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Case Ditails

Scenario
Case Name Explosion and fire of a refuse derived fuel (RDF) storage tank
Pictograph
Date August 14, 2003
Place Tado, Mie, Japan
Location Power plant
Overview Large amounts of RDF were kept in a RDF storage tank at a RDF fuel power plant and the RDF generated heat. The RDF storage tank was cooled by water spraying and so on. At that time, the first explosion occurred. Water spraying was executed as a countermeasure, but it was not effective. When construction for the next countermeasure was underway, the second explosion occurred five days after the first explosion and two firemen died. A total of 47 days were necessary from the first explosion to extinguish the tank completely. The instability of RDF itself and insufficient management due to ignorance or still unknown characteristics of RDF seem to be causes.
Incident There were some problems at a RDF storage tank of the Refuse Derived Fuel (RDF) power plant. Following the problems, an explosion occurred on August 14th. Spraying water was continued for a few days as a countermeasure, and an explosion occurred again 5 days later. Afterwards, the fire continued in the storage tank, and the remainder of the RDF was drawn off from the storage tank. On September 27th, 47 days after the explosion, the fire was declared to have been extinguished.
RDF (Refuse Derived Fuel): The name of a kind of fuel made from home waste (non-industrial waste). Waste that comes from homes is crushed and dried, lime is added, and it is compressed and molded into a crayon-like state. It is different from a solid fuel such as coal.
Processing Storage
Substance Hydrogen, Fig2
Carbon monoxide, Fig3
Methane, Fig4
Water, Fig5
Refuse derived fuel
Type of Accident Explosion, fire
Sequence 1. The course of problems related to a temperature rise and ignition until the explosion occurred.
On December 1st, 2002, operation started.
On December 23rd, there was an abnormal temperature rise at the lower part of the storage tank and RDF partially burned.
In July, 2003, smoke was generated during transfer work for RDF stored in another warehouse.
On July 20th, generation of steam was confirmed at the storage tank.
On July 23rd, it was confirmed that temperature rose in the storage tank and that ignition occurred, so part of the RDF was drawn off.
On August 11th, the fire in the storage tank was still not extinguished and work started to spray water onto the storage tank from five locations at the lower part of the storage tank.
On August 12th, Water-spraying sources were added and became 28 locations.
2. The course of the explosion.
On August 14th, 2003, Spraying water was continued.
15:05, the first explosion occurred, and four workers were injured.
About 17:00, spraying re-started and continued until 18th.
About 15:00 on August 18th, spraying through inspection holes at the upper part started.
About 16:00, spraying was interrupted, and the situation inside was observed.
About 9:40-12:00, 13:20- on August 19th, spraying was done.
About 14:00, hot work for opening the spraying nozzle started.
14:17, the second explosion occurred; two firemen died, and one worker was injured.
From the second explosion, spraying water on the storage tank was continued and it was confirmed the fire had been extinguished on September 27th.
Cause Based on the research after the accident, following causes are considered.
*The cause of a temperature rise and ignition.
1. Fermentation of organic matter.
It is confirmed that microorganisms that cause fermentation exist in RDF, and sufficient moisture for fermentation exists due to insufficient control.
2. A chemical reaction of inorganic matter.
By reacting with carbon dioxide, slaked lime generated heat. Carbonation of slaked lime occurred at the same time in the RDF where fermentation of organic matter occurred.
3. The initial temperature at receiving.
In usual operation, RDF at a high temperature is not produced, and producing of RDF at a high temperature can cause problems. Fermentation and oxidation are accelerated if high-temperature RDF is received.
4. Chemical oxidation.
As a large amount of RDF is stored in a tank of 4000 cubic meters, heat is accumulated if there is a generation of heat. The temperature would no doubt rise. Organic matter is easily oxidized, including such as scum of tempura, which is easily oxidized.
* The cause of the explosion.
1. Pyrolysis gas was generated.
Thermal decomposition occurred under air interception conditions at a high temperature. Simultaneously, a water gas reaction and a producer gas reaction occurred in parallel.
