M. Shum, M. Kelsh, Exponent Inc., Menlo Park, CA; L. Erdreich, M. Van Kerkhove, Exponent Inc., New York, NY; C. Scrafford, Exponent Inc., Washington, DC.
Epidemiologic studies of mobile phone handset use and risk of brain cancer have relied on self-reported use and billing records as exposure surrogates. None of these measures of duration includes the level of radiofrequency (RF) power output from mobile phones, which could be a significant factor in estimating exposure. Our goal was to measure environmental, behavioral, and engineering factors affecting RF power output of GSM mobile phones during operation on the network. Volunteers using software-modified phones (SMPs) made typical mobile phone calls, which involved a variety of personal and geographic situations. The SMPs recorded output power settings for all incoming and outgoing calls. Subjects from three study areas in the United States were recruited and instructed to log information regarding time, location, and activity for each call during a five-day study period. Fifty-three volunteers participated and 2537 calls were analyzed. Multivariate analysis indicated that study area was the largest factor affecting energy output, followed by user movement (stationary > moving), location (inside > outside), use of a hands-free device (no hands-free > hands-free), and urbanicity (suburban > urban). However, all combined factors accounted for a small amount of overall variance despite small p-values (combined factors explained 12% of the total variance). Average energy output per minute of use differed significantly within a twofold range among the three study areas. Weather and day of the week were not highly significant factors for predicting overall variation of power output. The effects on average energy output rate that we identified were usually less than 50%, sometimes much less, and generally comparable to the standard deviation. These results suggest that regional variation should be considered in epidemiologic studies. However, any conclusions are tentative due to the evaluation of only one mobile phone technology (GSM) and the relatively small sample size of volunteers in our study.
S. Lacey, J. Lippert, N. Esmen, University of Illinois at Chicago-Chicago, IL; G. Marsh, University of Pittsburgh, Pittsburgh, PA.
Nondestructive testing (NDT) is any technique used to inspect the integrity of a manufactured item without diminishing its future usefulness. Magnetic particle inspection (MPI) is one type of NDT that uses electromagnetism in the inspection procedure, thus potentially exposing the operator to electromagnetic fields (EMF). MPI is particularly useful in inspection of large parts that will have to work under high stress/strain; thus it is important in high-speed, high-pressure rotating equipment manufacturing. Currently there is no clear answer to what risks might be associated with occupational exposure to EMF. Although there are potential health risks, little has been done to systematically evaluate occupational exposures. To evaluate the exposure potential to EMF during an inspection process using MPI, peak EMF measurements were taken at one stationary horizontal MPI unit over a period of six days during the inspection of eight turbine engine shafts at a turbine engine overhaul and repair center. The measurements were made as close to the worker as possible without interfering with the inspection process.
Fifty-nine peak electromagnetic field values were recorded, ranging from 0 to 29.27 millitesla (mT). Approximately 77% of these measurements exceeded the ACGIH threshold limit value (TLV) of 1 mT for head and torso exposure, and 11% exceeded the TLV of 10 mT for hand and foot exposure. NDT is a widely used tool for inspection and quality control. The EMF values measured in this study far exceed all but one documented occupational EMF source. Further work is needed to characterize EMF exposures in diverse MPI operations with different inspection setups used in industrial operations.
D. Baron, ETS-Lindgren, Cedar Park, TX.
Potentially problematic interactions between electromagnetic fields (EMFs) and active medical implants, pacemakers, and implantable cardioverter defibrillators (ICDs) have been addressed for some time. New changes in the recommendations from at least one implant manufacturer may significantly affect workers in industrial environments with EMF sources operating at frequencies between 10 kHz and 10 MHz. Industrial processes, most typically induction heating equipment, operating in the VLF (3-30 kHz) and LF (30-300 kHz) frequency ranges, may require additional evaluation when determining safe working conditions for implant wearers. We discuss the changed action levels, compare them with general workplace threshold limit values, and provide examples showing the effects of the changed requirements on recommended work locations.
D. Baron, ETS-Lindgren, Cedar Park, TX.
A number of industrial processes use high levels of direct electrical current, which in turn generate potentially high DC or static magnetic fields. The AC power sources for these processes have the power to generate significant extremely low frequency magnetic fields. These DC currents are typically rectified AC; while they are unidirectional (flowing in one direction), they can have significant time-varying components. We evaluate how typical field instruments respond to these rectified AC currents and fields and how the measured results might be evaluated for biological or potentially hazardous effects. Evaluation of the field levels against generally recognized safety standards are addressed as well as the effects of harmonic content.
J. Zeigler, DuPont Personal Protection, Richmond, VA.
We have developed an easy way to visualize heat stress threshold limits and the factors that influence these thresholds. This technique is based on the wet bulb, globe, and temperature (WBGT) method. NIOSH, OSHA, ACGIH, and the U.S. military recommend and use this method for heat stress assessment and management. Psychrometric relationships are applied to the WBGT equations to obtain tangible heat stress thresholds based on temperature and humidity. To show the impact of protective clothing, the curves are adjusted with factors obtained from human wear trials, not from incomplete engineering models. The resulting curves illustrate the relative impact of rest-to-work ratios, work activity levels, acclimatization, and protective clothing on heat stress thresholds. By layering on historical weather data from 102 U.S. locations, the 24/7/365 potential for heat stress in these cities can be evaluated. Adding the weather data demonstrates that heat stress is a common hazard in almost all these localities for some part of the year, regardless of the type protective clothing worn. This approach does not take the place of actual workplace WBGT measurements or routine monitoring of employees. It is a tool for risk assessment, planning, and gauging the risk of heat stress. It provides a more tangible way to judge the potential benefit of heat stress management options such as protective clothing changes, higher rest-to-work ratios or night-vs.-day work schedules. It can be adopted to new protective clothing technologies with the incorporation of human trial data and to new localities with the addition of historical weather data.
