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Trends in chemical hazards in Japan
Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
Trends in chemical hazards in Japan Masahide Wakakura b
a,*
, Yoshiaki Iiduka
b
a Kanagawa Industrial and Technology Research Institute, 705-1 Shimoimaidumi, Ebina, Japan Mitsubishi Chemical Corporation Yokohama Research Center, 1000 Kamoshida-cho, Aoba-ku, Yokohama, Japan
Abstract In the past, the chemical industry in Japan has been the cause of a number of major industrial accidents. Subsequent to each accident, specific lessons have been learned. These lessons learned have been implemented in terms of safety education of the employees and/or safety measures of the equipment and facilities resulting in a rapid decrease of corresponding accident frequencies. In this paper, we summarized both recent and past major accidents caused by chemical substances in fixed installations in Japan. Case studies show that runaway reactions are among the main causes of major accident occurrences in the chemical process industry in Japan. A recent fatal poisoning accident caused by H2S gas generated during maintenance work again highlights the necessity of adequate safety management in a chemical factory. Therefore, even if hazard evaluation of chemical substances and chemical processes is necessary to prevent runaway reactions, human error is also an important factor contributing to reaction hazards [Wakakura, M. (1997) Human factor in chemical accidents, J. Safety Eng. High Press. Gas. Safety Inst. Japan, 34, 846]. 1998 Published by Elsevier Science Ltd. All rights reserved. Keywords: Chemical hazards; Japan; Safety
1. Introduction Although the number of major chemical accidents has been decreasing in the last years in Japan, industrial development in the chemical process industry has caused new problems related to safety. These problems are due to the use of various reactive chemicals such as crude materials, an increase of automatic processes or the use of multipurpose reactors, etc. All these different problems cause difficulty in ensuring the safety of chemical processes and their products by simply imposing new laws and regulations. Reflecting on this situation, the Japanese Chemical Engineering Society (JCES) started actions to ensure the protection of the health and safety of employees and the public as well as of the environment. The proper implementation of these actions guarantees such protection during production, transportation, use or disposal of the chemical products. Of course, each chemical company needs to develop such safety measures according to the type and extent of their specific processes. The
* Corresponding author
development of such an industrial safety system is, however, quite a basic task, dealing with lessons learned from previous accidents, a task which has to be supported by the fact that data concerning major chemical accidents have been collected and analyzed in the past. The trends of such accidents together with some recent case studies are described in this paper.
2. Tendency of major industrial accidents in Japan in the last 50 years Fig. 1 shows the frequency of injuries in industry in Japan (per 106 h). Before the 1960s this rate had a considerably high value when compared with Europe and the United States. However, this value has decreased rapidly since, and recently Japan has been classified as the country with the lowest industrial accident rate in the world. The Ministry of Labor has defined “major accidents” as follows: an accident resulting in fatalities, or an accident where three or more persons are injured.
0950–4230/99/$ - see front matter 1998 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 4 2 3 0 ( 9 8 ) 0 0 0 4 1 - 2
80
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
45 40
Frequency Rate (10-6)
35 30 25 20 15 10 5 0 52 955 958 961 964 967 970 973 976 979 982 985 988 991 994 1 1 1 1 1 1 1 1 1 1 1 1 1 1
19
Year
Fig. 1. Frequency rate of injuries in industry in Japan (per 106 h).
In 1996 about 40 000 employees died or suffered injuries while working in the manufacturing industry. The classification of the number of injuries in relation to the type of processes involved is shown in Fig. 2 (status 1996). A similar classification concerning fire and explosion accidents is shown in Fig. 3 (status 1996). Accidents caused by fire or explosions are the dominant types of accidents in the chemical process industry in comparison to any other type of industry.
3. Past major chemical accidents in Japan During the start up period of the chemical industry in Japan after World War II, fatal accidents occurred frequently in old type chemical plants, such as ammonia synthesis plants or in extraction processes involving the
Fig. 3. Classification of fire and explosion accidents according to type of processes involved (status 1996).
refinery of fat, as can be seen from the accident data given in Table 1. During the mid 1970s the chemical industry developed rapidly, and during the same period of time an increase in the number of fire, explosion and environmental pollution accidents due to releases in the petrochemical industry was observed. Since then the number of major chemical accidents has decreased, and any accident occurring recently is mainly due to the technical development of chemical processes or to the use of reactive or unstable chemicals. Moreover, the tolerance of the public with regard to accidental releases of chemical substances is decreasing more and more, which puts additional weight on the necessity to achieve high levels of safety in the chemical industry (Wakakura, 1997).
