Migration characteristics of CO under forced ventilation after excavation roadway blasting: A case study in a plateau mine

Multiple toxic gases, such as carbon monoxide (CO), are generated after excavation roadway blasting of plateau mines. To eliminate environmental pollution in a timely manner and avoid potential occupational hazards to miners, a three-dimensional unsteady roadway model was established based on field data of the Pulang copper mine in Yunnan province, China. Computational Fluid Dynamics (CFD) method was used to explore the space-time evolution characteristics of CO under different working conditions, and the grey correlation analysis was applied to study the correlation values of the influencing factors on the CO dispersion coefficient in the roadway. The results demonstrate that in the early stage of the roadway with forced ventilation, the mass concentration of CO in the vortex area near the working area was obviously higher than elsewhere, and in the later stage of ventilation, the mass concentration of CO at the bottom of the roadway was higher than that at the top. The most significant changes of the CO appeared within 500 s before ventilation. The mass-weighted average concentration of CO in the cross-section of the roadway presented a Gaussian-like distribution with respect to the ventilation time. The first stage represented a period of rapid growth, and the second stage exhibited a period of variable speed decline. The ventilation time when the mass concentration of CO in the roadway reached the upper limit of occupational exposure was generally between 700 s and 900 s, and the safe re-entry time was greater than 15 min. The grey correlation analysis revealed that the major influencing factors of CO migration in the roadway of the plateau mine, were, in a descending sequence, as follows: the distance between ventiduct mouth and working face, ventilation volume, and altitude, and the corresponding correlation coefficients were 0.9931, 0.7792, and 0.4366, respectively. The altitude was inversely proportional to the CO dispersion coefficient, and the distance between ventiduct mouth and working face was directly proportional to the ventilation coefficient corresponding to the CO dispersion coefficient. This research can provide guidance on optimising the ventilation design of roadways in plateau mines, thus ensuring the occupational health of cleaners.