| Case Name |
Fire of gas oil leaked from a drain plug of a 3/8 inch Y type strainer for ignition of a boiler at a power generator |
| Pictograph |
|
| Date |
July 6, 1995 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Power plant |
| Overview |
On July 6th, 1995. Gas oil leaked out from the drain plug of a strainer for gas oil for ignition on starting the boiler in a power plant. Gas oil splashed on the high-temperature boiler wall and ignited. A gasket with insufficient tightening force broke due to internal pressure where tightening force was weakest. The leaked oil made contact with the boiler wall, whose temperature was higher than the ignition point of the gas oil, and ignited.
Inadequate management of gasket torque seems to have been the cause of the accident. |
| Incident |
A fire occurred at gas oil piping for igniting the boiler of a power plant. The gas oil spouted out from a crack of the seat gasket of the drain plug of the strainer on gas oil piping (3/8inch) for ignition of No.4 boiler. The leaked oil made contact with the boiler wall, which was 1.5 m from the crack, and a fire occurred. Refer to Fig2. |
| Processing |
Consumption and usage |
| Process Flow |
Fig2.Explanation drawing of leaked position
|
| Substance |
Gas oil |
| Type of Accident |
Leakage, fire |
| Sequence |
06:00 on July 6th, 1995. Operation of No.4 boiler began.
11:12. A worker found oil leaking from upstairs on the second floor.
11:13. Flames were found from boiler walls of the third floor.
11:15. The fire was extinguished using 3 ABC powder fire extinguishers. An emergency shutdown of No.4 boiler performed by an emergency shutdown system.
11:32. Gas oil was found leaking from the Y-type strainer at inlet piping of an igniter-control box placed on the mid-fourth floor.
11:40. Rupture of the gasket was found, and it was replaced with a copper gasket. Inspections of similar spots were carried out. |
| Cause |
Sheet packing at a seal portion of the screw part was broken. The gasket, which was not tightened sufficiently, broke due to internal pressure where tightening force was weakest. The leaked oil made contact with the boiler wall, whose temperature was higher than the ignition point of gas oil, and ignited. The internal pressure of the gas oil piping was a maximum of 1.4 MPaG, and the shearing stress on the gasket was 0.42 kg/mm2 at that time. Stress at rupture is estimated to be 3.9 kg/mm2. The tensile strength of the gasket was 3.2 kg/mm2. Therefore, the unbalanced tightening of the gasket was a cause of the rupture. The boiler wall temperature was a maximum of 320 °C, which exceeded the ignition point (about 240 °C) of gas oil. |
| Response |
A fire was extinguished by fire extinguishers. The gasket was replaced with a copper gasket. Similar spots were checked. |
| Countermeasures |
1. On tightening the drain plug, the necessary tightening force is ensured using a torque wrench.
2. Review the information sending system in an emergency. Education and training should be carried out for all workers. |
| Knowledge Comment |
Strict management (prevention of leakage, etc.) is necessary for facilities where material (gas oil) that readily ignites is handled near a hot wall (boiler furnace wall). |
| Background |
Improper tightening force management. |
| Incidental Discussion |
The drain plug of 3/8 inch is the screw type. Usually, if the screw is fitted at the first time, it is hard to leak after the screw is tightened well. The accident seemed strange. |
| Reason for Adding to DB |
Examples of fires caused due to inadequate tightening of a gasket |
| Scenario |
| Primary Scenario
|
Carelessness, Insufficient Precaution, Carelessness of Operator, Poor Value Perception, Poor Safety Awareness, Insuficient Education/Training for Safety, Usage, Maintenance/Repair, Restration, Malfunction, Specifications Not Met, Capacity Not Met, Secondary Damage, External Damage, Fire
|
|
| Sources |
Kawasaki City Fire fighting station. Prevention division. Peace section. J railway Co., Ltd. K substation. Outline of gas oil fire at boiler igniter for power generator. Material of the Kawasaki City complex safety countermeasures committee (1995)
|
| Physical Damage |
Walls of No.4 boiler were damaged by fire. About two liters of gas oil burned. |
| 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)
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