| Case Name |
Deformation of a kerosene tank in which a blind plate was inserted by mistake |
| Pictograph |
|
| Date |
November 1, 1996 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Chemical factory |
| Overview |
During disconnection inspection repair of the breather valve of a cone roof tank, a blind plate was mounted instead of a vent pipe at the tank's upper flange after the breather valve was disconnected. The pump started under that condition, and the liquid inside was transferred. The tank was deformed because there was no inflow of gas when the level fell. |
| Incident |
A kerosene cone roof tank with a 160 kL capacity was damaged during inspection and repair of a breather valve. A blind plate instead of a U-shaped vent pipe was mounted by mistake at a nozzle flange after the breather valve was detached. Therefore, the tank pressure reduced when residual oil in the tank was transported to another tank by a pump, and a side plate and a base plate of the tank were deformed. |
| Processing |
Storage |
| Substance |
Kerosene fraction |
| Type of Accident |
Burst |
| Sequence |
On October 21st, 1996, a maintenance staff of the company ordered inspection and repair of the breather valve of the tank to a subcontractor orally.
On October 25th, the maintenance staff made a repair request by a repair confirmation document to the subcontractor. The subcontractor got approval for starting repairs from the manufacturing section that had responsibility for manufacturing and supervising of the plant. The maintenance staff directed disconnection of the breather valve and safety management on the field, and he said work should be done on the next day, October 26th.
On October 26th, the sub-contractor was given a seal from the maintenance staff to start repair work on the repair confirmation document, which was handed over on the day before. Next, a seal of the manufacturing section was given and work started. After the breather valve was detached, the sub-contractor's worker mounted a blind plate in the flange. The manufacturing section and the maintenance staff received a report on completion of the breather valve disconnection from the sub-contractor, and did not confirm this in the field. They stamped a seal in the final confirmation column of the repair confirmation document without confirmation, and the repair was considered to have been completed.
On November 1st, transfer of the inner liquid to another tank was carried out.
At 11:50, transfer work started.
At 13:10, transfer of 30 kL finished.
At 13:30, another transfer to a different tank started.
At 14:30, deformation of the tank was found. The pump was stopped.
A report was made to the fire station. Refer to Fig2. |
| Cause |
A blind plate was fixed after the sub-constructor's worker disconnected the breather valve of the cone roof tank. Naturally, the tank became airtight. Under this condition, the inner liquid was transferred to another tank by the pump. Then pressure in the tank reduced. |
| Response |
A blind plate was detached, and the residual liquid in the tank was transferred to another tank. |
| Countermeasures |
1. Repair methods were clarified. It was specified that a vent tube has to be mounted after a breather valve is disconnected for inspection in the general repair specifications. In addition, a new "breather valve disconnection plan for inspection" was made, and disconnection work of the breather valve was standardized. "The blind plate management points" were determined to avoid faulty handling of a blind plate.
2. Field validation of repair completion was done by the maintenance staff and the manufacturing section.
3. Details above were taught to the maintenance staff, the subcontractor and the manufacturing section. |
| Knowledge Comment |
1. Pressure design of a cone roof tank for both internal and external pressure is very low, it is almost "0." Therefore, the tank is easily deformed even with a slightly reduced pressure.
2. The understanding of the party and their efforts to execute the system at all times are required to obtain desirable results, even if the system is accurately formed.
3. Although the worker of the subcontractor knows his work well, he does not know the influences of the result of his work. The side giving an order should consider this fact. |
| Background |
1. A blind plate was mounted instead of a U-shaped vent pipe, which was planned originally, after the breather valve was disconnected. The main cause was a mistake in transmission of details of the repair. When the subcontractor's supervisor asked for confirmation that construction had been completed, the staff of the manufacturing section and the staff of the maintenance section put their seals on the repair confirmation document without confirming at the field. Such an attitude of the staff was a problem.
2. The subcontractor was one of the major subcontractors in the oil refining and petrochemical industry in Japan, and had worked for a very long period at the factory. It is assumed that there was a lack of attention from repair ordering to field validation, and it is guessed that a cozy relationship had developed. Usually, a vent tube mounted after breather valve disconnection is supplied by hand, and the way of repairing is indicated at that time, but this was not executed. Final field validation was not executed by the ordering company.
3. It may be true that both sides, the ordering company and the subcontractor, were not conscious of the almost "0" pressure design of the cone roof tank. The worker of the subcontractor might not have been educated on the fact. |
| Incidental Discussion |
It is typical human error. People might think a behavioral accident as human error at a plant. However, it is also human error that specified matters are not obeyed and that specified matters themselves are defective. For example, an accident of crushing of a tank by painting frame arrester (wire gauze for preventing flame propagation) with a breather valve is cited. In this case, the painter is not guilty because he painted as ordered. Protecting the space where the painter must not paint is the work of the order side and the subcontractor.
The repair work that caused the accident seems very simple work. There may be a general tendency that simple repair work is considered easy. This accident is the case. In terms of causes and countermeasures described in the accident report, there are sentences that "sufficient inspection before starting the pump was not carried out" and "Operators should carefully check before operating the pump." It is assumed that an operator should always check the breather valve before starting the pump. However, it can be said from my experience that the check is not always made on starting a pump normally.
For continuing execution of the check, it would be necessary to limit it to the first shipping and first receiving from/to the tank after maintenance work of the breather valve. |
| Reason for Adding to DB |
Example of a typical accident that damaged an atmospheric pressure tank |
| Scenario |
| Primary Scenario
|
Organizational Problems, Poor Management, Slackness of Management, Poor Value Perception, Poor Safety Awareness, Insuficient Education/Training for Safety, Misjudgment, Misjudgment of Situation, Planning and Design, Poor Planning, Poor Planning of Repair, Usage, Operation/Use, Mis Line-up, Bad Event, Mechanical Event, Reduced Pressure, Failure, Large-Scale Damage, Tank Rapture, Loss to Organization, Economic Loss, Direct Monetary Damage 10 million yen
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| Sources |
Kawasaki City, Fire fighting station, Prevention division, Peace section. N Petrochemicals Co., Ltd. K office K factory. Outline of outdoor tank deformation accident. Material of the Kawasaki City complex safety countermeasure committee (1997)
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| Physical Damage |
The tank main body was deformed. |
| Financial Cost |
¥10 million. (Material of the Kawasaki City Complex safety countermeasure committee) |
| Field |
Chemicals and Plants
|
| Author |
KOBAYASHI, Mitsuo (Office K)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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