| Case Name |
Explosion of 5-t-butyl-m-xylene on restarting an agitator during the nitration reaction |
| Pictograph |
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| Date |
April 14, 1970 |
| Place |
Osaka, Osaka, Japan |
| Location |
Chemical factory |
| Overview |
On April 14th, 1970, there was an explosion in the reactor of a 2.4.6-trinitro -5-t-butyl methaxylene manufacturing plant. A worker found the agitator had stopped while dropping the raw materials into mixed acid. Dropping of the raw materials was stopped at once and the agitation was restarted. Afterwards, he remembered that there was a possibility that restarting agitation rapidly promotes the reaction, and he stopped agitation immediately. However, soon smoke began to spout out, the reactor exploded, and a fire broke out, which severely damaged the plant building.
The reaction was carried out by dropping 5-t-butyl methaxyrene into mixed acid while agitating. |
| Incident |
Explosion occurred in a reactor which synthesized 2. 4. 6-trinitro-5-butyl methaxylene. The reaction process was as follows. First, the mixed acid (720 kg of 98% sulfuric acid, 750 kg of 98% nitric acid) was charged into the reactor, then 360 kg of 5-t-butyl-m-xylene was dropped into the reactor for nitration spending 14-15 hours during rotating the agitator, and the object substance was synthesized. By measuring the operation temperature every 30 minutes, the temperature in the reactor is maintained at 35-40 °C. Temperature control was carried out using a cooling jacket and controlling the dropping speed of 5-t-butyl-xylene. On the accident day, an operator found the agitator had stopped after 5 hours and 20 minutes from the beginning of dropping of raw materials to mixed acid. He restarted the agitator after stopping the dropping operation. Then, he remembered that there was a possibility that restarting of the agitation rapidly promotes the reaction, so the agitation was stopped immediately. However, soon smoke began to be generated and the reactor exploded and burned, damaging the building severely. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig3.Unit process flow
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| Chemical Reaction |
Nitration |
| Chemical Equation |
Fig2.Chemical reaction formula
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| Substance |
5-t-butyl-m-xylene, Fig4 |
| Sulfuric acid, Fig5 |
| Nitric acid, Fig6 |
| Type of Accident |
Explosion, fire |
| Sequence |
13:00 on April 14th, 1970: Charge of the mixed acid into the reactor was started.
13:30: Dropping of 5-t-butyl-xylene into the reactor started.
18:30: It was confirmed that reactor temperature was 37 °C.
18:50: At a temperature check, the temperature in the reactor was found to be lowering to 34 °C. It showed that the agitation had stopped. Therefore, dropping of raw material was stopped immediately, and the agitator was switched on. Afterwards, the operator remembered that restarting agitation might make the reaction progress rapidly, so he stopped agitation at once. Yellowish brown smoke began to spout from the vent of the reactor. So, he tried to open the bottom valve for blow down, but he could not approach the valve due to the smoke. Therefore, the two operators escaped and watched the situation. After a few minutes, a large amount of white smoke spouted from the vent, and the reactor exploded and burned. The lid flew about 15 m, and the main body of the reactor collapsed. |
| Cause |
Raw materials were being put into mixed acid while the agitator stopped. Therefore, raw materials and mixed acid separated into two phases in the reactor. As agitation was restarted in such conditions, these materials mixed suddenly, an exothermic reaction progressed rapidly, and the reactor exploded. |
| Countermeasures |
1. The cooling system with remote or automatic operation is adopted to cope with an emergency.
2. An emergency blow-down valve is controlled by a remote operation system.
3. An alarm indicating agitation stopping is equipped.
4. An instrument to stop dropping of raw materials which is linked to the alarm is installed.
5. The operation standard is prepared, making workers understand the following items completely.
(1) Temperature change with the time course of the reaction.
(2) Confirmation of the agitation during raw materials being charged.
(3) Watching of the temperature during raw materials being charged.
(4) Operation of the emergency cooling system.
In addition, procedures for all assumed abnormal cases are established, and education and training on these items are carried out thoroughly to the workers. |
| Knowledge Comment |
1. As a person panics or becomes confused when he experiences an abnormal situation, he might not make a normal judgment or might not act correctly even if he has a good knowledge.
2. Therefore, it is also important to design the system of facilities so that a plant can operate automatically in an emergency without depending on human beings. |
| Background |
1. There seems to have been a panic behavior of the operator. As the operator's attention was concentrated on restarting operation, there was an error in the work procedure.
2. There was no system that automatically announces the agitator stopped.
3. It is evident that restarting rapid agitation is dangerous. The countermeasures of the facilities seemed to be insufficient. |
| Incidental Discussion |
Although now it is usual that dropping of materials is stopped automatically when agitation is stopped and/or using start-up interlock of the agitator for restarting the agitator, such a device was not mounted at that time. In other words, the viewpoint of human error was lacking in the process design. However, at that time, it might have been difficult. |
| Reason for Adding to DB |
Example of accident caused due to miss-operation in an emergency |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Insufficient Analysis or Research, Insufficient Practice, Lack of Imagination, Nitration Reaction, Non-Regular Operation, Emergency Operation, Reflective Operation, Planning and Design, Poor Planning, Poor Design, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion/Fire, Loss to Organization, Economic Loss, Factory Building Completely Burnt
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| Sources |
Masamitsu Tamura, Masahide Wakakura, Explosion during nitration reaction of 5-t-butyl methaxyrene. Explosion under 2, 4, 6-trinitro-5-t-butyl-m-xylene manufacturing. Reaction danger - Accident case and analysis - pp. 81,82(1995)
Ministry of Labor Industrial Safety and Health Department safety section, Explosion during nitration of tert-butyl methaxylene. Safety of batch process, pp.66-67(1987).
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| Physical Damage |
A steel frame slated two-story factory with about 200 square meters burned. The windows of a nearby building were damaged. |
| Multimedia Files |
Fig4.Chemical formula
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Fig5.Chemical formula
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Fig6.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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