| Case Name |
Fire at an acetylene hydrogenation section on rapid re-startup after an emergency shutdown at an ethylene plant |
| Pictograph |
|
| Date |
July 7, 1973 |
| Place |
Tokuyama, Yamaguchi, Japan |
| Location |
Chemical factory |
| Overview |
On July 7th, 1973, an explosion and a fire occurred at an acetylene hydrogenation section of T factory ethylene plant of I petrochemical company. Because of a restart error after an emergency shutdown, there was an error in hydrogen feed control. As excessive hydrogen was injected and it hydrogenated ethylene, the reactor reached a high temperature. In addition, there was an exothermic ethylene decomposition reaction. A large fireball (60 m in diameter, duration time 5 seconds) was produced by an explosion of 1200 kg of ethylene. |
| Incident |
Although an ethylene plant in T factory of I petrochemical company underwent an emergency shutdown, the plant was soon re-started. Then, an acetylene hydrogenation reactor reached a high temperature, the outlet piping ruptured, and a fire occurred with leaking gas. It burned for 83 hours. A large fireball was generated. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig2.Acetylene hydrogenation reactor flow sheet
|
| Chemical Reaction |
Other (hydrogenation) |
| Chemical Equation |
Fig3.Chemical reaction formula
|
| Substance |
Ethylene, Fig4 |
| Hydrogen, Fig5 |
| Type of Accident |
Leakage, explosion, fire |
| Sequence |
1. An operator closed an instrument air valve at an ethylene manufacturing plant by mistake. Therefore, the plant entered into an emergency shutdown state.
2. After the operator noticed large flames coming out of a flare stack, he realized the valve closing error, and re-opened the valve.
3. In the control room, the plant restarted several minutes after the emergency shutdown.
4. An acetylene hydrogenation reactor, where a selective hydrogenation reaction of very small amounts of acetylene in the ethylene was done, re-started. At that time, an operator found that the temperature indicator of the reactor showed a very high temperature. He also found a hydrogen valve was not closed completely, so he closed the valve again.
5. Ethylene was introduced into the hydrogenation reactor to lower the reactor's temperature. Ethylene in the reactor began an exothermic decomposition reaction due to the very high temperature of the reactor. Piping at the outlet of the reactor was ruptured by the very high temperature, and ethylene gas leaked and ignited. |
| Cause |
Closing the instrument air valve by mistake caused all related instrument to fail, and the plant entered into an emergency shutdown state. The acetylene hydrogenation reactor also shut down. Instrument air was immediately recovered, and a restart of the plant was carried out. Due to judgment error at the restart of the acetylene hydrogenation reactor and a bad condition of the hydrogen control valve, supply of hydrogen was repeatedly started and stopped. As a result, ethylene in the reactor was hydrogenated and the temperature in the reactor rose. This high temperature progressed to an exothermic decomposition reaction of ethylene, and the temperature in the reactor became higher and higher. Therefore, the outlet piping cracked, ethylene leaked, and ignited.
Failure position: All control valves have been set in advance at a safe position (open, closed, and maintained) to shut down the plant safely when instrument air fails. The set position is called a failure position. |
| Countermeasures |
1. A pressure detection device at the secondary side should also be equipped for early detection of instrument air failure. Management should be thorough by coloring of instrument air piping, etc.
2. At a plant that requires an emergency shutdown, alarms should be divided into two stages: caution and emergency alarms. A temperature indicator should be installed to prevent an unusual reaction.
3. Auxiliary facilities such as a water gun should be prepared.
4. A remote shut-off valve should be installed for urgently isolating a section when facilities with a high hazard enter into abnormal operations.
5. Facilities for transferring material to another tank should be prepared to prevent a fire from burning for a long time if refrigerant gas ignites.
6. Various operation standards should be totally restudied, and control limits of pressure and temperature should be clarified. Moreover, measures to control the closing of valves should be standardized.
7. In addition, the security system should be strengthened, a chain of command in an emergency should be clarified, and education and
training should be carried out.
