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  Excavating Metro Tunnels with an EPB TBM under Risk of Methane Explosion

  New Istanbul Airport is being constructed over an old coal field area of 35 km away from the city center. Sometimes TBM used for tunnel excavation cuts coal seams bearing methane. This paper summarizes the safety problems encountered between chainages of 24+375 km and 24+575 km. A special safety program is used during tunnel excavation. For safety reasons, methane sensors were placed upon TBM cutterhead. However, hand hold methane measuring devices were also used along the tunnel, since methane is soluble within the water and travels kilometers away from its origin. Lower explosion limit (LEL) up to %3.5 was measured. Personal oxygen mask and an auxiliary ventilation system were also presented within the tunnel in order to use in emergency cases. Some case studies on methane and gas explosions which occurred during TBM excavation in Turkey and elsewhere were also presented in this paper. It is believed that the experiences gained from this case study will serve a basis to improve tunneling safety operations in similar tunneling conditions.

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