In conclusion it is of prime importance to fully understand in advance all of the issues involved in the underground structure to be built, such as its geology (any gas present), the environment (problems with dust discharging, noise nuisance), the climatic conditions (extreme temperatures, humidity levels), accessibility (setting up the ventilation equipment) but also the geometry and the different phases during excavation (constrain points for the ventilation ducting). The correct definition of the plant used during excavation as well as the different work phases is essential for the definition of an efficient ventilation system particularly with regards to the airflow rates to be achieved. Experience shows that too frequently the points described above are not analysed with sufficient acuity resulting in a lack of efficiency of the ventilation and consequently a health hazard for the personnel working in the tunnel.
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