| Case Name |
Big explosion caused due to runaway reaction of raw materials left after a small explosion due to a power failure at an AS resin plant |
| Pictograph |
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| Date |
August 20, 1982 |
| Place |
Sakai, Osaka, Japan |
| Location |
Chemical factory |
| Overview |
Due to a power failure, an agitator and cooling water for polymerization reactors stopped at an AS resin factory, and cooling measures were insufficient. A reaction rate increased and the amount of generated gas rose sharply. Since the design of the deodorization furnace that burns the gas was based on the usual operation value, the gas was automatically bypassed die to the overload. Consequently, the un-burnt gas flowed directly into the exhaust gas stack. The gas was in the range of explosion and an explosion occurred in the lower part of the stack due to a high temperature. As the plant was ordered to shut down, only work required for safety was done after restoration from the power failure. Raw materials and catalysts for one polymerization were charged into the mixing drum for supplying a monomer of another AS polymerization unit just before the power failure. However, it was left under the influence of the first accident. An exothermic reaction gradually began, causing a large explosion 42 hours later and caused serious damage also to the neighborhood.
An exothermic reaction was not considered to progress because the substances in the monomer mixing drum were at a comparatively low temperature.
However, it became clear that as the reaction progressed gradually, the temperature rose, resulting in a runaway reaction according to experiments after the accident. |
| Incident |
In the batch reactors in an AS resin factory, a voltage drop occurred at four reactors out of six polymerization reactors. The cause was a power failure due to a fault in electromagnetic switching apparatus for motors in the electric power room. The agitator and cooling water pump of the polymerization reactors stopped, and the temperature began to rise. Workers tried to cool "C" and "G" reactors by manual operation where there was a rapid temperature rise. However, the temperature continued to rise and the reaction did not stop. A lot of gas flowed into the exhaust gas-processing unit, and an explosion occurred within the duct.
Operations of the plants of the factory were shut down sequentially, and only work required for safety was done. However, there was an oversight and it caused monomer gas to leak out from a monomer mixing tank of another synthesis series on the next day. After the gas leaked out in the factory, a large explosion occurred. All of the injuries were caused by the second accident.
The exhaust gas processing units in which the first explosion occurred are shown in Fig2. An outline of the reactors is shown in Fig3. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig2.Unit process flow
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Fig3.Unit process flow
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| Chemical Reaction |
Polymerization |
| Substance |
Acrylonitrile, Fig4 |
| Styrene, Fig5 |
| Type of Accident |
Leakage, explosion, fire |
| Sequence |
On August 19th, 1982, 23:10-00:10. Two kinds of raw material and a polymerization initiator were supplied to the monomer mixing drum of D polymerization unit.
23:25. As a voltage drop occurred in the polymerization unit, an investigation was started.
23:50. A power failure was caused by electromagnetic switching apparatus of power equipment burning out. The temperature of the polymerization reactor of AS plant began to rise. Although the operator tried to cool two polymerization reactors by water injection etc., the temperature rise did not stop.
On August 20th 00:15. An alarm sounded at the deodorization furnace that burned exhaust gas from the polymerization reactors. The exhaust gas bypassed the deodorization furnace and was discharged directly to the burnt gas stack.
00:25. When the combustible gas concentration in the duct of the deodorization furnace reached 80% of the lower explosion limit, an explosion occurred in the lower part of the stack.
00:28. Residents notified the fire department.
00:31. Extinguishing of fire was checked.
After 01:00. Temporary power supply was recovered.
Since the factory received an order to stop operation of the plant as a result of the first explosion, only work required for safety was done. It was continued until the 21st.
On August 21st, 17:12. Gas began to blow off from "D" series monomer mixing drum, and gas accumulated.
17:25. The persons concerned gathered. Gas was ignited by a spark from electric equipment during water-spraying, and a large explosion occurred. |
| Cause |
As the plant was not sufficiently prepared for a power failure, the first explosion occurred. For example, when the reactor showed a temperature rise, there was no cooling water and no agitation after the power failure, so the operator had to open the manhole of the reactor and inject cold water into the reactor. It seems that the deodorization furnace which burns exhaust gas from the reactors had been designed only for treating the usual quantity. For this reason, exhaust gas was bypassed automatically in an emergency. The gas bypassed the furnace and was introduced directly to the stack for burnt gas, and an explosion occurred.
