Fig.3-1 Result of Vessel No. 702 (Unloading and Cleaning Operation)
Fig.3-2 Result of Vessel No. 801 (Unloading and Cleaning Operation)
Fig.3-3 Result of Vessel No. 703 (Loading, Voyage and Unloading Operation)
Fig.3-4 Result of Vessel No. 802 (Loading, Voyage and Unloading Operation)
Atmospheric temperature during measurement and sampling time are also indicated in this table. Thirteen vessels and twenty-one operations were investigated on the working environment level.
4.1 Vessel
Some results for each vessel are shown in Fig.3-1 through 3-4. Horizontal axis is operation time. Vertical axis is averaged concentration during each operation. The concentration is affected by many factors, wind direction, wind velocity, insolation, atmospheric temperature, leakage and so on. Although concentration value scatters, it can be said qualitatively that high concentration is observed during tank cleaning operation and at cargo pump room. Concentration in mess room indicates lower value than that of cargo pump room and vent post.
4.2 Operation
Time average concentration at three working places during four operations is shown in Fig.4-1 through 4-4.
The concentration during tank cleaning operation indicates maximum value in the four operations. High concentration, larger than 1(ppm) is measured at vent post and cargo pump room during this operation. Some of data for mess room exceed 1(ppm). The source of benzene gas emitted from cargo tank during cleaning operation is residue of liquid benzene adhering to tank bottom, walls and ceiling after unloading operation. The largest amount of benzene is emitted during this operation. Meanwhile the concentration during loading and voyage operation is one order magnitude lower than that of tank cleaning operation.
4.3 Working Place
The concentration in mess room indicates lower value than that of the other two working places during all operations.
