Occupational exposure to vibration through the use of power- and pneumatic hand-tools results in cold-induced vasospasms, finger blanching, and alterations in sensorineural function. Collectively, these symptoms are referred to as hand-arm vibration syndrome (HAVS). Currently the International Standards Organization (ISO) standard ISO 5349-1 contains a frequency-weighting curve to help workers and employers predict the risk of developing HAVS with exposure to vibration of different frequencies. However, recent epidemiological and experimental evidence suggests that this curve under-represents the risk of injuries to the hands and fingers induced by exposure to vibration at higher frequencies (>100 Hz). To improve the curve, better exposure-response data need to be collected. The goal of this review is to summarize the results of animal and computational modeling studies that have examined the frequency-dependent effects of vibration, and discuss where additional research would be beneficial to fill these research gaps.
This invited paper reviews experimental studies of the frequency-dependence of absolute thresholds for the perception of vibration, equivalent comfort contours, temporary changes in sensation caused by vibration, and reductions in finger blood flow caused by hand-transmitted vibration. Absolute thresholds depend on the contact conditions but for a typical hand grip the thresholds show greatest sensitivity to acceleration around 125 Hz. The frequency-dependence of discomfort caused by hand-transmitted vibration depends on vibration magnitude: similar to absolute thresholds at low magnitudes, but the discomfort at higher magnitudes is similar when the vibration velocity is similar (at frequencies between about 16 and 400 Hz). Hand-transmitted vibration induces temporary elevations in vibrotactile thresholds that reflect the sensory mechanisms excited by the vibration and are therefore highly dependent on the frequency of vibration. Hand-transmitted vibration reduces finger blood flow during and after exposure; when the vibration velocity is similar at all frequencies there is more vasoconstriction at frequencies greater than 63 Hz than at lower frequencies. A single frequency weighting cannot provide a good indication of how all effects of hand-transmitted vibration depend on vibration frequency. Furthermore, a single frequency weighting provides only an approximate indication of any single response, because many factors influence the frequency-dependence of responses to hand-transmitted vibration, including the magnitude of vibration, contact conditions, and individual differences. Although the frequency weighting in current standards extends from 8 to 1,000 Hz, frequencies greater than 400 Hz rarely increase the weighted value on tools and there is currently little psychophysical or physiological evidence of their effects.
Although the risks associated with vibration exposure have been known for a long time, the importance of risk prevention has increased in Europe since the implementation of the Machine Directives in 1989 (1989/392/EC) and the Vibration Directive in 2002 (2002/44/CE). These Directives challenged manufacturers to design low-vibration tools, and employers to manage the site-specific risks of vibration exposure. Field experience has shown that many companies using vibrating tools have never carried out a risk-management program, and that they continue to ignore their responsibilities in the Vibration Directive. Because of this, European States are now developing alternative approaches to prevention, which typically shift the balance of risk management responsibility entirely onto employers. The ongoing challenge will be to increase workplace awareness of, and attention to, the risks of vibration exposure.
This paper provides an overview of the exposure-response relationship for the vascular component of the hand-arm vibration syndrome, called vibration-induced white finger (VWF). Over the past two decades, several epidemiological studies have shown a poor agreement between the risk for VWF observed in various occupational groups and that predicted by models included in annexes to International Standard ISO 5349 (ISO 5349:1986, ISO 5349-1:2001). Either overestimation or underestimation of the occurrence of VWF have been reported by investigators. It has been argued that the current ISO frequency-weighting curve for hand-transmitted vibration, which assumes that vibration-induced adverse health effects are inversely related to the frequency of vibration between 16 and 1250 Hz, may be unsuitable for the assessment of VWF. To investigate this issue, a prospective cohort study was carried out to explore the performance of four alternative frequency weightings for hand-transmitted vibration to predict the incidence of VWF in groups of forestry and stone workers. The findings of this study suggested that measures of vibration exposure which give relatively more weight to intermediate and high frequency vibration produced better predictions of the incidence of VWF than that obtained with the frequency weighting currently recommended in International Standard ISO 5349-1:2001.
