Case Ditails

Scenario
Case Name Leakage and explosion of a vinyl chloride monomer caused due to damage of a valve at distillation column feed piping at a manufacturing plant of vinyl chloride monomers
Pictograph
Date October 28, 1973
Place Jouetsu, Niigata, Japan
Location Chemical factory
Overview The accident occurred in October, 1973. When changing a filter element of a crude monomer feed line to a distillation column at a vinyl chloride polymer plant of N factory of S chemical Industry, the filter was opened to the atmosphere. Vinyl chloride gas leaked through the inlet block valve. The operators tried to close the valve, and applied an excess force which damaged the valve. A large quantity of vinyl chloride monomers leaked, and there was a fire and an explosion. The valve was made of cast iron, and had corroded.
Incident There was a fire and an explosion at a vinyl chloride monomer manufacturing plant of a factory manufacturing vinyl chloride polymer. While exchanging a filter element at the halfway point of the crude monomer (vinyl chloride) feed line to a distillation column from a tank, operators found vinyl chloride monomer gas leaking from an inlet block valve. Intending to re-close the valve tightly, they used excessive force and the valve ruptured. About 4 tons of vinyl chloride monomer in the tank was released through the filter. The monomer was ignited by an ignition source and exploded. The fire spread to the monomer factory and the polymer factory. A report suggested the ignition source was an electric spark in the refrigerator.
Processing Manufacture
Individual Process Feed and charge
Substance Vinyl chloride, Fig2
Type of Accident Leakage, explosion, fire, environmental pollution, health hazards
Sequence The "Event" column indicates how the fire occurred. It took about 15 minutes after flames spouting out until the explosion occurred. In this interval, the operators took refuge at the direction of their superior who judged the situation to be dangerous. However, the superior went back into the factory to confirm that switches were turned off etc., and he was killed in the explosion. Although his return was reckless, his motivation is understandable. Afterwards, the whole factory was consumed in flames with repeated small explosions. The fire was extinguished after about 47 hours.
Cause The yoke of the valve was broken by a valve-handling error during repair work. Therefore, the valve became fully opened, and the vinyl chloride monomer in the piping up-stream of the valve and the tank escaped. Leakage from the inlet block valve of 3-inch was found. Operators tried to close it by force using a 50 cm length handle-turning shaft (handoru mawashi). As a result, the yoke of the valve was damaged. This seems to have been a problem of operational management.
In addition, the valve was made of cast iron, which is more fragile than cast steel, and the valve had corroded. It can be said that there was inadequate management of facilities.
handoru mawashi: A tool used to turn the handle of a valve. The mouth of the U-shaped tool is welded at the tip of the pipe, and by hooking the valve handle with the U-shaped part, the reverse end of the pipe is turned, and the handle of the valve rotates. Using a 50 cm length of shaft for a 3-inch valve was excessive.
Countermeasures Improving operation and facility management.
Proper management of repair work. For instance, prohibiting the use of only one valve to separate the process and open air, and restricting use of "handoru mawashi".
For maintenance, checks on corrosion of valves, etc. are conducted.
Changing to a valve made of cast steel from one made of cast iron.
Knowledge Comment If excessive force is applied to a valve and a valve spindle on turning of a valve, it is natural for the valve to be damaged, so all factories should prohibit such treatment of valves. There should be mechanical and/or process reasons that requires excessive force to open and close a valve. It is necessary that the people involved understand the reasons and prepare appropriate countermeasures. The fact that destruction of only one valve could lead to a major accident should be considered.
Background It is absolutely a taboo to put an excessive force on a valve. This is one of the basic work skills of the plant operation. Only a tool of a size that is in proportion to the size of the valve should be used, if a tool for turning a valve is used. As it was a cast iron valve, more care was necessary. There was some indication of valve corrosion, and safety management seemed to be insufficient throughout the company.
Sequel Consideration of safety management was not sufficient because of the fast-growing economy at that time. After a series of accidents in Japan, improvements in systems to prevent disasters at facilities and changes to laws were made.
Incidental Discussion A valve made of cast iron was used. A cast iron valve is much more fragile than a cast steel valve. It seems that at present a cast iron valve is not designated for a high-pressure gas plant.
Reason for Adding to DB Example of disaster caused due to damage of a valve
Scenario
Primary Scenario Carelessness, Insufficient Precaution, Inadequate Handling, Organizational Problems, Poor Management, Slackness of Management, Malicious Act, Rule Violation, Safety Rule Violation, Usage, Maintenance/Repair, Insufficient Inspection, Failure, Fracture/Damage, Rupture, Secondary Damage, External Damage, Explosion, Bodily Harm, Death, 1person died, Bodily Harm, Injury, Loss to Organization, Economic Loss, Direct Monetary Damage 800 million yen
Sources Ministry of International Trade and Industry, Investigation report on the accident at a vinyl chloride monomer manufacturing plant in S chemical industry Co., Ltd. N factory (1973).
Tetsuzo Kitagawa, Leakage of vinyl chloride due to valve damage. Analysis of explosion hazard. pp.167-169(1980).
Number of Deaths 1
Number of Injuries 23
Physical Damage A vinyl chloride monomer factory, a polymerization factory, a drying factory, office buildings, etc. were destroyed by fire. Windows and roofs of public buildings and private houses in total about 660 buildings within a 2.2 km radius were damaged by the blast.
Financial Cost ¥781million
Consequences Crops occupying 160,000 square meters were damaged by hydrogen chloride gas generated during the fire.
Multimedia Files Fig2.Chemical formula
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)
Scenario