Risk Analysis Of Volatile Organic Compounds Using Their Indoor Diffusion Characteristics
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T. Oyabu, T. Higashino & H. Nanto
Diffusion characteristics of VOCs (Volatile Organic Compounds) were investigated using tin oxide gas sensors. The chemicals cause various kinds of symptoms to humans, for example sick building syndrome. In this study, the eight sensors were installed in a room. Four sensors were set in a vertical direction and the others on a plane surface. These sensors were of the same type. The VOC is put in a generation source, and the sensor output increases as the chemical diffuses. The output becomes higher as the concentration in the room becomes higher. The following chemicals were adopted as air pollution sources, namely formaldehyde, toluene and xylene. The sensor output is changed slightly even by a calm wind velocity. Therefore, the differential characteristic of sensor output was adopted and the noise component was removed as far as possible. A threshold value vth to the characteristic was set up. It is understood that the examining chemical reaches the installed sensor point when the characteristic is in excess of the value. The speed reached was newly proposed using the threshold time tth at which the output exceeded vth. The speed s [cm/min] is indicated using the distance d and tth, namely s = d/tth. The d means the distance between the sensor position and the generation source. As a result, the speed for the sensor that is installed near a ceiling (the height is 260 cm from the floor) is fast, and it became obvious that the s was larger to the smaller molecular chemical. The speed of formaldehyde for the sensor installed near the ceiling was 700 [cm/min] and the one for the sensor installed at the height of 100 cm from the floor was 370 [cm/min]. This is about double the difference in speed. Keywords: VOC, gas diffusion, chemical sensor, sick house syndrome.
VOC, gas diffusion, chemical sensor, sick house syndrome