Exposure to hand-transmitted vibration is usually assessed according to International Standard ISO 5349-1:2001 using the frequency weighting Wh. This paper compares eight frequency weightings that might be used to supplement or replace Wh. The comparison is based on a data from two databases, one containing over 7200 measured hand-arm vibration (HAV) spectra from a wide range of industrial machines the other recording exposure history and injury for workers referred to the Health and Safety Laboratory. Acceleration spectra from the machinery database are analysed to give weighted values for the alternative frequency weightings. These weighted values are compared and then used to estimate a set of alternative lifetime vibration dose values for subjects in the referral database. Statistical comparison of these lifetime dose values against assessments of hand-arm vibration syndrome (HAVS) and sensorineural HAVS prevalence suggests that values based the two weightings Wh and Wh50lp (the Wh weighing low-pass filtered at 50 Hz) provide the strongest indicators for developing these injuries. For vascular HAVS there was no clear evidence to advocate any individual frequency weighting. For all injury categories the strongest relationships were for the first power of acceleration magnitude.
An analysis has been performed to derive a frequency weighting for the development of vibration-induced white finger (VWF). It employs a model to compare health risks for pairs of population groups that are selected to have similar health outcomes from operating power tools or machines with markedly different acceleration spectra (rock drills, chain saws, pavement breakers and motorcycles). The model defines the Relative Risk, RRf(trial), which is constructed from the ratio of daily exposures and includes a trial frequency weighting that is applied to the acceleration spectra. The trial frequency weighting consists of a frequency-independent primary frequency range, and subordinate frequency ranges in which the response to vibration diminishes, with cut-off frequencies that are changed to influence the magnitude of RRf(trial). The frequency weighting so derived when RRf(trial) = 1 is similar to those obtained by other methods (Whf, WhT). It consists of a frequency independent range from about 25 Hz to 500 Hz (–3 dB frequencies), with an amplitude cut-off rate of 12 dB/octave below 25 Hz and above 500 Hz. The range is compatible with studies of vasoconstriction in persons with VWF. The results provide further evidence that the ISO frequency weighting may be inappropriate for assessing the risk of developing VWF.
The objective of this study is to propose a theory on the biodynamic frequency weighting for studying hand-transmitted vibration exposures and vibration-induced effects. We hypothesize that the development of a vibration effect is the result of two consecutive but synergistic processes: biodynamic responses to input vibration and biological responses to the biomechanical stimuli resulting from the biodynamic responses. Hence, we further hypothesize that the frequency-dependency (W) of the effect generally includes two components: a biodynamic frequency weighting (W1) and a biological frequency weighting (W2), or W=W1• W2. These hypotheses are consistent with the stress and strain analysis theory and methods widely used in structural dynamics and biomechanics. The factorization may make it easier to study the complex frequency-dependency using different approaches: the biodynamic frequency weighting depends on the passive physical response of the system to vibration, and it can thus be determined by examining the biodynamic response of the system using various engineering methods; on the other hand, the biological frequency weighting depends on the biological mechanisms of the effects, and it can be investigated by studying the psychophysical, physiological, and pathological responses. To help test these hypotheses, this study reviewed and further developed methods to derive the finger biodynamic frequency weighting. As a result, preliminary finger biodynamic frequency weightings are proposed. The implications of the proposed theory and the preliminary biodynamic frequency weightings are also discussed.
Recently, aluminium (Al) has been proposed to be one of the environmental factors responsible for cause Alzheimer’s disease (AD). However, the relationship between Al and AD is controversial. To investigate the effects of subchronic Aluminium-maltolate (Al (mal)3) exposure on the behavioral, electrophysiological functions. Forty Sprague-Dawley (SD) rats were randomly distributed into five groups. Over two months, rats in the saline group received daily intraperitoneal (i.p.) injections 0.9% saline, rats in the maltolate group received 7.56 mg/kg maltolate, and rats in the 0.27, 0.54, 1.08 mg/kg Al (mal)3 groups received i.p. administrations of these three doses, respectively. Neural behavior was assessed in Morris water maze. Long-term potentiation (LTP) in hippocampus was recorded. Al content in the neocortex was determined using a graphite furnace atomic absorption spectrophotometer. Our studies indicate that subchronic Al (mal)3 exposure significantly impaired spatial learning and memory abilities, suppressed the LTP in the CA1 hippocampal area, and elevated Al levels in cerebral cortex in a dose-dependent fashion. In conclusion, low doses of Al (mal)3 can still lead to dramatic Al accumulation in the brain, severely impair learning and memory capacities, and hippocampal LTP.