2. Combustible gas was generated by anaerobiotic fermentation.
3. Due to contamination with air, a combustible gas mixture was generated.
Countermeasures 1. RDF quality management.
Control items should be added to the items covered until now. For example, items concerning fermentation and heat generation such as the amount of moisture, the degree of pulverizing, temperature etc. The calcium content also should be controlled so that RDF fermentation should be suppressed.
2. RDF storage management. The elements that promote fermentation, etc. should be eliminated.
(1) Facilities and management are improved to avoid moisture absorption to the utmost in RDF transportation and receiving.
(2) In terms of storage, heat generation and ignition of RDF should be checked by measuring the internal temperature, gas concentration of carbon monoxide and methane in the storage tank. Long-term storage should be avoided. If long-term storage is necessary, the temperature must be controlled. The structure of the storage tank should prevent air up-flows from the lower part. Storage management should be executed so as not to leave dead spaces in terms of operation and structure. Multiple storage tanks are to be arranged.
3. The fire protection system should be improved, and a disaster prevention standard should be instituted.
4. In dealing with heat generation and ignition, complete fire extinguishing with a large volume of water and rapid discharge of RDF after extinguishing are desirable.
In addition, an operation management system, cooperation with RDF facilities, cooperation with persons in the region, information integration of accident technology, etc. are to be considered.
Knowledge Comment 1. New technology brings new hazards. This accident is typical.
2. A large accident could have been prevented if thorough investigation and research with countermeasures had been performed at the first small signs of trouble. It is important to detect hazards at an early stage.
3. Garbage is combustible. It burns naturally when it is dry and generates heat by fermentation.
Background 1. There were preceding accidents. The explosion might not have occurred if investigation and research had been carried out thoroughly at that time. Is there a problem with the support system for operation members?
2. At the research and development stage, only the benefits of the project might have been given first priority, and there might have been insufficient research on the safety on RDF itself and/or matching of RDF with the facilities. Wastes that mainly contain organic matter are combustible, and it is natural that they ignite easily if they are dry. Moreover, if fermentation germs remain and a little moisture exists, fermentation occurs and this generates heat. Naturally, the heat release is also difficult to control in a large storage tank.
Incidental Discussion Although it is a good attempt to pelletize garbage to handle it easily and to use pellets as an energy source, recognition of safely was insufficient. The properties of garbage or general refuse are very unstable. Accidents are very frequent at a waste disposal site. It is supposed RDF that easily generates heat or ignites might be manufactured with contamination with organic matter readily ferments, such as scum of tempura. Isn't it necessary to classify garbage? I have heard from a person related to power generation that the technology for power generation using RDF was established about ten years ago and countermeasures should have been proven by now.
Reason for Adding to DB Example of explosion caused due to no utilization of initial failure information on the technology
Scenario
Primary Scenario Poor Concept, Poor Strategy or Concept, Judge by Only the Merit, Organizational Problems, Inflexible Management Structure, No Study at the First Failure, Misjudgment, Misjudgment of Situation, Planning and Design, Poor Planning, Poor Design, Non-Regular Movement, Movement During Transition, Thoughtless Phenomena, Secondary Damage, External Damage, Fire/Explosion, Bodily Harm, Death, 2 person died, Bodily Harm, Injury, 5 person injured, Loss to Organization, Economic Loss, Damage to Society, Change in Perception, Discredit to the Administration
Sources Refuse derived fuel power plant accident investigation expert committee, The refuse derived fuel power plant accident investigation final report, (2003)
Number of Deaths 2
Number of Injuries 5
Physical Damage A storage tank roof was partially damaged. Part of the tank burned. RDF partially burned in the tank.
Consequences On August 21st, 2003, the following persons evacuated from the site: Enterprise Agency staff and operators, about 200 persons in the power plant. From 22nd to 24th, over 150 inhabitants of the adjacent municipality complained of sore head and eyes. A health consultation office was opened.
Multimedia Files Fig2.Chemical formula
Fig3.Chemical formula
Fig4.Chemical formula
Fig5.Chemical formula
Field Chemicals and Plants
Author KOBAYASHI, Mitsuo (Office K)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
Scenario