Liljelind Ingrid, Wahlström Jens, Nilsson Leif, Toomingas Allan, Burström Lage
Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine, Umeå University, SE-901 87 Umeå, Sweden.
Ann Occup Hyg. 2011 Apr;55(3):296-304. doi: 10.1093/annhyg/meq094. Epub 2011 Feb 21.
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.
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.
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.
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.
对手持工具振动暴露的测量通常只在单次进行。然而，重复测量对于精确估计实际剂量可能至关重要。此外，了解暴露的决定因素可用于改善工作条件。本研究的目的是评估不同磨削操作过程中的手臂振动（HAV）暴露情况，以获得方差分量的估计值并评估工作姿势的影响。
10名经验丰富的操作人员在工作场所的模拟工作任务中使用两台相同品牌的压缩空气驱动角磨机。研究的一部分包括在两种不同工作姿势下使用磨机：在标准工作台（低位）和在墙上，手臂抬高且工作区域根据每个操作员的身高进行调整（高位）。工人重复该任务三次。在研究的另一部分，调查砂轮磨损情况，对于每台磨机，操作员使用两个新砂轮，每个砂轮操作员连续进行两次1分钟的磨削任务。两次磨削任务均在一块低碳钢上的低碳钢焊缝熔池上进行。根据ISO标准5349 [1分钟内等效手臂加权加速度（m s(-2)）的平均值]进行测量。使用混合效应模型和随机效应模型来研究固定变量的影响并估计方差分量。
在工作台和墙上执行任务时评估的等效手臂加权加速度分别为3.2和3.3 m s(-2)。在混合效应模型中，工作姿势不是一个显著变量。“操作员”和“磨机”这两个变量共同仅解释了12%的暴露变异性，“砂轮”解释了47%；仍有41%的残余变异性未得到解释。在随机效应模型中研究砂轮磨损的影响时，37%的变异性与砂轮相关，而与操作员或磨机相关的变异性最小，37%未得到解释。磨机和操作员的交互效应解释了18%的变异性。在砂轮磨损测试中，磨机1在第一次和第二次磨削分钟期间的等效手臂加权加速度分别为3.4和2.9 m s(-2)，磨机2的分别为3.1和2.9 m s(-2)。对于磨机1，第一次磨削分钟期间的等效手臂加权加速度显著高于第二次（P = 0.04）。
磨削操作期间的工作姿势似乎不会影响HAV水平。在本研究中，砂轮解释了大部分变异性，但仍有近40%的方差未得到解释。等效手臂加权加速度的相当大的变异性对群体和个体层面的风险评估都有影响。