The above are important points which should be contained in future
investigation committee reports. |
| Knowledge Comment |
1. There was selective hydrogenation of diolefin in olefin. Although hydrogenation of diolefin was intended at an ultra-trace level with no reaction of mono-olefin, the mono-olefin reacted due to a control error. In the reaction system, which is controlled by slight differences in operation conditions, operators are required to be aware of the hazards, and safety countermeasures such as duplication should be taken.
2. Ethylene equipment is a gas plant in which gas flows. A feature of the gas plant is a rapid change, because residence time is shorter than in a liquid plant. A gas plant should not restart without adequate consideration. It is the same in an oil plant. |
| Background |
1. The instrument air valve, which was the initial cause, was forbidden to be turned on and off. Moreover, it was located over 100 m away from the plant air valve which should be operated. In addition, a 6-inch plant air valve was mistaken for a 4-inch instrument air valve, and was opened. Why and how did such an error happen? Operation management should prevent problems by confirming directions and operations. Why was a valve that was prohibited to be turned on and off not protected? Naturally, measures to prevent the valve from being turned on and off had to be taken. It is assumed that there was a problem in the management of the facilities.
2. Without confirming its condition, the hydrogenation section was restarted. The hydrogenation process uses a slight difference in the hydrogenation properties of ethylene and acetylene. The contents were mostly ethylene, and if all of the ethylene is hydrogenated, it reaches a high temperature and there occurs an ethylene decomposition reaction which is more severely exothermic. The operators had to understand well those mentioned above. The restart should have been done with care after sufficiently confirming the condition. We cannot understand why the restart was hurried, and this was the greatest factor causing the fire.
3. Stopping hydrogen after the restart was tried using one control
valve. It is common sense among operators that a flow does not decrease
to zero even if the control valve is closed perfectly. Maybe they could not
afford to consider this fact due to an emergency, but it was a serious error in operation judgment.
Introducing ethylene at a high temperature from another plant was also
an error in operation judgment.
4. The operation manual might not have been completed. The items 1, 2, 3 above are the basis of operation. There should be thorough education on operations after an emergency shutdown. |
| Incidental Discussion |
Extensive knowledge was obtained on the formation of a fireball. It is included in a textbook on fire research.
Large flames came out of the flare stack when the ethylene plant was shut down. There was a panic restart, and compensation was excessive.
The investigation committee accident report concluded: "Under the recognition that manufacturing and safety are inseparable, a person responsible for administration is required to clarify the position of the safety management department, and to strengthen safety countermeasures." |
| Reason for Adding to DB |
Example of hazards in a simple re-start of facilities after an emergency shutdown |
| Scenario |
| Primary Scenario
|
Misjudgment, Misjudgment of Situation, Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Organizational Problems, Poor Management, Slackness of Management, Reduction, Non-Regular Operation, Emergency Operation, Planning and Design, Poor Planning, Poor Design, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion/Fire, Bodily Harm, Death, Loss to Organization, Economic Loss, Direct Monetary Danage 2500 million yen and + No Running Loss
|
|
| Sources |
High Pressure Gas Safety Inst. of Japan, Investigation report of accident at T factory No. 2 ethylene manufacturing plant of I petrochemical Co., Ltd. July 28th, 1973 (1973).
Testuzo Kitagawa, Ethylene leakage by the closeout of the instrument air piping. Analysis of the explosion hazard. pp.166-167 (1980).
Chemical Industries Association Cases of accidents in columns and vessels. Accident disaster case and countermeasures. 4. Safety countermeasure technologies of a chemical plant. pp. 251-254 (1979)
Tokuyama City Fire fighting head quarter. Outline of I petrochemicals Co., Ltd. T factory No.2 ethylene plant fire
|
| Number of Deaths |
1 |
| Physical Damage |
Distillation columns, receivers, reactors, piping of pumps were destroyed. Heat exchangers, receivers and drums, reboilers and heaters and condensers were partially destroyed by fire and became unusable. About 150 tons of ethylene, about 250 tons of propylene, and about 100 tons of process gas also burned. |
| Financial Cost |
¥25 hundred million. (Outline of I petrochemicals Co., Ltd. T factory No.2 ethylene plant fire ) |
| Multimedia Files |
Fig4.Chemical formula
|
|
Fig5.Chemical formula
|
| Notes |
This is a famous accident in which a large fireball (over the 50 m in diameter) was formed |
| 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)
|
|
