| Case Name |
Explosion on restarting agitation during the sulfonation reaction of toluene |
| Pictograph |
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| Date |
August 30, 1970 |
| Place |
Osaka, Osaka, Japan |
| Location |
Chemical factory |
| Overview |
On August 30th, 1970, an explosion occurred in a reactor of the m-benzene sulfonic acid and p-toluene sulfonic acid manufacturing plant. This reactor was for the sulfonation of benzene and toluene. The agitator stopped by a problem in the power supply when toluene was dropping into the reactor. The electric system was repaired, and the agitation was restarted after 30 minutes. The un-reacted toluene reacted rapidly because agitation was restarted under the conditions where un-reacted toluene had accumulated in the layer in the reactor. The temperature rose due to the heat of the reaction, toluene evaporated, became gaseous, and spouted out. It is considered that a combustible gas-air mixture was generated. It ignited and exploded. One person died and six persons were injured in this accident. |
| Incident |
An accident occurred in a plant that manufactured m-benzene disulfonic acid and p-toluene sulfonic acid through sulfonation of benzene and toluene. A fuse melted when toluene dropped into the reactor, and the agitator stopped. The fuse was changed, and then the agitation was restarted after 30 minutes. The toluene spouted from the reactor, ignited and exploded. One person died and six persons were injured. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig3.Unit process flow
|
| Chemical Reaction |
Sulfonation |
| Chemical Equation |
Fig2.Chemical reaction formula
|
| Substance |
Toluene, Fig4 |
| Sulfuric acid, Fig5 |
| Type of Accident |
Leakage, explosion |
| Sequence |
On August 30th, 1970: Benzene sulfonic acid was manufactured in the first process of blowing benzene into sulfuric acid. The second process in which m-benzene disulfonic acid is produced by adding sulfuric anhydride to benzene sulfonic acid finished, and cooling was started.
14:10: The addition of 280 kg of toluene was started in the third process after being confirmed that the temperature was 110 °C. The operator moved to another task.
15:30: Another operator found that the agitator had stopped. Toluene should have dropped spending about one hour with agitation.
15:55: The agitation was restarted. As the cause of the breakdown of the agitator was a melted fuse, the fuse was replaced and the agitation was restarted. Vapor immediately began to spout from a flange of the reactor. An operator who felt danger cut the power supply to the agitator.
16:02: An explosion occurred. It happened while an electrical staff had run into the switch room about 10 m far from the reactor to cut off the main switch. In addition, an explosion also occurred at an adjacent factory 5 m away. |
| Cause |
Agitation was restarted with un-reacted toluene remaining in the layer. Therefore, the un-reacted toluene rapidly reacted with sulfuric acid. As the temperature had risen because of the reactive heat, the remaining toluene evaporated and spouted. It is presumed that a combustible gas-air mixture was generated and was ignited. Then it exploded. |
| Countermeasures |
1. An alarm device for agitation stopping is installed. If possible, an interlock system to stop toluene dropping linked with this will be installed.
2. Facilities that can discharge the contents of the reactor safely in an emergency are installed.
3. The work standard has been reviewed, and the following are taught to operators thoroughly as important points.
(1) Temperature change with reaction time passing.
(2) Confirmation of the agitation conditions during charging raw materials.
(3) Confirmation of temperature during charging raw materials.
(4) Operation of emergency cooling system.
In addition, a procedure for responding to all assumed abnormal cases should be established, and related education and training for operators are provided.
4. A rupture disk or a safety valve is installed in preparation for pressure rise, and its outlet connects to a safe location. |
| Knowledge Comment |
1. Under abnormal circumstances, a person often takes the wrong action because he or she can not make a normal judgment due to panic.
2. When an operation cannot be easily restarted, as in this example, it is necessary to think about a system that can deal with the situation appropriately. For example, a large tank with diluents that can rapidly draw-off the liquid in a vessel, or a device cooling to a safety reactive rate should be installed. |
| Background |
The safety response for a dangerous reaction seemed not to have been understood. For example:
1. Education and training to employees were insufficient. Agitation was restarted although it was prohibited in the work standard. Or, the employee might have panicked.
2. Taking account of human error is lacking in the process design. For instance, there was not an emergency device for stopping toluen dropping by stopping the agitator automatically, or start-up interlock for restarting the agitator. |
| Reason for Adding to DB |
Example of accident due to emergency procedure error by an operator |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Insuficient Education/Training for Safety, Carelessness, Insufficient Understanding, Sulfonation Reaction, Planning and Design, Poor Planning, Poor Design, Malicious Act, Rule Violation, Safety Rule Violation, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion/Leakage, Bodily Harm, Death, 1 person died, Bodily Harm, Injury, 6 person injured, Loss to Organization, Economic Loss, 2 factory buildings burnt
|
|
| Sources |
Tamura Masamitsu, Masahide Wakakura, Explosion during sulfonation reaction of toluene. Reaction danger -Accident case and analysis -pp.102, 103(1995).
|
| Number of Deaths |
1 |
| Number of Injuries |
6 |
| Physical Damage |
Two buildings of a slated wooden one-storied workshop, a total of 300 square meters burned down. The windows of houses and stores near the factory were damaged. |
| 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 |
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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