| Case Name |
Fire of quenching oil caused due to a hot object remaining above the quenching oil bath |
| Pictograph |
|
| Date |
February 20, 1998 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Metal products factory |
| Overview |
At a heat-treatment factory for machine parts, two employees set a tray, which carried 1.8 tons of treated objects at 880 °C from the heating furnace to the lift stand of a quenching oil bath by a charging car for heat treatment. The fork of the charging car could not be pulled out from the lift stand. As the treated objects stayed there, quenching oil in the bath was heated, and a fire occurred. |
| Incident |
At a heat treatment factory for machine parts, a fork of a charging car (an automatic transporting machine), which carried treated objects was set to a lift stand of a quenching oil bath to charge the treated objects at 880°C from a heating furnace to the quenching oil bath. One of the four chains that supported the lift stand broke, the lift stand tilted, and the fork could not come out. The high-temperature treated objects stopped above the quenching oil in the quenching oil bath. The surface of the quenching oil was heated by a high temperature, and a fire occurred. Refer to Fig2. |
| Processing |
Consumption and usage |
| Substance |
Quenching oil |
| Type of Accident |
Fire |
| Sequence |
18:40 on February 19th, 1998; night shift operators started work. There were no abnormalities in a hand-over note.
00:05 on February 20th; hardening treatment for 1.6 tons of treated objects in the heating furnace was performed. There were no abnormalities.
02:00; 1.8 tons of treated objects from another heating furnace were transferred by a charging car to a quenching bath.
02:05; a tray on which the treated objects placed was set at the lift of the quenching oil bath. The fork of the charging car could not pull off from the lift stand.
02:06; operation of the charging car was switched to manual, and an attempt was made to free the fork of the charging car, but it failed.
02:20; on repeating the same procedure, flames rose 40 cm from the circumference of the tray. An operator tried to extinguish them with an extinguisher, but failed. He tried some other measures, but all failed, and the flames became 1 m high. Carbon dioxide manual extinguishment facilities of the quenching bath did not start because the tray on the lift obstructed a discharging nozzle of the extinguisher.
02.53; an emergency call to the public fire fighting station was made.
04:04; public fire fighters extinguished the fire with foam. |
| Cause |
Malfunction or poor actuation of the charging car was the cause. In addition, it is thoughtless to transfer high-temperature treated objects above quenching oil, which is flammable. These problems might have caused from the design.
Extinguishing equipment could not operate. |
| Countermeasures |
The fire station authorities commanded the following improvements;
1) Renewal of all chains and a periodic overhaul of all facilities.
2) Level adjustment of the lift stand and preparation of the operation manual on fork operation.
3) Training and education for emergency response. |
| Knowledge Comment |
1. Although quenching oil is comparatively safe, it can ignite in some cases because the temperature of quenching oil sometimes becomes high due to very severe usage conditions with high-temperature metal immersed in the oil bath. Therefore, temperature control of quenching oil is important. At the same time, the fact that the flash point and ignition point become lower over long-term use should be noted.
2. For rationalization of repair work, breakdown maintenance might often be chosen rather than preventive maintenance. However, breakdown maintenance should be discontinued if a problem could be the cause of a fire and an accident. The influences of the trouble should be sufficiently studied beforehand when breakdown maintenance is chosen. |
| Background |
1. The broken chain had not been checked or maintained for 18 years, which caused the accident. The breaking strength had dropped from 8 tons in the manufacturing specifications to 5 tons. Moreover, thinking of the severe operating conditions of the chain, it indicates imperfect facilities management. A conception that the breakdown maintenance was sufficient for this machine seemed to be the cause.
2. The quenching oil used was not quenching oil regulated by the fire protection law. Its flash point was lower. Contravention of the law was indicated.
3. There might have been a problem with design or maintenance management as the fire extinguishing facilities did not operate. |
| Incidental Discussion |
Quenching oil might often be considered very safe against fire hazards, but quenching oil fires are common. It is necessary to carry out temperature control considering the flashpoint of quenching oil. Moreover, the flashpoint and the ignition point might be lowered with age. The flashpoint of the quenching oil in this accident was as low as 194°C. |
| Reason for Adding to DB |
Example of fire of quenching oil, which was believed to be safe, due to operation conditions |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Planning and Design, Poor Planning, Poor Design, Usage, Maintenance/Repair, No Inspection for 18 Years, Bad Event, Chemical Phenomenon, Burning, Secondary Damage, External Damage, Fire
|
|
| Sources |
Kawasaki city Fire fighting station. Prevention division. Peace section, Fire at quenching oil bath. Material of the Kawasaki City complex safety countermeasure committee (1998)
|
| Physical Damage |
A set of quenching oil bath, a motor for a door of a heating furnace, electrical instrumentation, the ceiling and internal walls, electrical wiring, and a fire alarm system were damaged by fire. |
| Multimedia Files |
Fig2.Hardening process schematic diagram
|
| Notes |
Characteristics of quenching oil that was used were measured, the results are; flash-point 194 °C and ignition point 325-328 °C, which means the temperature was lower than regulated values.
The oil temperature in use was 50-60 °C, and cooling water supply started automatically when the oil temperature rose to 50 °C. |
| Field |
Chemicals and Plants
|
| Author |
KOSEKI, Hirosi (National Research Institute of Fire and Disaster)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
