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- Liljelind, Ingrid, et al.
(författare)
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Determinants Explaining the Variability of Hand-Transmitted Vibration Emissions From Two Different Work Tasks : Grinding and Cutting Using Angle Grinders
- 2013
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Ingår i: Annals of Occupational Hygiene. - : Oxford University Press. - 0003-4878 .- 1475-3162. ; 57:8, s. 1065-1077
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Tidskriftsartikel (refereegranskat)abstract
- Background: There are numerous factors including physical, biomechanical, and individual that influence exposure to hand-transmitted vibration (HTV) and cause variability in the exposure measurements. Knowledge of exposure variability and determinants of exposure could be used to improve working conditions. We performed a quasi-experimental study, where operators performed routine work tasks in order to obtain estimates of the variance components and to evaluate the effect of determinants, such as machine–wheel combinations and individual operator characteristics.Methods: Two pre-defined simulated work tasks were performed by 11 operators: removal of a weld puddle of mild steel and cutting of a square steel pipe. In both tasks, four angle grinders were used, two running on compressed air and two electrically driven. Two brands of both grinding and cutting wheels were used. Each operator performed both tasks twice in a random order with each grinder and wheel and the time to complete each task was recorded. Vibration emission values were collected and the wheel wear was measured as loss of weight. Operators’ characteristics collected were as follows: age, body height and weight, length and volume of their hands, maximum hand grip force, and length of work experience with grinding machines (years). The tasks were also performed by one operator who used four machines of the same brand. Mixed and random effects models were used in the statistical evaluation.Results: The statistical evaluation was performed for grinding and cutting separately and we used a measure referring to the sum of the 1-s r.m.s. average frequency-weighted acceleration over time for completing the work task (a sa). Within each work task, there was a significant effect as a result of the determinants ‘the machine used’, ‘wheel wear’, and ‘time taken to complete the task’. For cutting, ‘the brand of wheel’ used also had a significant effect. More than 90% of the inherent variability in the data was explained by the determinants. The two electrically powered machines had a mean a sa that was 2.6 times higher than the two air-driven machines. For cutting, the effect of the brand of wheel on a sa was ~0.1 times. The a sa increased both with increasing wheel wear and with time taken to complete the work task. However, there were also a number of interaction effects which, to a minor extent, modified the a sa. Only a minor part (1%) of the total variability was attributed to the operator: for cutting, the volume of the hands, maximum grip force, and body weight were significant, while for grinding, it was the maximum grip force. There was no clear difference in a sa between the four copies of the same brand of each machine.Conclusions: By including determinants that were attributed to the brand of both machine and wheel used as well as the time taken to complete the work task, we were able to explain >90% of the variability. The dominating determinant was the brand of the machine. Little variability was found between operators, indicating that the overall effect as due to the operator was small.
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| 2. |
- Liljelind, Ingrid, 1968-, et al.
(författare)
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Variability in Hand-Arm Vibration During Grinding Operations
- 2011
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Ingår i: Annals of Occupational Hygiene. - : Oxford Journals. - 0003-4878 .- 1475-3162. ; 55:3, s. 296-304
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Tidskriftsartikel (refereegranskat)abstract
- Background: Measurements of exposure to vibrations from hand-held tools are often conducted on a single occasion. However, repeated measurements may be crucial for estimating the actual dose with good precision. In addition, knowledge of determinants of exposure could be used to improve working conditions. The aim of this study was to assess hand–arm vibration (HAV) exposure during different grinding operations, in order to obtain estimates of the variance components and to evaluate the effect of work postures. Methods: Ten experienced operators used two compressed air-driven angle grinders of the same make in a simulated work task at a workplace. One part of the study consisted of using a grinder while assuming two different working postures: at a standard work bench (low) and on a wall with arms elevated and the work area adjusted to each operator’s height (high). The workers repeated the task three times. In another part of the study, investigating the wheel wear, for each grinder, the operators used two new grinding wheels and with each wheel the operator performed two consecutive 1-min grinding tasks. Both grinding tasks were conducted on weld puddles of mild steel on a piece of mild steel. Measurements were taken according to ISO-standard 5349 [the equivalent hand–arm-weighted acceleration (m s−2) averaged over 1 min]. Mixed- and random-effects models were used to investigate the influence of the fixed variables and to estimate variance components. Results: The equivalent hand–arm-weighted acceleration assessed when the task was performed on the bench and at the wall was 3.2 and 3.3 m s−2, respectively. In the mixed-effects model, work posture was not a significant variable. The variables ‘operator’ and ‘grinder’ together explained only 12% of the exposure variability and ‘grinding wheel’ explained 47%; the residual variability of 41% remained unexplained. When the effect of grinding wheel wear was investigated in the random-effects model, 37% of the variability was associated with the wheel while minimal variability was associated with the operator or the grinder and 37% was unexplained. The interaction effect of grinder and operator explained 18% of the variability. In the wheel wear test, the equivalent hand–arm-weighted accelerations for Grinder 1 during the first and second grinding minutes were 3.4 and 2.9 m s−2, respectively, and for Grinder 2, they were 3.1 and 2.9 m s−2, respectively. For Grinder 1, the equivalent hand–arm-weighted acceleration during the first grinding minute was significantly higher (P = 0.04) than during the second minute. Conclusions: Work posture during grinding operations does not appear to affect the level of HAV. Grinding wheels explained much of the variability in this study, but almost 40% of the variance remained unexplained. The considerable variability in the equivalent hand–arm-weighted acceleration has an impact on the risk assessment at both the group and the individual level.
