2012 Volume 128 Issue 4_5 Pages 209-217
Ventilation measurements were carried out at a shallow underground quarry with relatively large internal volume of 14,600 m3 in order to evaluate its effective ventilation characteristics. From velocity measurements with an ultrasonic anemometer at the exit airway connected to the underground space, the space was ventilated by natural wind flow with direction changes intermittently. It was difficult to measure the ventilation flow with usual method on flow quantity provided from inlet portal, because the space volume was too big and the flow was unsteady to measure flow velocity in the space.
In present study, a tracer gas method was applied to evaluate ventilation characteristics of the space. A photo-acoustic gas monitor, that has high sensitivity of 10 ppb resolution for SF6 used as the tracer gas, was set in the space to measure air exchange rate based on the gas concentration-time decay curves. The seasonal change was investigated based on 13 times of measurements during Sept. 30, 1996 to Dec. 21, 1997. Dust concentrations were also measured at the same time in the space. The relationships between ventilation, thermal environment of the space and dust concentration were discussed. It has been analyzed that the reason of seasonal changes in ventilation and dust concentration comes from mainly temperature difference between air of outer atmosphere and internal air or rock surface in the space. Especially, the reason why lower ventilation flow and higher dust concentration generate in summer season was discussed and concluded as that internal air with lower temperature is stable due to its larger density compared with outer atmosphere, then the natural ventilation flow was restrained.