Attention of workers was paid to dealing with the first explosion and necessary work was not done.
Consequently, the second explosion caused more serious damage. That is, although the substances in D monomer mixing drum had to be shifted to D polymerization reactor, they were left in D monomer mixing drum. The temperature rose due to the reaction, and a runaway reaction occurred 42 hours later.
The delay of emergency measurements for exhaust gas equipment, which was complicated, was also one of the causes of the first explosion. |
| Response |
Fire extinguishing work. A report to the fire department. |
| Countermeasures |
Improving a job standard based on reaction characteristics. Prior evaluation of process danger. Review the management system including that for an emergency. Separating a factory from residences. |
| Knowledge Comment |
1. While there was not enough information, a lot of person had gathered, and the damage became large. There was also a choice for all workers of taking refuge in an emergency, without extinguishing the fire. It is dangerous for all workers to take the same action in an emergency.
2. There was a state of panic. It is difficult to take immediate measures for workers on the site, so a supervisory system is necessary. |
| Background |
In terms of both equipment and operation, countermeasures against a power failure were also insufficient. That is, measures for an emergency at all stages of a batch reaction were not taken due to insufficient process engineering and equipment. The cause of the second explosion was not having information in advance about the reaction in the monomer mixing drum. As measures for dealing with the first explosion were limited to work required for safety, the monomer mixing drum was not noticed to be in a dangerous state. Prohibition of plant operation was ordered. Because of on-site preservation, workers might not be able to treat the site, but if a person related knew the possibility of a runaway reaction in a monomer mixing drum beforehand, the second explosion might be able to be prevented. |
| Incidental Discussion |
All of the related managers of the factory suffered damage from a second explosion. This is because a meeting was held in connection with a gas leak after a countermeasures meeting, and they gathered at the site of the leak. It is shown that in an emergency it is necessary to assign roles in advance mire than usual.
The accident is a good lesson because of the scale of damage due to the secondary explosion.
However, there was a big problem in the study of exothermic reactions. A safe method of shutting down at the time of a power failure was not established. Study of the exhaust gas combustion furnace in an emergency was inadequate. The rise of temperature of low-temperature reaction materials was not considered due to neglecting a slow reaction at a low temperature. |
| Reason for Adding to DB |
Example of big explosion caused due to a management mistake after a small explosion |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Insufficient Analysis or Research, Insufficient Prior Research, Insufficient Study for Reaction Danger, Misjudgment, Misjudgment of Situation, No Judgment by Overseeing the Whole, Planning and Design, Poor Planning, Poor Design, Non-Regular Action, Emergency Action, Panic, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Leakage/Explosion, Loss to Organization, Economic Loss, Direct Monetary Damage 1000 million yen, Damage to Society Social Systems Failure, About 9,000 person and 1,800 houses damaged
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| Sources |
Edited by Japan Society for Safety Engineering. Yoichi Uehara, Outline of AS resin plant explosion accident, Collection of examples of fire explosion accidents, pp.97-111 (2002).
Sakai & Takaishi fire-fighting association, D Chemical industry S factory resin factory explosion fire accident report. (1983).
Ikuo Fukuyama, The explosion accident due to runaway reaction, SE series, Learning from an accident. pp.20-23 (1987).
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| Number of Deaths |
6 |
| Number of Injuries |
204 |
| Physical Damage |
An exhaust gas duct was destroyed at about ten places over 50% of its full length. Part of the blower, cooling tower, recovery tower, and other piping ruptured. In ten buildings, including a warehouse, parts of the slate roof, side wall, windows, etc. were damaged. |
| Financial Cost |
¥ 1,004 million in only the factory. (D Chemical industry S factory resin factory explosion fire accident report) |
| Consequences |
1788 buildings were damaged. 8876 residents were injured. |
| Multimedia Files |
Fig4.Chemical formula
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Fig5.Chemical formula
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| Field |
Chemicals and Plants
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| Author |
ITAGAKI, Haruhiko (Japan National Institute of Occupational Safety and Health)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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