.3 MHz). © 2015 JOEH, LLC. Source

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