Comprehensive Ventilation Measurements of Large Underground Facility by Tracer Gas Method

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The purpose of this study is to develop the measurement method of ventilation characteristics using tracer gas in a large-scale underground quarry which has about 30,000 m3 inside volume. Usually this kind of ventilation and thermal environment measurements are difficult to measure with usual ventilation measurements, because the airflow direction and velocity are always fluctuating (not uniform) and affected by the external weather conditions.The measurements of the underground facility were carried out once a month over one and half year with the tracer gas method proposed by the authors. Also air flow environment (temperature, humidity and dust concentration) and rock surface temperature were measure at 15 points in the underground facility at the same time with tracer gas measurements.The SF6 was used as the tracer gas, because of it is very rare gas in the air and non-harmful to human body. The tracer gas concentration was measured with the gas monitor which is very sensitive to S … More F6 (resolution : 10 ppb), then the age of air and air exchange rate were able to be measured with this measurement system.The summary of present measurements is as follows :1) Tracer gas method developed have been successfully applied to measure the ventilation airflow rate in the underground facility with large inside volume ventilated by natural airflow.2) The ventilation air flow rate at summer time is much decreasing compared with winter time.3) The dust concentration at summer time is increasing at summertime with decreasing the airflow rate.4) The temperature difference between internal and external air of the facility becomes larger at the summer time than that of winter time because the air is cooled by contact with the internal rock surface with low temperature.The reason of increasing of dust concentration at summer time is based on the large temperature difference between internal and external air, then the air density of the internal air becomes large. This increases the stability of internal air against flowing air.The countermeasure against decreasing ventilation airflow rate should be exhausted by tubing with a blowing fan. Less