Case Ditails

Scenario
Case Name Leakage and explosion of benzene vapor due to a pressure rise in the reactor where steam for heating could not be completely stopped
Pictograph
Date January 27, 1956
Place Kanagawa prefecture, Japan
Location Chemical factory
Overview At a diethyl maleate manufacturing plant, benzene, ethanol and maleic acid were charged into the reactor, and then sulfuric acid was added (catalyst quantity), and the mixture was heated to 40 °C. Then the valve for heating steam was closed. Agitation was stopped, because the temperature had reached 60 °C. Afterwards, the temperature continued to rise, and benzene and ethanol vapor spouted when the temperature reached 83 °C. Then the vapor ignited and exploded. The steam valve was not closed tightly, and it is speculated that steam was supplied, the reaction temperature rose, and there was a runaway reaction. A fire from the boiler or non-explosion-proof electrical devices was the fire source, leading to ignition and an explosion.
Incident At a diethyl maleate manufacturing plant, heating of a reactor started after charging benzene and ethanol into the reactor at the fixed amount. Steam for heating was stopped because the temperature reached the fixed temperature, however, the steam valve was not closed completely. The temperature in the reactor rose, and a runaway reaction occurred. In addition, the temperature rose further. Therefore, a large amount of combustible vapor blew off and was ignited by a fire source nearby, followed by an explosion and a fire. Refer to Fig2.
Processing Manufacture
Individual Process Reaction
Process Flow Fig3.Unit process flow 1
Chemical Reaction Esterification
Chemical Equation Fig4.Chemical reaction formula
Substance Benzene, Fig5
Type of Accident Leakage, fire
Sequence In the morning on January 27th, 1956, 130L of benzene was charged into a reactor; then 144 kg of maleic acid, 160L of ethanol, and a small amount of sulfuric acid were charged.
At about 10:00, heating steam began to be fed into a jacket, and heating started.
As the temperature of the reactor had reached 40 °C, a steam valve was closed as usual. After stopping the supply of steam, the temperature usually rises at 1 °C/min due to an exothermic reaction.
As the temperature reached 60 °C, agitation in the reactor was stopped.
When the temperature reached 83 °C, benzene and ethanol vapor blew off.
Usually, agitation is stopped at 60 °C, and the temperature is balanced at 80 °C, because ethanol and benzene begin to vaporize at 70 °C, and the vapor is condensed at the condenser and refluxed.
Cause The reason why the benzene vapor blew off was an abnormal temperature rise in the esterification reactor. The cause was considered to be that the steam valve was not completely closed. Therefore, the steam continued to flow, the temperature continued to rise, an exothermic reaction was promoted, and the temperature in the reactor became abnormally high. In addition, insufficiency of the cooling capacity of the condenser seemed to be another cause.
The ignition source is speculated to be an electrical spark at a knife switch without explosion-proof measures in the reactor room or the fire of the boiler.
There were too many hazardous factors around the reactor; temperature-control devices for the reactor were insufficient, the capacity of the condenser was not sufficient, so benzene vapor blew off at a reaction temperature only 3 °C higher than a normal operation temperature, a vent piping for venting excess vapor was too small, the outlet of the vent piping was in the same room, and there was a boiler operating in the same room. Moreover, switches and electric lamps were of a non-explosion-proof type.
It seemed also the accident cause that operators of the plant in the
room had insufficient knowledge and experience about safety operation.
Countermeasures 1. The capacity of the condenser should be adapted to the capacity of the reactor.
2. Exhaust gas of the reactor should be directly introduced to a safe place outdoors by installing safety valves or rupture disks with a sufficient and reliable capacity.
3. Installing a pressure regulator between the boiler and the reactor to lower pressure if steam pressure is high and a saturated temperature is also high. However, this might not so effective for this kind of accident.
4. All electric devices in the reactor room should be explosion-proof.
5. The employer should provide operators with sufficient knowledge and skills (thorough education).
6. The reactor should be equipped with temperature control equipment.
Knowledge Comment 1. The reaction at the initial stage of a batch operation is unstable, and sometimes an accident can occur due to misjudgment or mishandling in that unstable condition. Not only should the operation manual be systematized, but also sufficient education should be given on the reaction and the facilities in which the reaction occurs. It is necessary to have a design that allows for human error to some extent.
2. Trouble occurs at the weakest place. In this accident, the explosion occurred where explosion-proof electric devices were insufficient. Balanced facilities should be chosen.
Background 1. The facilities did not have enough capacity for this reaction. The defects mentioned in "Cause" showed a clear mistake in the process design.
2. Some of the electric devices were not an explosion-proof type. Mechanical design imperfection was also a problem.
3. The trigger was that the valve did not close perfectly. The cause of the leak was not clear; whether human error or a seat leak at the valve. However, valves in use often leak even if they are fully closed. From this standpoint, it is necessary to install double valves. The facilities were insufficient for a batch reaction.
4. This fire was an old accident, which occurred in 1956, and the plant seemed to be unsafe even for the technological level in those days. It can be said that there was a fundamental defect in safety consciousness.
Reason for Adding to DB Typical example of a runaway reaction
Scenario
Primary Scenario Poor Value Perception, Poor Safety Awareness, Insufficient Recognition of Risk, Ignorance of Procedure, Disregard of Procedure, Disregard of Working Procedure, Esterification, Planning and Design, Poor Planning, Poor Design, Unbalance of Heating and Condensation, Regular Operation, Erroneous Operation, Erroneous Operation by Mis Misjudgment, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion, Bodily Harm, Death, Bodily Harm, Injury
Sources M.Tamura, M. Wakakura, Explosion of benzene vapor. Reaction dangers- Accident case and analysis-p.138 (1995).
Supervised by Ministry of Labor, Labor Standards Bureau Industrial accident prevention measures division, Safety section. Edited by the Japan Industrial Safety and Health Assoc. Explosion of benzene that spouted from a reactor. Cases of significant accidents and research on explosions and fire in the past 10 years. pp.95-97 (1967)
Number of Deaths 1
Number of Injuries 4
Physical Damage A reactor and a building were damaged.
Financial Cost ¥3.3 million. (The property insurance rate estimation association).
Multimedia Files Fig2.Esterification reactor figure
Fig5.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