Case Ditails

Scenario
Case Name Explosion caused due to valve operation trouble during an emergency shutdown of a compressor at a vinyl chloride plant
Pictograph
Date September 18, 1968
Place Takaoka, Toyama, Japan
Location Chemical factory
Overview At a vinyl chloride manufacturing plant, an emergency shutdown was carried out due to instrument air failure, with separation of the cracked gas compressor. This shutdown was miss-operated, cracked gas was discharged, and an explosion occurred with consequential fire. The shutdown procedure was complicated, and there was danger of combustible gas blowing in case of miss-operation. There was a problem in the system, which allows combustible gas easily blow out by a miss-operation. Moreover, the complicated shutdown operation made operators tense and induced errors.
Incident At a vinyl chloride manufacturing plant, an automatic emergency shutdown system was operated due to instrument air failure. This operation means cutting off naphtha cracked gas between a quenching tower outlet and a cracked gas compressor, and between the compressor and a carbon dioxide removal column. Therefore, an emergency shutdown of the compressor was required in order to protect the cracked gas compressor. Valve closing of the intercooler for direct cooling was delayed because the shutdown procedures for the compressor were complicated. Then, combustible cracked gas blew out and an explosion occurred with consequent fire in the compressor room.
Processing Manufacture
Individual Process Transfer
Process Flow Fig2.Elevation of facilities
Fig3.Unit process flow
Substance Naphtha cracking gas for Vinyl chloride monomer
Type of Accident Leakage, Explosion, Fire
Sequence 09:30 on September 18th, 1968. The cracking furnace was ignited, and naphtha cracking started.
17:05 The automatic emergency shutdown system was operated due to a instrument air failure. Therefore, the cracked gas compressor was separated and the cracked gas circulated in the compressor.
17:07 Two operators opened the manual recirculation valve of the compressor following the operation standard for the emergency shutdown, and they returned to the control room. It was reported that the drain valve of the direct cooler (intercooler) at the interstage of the compressor had opened, and they went there to close the drain valve again. The cracked gas had already blown out.
17:12 An explosion occurred in the compressor room. Consequently the cracked gas and lubricating oil, etc. caught fire.
17:25 The gas holder outlet valve was shut to stop combustion of the cracked gas.
17:38 Oil in the compressor burned out.
Cause The naphtha cracked gas (main component: hydrogen, carbon monoxide) exploded, having blown out from the drain valve of the intercooler of the compressor. The drain valve had to be immediately closed at an emergency shutdown after opened. However, it was left open. There were two possible ignition sources. One is the turbine oil permeated heat insulation material of the high-pressure steam piping which oxidized at a high temperature, and self-ignited. However, it seems improbable that leakage of combustible gas and spontaneous ignition of oil coincide. The other is a small hydrogen flame from a FID detection gas chromatograph, which was set up and in use in the compressor room.
Response The gas holder outlet valve was shut to stop combustion of cracked gas.
Countermeasures Strengthening the disaster prevention system. In particular, restudy of the management system of automatic systems.
Simplifying procedure for an emergency shutdown. Improving the operation manual. Educating and training employees.
Improving maintenance to prevent oil adhering to heat insulation material of high-pressure steam piping.
Preventing combustible gas leakage to outside of the system.
Considering operability of equipment and ventilation.
Knowledge Comment Procedures in an emergency should be simplified as much as possible. In work requiring a complicated operation, a system design by which one error does not cause a major accident should be chosen.
Background The main cause of the accident was not closing the open drain valve during an emergency shutdown of the compressor. It is necessary to open the manual recirculation valve, and then immediately shut the drain valve of the intercooler to prevent reverse thrust in the compressor during an emergency shutdown. The drain valve must be closed before cracked gas escapes to the pit. It is considered that the operators forgot to shut the drain valve because the operating procedure was complicated. There was a problem in the design of equipment and operating procedure which allowed combustible gas to easily blow out by such an error.
Incidental Discussion Although the technological level of the design of this plant and features of naphtha cracked gas for vinyl chloride are not well known, it is questionable whether only one type of such a compressor existed, requiring complicated valve operation. Moreover, the design that allows the dissolution of gas into cooling water of the intercooler might be a problem. How would it designed at present ?
Reason for Adding to DB Example of explosion caused due to mishandling of a valve
Scenario
Primary Scenario Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Insufficient Analysis or Research, Insufficient Practice, Lack of Imagination, Planning and Design, Poor Planning, Poor Design, Non-Regular Operation, Emergency Operation, Emergency Shutdown, Secondary Damage, External Damage, Explosion, Bodily Harm, Death, 3 person died, Bodily Harm, Injury, 7 person injured, Loss to Organization, Economic Loss, Direct Monetary Damage 300 million yen, Damage to Society, Social Systems Failure, Damaged 6 km radius
Sources T plant of N Co. accident investigation committee. The explosion research report for T plant of N Co. (1969).
High Pressure Gas Safety Inst. of Japan. Examples of accidents in plants, Examples of high-pressure gas accidents. pp.108-109(1982).
Chemical Industries Association. Examples of accidents (compressor). Examples of accidents and countermeasures. Vol. 4 of safety countermeasure technology for chemical plants. pp.274-275(1979).
Tetsuzo Kitagawa. Leakage of cracked gas from open drain valve. Analysis of the explosion hazard. pp.164-166(1980).
Number of Deaths 3
Number of Injuries 7
Physical Damage Extensive damage to a compressor room. Fire exposure losses of a cracked gas compressor, an air compressor and turbines. Damage to windows of 162 private houses within a 6 km radius.
Financial Cost ¥ 300 million. (Investigation report of the accident at T factory of N Co).
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)
Scenario