We conducted a cohort study of 7,760 dentists in Taiwan between 2003 and 2007 to assess the risk of outpatient visit among dentists. Control groups included physicians and other health personnel. Over the 5-yr study period, the dentist cohort made a total of 270,712 outpatient visits, representing an incidence rate of 7,038 visits /103 person-years. Compared to physicians, dentists experienced a significantly reduced covariate adjusted rate ratio (ARR) for all-cause visits (ARR=0.59, 95%CI=0.58–0.59), as well as for nearly all other causes, except neoplasm (ARR=1.06, 95%CI=1.02–1.09). Compared to other health personnel, the dentists still experienced a significantly reduced ARR for all causes (ARR=0.70), but had a slightly but significantly increased risk for endocrine/metabolic/immunity (ARR=1.04, 95%CI=1.02–1.05) and mental (ARR=1.04, 95%CI=1.01–1.07) disorders. Although the dentists in Taiwan utilized lesser outpatient visits than did their medical colleagues, they tended to have slightly higher rates of outpatient visits for neoplasm, endocrine/metabolic/immunity disorders, and mental illnesses. Policy makers and hospital administrators must not overlook dentists’ potentially unseen health problems. A mandatory periodical physical examination for dentists can seriously be considered.
This study identified contributing risk factors in the occurrence of work-related injuries among university students employed at a single university. Four hundred seventy-six student employees completed the survey in March 2010. The majority of respondents were female (66%) and the average age of all respondents was 20.7 yr. A pre-validated survey instrument was taken from the Youth Employment and School Study (YESS) and contained scales for the risk factors of interest. Results show significant differences in the amount of work-school conflict, boredom, workplace hazards, and workload between injured and non-injured groups. Odds ratios show that physical hazards and heavy workload have a significant two-fold increase on the likelihood of 1–3 injuries (OR=1.80, 1.09–3.00; OR=1.72, 1.12–2.60), and a 2 to 3 fold increase in 4 or more injuries (OR=2.94, 1.65–5.24; OR=2.34,1.51–3.64). Good supervisor relations appear to reduce injury risk (OR=0.48, 0.25–0.91; OR=0.59, 0.32–1.09). Reducing workload stress, teaching students how to manage the workload, reducing exposure to physical hazards, and providing examples of standard work practices may reduce the number of injuries seen in the population.
Local exhaust ventilation (LEV) systems and integrated collectors were designed and implemented in a mining company in order to control emitted air pollutant from furnaces. The LEV was designed for capture and transition of air pollutants emitted from furnaces to the integrated collectors. The integrated collectors including four high efficiency Stairmand model cyclones for control of particulate matter, a venturi scrubber for control of the fine particles, SO2 and a part of H2S to follow them, and a packed scrubber for treatment of the residual H2S and SO2 were designed. Pollutants concentration were measured to determine system effectiveness. The results showed that the effectiveness of LEV for reducing workplace pollution is 91.83%, 96.32% and 83.67% for dust, SO2 and H2S, respectively. Average removal efficiency of particles by combination of cyclone and venturi scrubber was 98.72%. Average removal efficiency of SO2 and H2S were 95.85% and 47.13% for the venturi scrubber and 68.45% and 92.7% for the packed bed scrubber. The average removal efficiency of SO2 and H2S were increased to 99.1% and 95.95% by the combination of venturi and packed bed scrubbers. According to the results, integrated collectors are a good air pollution control option for industries with economic constraints and ancient technologies.
Long working hours adversely affect workers’ safety and health. In 2004, Korea passed legislation limiting the working week to 40 h, to improve quality-of-life and to increase business competitiveness. In the present study, we explored the characteristics of work in Korea and compared our data of the second Korean Working Conditions Survey (KWCS) with those of the first KWCS. We found that the average number of hours worked weekly has been reduced but the proportions of workers who work for more than 48 h per week has increased over the 4 yr between the two Korean surveys in all categories studied (male, female, employee, self-employed, and employer). We also found that self-employed and employers work much longer hours than do employees, who are protected by the Labor Standards Act. This was particularly true in the accommodation and food service sectors. In conclusion, Korean workers work longer than do workers of EU countries. The use of average figures masks differences in the numbers of working hours among those engaged in various types of employment, or in certain work sectors. Therefore, the Korean government should not simply monitor reductions in average weekly working hours, but should identify employees working for over 60 h weekly, and reduce their working time.