| Case Name |
Explosion caused due to miss-handling of only one remote control valve separated from atmosphere in the polymerization reactor at a polypropylene manufacturing plant |
| Pictograph |
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| Date |
October 8, 1973 |
| Place |
Ichihara, Chiba, Japan |
| Location |
Chemical factory |
| Overview |
On October 8th, 1973 (day of the accident), cleaning operation of an auxiliary cooler of No.6 polymerization reactor was carried out. A factory power failure occurred. The operators tried to open the remote shut-off valve at the outlet of No.4 polymerization reactor. It was dark near the panel board due to the power failure, and the remote shut-off valve of No.6 polymerization reactor was opened by mistake. A large amount of propylene and hexane leaked. A large-scale explosion occurred and four persons were killed. |
| Incident |
At a polypropylene manufacturing plant, a large explosion occurred during a power failure. When two auxiliary coolers were being cleaned, a power failure occurred. A large leakage of liquefied propylene occurred due to miss-operation of a valve during the power failure. A few minutes later, a large explosion occurred with consequent fire. Plant equipment in an area of about 300 m north and south, about 100 m east and west were destroyed by fire and four persons were killed. Refer to Fig2. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Process Flow |
Fig3.Unit process flow
|
| Chemical Reaction |
Polymerization |
| Substance |
Propylene, Fig4 |
| Hexane, Fig5 |
| Type of Accident |
Leakage, Explosion, Fire |
| Sequence |
On October 8th, 1973 (day of the accident), a cleaning operation of an auxiliary cooler of No.6 polymerization reactor was carried out from the morning. The shut-off remote valve in the piping from the polymerization reactor to the circulation pump was blocked. The flange connecting the polymerization reactor to the cooler was detached, and in addition, the suction valve of the circulating pump was opened. That is, No.6 polymerization reactor was separated only by one remote control valve from atmospheric air.
About 21:55. Cleaning operation of an auxiliary cooler of No.4 polymerization reactor started.
About 22:01. A factory power failure occurred due to switch insulation oil degradation in the transformer. Therefore, solvent injection for cleaning No.4 polymerization reactor was stopped and operators tried to open the remote shut-off valve at the outlet. It was dark near the panel board due to the power failure, and the remote shut-off valve of No.6 polymerization reactor was opened by mistake. Most of the No.6 polymerization reactor's contents (60 °C, 1 MPaG, 5.4 tons of liquefied propylene, 8.8 tons of polymers, and 26 tons of hexanes) leaked. Propylene vapor which evaporated by the leakage diffused throughout the factory.
About 22:07. Gas explosion occurred near the pelletizing plant, which was located about 60 m south of the polymerization reactor.
As polymerization reaction is possible during the cleaning of the auxiliary heat exchanger if the feed rate to the reactor was lowered, the operation of the reactor was continued with the detached heat exchanger. |
| Cause |
The outlet side of remote shut-off valve of No.6 polymerization reactor was opened by mistake instead of that of No.4 reactor. Then, a leakage of propylene, etc. occurred and a large amount of propylene vapor diffused throughout the plant site. Ignition was generated by electric sparks in the pelletizing plant, etc., and a large-scale gas explosion occurred. |
| Countermeasures |
As preventive measures against recurrence, the following points are considered. The lighting of the panel must be maintained even during a power failure. The switches on the panel board must be arranged so as not to be mishandled. In the case of separation with the atmosphere by just one valve, a blind plate must be inserted. There must be equipped a lock so that the valve cannot easily open, especially during maintenance. |
| Knowledge Comment |
A panel arrangement preventing miss-operation and lighting equipment to be used in a power failure are needed. It is necessary to take measures that make operation impossible during repairs. Separation from the atmosphere by only one remote control valve must be avoided. |
| Background |
The main factor was miss-operation of the shut-off valve of No.6 polymerization reactor. The switches of shut-off valves of all polymerization reactors were located on a same panel board, and the panel board was dark at that time due to a power failure. These situations might have caused the miss-operation. In addition, a factor in the background was the arrangement of switches on the panel board, which was easy to be mistaken. The remote control valve might be opened for various reasons, so a blind plate should be inserted when the piping is open.
In conclusion, the accident seemed to occur by poor panel design with lack of consideration on safety engineering and by improper maintenance management. |
| Incidental Discussion |
Power failure, arrangement of switches that easily causes a mistake, an open suction valve, which should have been closed, came together to cause the accident. It can be said that the accident could have been prevented if equipment that induces miss-operation was improved, and repairing procedures were performed with sufficient safety. |
| Reason for Adding to DB |
Example of explosion caused due to miss-operation of a valve during a power failure |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Carelessness, Insufficient Understanding, Insufficient Recognition of Risk, Planning and Design, Poor Planning, Poor Planning of Repair, Non-Regular Operation, Emergency Operation, Operate Wrong Valve, Secondary Damage, External Damage, Explosion/Fire, Bodily Harm, Death, 4 person died, Bodily Harm, Injury, 9 person injured, Loss to Organization, Economic Loss, The plant burnt
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| Sources |
Ministry of International Trade and Industry. C petrochemical Co., Ltd. accident investigation committee. Accident investigation report at polypropylene manufacturing plant The C petrochemistry Co., Ltd. G factory. (1973).
High Pressure Gas Safety Inst. of Japan. Summary of accident report. Chiba complex protection research report. pp.34-35(1978).
Tetsuzo Kitagawa. Large leakage of liquefied propylene caused by an operation mistake of valve. Analysis of explosion hazard. pp.158-160 (1980).
Chemical Industries Association. The accident disaster case example. Polymerization reactor. Cases of accidents and safety countermeasure technology for chemical plants. Vol.4. pp.281-282(1979).
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| Number of Deaths |
4 |
| Number of Injuries |
9 |
| Physical Damage |
Damage to a polymerization plant, a pellet manufacturing plant, and an aldehyde manufacturing plant (piping). The windows of surrounding private houses were damaged. |
| Multimedia Files |
Fig2.Disaster situation figure
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Fig4.Chemical formula
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Fig5.Chemical formula
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| Field |
Chemicals and Plants
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| Author |
DOBASHI, Ritsu (School of Engineering, The University of Tokyo)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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