ENVIRON International Corporation, Chicago, Illinois, USA.
J Occup Environ Hyg. 2011 Apr;8(4):194-209. doi: 10.1080/15459624.2011.557936.
Fluid sealing devices (gaskets and packing) containing asbestos are manufactured and blended with binders such that the asbestos fibers are locked in a matrix that limits the potential for fiber release. Occasionally, fluid sealing devices fail and need to be replaced or are removed during preventive maintenance activities. This is the first study known to pool over a decade's worth of exposure assessments involving fluid sealing devices used in a variety of applications. Twenty-one assessments of work activities and air monitoring were performed under conditions with no mechanical ventilation and work scenarios described as "worst-case" conditions. Frequently, the work was conducted using aggressive techniques, along with dry removal practices. Personal and area samples were collected and analyzed in accordance with the National Institute for Occupational Safety and Health Methods 7400 and 7402. A total of 782 samples were analyzed by phase contrast microscopy, and 499 samples were analyzed by transmission electron microscopy. The statistical data analysis focused on the overall data sets which were personal full-shift time-weighted average (TWA) exposures, personal 30-min exposures, and area full-shift TWA values. Each data set contains three estimates of exposure: (1) total fibers; (2) asbestos fibers only but substituting a value of 0.0035 f/cc for censored data; and (3) asbestos fibers only but substituting the limit of quantification value for censored data. Censored data in the various data sets ranged from 7% to just over 95%. Because all the data sets were censored, the geometric mean and geometric standard deviation were estimated using the maximum likelihood estimation method. Nonparametric, Kaplan-Meier, and lognormal statistics were applied and found to be consistent and reinforcing. All three sets of statistics suggest that the mean and median exposures were less than 25% of 0.1 f/cc 8-hr TWA sample or 1.0 f/cc 30-min samples, and that there is at least 95% confidence that the true 95th percentile exposures are less than 0.1 f/cc as an 8-hr TWA.
含有石棉的液体密封设备（垫圈和填料）由粘结剂制造和混合而成，使石棉纤维被锁定在一个基质中，从而限制纤维释放的可能性。偶尔，液体密封设备会失效，需要更换或在预防性维护活动中拆除。这是已知的第一项汇集了十多年来涉及各种应用中使用的液体密封设备的暴露评估的研究。在没有机械通风的条件下进行了 21 项工作活动和空气监测评估，并描述了“最坏情况”条件下的工作场景。频繁地，工作是使用激进的技术和干式去除方法进行的。按照国家职业安全与健康研究所方法 7400 和 7402 收集和分析个人和区域样本。共分析了 782 个样本的相差显微镜，499 个样本的透射电子显微镜。统计数据分析集中在个人全班次时间加权平均值（TWA）暴露、个人 30 分钟暴露和区域全班次 TWA 值的总体数据集上。每个数据集包含三种暴露估计值：（1）总纤维；（2）仅石棉纤维，但对被删失数据采用 0.0035 f/cc 的替代值；（3）仅石棉纤维，但对被删失数据采用定量限替代值。各个数据集的被删失数据范围在 7%到略高于 95%。由于所有数据集均被删失，因此使用最大似然估计法估计了几何平均值和几何标准差。应用了非参数、Kaplan-Meier 和对数正态统计，并发现它们是一致和增强的。所有三组统计数据均表明，暴露的平均值和中位数均小于 0.1 f/cc 8 小时 TWA 样本或 1.0 f/cc 30 分钟样本的 25%，并且至少有 95%的置信度表明真实的 95%百分位数暴露小于 0.1 f/cc 作为 8 小时 TWA。