T. Bernard, S. Schwartz, C. Ashley, University of South Florida, Tampa, FL.
Most exposure limits for heat stress assume sustained exposures and thus seek to maintain thermal equilibrium. Often work is required under conditions in which thermal equilibrium cannot be maintained. The present study was undertaken to specify an exposure-driven time limit based on the wet bulb, globe, and temperature (WBGT) method. Three clothing ensembles (work clothes, water barrier coveralls, and vapor barrier coveralls) were worn during exposures to five levels of heat stress at a moderate rate of work. The five levels of heat stress were 1, 2, 3, 5, and 9°C-WBGT above the average sustainable level of heat stress determined in prior studies, which in turn were above the threshold limit value for heat stress and strain. Nine men and four women wore each ensemble under each heat stress condition. The safe exposure time was selected as the first occurrence of a core temperature of 38.5°C, heart rate of 90% of age-estimated maximum heart rate, or volitional fatigue. A mixed-model three-way analysis of variance between groups (ANOVA) with subjects as the random factor was used to confirm that the metabolic rate was the same across all conditions. There were significant differences in time due to the level of heat stress. The average times were 78, 73, 54, 41, and 29 min for increasing levels of heat stress. There were significant differences in the times due to clothing. The similarity in metabolic rate indicated good control over the level of heat stress within ensembles. The differences among ensembles were small due to the experimental design, which tried to minimize the differences based on adjustments for clothing. A relationship between WBGT and safe exposure time was determined from the lower 5% confidence interval for work clothes. This relationship was protective for both the water barrier and vapor barrier clothing, based on published clothing corrections.
M. Wan, Kaiser Permanente, Pasadena, CA; T. Bernard, C. Ashley, Y. Wu, University of South Florida, Tampa, FL.
Heat strain indicates an individual’s response to working in hot environments. This study evaluated the discrimination ability of metrics of heat strain. The metrics were core, ear canal, oral, and disk temperatures; and heart rate including moving time averages, recovery heart rate, and physiological strain index. The null hypotheses were that (1) the metrics individually could not discriminate between acceptable and unacceptable heat strain, (2) there were no significant differences among these metrics, and (3) there were no significant differences in the applicability of the metrics due to clothing or heat stress level. The experimental design was a case crossover. Two clothing ensembles were work clothes and vapor-barrier coveralls with hood. Two heat stress levels were 5°C WBGT and 10°C WBGT above the threshold limit value adjusted for clothing. Eight acclimated individuals (ages 18-36 years) participated. The transition point, when a participant’s status changed from control (acceptable heat strain) to case (unacceptable), was the first occurrence of core temperature equal to or greater than 38.5°C, heart rate equal to or greater than 90% of maximum, or volitional fatigue. The data at the transition point were the case data; the data 10 min prior to that point were the control data. Based on analyses using receiver operating characteristic curves, the physiological metrics can distinguish between acceptable and unacceptable heat strain with average area under the curves between 0.53 and 0.86. There were no differences among the metrics based on the 95% confidence intervals of the areas under the curve. Based on factorial analysis of variance and exact conditional logistic regression, clothing did not influence the metrics. There were insufficient data to evaluate the role of heat stress level.
F. Akbar-Khanzadeh, University of Toledo, Toledo, OH; F. Golbabaei, M. Sajjadi, K. Nourijelyani, Tehran University of Medical Sciences, Tehran, Iran.
This study was conducted in a cold food storage warehouse complex to evaluate cold stress and its effects on workers. A total of 29 exposed subjects (10 forklift drivers and 19 general laborers) and 33 control subjects participated in the study. Climatic factors were determined within the complex and insulation required indices (IREQ min and IREQneut) were calculated. IREQ min and IREQneut were compared to the workers’ estimated cloth insulation. Physiological factors, including selected elements of the workers’ blood chemistry, were examined. The workers’ general health conditions were also surveyed using a questionnaire and their medical files. The calculated average IREQ min in cold spaces with the temperature above zero °C and below zero °C were 1.7 and 3.63 clo, respectively. No significant differences were observed in the physiological factors between the exposed and control subjects. The skin temperature, especially on the tip of the subjects’ noses, fingers, and toes, was considerably lower in the exposed subjects than in the control subjects. Subjects complained mostly of pain in their knees and musculoskeletal system and also of pleurodynia. The rate of complaints of pain was higher in the exposed subjects than in the control subjects. The forklift drivers, who were exposed to much higher levels of cold stress than the other subjects, showed more elevated skin cooling and pain in their legs. It was concluded that the workers exposed to cold stress suffered from cold related chronic diseases, and it is recommended that the safety program in this establishment be improved to protect this group of workers.