Heitbrink W A, Earnest G S, Mickelsen R L, Mead K R, D'Arcy J B
U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Cincinnati, OH 45226, USA.
Am Ind Hyg Assoc J. 1999 Nov-Dec;60(6):785-8. doi: 10.1080/00028899908984502.
To evaluate the efficacy of engineering controls in reducing worker exposure to metalworking fluids, an evaluation of an enclosure for a machining center during face milling was performed. The enclosure was built around a vertical metal machining center with an attached ventilation system consisting of a 25-cm diameter duct, a fan, and an air-cleaning filter. The evaluation method included using sulfur hexafluoride (SF6) tracer gas to determine the ventilation system's flow rate and capture efficiency, a respirable aerosol monitor (RAM) to identify aerosol leak locations around the enclosure, and smoke tubes and a velometer to evaluate air movement around the outside of the enclosure. Results of the tracer gas evaluation indicated that the control system was approximately 98% efficient at capturing tracer gas released near the spindle of the machining center. This result was not significantly different from 100% efficiency (p = 0.2). The measured SF6 concentration when released directly into the duct had a relative standard deviation of 2.2%; whereas, when releasing SF6 at the spindle, the concentration had a significantly higher relative standard deviation of 7.8% (p = 0.016). This increased variability could be due to a cyclic leakage at a small gap between the upper and lower portion of the enclosure or due to cyclic stagnation. Leakage also was observed with smoke tubes, a velometer, and an aerosol photometer. The tool and fluid motion combined to induce a periodic airflow in and out of the enclosure. These results suggest that tracer gas methods could be used to evaluate enclosure efficiency. However, smoke tubes and aerosol instrumentation such as optical particle counters or aerosol photometers also need to be used to locate leakage from enclosures.
为评估工程控制措施在减少工人接触金属加工液方面的效果，对一台加工中心在端面铣削过程中的防护装置进行了评估。该防护装置围绕一台立式金属加工中心建造，配有一个由直径25厘米的管道、一台风扇和一个空气净化过滤器组成的通风系统。评估方法包括使用六氟化硫（SF6）示踪气体来确定通风系统的流量和捕集效率，使用可吸入气溶胶监测仪（RAM）来识别防护装置周围的气溶胶泄漏位置，以及使用烟雾管和风速仪来评估防护装置外部周围的空气流动。示踪气体评估结果表明，该控制系统在捕集加工中心主轴附近释放的示踪气体方面效率约为98%。这一结果与100%的效率没有显著差异（p = 0.2）。直接向管道中释放SF6时测得的浓度相对标准偏差为2.2%；而在主轴处释放SF6时，浓度的相对标准偏差显著更高，为7.8%（p = 0.016）。这种变异性增加可能是由于防护装置上下部分之间的小间隙处存在周期性泄漏，或者是由于周期性停滞。使用烟雾管、风速仪和气溶胶光度计也观察到了泄漏。刀具和流体的运动共同导致了空气周期性地进出防护装置。这些结果表明，示踪气体方法可用于评估防护装置的效率。然而，还需要使用烟雾管和气溶胶检测仪器，如光学粒子计数器或气溶胶光度计，来定位防护装置的泄漏位置。
