| Case Name |
Hydrogen chloride gas leakage from a reactor due to the pressure rise from an abnormal reaction at a chloroform manufacturing plant |
| Pictograph |
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| Date |
May 22, 1983 |
| Place |
Tokuyama, Yamaguchi, Japan |
| Location |
Chemical factory |
| Overview |
Accident occurred on May 22nd, 1983. The switching operation of the compressors was carried out while operating the chloroform manufacturing plant. At that time, chlorine feed rate was not decreased to the fixed flow rate. As a result, the concentration of iron chloride that inhibited the reaction increased, and the reaction was suppressed. Therefore, reactor pressure began to fall. The gaseous chlorine flowed into the reactor excessively, because the chlorine feed control valve was set on manual and the reactor pressure was lowered. Afterwards, accumulated chlorine reacted rapidly, because the reaction rate recovered. The pressure increased, suddenly generating hydrogen chloride gas, and hydrogen chloride gas spouted from the flange of the reactor. Gas flowed out into an urban area outside the plant site, and there were scores complaints from residents. |
| Incident |
Switching operation of compressors that supplied gaseous chlorine was made while chloroform manufacturing was being conducted by liquid phase reaction. As the switching operation of the compressors was improper, hydrogen chloride gas shot up from the flange of the reactor. The gas flowed into an urban area outside the plant site, and there were scores complaints from citizens. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig2.Unit process flow
|
| Chemical Reaction |
Halogenation |
| Substance |
Chlorine, Fig3 |
| Type of Accident |
Leakage, environmental pollution |
| Sequence |
The previous shift handed over that the amount of gaseous chlorine leakage from the gland of B compressor for supplying chlorine for the second reactor increased..
09:00 on May 22nd, 1983: The shift leader reported an increase in the amount of the chlorine leakage from B chlorine compressor to the group head, and received instructions on switching to A compressor.
10:00. Warm-up operation of A compressor was started to switch from B machine to A machine.
13:44. The chlorine feed rate control valve was switched from automatic to manual because the feed rate might fluctuate when the compressor is switched.
13:46. The operation switching the load from B compressor to A compressor was started because warming-up and pressure rise of A compressor were completed.
13:48. The pressure of the reactor decreased while the load was moved from B compressor to A compressor. Switching of the load to A compressor was interrupted, and the load was returned to B compressor. Simultaneously, the pressure control valve of the reactor was switched from automatic to manual.
13:50. The chlorine feed rate was noticed to increase sharply. The chlorine feed control valve was controlled manually, and was adjusted to a fixed quantity at 13:55.
13:59. Suddenly, the pressure of the reactor rose. The pressure control valve of the reactor was completely opened. However, as the pressure increase did not stop, the discharge valve connected to the scrubber was opened completely.
14:00. The emergency cut-off device operated, and raw material feed stopped. The safety valve operated immediately after that, and chlorine shot up from the reactor flange at the same time. |
| Cause |
The feed rate of chlorine did not decrease to the prescribed flow rate when the chlorine supply compressors were switched. Therefore, the amount of iron chloride for reaction control increased, and the reaction was suppressed. As a result, the amount of hydrogen chloride gas generation decreased, and the reactor pressure began to fall. Since the chlorine flow control valve was operated in a manual mode, the differential pressure of the flow control valve of chlorine feed increased due to the pressure of the reactor falling, and gaseous chlorine flowed into the reactor excessively. Afterwards, chlorine that had accumulated reacted rapidly because the reactive rate recovered. The pressure increased suddenly on generating of hydrogen chloride gas, and hydrogen chloride gas spouted from the flange of the reactor. |
| Countermeasures |
1. Review and improvement of the operation standard were done.
2. Countermeasures for facilities were improved.
(1) The chlorine feed system was changed from compression gas supply to the evaporation supply method of liquid chlorine, for preventing fluctuation of chlorine gas flow rate.
(2) Warning devices were classified according to the importance of the problem. |
| Knowledge Comment |
The following should be noted for human beings in an emergency: Complicated operations and checks of numerical values displayed by instruments should not be required. The reliability of complicated operations should be insufficient because the reliability of human judgment and action is sharply reduced compared to usual times. |
| Background |
1. The work standard was inadequate. Therefore, operation to decrease chlorine gas was not carried out, and the set value of the emergency shutdown system operating due to lowering of reaction temperature was unsuitable. The human error mentioned above occurred.
2. The alarm that informs of an abnormality such as increase in chlorine flow was insufficient. |
| Reason for Adding to DB |
Example of accident caused due to human error of an operator expected complicate operations and/or a concentration in emergency |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Insufficient Analysis or Research, Insufficient Practice, Lack of Imagination, Halogenation Reaction, Planning and Design, Poor Planning, Poor Design, Non-Regular Operation, Emergency Operation, Opeartion accompanied with Machine Switching, Bad Event, Chemical Phenomenon, Abnormal Reaction, Failure, Large-Scale Damage, Leakage, Secondary Damage, Damage to Environment, Environmental Pollution
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| Sources |
High Pressure Gas Safety Inst. of Japan, Chloro-methane manufacturing plant, Hydrogen chloride gas leak accident by pressure rise due to unusual reaction in a reactor, Accident examples of Petroleum refinery and Petrochemical units. pp.146-148(1995).
|
| Physical Damage |
Deformation of a flange on the second reactor. A gasket was damaged. |
| Consequences |
Hydrogen chloride gas flowed into the town center. |
| Multimedia Files |
Fig3.Chemical formula
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| Field |
Chemicals and Plants
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| Author |
OGAWA, Terushige (Graduate School of Environment and Information Sciences, Yokohama National University)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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