| Case Name |
Explosion due to excess charge of oxidizer following malfunction of instrument during manufacturing of carboxymethylcellulose |
| Pictograph |
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| Date |
March 13, 1971 |
| Place |
Himeji, Hyogo, Japan |
| Location |
Chemical factory |
| Overview |
Due to a failure of a computer that controls the supply of hydrogen peroxide water automatically, hydrogen peroxide water was charged at 20 times as much as the predetermined quantity to the reactor of a carboxymethylcellulose (CMC) manufacturing plant. Sodium hydroxide was added. As a result, a large amount of oxygen was generated. It was considered that isopropanol and oxygen formed a combustible gas-air mixture. Steam flowed into the reactor jacket, and the reactor internal wall was heated. Due to the high temperature of the wall, organic peroxide or a mixture of sodium oxide and an organic substance adhering to the wall ignited and exploded (speculation). |
| Incident |
Carboxymethylcellulose (CMC) was being manufactured at a reactor where isopropanol, hydrogen peroxide aqueous solution, and sodium hydroxide were being added to ground pulp. The reactor exploded on-stream. (CMC is used in viscosity extenders of drinks, etc.) |
| Processing |
Manufacture |
| Individual Process |
Feed and Charge |
| Process Flow |
Fig2.Unit process flow
|
| Chemical Reaction |
Oxidation |
| Substance |
Hydrogen peroxide, Fig3 |
| Sodium hydroxide, Fig4 |
| Monochloroacetic acid, Fig5 |
| Type of Accident |
Explosion |
| Sequence |
In a reaction preparation drum of a CMC manufacturing plant, 90% isopropanol aqueous solution slurry of pulp was being made, and 30% hydrogen peroxide water was added to the slurry by an automatic controller operated by a computer. An alarm lamp showed over-supply of hydrogen peroxide water. Supply of hydrogen peroxide water was stopped after switching a supply mode to manual operation. The contents of the drum were transferred to the reactor, and it was cooled. The reaction began upon adding sodium oxide. In addition, on adding monochloroacetic acid, it was agitated. During agitation, the temperature rose, and an explosion occurred. |
| Cause |
Due to a failure of the computer that controlled the automatic supply of hydrogen peroxide water, charged hydrogen peroxide water was 20 times as much as the predetermined quantity. Therefore, a large amount of oxygen was generated by the addition of sodium hydroxide, and it seemed to have formed a combustible gas-air mixture with isopropanol. As steam flowed into reactor jackets in error, the reactor's internal wall temperature became high, which seems to have ignited low ignition point materials (organic peroxide or a mixture of Na2O and organic peroxide) adhering to the wall. |
| Countermeasures |
1. Mechanical measures to prevent formation of an excessive oxygen condition should be taken.
2. Mechanical measures should be taken so that there is no possibility of overcharging peroxide.
3. It is dangerous that all operations are controlled automatically by a computer. At important safety points, monitoring is required by an operator, with adoption of automatic alarm devices independent of the controlling computer and installation of automatic emergency devices, etc.
Concrete methods are shown below.
1) An oxygen analyzer is installed in the reactor. The alarm sounds immediately if the concentration exceeds the control range.
2) Inert gas such as nitrogen should be introduced into the system immediately when oxygen concentration exceeds the control range.
3) To prevent steam leakage, the block valve to the reactor jacket should be doubled or steam should bypass the jacket before the block valve.
4) If overcharging of oxidizer is displayed, the operation must not be continued until there is an investigation of the situation and
confirmation of safety.
5) Upon adoption of computer control at the plant, checks by operators and a back-up system isolated from computer control are required for safety. |
| Knowledge Comment |
There seems to be increasing dependence on computer systems. It is necessary to increase redundancy and consider systems that automatically informs of any trouble and that allow intervention by operators, in the case of a computer failure. |
| Background |
1. Over-reliance on computers. The lamp indicating over-charging might have been ignored. The quantity of 20 times as much as the specified quantity would not have been supplied if adding was stopped directly after the indicating lamp lit. The reason was over-reliance on the computer or lack of attention.
2. Safety design was insufficient. If over-charging was very dangerous, a preventive method should have been considered.
3. It seems that operating discipline had not been established because workers proceeded to the next step of the operation even though an excessive amount of hydrogen peroxide was fed.
4. The reason why steam flowed into the reactor jacket is not known. It is considered that the problem might not have happened during normal operation, even if steam leaked slightly. The cause of steam flowing might be that the possibility of a seat leak at the valve was not considered, rather than a mistake in operation. |
| Reason for Adding to DB |
Runaway reaction occurred due to malfunction of instrumentation. |
| Scenario |
| Primary Scenario
|
Misjudgment, Misperception, Mis-Convincement, Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Oxidation, Planning and Design, Poor Planning, Poor Design, Usage, Operation/Use, Operation at Computer Trouble, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion, Bodily Harm, Death, 1 person died, Loss to Organization, Economic Loss, Direct Monetary Damage 150 million yen
|
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| Sources |
Japan Assoc. of Fire Science and Engineering. Chemical fire committee. D.38.2 Hydrogen peroxide. Case 262. Examples of chemical fires (2). p.148 (1974)
Tamura Masamitsu, Masahide Wakakura, Explosion and fire when manufacturing carboxymethylcellulose. Reaction danger-accident case and analysis - p.53 (1995)
Ministry of Labor. Industrial Safety and Health Department, Safety section, Fire and explosion due to computer control failure in carboxymethylcellulose manufacture plant. Safety of batch process. pp.48-49 (1987)
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| Number of Injuries |
1 |
| Physical Damage |
A reactor was badly damaged |
| Financial Cost |
¥150 million. |
| Multimedia Files |
Fig3.Chemical formula
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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 |
KOSEKI, Hirosi (National Research Institute of Fire and Disaster)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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