To estimate the quantitative relation between exposure to respirable silica dust and risk of an attack of silicosis, 1151 workers exposed to silica dust and employed from 1958 to 1987 in a tungsten mine in China were investigated. The results showed that the ratio of respirable silica dust concentration to total silica dust concentration was 0-529. Then, the total silica dust concentration in historical surveillance and monitoring data was converted to respirable silica dust concentration. The free silica content in respirable dust determined by x ray diffraction averaged 24-7%. Multiple logistic regression was used for the dichotomous dependent variables (presence or absence of silicosis). The independent variables in the multiple logistic regression with presence of silicosis as the dependent variable were age when first exposed, tuberculosis (presence or absence), and cumulative exposure to respirable silica dust. The partial regression coefficient of individual cumulative exposure was estimated as 0-079. It implied a positive association between exposure to respirable silica dust and risk of an attack of silicosis. The exposure limit for respirable silica dust was estimated as 0-24 mg/m' under given conditions.Respirable dust is defined as that reaching the alveoli and is assumed to be associated more with pneumoconiosis than is total dust. As a result, health standards for respirable dust have been introduced by many countries-for example, America, Japan, Australia-in the context of prevention of pneumoconiosis. We are presently conducting a retrospective epidemiological study of selected workers from a tungsten mine in China to establish the quantitative relation between exposure to respirable silica dust and silicosis. The aim of the present study is to provide epidemiological evidence for setting and
Results
RESPIRABLE AND TOTAL DUST CONCENTRATIONSThe figure shows the correlation between respirable and total dust concentrations at workplaces in the underground mine. A linear trend was found. Table
Not only is the thermal environment of the coal mining face related to the temperature of the surrounding rock, it is also closely associated with the ventilation model of the working face. In this study, the numerical methods were applied to study the impact of two major ventilation systems on the airflow temperature of working face in coalmine. Firstly, a heat transfer model of the surrounding rock and airflow was established to reveal that the wall roughness of the surrounding rock could enhance heat transfer between the surrounding rock and the airflow. Moreover, an analysis was conducted of the heat transfer between the airflow and the surrounding rock under different modes of ventilation in the first mining face. According to the analytical results, the temperature of airflow in the U-type ventilation system is lower than in the Y-type ventilation system. For the next adjacent coal mining face, however, the Y-type ventilation system is more conducive in reducing the temperature of the airflow. Therefore, with regard to the mine as a whole, the Y-type ventilation system is more effective than a U-type system in reducing heat and humidity in the ambient environment.
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