| Case Name |
Sinking of a floating roof due to inundating of pontoons and retained rain-water on the roof at a floating roof naphtha tank |
| Pictograph |
|
| Date |
October 17, 1987 |
| Place |
Kurashiki, Okayama, Japan |
| Location |
Refinery |
| Overview |
The floating roof of the floating roof tank at the refinery sank. Due to a heavy rainfall, which continued for more than 1 hour 30 minutes, the floating roof sank into the naphtha. The causes of sinking are that a large amount of rainwater remained because the roof drain sump mouth was blocked with dust, and water entered the two pontoons because someone forgot to close the cap on the nozzle of the pontoons, and an abnormal load was put on the pontoons. As an indirect cause, daily checks and the inspection standard in unusual weather were not defined. |
| Incident |
The floating roof of a floating roof tank at a refinery sank during a rainstorm. It sank into the naphtha due to the weight of rainwater which remained on the floating roof of the naphtha tank. |
| Processing |
Storage |
| Substance |
Naphtha |
| Type of Accident |
Rupture |
| Sequence |
19:40 on October 16th, 1987. A storm and high surf warning was issued.
23:30. The amount of rainfall was 36 mm/hour.
00:00. on October 17th. The amount of rainfall was 38 mm/hour.
05:00. The storm and high surf warning was canceled.
About 12:00. An operator on patrol detected the smell of naphtha, but no abnormality in the tank could be found.
About 13:00. Abnormality of a floating roof was found. Naphtha overflowed onto the roof from the tank's north side.
13:15. Contact was made to the general manager of the safety and environment division from the deputy manager via the general manager of the manufacturing division.
13:30. The factory disaster prevention team was called out.
13:50. Transfer of naphtha from the tank started.
14:05. The public fire brigade was called out.
14:45. The side wall and a guide pole were deformed with a queer sound.
19:30. The public fire brigade was on standby.
00:35 on October 18th. Introduction of carbon dioxide started at the upper part of the tank.
16:10 on October 21st. The carbon dioxide seal was switched to injection of air foam.
28th. All naphtha in the tank was evacuated. The disaster prevention
warning at the factory was canceled. |
| Cause |
There was a record-breaking rainfall (38 mm/hour) caused by typhoon No.19. A large amount of rainwater remained on the roof because the roof drain sump mouth was blocked with dust. Water got into two pontoons located at the north side because someone forgot to close the cap of the nozzle (inside diameter: 13 mm) for airtight tests of the pontoon. An abnormal load was put on the roof and it sank into the naphtha. |
| Response |
Carbon dioxide was introduced into the upper part of the tank. Then, it was switched to injection of air foam. Naphtha and water in the tank were evacuated. Ventilation and cleaning of the tank were carried out after the tank was emptied. |
| Countermeasures |
1. Improvement of the roof drain sump. The primary cause of the accident was plugging of the ball check valve cover. So the cover of the ball check valve was changed from a punching plate to expanded metal. This change of structure makes it difficult for dust to cause a blockage.
2. Preventing rain water from coming into the pontoon. The airtight test was changed to a method using the pontoon manhole, and the nozzle for the test was removed.
3. Improvement in the function of roof drain facilities. The floating roof was changed to a single deck type, and a center collection drainage system was adopted as the roof drain facilities.
4. Review of the inspection standard.
5. Inspection in unusual weather is performed.
6. Improvement of operation control management. |
| Knowledge Comment |
Invasion of rain-water from a rainstorm caused the accident. The accident could have been prevented if an inspection had been performed considering the rainstorm. The first step to prevent a failure is to execute maintenance and management based on an understanding of the structural principles of the machinery. |
| Background |
The main cause of the accident seems to have been inadequate management. The inspection standard for daily checks and for unusual weather was not clear. The operators forgot to close the vent nozzles of a pontoon, which acts as a buoyancy bag. Besides, cleaning of the floating roof upper surface was insufficient. These two facts showed the management state. |
| Incidental Discussion |
The accident seems to have been a result of disregarding daily management. Countermeasures (1) - (3) would be unnecessary if daily management was sufficient. |
| Reason for Adding to DB |
Example of accident caused due to omission of daily checks |
| Scenario |
| Primary Scenario
|
Organizational Problems, Poor Management, Slackness of Management, Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Carelessness, Insufficient Understanding, Insufficient Recognition of Risk, Malicious Act, Rule Violation, Safety Rule Violation, Failure, Large-Scale Damage, Sink, Loss to Organization, Economic Loss, Direct Monetary Damage 28 million yen
|
|
| Sources |
High Pressure Gas Safety Inst. of Japan. Table 4-1. Major examples of domestic accidents not related to High Pressure Gas Control Law. High pressure gas protection overview. pp.138-141(1988).
High Pressure Gas Safety Inst. of Japan. Naphtha tank accident. Accident examples of Petroleum refinery and Petrochemical units. pp.210-212(1995).
|
| Physical Damage |
Sinking of a floating roof |
| Financial Cost |
¥ 28 million (Accident examples of Petroleum refinery and Petrochemical units) |
| Multimedia Files |
Fig2.Accident-generation factor figure
|
| Field |
Chemicals and Plants
|
| Author |
DOBASHI, Ritsu (School of Engineering, The University of Tokyo)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
