| Case Name |
Fire from a vent stack of an extruder during a shutdown at a polyethylene manufacturing plant |
| Pictograph |
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| Date |
October 25, 1973 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Chemical factory |
| Overview |
The low-density polyethylene manufacturing plant was stopped for turnaround shutdown maintenance. Polymerization reaction was stopped after part of the resin in the separator at the outlet of the reactor was extruded by the extruder. The instrument air valve of the extruder was closed by mistake, and the remote control supply valve to the extruder was opened, the pressure of 6.0 MPa in the separator raised the internal pressure of the extruder, which resulted in resin spouting from the rupture disk and a fire. In addition, the delay in dealing with the situation aggravated the damage. Measures for preventing mishandling of equipment and the manual for emergency were prepared. |
| Incident |
At a low density polyethylene manufacturing plant, polyethylene remaining in the low-pressure separator at the outlet of the reactor was discharged into the extruder to the appropriate level after the polymerization reaction stopped for the turnaround shutdown maintenance. As the rupture disk of the extruder operated, polyethylene and ethylene gas spouted, and a fire broke out. At a low-density polyethylene plant, a high-pressure separator and a low-pressure separator are installed in series at the outlet of the reactor. The extruder was supplied with molten polyethylene, which accumulated at the bottom of the low-pressure separator. Removing dissolved ethylene is one of the functions of the extruder. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Substance |
Polyethylene, Fig2 |
| Ethylene, Fig3 |
| Type of Accident |
Leakage, fire |
| Sequence |
07:52 on October 25th, 1973: The reaction was stopped for turnaround shutdown maintenance. Molten polyethylene in the low-pressure separator was discharged into the extruder to the appropriate level.
09:39: There occurred explosive sounds around the rupture disk of the extruder vent stack. Molten resin spouted from the rupture disk. Although an attempt was made to close the extruder block valve, it was not possible to close it completely.
09:40: A fire occurred after a sudden explosive sound.
09:43: The plant's fire brigade started to extinguish the fire, and the public fire service followed.
09:55: The fire was extinguished. |
| Cause |
The instrument air valve for operating the automatic valve at the inlet of the extruder was stopped by mistake. Subsequently, the automatic valve opened, and the extruder was supplied with molten resin remaining in the low-pressure separator. As the extruder had already stopped, resin supplied made the rupture disk operate and it flowed out into the air, together with gas components such as ethylene, which had melted into a molten resin, and was ignited by static electricity. The block valve could not stop the ethylene spouting due to a spanner trapped inside. |
| Response |
Water spraying for extinguishing the fire by the plant's fire brigade. |
| Countermeasures |
The valve on the instrument air was locked with wire to prevent mishandling (sealing). To prevent ethylene ignition, snuffing steam piping was installed in the vent stack to keep the constant steam atmosphere. The manual was revised to correct ambiguous descriptions. The failure position of the automatic valve was changed to shut. |
| Knowledge Comment |
Safety education for the turnaround shutdown maintenance is mandatory not only for employees, but also for subcontractors. The decision has to be made carefully on the failure position of the remote control valve assuming all possible problems. |
| Background |
1. The pressure of the upstream low-pressure separator remained at 6.0 MPa. In such a case, the practice of separating with one remote control valve is not desirable.
2. The failure position of the automatic valve should have been studied. It is considered that at the instrument air failure during operation, it is better to open the valve because it avoids an emergency stop. However, at instrument air failure at the whole plant, the valve should be closed, because the entire plant goes toward the stop direction. It is considered appropriate to shut it in an emergency, because the pressure of ethylene gas at 6.0 MPa is placed if it opens when the extruder stopped. It is regarded as a design fault in the operation mechanism of the automatic control valve.
3. The spanner was trapped in the block valve. It is supposed to have been dropped during the maintenance work on the upstream separator. There seemed to have been mismanagement of maintenance work.
4. The valves on the instrument air are usually not handled. They should be handled under the directions of a responsible person.
Countermeasures such as sealing should be taken to avoid mishandling or
misjudgment. Operation and management of the site should be
restudied. |
| Incidental Discussion |
In the accident report, it is stated that static electricity was considered to be the source of ignition because polyethylene spouted during the accident was at 245 °C, which is lower than its ignition point of 450 °C, and measures to control static electricity were stipulated, Although measures against static electricity are always necessary, they are not panaceas for fire because the ignition temperature of polyethylene is about 250°C, not 450 °C (as written in old literature). This old inaccuracy value of ignition temperature can cause accidents. |
| Reason for Adding to DB |
A typical accident of spouting caused due to mishandling of a valve |
| Scenario |
| Primary Scenario
|
Misjudgment, Misperception, Misread, Organizational Problems, Poor Management, Insufficient Preparation, Usage, Maintenance/Repair, Regular Operation, Erroneous Operation, Mistake of Operation Object, Bad Event, Mechanical Event, Rapture Disk Operated, Secondary Damage, External Damage, Fire
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| Sources |
Kawasaki City Complex safety countermeasure committee. NU Co., Ltd. K Operation center. No. 1 synthesis factory. Causes of fire research report (1974).
High Pressure Gas Safety Inst. of Japan. Examples of Accidents at Complexes. pp.197-198(1991).
Japan Soc. for Safety Engineering. Maintenance work is completed carefully. Accident happens in such case. Basis for accident prevention. pp.45-46(1991).
|
| Physical Damage |
100 kg of ethylene gas, 100 kg of polyethylene burned. The pressure-control system burned out. |
| Financial Cost |
¥500,000 (Investigation report for the fire causes, K operation center) |
| Multimedia Files |
Fig2.Chemical formula
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Fig3.Chemical formula
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| Field |
Chemicals and Plants
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| Author |
WAKAKURA, Masahide (Kanagawa Industrial Technology Research Institute)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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