Case Ditails

Scenario
Case Name Rupture of a vacuum distillation drum for 4-chloro-2-methylaniline caused due to air leakage and misjudgment
Pictograph
Date December 4, 1973
Place Kamisu, Ibaragi, Japan
Location Chemical factory
Overview On December 4th, 1973; Crude CMA was refined in a refining drum, and purified CMA was obtained from the upper part of the manufacturing plant for 4-chloro-2-methylaniline (CMA). The residual liquid at the bottom of the refining drum was transferred to a processing drum, and CMA that remained in the residual liquid was recovered. While redistilling in a vacuum, tar was generated by an air leakage from a flange. Gaseous chlorine was formed by a reaction of CMA with high-temperature tar because colored CMA had been transported to the place where the temperature rose due to the abnormal reaction. The tar in the residual liquid blew up, and all of the piping connected to the processing drum was blocked. As a result, pressure and temperature rose, and the processing drum ruptured. Three operators died, and three operators were injured.
Incident The processing vessel of the company 's in-house development manufacturing equipment for 4-chloro-2-methylaniline (CMA) exploded. Crude CMA was refined in the refining drum, and purified CMA was obtained from the upper part of the refining drum. The residual liquid was transferred into the processing drum, and was redistilled in a vacuum to recover CMA from residual liquid at the bottom. An abnormal reaction occurred while re-distilling, and the processing drum exploded. Three operators died, and three operators were injured.
Processing Manufacture
Individual Process Distillation
Process Flow Fig3.Unit process flow
Chemical Reaction Other
Chemical Equation Fig2.Chemical reaction formula
Substance 4-chloro-2-methylaniline, Fig4
Type of Accident Rupture
Sequence On December 4th, 1973, 04:40: Crude CMA was refined in the refining drum. CMA was taken out from the upper part of the vessel. The residue at the bottom was transferred to the processing drum, and re-distillation started in a vacuum.
06:40: Refined CMA distilled from the processing drum turned black. The valve was switched for stopping its transfer to the product tank, and for returning it to the purification drum. The valve from the purification drum to the processing drum had been closed at this time.
08:30: It is presumed that distillation to the refining drum had been completed. To take tar out of the processing tank residue, the processing drum was pressured to atmospheric pressure with nitrogen.
08:40: As the processing drum bottom valve did not open, distillation from the upper vapor layer was restarted.
09:10: The agitator of the processing drum stopped. It was judged that the viscosity of the tar had increased.
09:15: The remained liquid in the distillation drum seemed to be transferred to the processing drum. At this time, as the operator found that the processing drum temperature had risen to 200 °C or more, which was abnormally high compared to the normal 170 °C, the drum was decompressed again. However, the temperature and the pressure did not drop. Operators tried pressure release and sprayed water for cooling.
09:39. The rupture accident occurred.
Cause Air leaked into the processing vessel for vacuum distillation, and the distillation residue oxidized and generated heat. The gasket of the flange for the valve on the steam line in the upper part of the processing drum was replaced the previous day. For some reason, air leaked into from the part of the Teflon-wrapped gasket. In addition, cuprous oxide that originated from the catalyst became cupric chloride in the presence of oxygen and hydrogen chloride. This became like tar and blocked piping of the vacuum system, etc. As the valve from the refining drum to the processing drum was opened under this condition, CMA entered the processing drum. Since hydrogen sulfide gas was generated by the reaction between CMA and high-temperature tar and the tar blocked all of the piping, the internal pressure of the drum rose and a rupture occurred. The direct cause is air leakage due to a maintenance work error and the misjudgment of transferring of colored CMA.
Countermeasures 1. The safety management system is strengthened, and authority and responsibility of the safety management supervisor are clarified.
2. Optimization of the personnel organization of operators of each shift team is conducted. Besides, education and training are carried out for appropriate responses in emergencies.
3. In facilities with a possibility of abnormal internal pressure rising, safety equipment such as an alarm device, a safe rupture disk, quenching facilities, and blowdown equipment are installed.
4. Blockage prevention measures for piping and valves such as installation of heating facilities or large diameter piping are provided.
5. Leak inspection of the vacuum system is carried out periodically, and flange gaskets with high reliability are used.
6. All emergency operations are possible by remote control.
7. The work standard including emergency measure is maintained.
8. If even a small abnormality is found in a process, the cause is investigated, and improvement action is taken.
Knowledge Comment 1. At the process design, all scenarios for all phenomena that were assumed should be studied, and safety countermeasures should be built in. An examination of air leakage is indispensable for a vacuum system. Moreover, action of impurities must be studied.
2. If even a small abnormality in the process is found, the cause is thoroughly investigated, improvement measures should be taken.
3. If there is an abnormality that has a possibility of human injuries from fire or explosion, it is necessary to operate the process by remote control.
Background 1. Hazard analysis on a process using newly developed technology is insufficient.
2. Neither cause investigation nor improvement action were carried out although some abnormal heat generation phenomena had occurred. It is speculated that the manager has a poor consciousness of the process hazard of the plant.
3. Air leaks are frequent in a vacuum system. The work management that causes air leak on the next day after a repair might be a problem.
Reason for Adding to DB Example of accident caused due to insufficient safety assessment in the process design and lack of intention to find potential hazards after start-up of operation
Scenario
Primary Scenario Organizational Problems, Poor Management, Slackness of Management, Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Insufficient Analysis or Research, Insufficient Prior Research, Insuficient Study of Impurities, Planning and Design, Poor Planning, Poor Design, Usage, Maintenance/Repair, Obsevation, Bad Event, Chemical Phenomenon, Abnormal Reaction, Failure, Large-Scale Damage, Rapture, Bodily Harm, Death, Bodily Harm, Injury, Loss to Organization, Economic Loss
Sources High Pressure Gas Safety Inst. of Japan, Kashima Complex protection research report, pp.42-43(1981).
High Pressure Gas Safety Inst. of Japan, Examples of accidents at complex, pp..53-59(1991).
Ministry of Labor Industrial Safety and Health Department, Safety section, 4-chloro-2-methylaniline manufacturing equipment explosion research report, (1974).
Masamitsu Tamura, Masahide Wakakura, Explosion, of 2-chloro4-methylaniline, Reaction danger - Accident case and analysis - p.98(1995).
Number of Deaths 3
Number of Injuries 3
Physical Damage A residue processing drum, piping, insulation, and the building floor (10 square meters of the mezzanine, 40 square meters of the second floor, and 6 square meters of the third floor) were damaged and 500 kg of CMA products dispersed.
Multimedia Files Fig4.Chemical formula
Field Chemicals and Plants
Author OGAWA, Terushige (Graduate School of Environment and Information Sciences, Yokohama National University)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
Scenario