TS-17
Working Environment Level on Chemical Tanker Engaged in Benzene Transfer Operation
Takahiro MAJIMA*, Katsuji YAMAGUCHI*, Shinobu FUJII*, Hiroshi YAMANOUCHI*, Shinji SAKAMOTO* and Takashi YAMAO**
ABSTRACT
International Maritime Organization (IMO) recognized that chronic exposure to benzene vapors in air may cause leukemia even if the concentration is very low, such as a few parts per million. It is necessary to investigate the actual conditions of work environment level on chemical tankers engaged in benzene transfer operation. And exposure level to benzene gas is needed to grasp health condition of crews onboard.
Benzene transfer is divided into four operations, loading, navigation, unloading and tank cleaning. We conducted onboard measurements to clarify actual work environment level during each transfer operation. And airborne concentration of benzene gas was obtained.
Furthermore the carcinogenic risk was calculated using the averaged concentration obtained from onboard measurement. It is indicated that the wearing personal protection equipment such as air purifying mask is effective to reduce the excess risk of cancer.
Key Words: benzene, concentration, working level, exposure, carcinogen, human health risk assessment, onboard measurement, chemical tanker
1. INTRODUCTION
International Maritime Organization (IMO) recognized that chronic exposure to benzene vapors in air may cause leukemia even if the concentration is very low, such as a few parts per million. It is necessary to investigate the actual conditions of work environment level on chemical tankers engaged in benzene transfer operation.
As benzene is used widely to make some types of rubbers, lubricants, dyes, drugs, pesticides and so on, it is produced about several million tons and approximately 30% is transferred by chemical tanker for one year in Japan. Although low level exposure to benzene can cause cancer, crews engaged in benzene transfer operation handle pure liquid benzene. The exposure concentration to benzene gas is expected high value and it is necessary to grasp health condition of crews.
Marine transfer operation for chemicals is divided into four operations, loading, voyage, unloading and tank cleaning. We conducted onboard measurements to clarify actual work environment level during each transfer operation.
Three typical working places, mess room, vent post and cargo pump room were selected to sample gas, and subsequently analyzed by gas chromatograph to obtain concentration of benzene.
The followings are found.
1) Working environment level depends on working place and operation. The largest concentration was observed during tank cleaning operation and in pump room during unloading operation. Meanwhile the smallest concentration was measured in accommodation during all operations other than tank cleaning operation.
2) Carcinogenic risk of crew caused by benzene transfer operation is quantified using average concentration obtained from onboard measurement.
3) If crew puts on personal protection equipment such as air purifying mask when working in pump room, the average exposure concentration decrease to lower than 1(ppm) and carcinogenic risk is reduced more than 50%.
2. MARINE TRANSFER OPERATION
2.1 Chemical Tanker
499 Gross Tonnage chemical tanker is used often for benzene transfer in Japan. Schematic view of this vessel is drawn in Fig.1. The dimension of this vessel is 63(m) in length, 10(m) in breadth and 5(m) in depth. The benzene gas evaporated from liquid benzene in cargo tank is emitted from vent post located at the center of weather deck. The height of vent post is 6(m) from the deck and distance between vent post and accommodation is about 26(m). This tanker has eight cargo tanks arranged four in the longitudinal direction and two in the transverse direction. The largest tank has the dimension of 9(m) in length, 4(m) in breadth and 5(m) in depth.
