Case Ditails

Scenario
Case Name Leakage of hydrogen sulfide gas caused due to overlapping of some errors during shutdown maintenance for off-site piping at a refinery
Pictograph
Date May 30, 1995
Place Kawasaki, Kanagawa, Japan
Location Refinery
Overview A hydrogen sulfide gas leakage accident occurred at a refinery in Kanagawa prefecture on May 30th, 1995, when off-site piping repair work was carried out as a part of shutdown maintenance. A block valve at the outlet of a pressure control valve was to be removed. At the same time, repair to an air supply line for the pressure control valve was also underway. The air supply to the pressure control valve was stopped, and the control valve was fully opened. As the inlet block valve of the pressure control valve was also open, hydrogen sulfide gas leaked upon removing the outlet block valve. There were many fatalities and injuries. A blind plate was inserted but the position was wrong so it also came off when the outlet block valve was removed.
Incident On off-site piping work during shutdown maintenance at a refinery, there were several communication errors and errors in preparations. Leakage of hydrogen sulfide occurred and resulted in many fatalities and injuries due to intoxication.
Processing Manufacture
Individual Process Maintenance
Process Flow Fig2.Unit process flow
Substance Hydrogen sulfide, Fig3
Type of Accident Leakage
Sequence 1. There was off-site work on piping for hydrogen sulfide. Hydrogen sulfide gas was still flowing in the piping, but it is not confirmed whether there was any sign of gas flowing.
2. A blind plate was inserted at the upstream-side flange of an outlet block valve of a pressure control valve that was to be removed for repair. The inlet block valve of the pressure control valve was open.
3. Air supply to the pressure control valve in an instrument air line was stopped to repair an operation air supply line. The control valve was programmed to automatically open when the air supply is shut-off.
4. As the downstream side valve was being removed, the inserted blind plate also came off because it was inserted at the flange of the valve. Then the piping was opened and hydrogen sulfide leaked into the atmosphere.
Cause 1. The blind plate was inserted at the wrong position. It was inserted at the flange of the piping where the valve was to be removed. The reason for this mistake is not clear.
2. Communication between two separate repair operations on the same piping was inadequate. Each operation was conducted by a different worker. It is not clear why the two operations were planned at the same time.
3. When the downstream valve was removed, it was clear that the pressure control valve was the only valve that stopped the gas flow. It was not appropriate because the pressure control valve was not designed to be leak-resistant.
4. The biggest problem is that attention was not paid to the fact that toxic gas was still flowing in the piping.
Response The pressure control valve and the block valve were closed.
Countermeasures 1. Thorough education.
2. Strengthening a safety control system.
3. Strengthening safety measures for hazardous operations.
4. Setting standards for separating dangerous materials and atmosphere.
5. Sharing related information.
6. Organizing a committee on safety.
Knowledge Comment 1. As a control valve is a remotely operated valve, it can be operated unexpectedly. Moreover, a normal control valve must leak though it is closed tightly. Therefore, a repair plan that depends on only one control valve shut-off is absolutely not allowed.
2. At off-site piping, operation gas usually flows in the piping. (It is living.) Careful repair planning and close communication are essential.
Background 1. The repair management system was not inadequate. It was not known whether there was any sign that gas was still flowing in the piping. Besides, two works on the same piping were being done by different workers and communication between the two was inadequate. These two facts show that the management system was inadequate for work on piping in operation.
2. A gas flow cannot be stopped by only one pressure control valve. Pressure control valves are not designed for such a function. Moreover, the valves are opened by remote control. So it was strictly inhibited to cut off only with a control valve. The cause must be inadequate education or misunderstanding of the workers.
3. The position for inserting the blind plate was instructed by mistake or was not checked properly. The position should not be decided by a worker alone, but should be decided by a group leader after confirming safety.
4. The human error might be resulted from defects in the administrative system of the plant.
Incidental Discussion There were several comments of the executives of the company in newspapers after the accident. They indicated that the accident was due to human error by executives.
Reason for Adding to DB Failure of a repair plan on the assumption of closing with only one control valve
Scenario
Primary Scenario Poor Value Perception, Poor Safety Awareness, Mal Safety Management/Education, Carelessness, Insufficient Understanding, Insufficient Recognition of Risk, Usage, Maintenance/Repair, Poor Planning of Repair, Incorrect Reaction, Poor Communication, No Communiction, Secondary Damage, External Damage, Leakage, Bodily Harm, Death, 4 person died, Bodily Harm, Sickness, 44 Person Poisoning
Sources Kawasaki City Fire fighting station. Shigemi Matsuo. Hydrogen sulfide gas leak accidents at dangerous facilities. Dangerous material accident case seminar. pp.25-31(1997). pp.26, 502-503
Explosion and fire defense countermeasures guidelines committee for supervising the chemical industry. Chiba Labor Standards Bureau supervision. Construction communication adjustment conference. Guideline or explosion and fire defense in the chemical industry. pp. 80-82 (1996).
Kawasaki City Fire fighting station. Prevention division. Peace section. Outline of hydrogen sulfide gas leak accident at T fuel K factory Material of the Kawasaki City Complex safety countermeasures committee.(1995)
Fire and Disaster Management Agency. Major cases of accidents, Leakage of hydrogen sulfide gas during valve exchange repair at a turnaround shutdown maintenance; Main accident cases of dangerous material. pp.26, 502-503
Number of Deaths 3
Number of Injuries 44
Multimedia Files Fig3.Chemical formula
Field Chemicals and Plants
Author YOSHINAGA, Jun (Graduate School of New Frontier Sciences, The University of Tokyo)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
Scenario