On the prediction of toxic fumes from underground blasting operations and dilution ventilation. Conventional and numerical models

摘要

One of the techniques used to excavate tunnels and underground spaces is the drilling and blasting method. Blasting is an intermittent activity and the concentration of contaminants in the affected parts often greatly exceeds the maximum concentrations (Time-Weighted Average and Ceiling Limit) for a period of time until the fumes are diluted by the ventilation currents.There are different algorithms for calculation of gas clearance after blasting in development headings. As seen in Tomo et al. (2013), these models are only appropriate when the area of the gallery, the auxiliary ventilation system and the mass of explosive used are very close to the characteristics of the tests conducted from which the mentioned algorithms were obtained. With re-entry time after blasting in a development heading of 30 min of difference between some models and others.The first aim of this study was to develop algorithms based on experimental measurements and to include the fundamental parameters of dilution directly in these algorithms: cross-sectional area of the drive (area of the face advance), mass of explosive used in the blast, time for the air to clear, distance from the end of the ventilation duct to the face and quantity of air sweeping the face (flow of the auxiliary ventilation). Models indicating reentry times of 32 and 5 min for the particular conditions of the studied zone.The second aim of this study was to develop 4D models of gas behaviour by Computational Fluid Dynamics (CFD). CFD model results were validated and compared with experimental measurements and with the mathematical algorithms developed in this study. Based on these CFD models, other dilution behaviour models of blasting gases can be developed for other cross-sectional areas, other mass of explosive and other ventilation parameters.These mathematical algorithms and CFD models represent powerful tools to be able to analyse dilution of fumes by the ventilation and re-entry of the workers after blasting in a development heading (third aim of this study).In the first two aims the test gallery had a section of 12 m(2) and CO was the gas analysed. The third aim was carried out in a tunnel of 67 m(2) and NO2 was the gas analysed. The results obtained prove the importance of the analysis by Computational Fluid Dynamics.