Concentration, Propagation and Dilution of Toxic Gases in Underground Excavations under Different Ventilation Modes

Javier Menéndez, Noe Merlé, Jesús Manuel Fernández-Oro, Mónica Galdo, Laura Álvarez de Prado, Jorge Loredo and Antonio Bernardo-Sánchez
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Javier Menéndez: Mining and Civil Department, SADIM Engineering, 33005 Oviedo, Spain
Noe Merlé: Mining and Civil Department, Duro Felguera, Parque Científico Tecnológico, 33203 Gijón, Spain
Jesús Manuel Fernández-Oro: Fluid Mechanics Department, University of Oviedo, 33271 Gijón, Spain
Mónica Galdo: Fluid Mechanics Department, University of Oviedo, 33271 Gijón, Spain
Laura Álvarez de Prado: Department of Mining Technology, Topography and Structures, University of León, 24071 León, Spain
Jorge Loredo: Mining Exploitation Department, University of Oviedo, 33004 Oviedo, Spain
Antonio Bernardo-Sánchez: Department of Mining Technology, Topography and Structures, University of León, 24071 León, Spain

IJERPH, 2022, vol. 19, issue 12, 1-21

Abstract: The drill-and-blast method is widely used for the excavation of hard rock tunnels. Toxic gases such as carbon monoxide and nitrogen oxides are released immediately after blasting by the detonation of explosives. To provide a safe working environment, the concentration of noxious gases must be reduced below the threshold limit value according to health and safety regulations. In this paper, one-dimensional mathematical models and three-dimensional CFD numerical simulations were conducted to analyze the concentration, propagation and dilution of the blasting fumes under different operating conditions. Forced, exhaust and mixed ventilation modes were compared to determine the safe re-entry times after blasting in a 200 m-long tunnel excavated using the top-heading-and-benching method. Based on the numerical simulations, carbon monoxide was the most critical gas, as it required a longer ventilation time to reduce its concentration below the threshold limit value. The safe re-entry time reached 480 s under the typical forced ventilation mode, but was reduced to 155 s when a mixed ventilation system was used after blasting, reducing the operating costs. The reduction of the re-entry time represents a significant improvement in the excavation cycle. In addition, the results obtained show that 1D models can be used to preliminary analyze the migration of toxic gases. However, to reliably determine the safe re-entry times, 3D numerical models should be developed. Finally, to verify the accuracy of the CFD results, field measurements were carried out in a railway tunnel using gas sensors. In general, good agreements were obtained between the 3D numerical simulations and the measured values.

Keywords: toxic gases; underground excavations; tunneling; blasting; numerical modeling; field measurements (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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