Monitoring of Harmful Gas for Yangbajing 1# Tunnel in High Altitude Plateau

Under the natural ventilation conditions, two stages nitrogen oxides (NOx, converted from NO
₂
), carbon monoxide (CO) in the air of Yangbajing 1# tunnel were monitored. Time and space distribution of NOx and CO content in the tunnel was analyzed. Just only 4 min after the trains run through the monitoring points, NOx concentration were less than 2 mg/m
³
, CO concentration were less than 3mg/m
³
. The results of on-site samplings of harmful gas indicated that, the concentration of CO and NOx in the Yangbajing1# Tunnel, above 3000m from sea-level, diesel-hauled, length more than 3Km, can satisfy the requirements in the Code for Design on Operating Ventilation of Railway Tunnel (TB10068-2010) under the natural ventilation conditions. So, the natural ventilation threshold (2Km) in the code should be revised for railway tunnels in high altitude plateau.