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| 3. |
- Lindegård, Agneta, et al.
(författare)
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Perceived exertion, comfort and working technique in professional computer users and associations with the incidence of neck and upper extremity symptoms.
- 2012
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Ingår i: BMC Musculoskeletal Disorders. - London : BioMed Central. - 1471-2474. ; 13, s. 38-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The aim of this study was to investigate whether perceived exertion, perceived comfort and working technique is associated with the incidence of neck and upper extremity symptoms among professional computer users. METHODS: At baseline a self-administered questionnaire was distributed to 853 participants from 46 different work sites (382 men and 471 women) who, at baseline, had been free from neck and upper extremity symptoms during the preceding month. Work-related exposures, individual factors, and symptoms from the neck and upper extremities were assessed. Observations of working technique were performed by ergonomists using an ergonomic checklist. Incidence data were collected by means of 10 monthly questionnaires, asking for information on the occurrence of neck, shoulder and arm/hand symptoms. Perceived exertion was rated on a modified Borg RPE scale ranging from 0 (very, very light) to 14 (very, very strenuous). Perceived comfort was rated on a 9-point scale ranging from -4 (very, very poor) to +4 (very, very good) in relation to the chair, computer screen, keyboard, and computer mouse. RESULTS: The median follow up time was 10.3 months. The incidence of symptoms from the neck, shoulders and arm/hands were 50, 24 and 34 cases per 100 person years, respectively.Higher perceived exertion in the neck, shoulder or arm/hands was associated with an increased risk of developing symptoms in the corresponding body region. Moreover, a dose-response relationship between the level of exertion and the risk of developing symptoms was recorded for all three regions. There was an association between low comfort and an increased risk for neck symptoms, but not for shoulder and arm/hand symptoms, although a trend towards such an association (not statistically significant) could be seen. Working technique was, in this study, not associated with the risk of developing symptoms in any of the investigated body regions. CONCLUSION: There was a strong association between high perceived exertion and the development of neck, shoulder, and arm/hand symptoms. Moreover, there was an association between poor perceived comfort and neck pain. Surveillance of computer users may include perceived exertion and comfort to target individuals at risk for neck and upper extremity symptoms.
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| 4. |
- Wahlström, Jens, 1972, et al.
(författare)
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Perceived muscular tension, job strain, physical exposure, and associations with neck pain among VDU users; a prospective cohort study.
- 2004
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Ingår i: Occupational and environmental medicine. - : BMJ. - 1470-7926 .- 1351-0711. ; 61:6, s. 523-8
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: To determine whether perceived muscular tension, job strain, or physical exposure are associated with increased risk of developing neck pain among VDU users. METHODS: A baseline questionnaire was answered by 1283 respondents, of whom 671 were free from neck pain at baseline. Perceived muscular tension, job strain, and physical exposure were assessed at baseline. Information about newly developed neck pain was collected in 10 follow up questionnaires and the case definition was the first report of such pain in any of the follow up questionnaires. Median follow up time was 10.9 months. RESULTS: Both men and women who perceived muscular tension at least a few times per week, compared to those who had not perceived muscular tension the preceding month, had an incidence rate ratio (IRR) of 1.9 (95% CI 1.25 to 2.93) for developing neck pain, when stratifying for sex. High perceived muscular tension was associated with an increased risk (IRR 1.6, 95% CI 1.02 to 1.91), even when controlling for job strain, physical exposure, and age in the model stratified by sex. CONCLUSIONS: Perceived muscular tension was associated with an increased risk of developing neck pain among VDU users. The combination of high job strain and high perceived muscular tension was associated with higher risk of developing neck pain than the combination of high physical exposure and high perceived muscular tension. There was an indication of an excess risk due to interaction between high physical exposure and high job strain.
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