But it closes to 1(ppm) during tank cleaning operation. Air around chemical tanker is drawn into accommodation by the ventilator located above wheel room. Meanwhile the concentration in cargo pump room is the highest value among three working places. Cargo pump in chemical tanker is filled with liquid benzene during loading, voyage and unloading operation. And air including high concentration of benzene gas passes through cargo pump during tank cleaning operation. It is difficult to prevent cargo pump's leakage of benzene gas perfectly. Consequently, high concentration is observed in cargo pump room.
The concentration in cargo pump room during unloading operation is highest value. On the other hand, The concentration in mess room during voyage is the smallest value.
4.4 Summary of Concentration
Table 2 shows the arithmetic mean concentration at three working places during each operation. These data are plotted in Fig.5. It is found from this figure that the concentration in pump room is larger than that of the other working places. And highest concentration is indicated at cargo pump room during tank cleaning operation and lowest concentration is represented at mess room during voyage operation.
