| Case Name |
Explosion in an intermediate tank during turnaround shutdown maintenance at a dimethylformamide manufacturing plant |
| Pictograph |
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| Date |
September 29, 1990 |
| Place |
Yokohama, Kanagawa, Japan |
| Location |
Chemical factory |
| Overview |
Operation of a dimethyl formamide (DMF) synthesis tower had been stopped for turnaround shutdown maintenance on the day before the accident. Crude DMF generated in the synthetic tower was drawn off to an intermediate tank, and sent to the refining section. At this time, about 1 kL of crude DMF remained at the bottom of the tank. On the day of the accident, residual liquid was drawn off in preparation for cleaning the tank. An explosion occurred in the tank because of instruction violations and disregard for safety. The worker near the opened manhole received burns to the trachea, and died after hospitalization.
Among the direct causes, the most important problem was not using an explosion-proof pump in an atmosphere where a combustible gas-air mixture might exist. It can be pointed out that non-observance of the work procedure and the use of an electric pump of a non-explosion-proof type are the responsibility of the manager and the supervisor, rather than the workers. |
| Incident |
A manhole was opened to clean a dimethylformamide (DMF) intermediate tank, and work to draw off residual liquid into a drum can using a portable pump was carried out. At that time, gas in the tank exploded, and a worker in front of the manhole was injured. The worker died of trachea burns 45 days later. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Substance |
N,N'-dimethyl formamide, Fig2 |
| Hydrogen, Fig3 |
| Carbon monoxide, Fig4 |
| Dimethylamine, Fig5 |
| Sodium methylate, Fig6 |
| Type of Accident |
Explosion |
| Sequence |
Operation of a DMF synthesis tower was stopped for turnaround shutdown maintenance at 9:55 on September 25th, 1990, the day before the accident. Crude DMF formed in the synthesis tower was drawn off into an intermediate tank. Crude DMF was sent to the refining section. About 1 kL of crude DMF remained at the bottom of the intermediate tank at this time.
In preparation for cleaning the tank, residual liquid was drawn off. On September 26th, four workers started to open the manhole of the tank to draw off residual crude DMF. A portable pump was arranged, and drawing off of residual liquid into a drum can started. At this time, the temperature in the tank was 68 °C. The flash point of DMF is 58 °C. A suction pipe was inserted from the opened manhole, and the switch of the driving motor was turned on. After 1 or 2 minutes, the gas in the tank exploded about at 16:20, and 7 m flames jetted out. A worker in front of the manhole was injured, and died of trachea burns 45 days later. |
| Cause |
An accident occurred as a result of accumulation of misjudgments and disregard of instructions. The causes are enumerated as follows.
1. Draw-off work started although the tank had not cooled sufficiently.
2. As it was filled with combustible gas, nitrogen gas was supplied in the tank to dilute the gas. However, the nitrogen flow was stopped before the scheduled time.
3. The portable pump was not of an explosion-proof type.
4. It was directed in the manual that the side manhole was to be opened after the upper manhole had been opened. However, only the side manhole was actually opened. As a result, there was insufficient ventilation. |
| Response |
The victim was taken by ambulance to a hospital. |
| Countermeasures |
All portable pumps in the factory were changed to an air-driven type.
Safety education and training were strengthened. In particular, important safety points were emphasized. |
| Knowledge Comment |
It is necessary to make workers understand the hazards of work and safety measures. In addition, it is management's and supervisor's obligation to guide safety work, and to confirm that safety work is done. |
| Background |
It is assumed that the following human errors of workers of the subcontractor caused the accident.
1. The level of the safety consciousness of the workers was low.
2. Workers' knowledge of the hazards of the work was insufficient.
3. As a result, the operation procedure was disregarded.
The workers of the subcontractor were educated tentatively through yard access education. Nevertheless, it is considered that the manager and the supervisor who had allowed the procedure to be disregarded were responsible. The workers of the subcontractor, especially the workers who temporarily accessed the yard for turnaround shutdown maintenance were ignorant of the hazards in a chemical factory. The plant manager and the subcontractor are responsible for safety at the site and safe construction. |
| Incidental Discussion |
It is thoughtless to use a non-explosion proof portable pump to draw off residual oil in a vessel for maintenance. Even if it is for temporary use during construction, electric equipment in a chemical plant should be explosion-proof. |
| Reason for Adding to DB |
Example of explosion caused due to compliance trouble on work procedure during turnaround shutdown maintenance |
| Scenario |
| Primary Scenario
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Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Organizational Problems, Inflexible Management Structure, Insufficient Education/Training, Carelessness, Insufficient Understanding, Insufficient Recognition of Risk, Planning and Design, Poor Planning, Poor Overhaul Planning, Malicious Act, Rule Violation, Neglect of Order Book, Secondary Damage, External Damage, Explosion, Bodily Harm, Death, 1 person died, Loss to Organization, Economic Loss, Tankm etc. Damage
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| Sources |
Fire and Disaster Management Agency, Explosion while treating residual oil in a tank. Accident cases of dangerous materials, 1990 pp.70-72.
High Pressure Gas Safety Inst. of Japan, Dimethyl formamide factory, Explosion of residual gas in a tank. Accident examples of Petroleum refinery and Petrochemical units, pp.194-195, (1995).
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| Number of Deaths |
1 |
| Physical Damage |
The electric pump burned out. |
| Financial Cost |
¥ 80,000. (Fire and Disaster Management Agency). |
| Multimedia Files |
Fig2.Chemical formula
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Fig3.Chemical formula
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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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