| Summary: | 碩士 === 中國醫藥大學 === 職業安全與衛生學系碩士班 === 101 === Concrete drilling operations in the construction industry often results in high dust exposure concentrations of involved workers. High dust exposure concentrations can cause many negative health effects associated with exposure to free silica components. In view of the dust sampling process was complex and affected by workers’ willingness, so conducting sampling was difficult in the field. In addition, the analysis of free silica was very complex and expensive, which lead to adequate number of samples was hard to obtain. This study is aimed at using a surrogate method (including the use of both drill rotating speeds and drill bit sizes), from less expensive and interference as pects, to predict both of the workers’ dust, free silica exposure concentrations and size distribution characteristics. The study uses concrete drilling operationsion construction industry as an example. The whole study was conducted in an exposure chamber (L×W×H=300cm×240cm×360cm), to simulate the emissions of dusts and free silica under six different operating conditions (including four different drill rotating speeds of 265rpm, 315rpm, 460rpm, 587rpm, and three different drill bit sizes of 16mm, 28mm, 32mm). The dust sampling was conducted using a Marple cascade impactor and Aerodynamic Particle Sizer (APS). For Marple cascade impactor obtained dust samples, their free silica contents were analyged per NIOSH 7500 and OSHA ID-142 method. Linear regression analyses were conducted for establishing models for exposure concentration prediction purposes.
Five major research results were obtained from the present study, including: (1) the free silica size distribution was consistently in a bimodal form under six different operating conditions; (2) The drill rotating speeds increases would lead to an increase in dust exposure concentrations levels in all tested conditions. As the drill bit sizes increases, a decrease in dust exposure concentrations of total dust (Ctot), coarse particles (Ccoarse), inhalable dust (Cinh), inhalable coarse particles (Cinh-coarse)、thoracic coarse particles (Ctho-coarse), and respirable coarse particles (Cresp-coarse) could be obtained, but an increase in fine particles (Cfine), respirable dust (Cresp), and respirable fine particles (Cresp-fine) concentrations; (3) For the free silica content, the increase in drill rotating speeds would lead to increase of the exposure concentrations levels for all tested conditions. As the drill bit sizes increases, the decrease in exposure concentrations levels with total silica (Cstot), coarse particles (Cscoarse), inhalable silica (Csinh), inhalable coarse particles (Csinh-coarse)、thoracic coarse particles (Cstho-coarse), and respirable coarse particles (Csresp-coarse) could be obtained. But the increase in exposure concentrations levels of fine particles (Csfine), respirable silica (Csresp), and respirable fine particles (Csresp-fine), and decrease in exposure concentrations levels with inhalable fine particles (Cinh), thoracic silica (Cstho), and thoracic fine particles (Ctho-fine) could also be seen; (4) The predicting models obtained from the surrogate method can effectively explain 98.4%, 98.8%, 99.2%, and 95.6% variations of measured Ctot, Cinh, Ctho, and Cresp; (5) The predicting models obtained from the mothod can explain 98.5%, 99.0%, 96.4%, and 98.3% variations of Cstot, Csinh, Cstho, and Csresp, respectively.
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