CLEARING THE AIR ON LONG TUNNEL DRIVES

This article explains air ventilation best practices on long tunnel drives. Focusing on ventilation requirements, the article discusses threshold values for acceptable concentrations of gas, dust and fumes. Satisfactory ventilation in long tunnel drives also requires appropriate fans and ducts. For drill and blast tunnelling, ventilation principles such as suction, booster schemes, large capacity blow in, and blow in-blow out are discussed. In TBM tunnelling, there are no blasting fumes, and exposure to diesel exhaust is reduced. However, noise, vibration, mineral dust, and heat from TBM rock faces present serious challenges. Efforts must be taken to mitigate these effects. The article briefly mentions new systems such as computer monitored intelligent tunnel ventilation systems that monitor fan effects. In general, successful ventilation in long tunnel drives requires axial propeller fans, strong flexible ducts that allow high pressure, straight alignment of the duct, low friction in duct joints, and diligent maintenance to keep leakage at a minimum.