4. Accident database
Fig. 2. Classification of injuries according to type of processes involved (status 1996).
The Industrial Fire Report (http://www.fdma.go.jp: Fire and Management Agency) and the Hazard and Accident Database of Hazardous Materials (http://www.aist.go.jp/RIODB: The Ministry of Trade and Industry) are the two official information documents concerning major industrial accidents in Japan which are provided on the WWW. Unfortunately, the information given is too limited in order to use it for case studies and/or to obtain any information for the purposes of loss prevention. On the other hand, the Accident and Disaster Information Database (ADID) provided by the Accident and Disaster Information Center (ADIC) gives effective information about natural and industrial disasters by means of a PC network. Recently, access to ADIC has also been made avail-
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
81
Table 1 Major chemical accidents in Japan after World War II Year
Accident description
1949 1952 1954
Explosion and fire in a fat extraction factory 5 Explosion in ammonium sulfate separation process 7 Explosion and fire caused by hexane which spouted in an oil and fat 21 extraction factory Explosion of hexane in a soybean oil extraction factory 11 Explosion of liquid air at gas separation device in ammonia synthesis process 11 An explosion and fire of hexane in oil and fat extraction factory 11 Runaway reaction in the polymerization of propylene oxide 18 Decomposition and explosion in high pressure polyethylene plant 38 A fire with combustible vapor in tire reproduction factory 11 Runaway reaction of acrylic polymerization reaction 0 Runaway reaction in reactor to produce medicine caused explosion 2 Reaction was runaway and reactor exploded during isomerization 6 Runaway reaction trigged by restart of agitation after power failure 6 Explosion in the manufacturing process of benzoyl peroxide 9
1956 1958 1960 1964 1964 1969 1973 1978 1978 1982 1990
No. of deaths
able on the WWW (http://www.rise.waseda.ac.jp/adic/ index—e.html). For the future, exchange of information included in databases in the area of industrial safety can be expected by means of cooperation with other countries or international institutions, such as the European Commission’s Major Accident Reporting System (MARS) (see another paper in this special issue: C. Kirchsteiger, The functioning and status of the EC’s major accident reporting system on industrial accidents). By analyzing data from ADID the trend of accidents in the chemical industry in Japan can be summarized as shown in Table 2. Total accident numbers do not seem to have changed significantly in the last 30 years, but reaction hazards are gradually increasing.
No. of injuries 2 11 162 7 40 10 171 0 7 101 10 9 184 17
distillation tower was destroyed due to the explosion, and splinters were dispersed within a range of 900 m. All panes within a radius of 50 m of the distillation tower were destroyed. Two employees died due to injuries caused by direct impact of splinters, and 13 people were injured (Yoshida et al., 1996). 5.1.2. Process Fig. 4 shows the process flow. After sulphonation in the detergent manufacturing plant, 2.5% hydrogen peroxide and 25% methanol were added for bleaching. The mixture of water and methanol was then distilled and the methanol was recovered. 5.1.3. Cause It has been suggested that the detonation was caused by the presence of a small amount of permethanol [CH3O–OH] in the used methanol. The permethanol then condensed during the drive stop process of the distillation resulting in the explosion. The reaction mechanism resulting in the production of permethanol is shown in the following chemical reaction. Sulfuric anhydride remaining in the bleaching liquid reacted with methanol, resulting in the formation of methylsulfate produced as a by-product. Then, the methylsulfate
5. Case studies
5.1. Explosion in the methanol distillation tower (1991) 5.1.1. Summary The explosion accident occurred during a distillation process used to recover methanol. The upper part of the Table 2 Trend in the consequences of accidents in the chemical industry in Japan Consequence
1968–1977(%)
1978–1987(%)
1988–1997(%)
Pollution, poisoning Fire, explosion (liquid) Fire, explosion (gas) Explosion (unstable material) Dust explosion Self ignition Runaway reaction Total
134 (30) 132 (25) 97 (22) 16 (4) 15 (3) 19 (4) 37 (8) 450 (100)
82 (26) 84 (26) 81 (25) 13 (5) 15 (5) 12 (4) 29 (9) 312 (100)
97 (29) 79 (24) 71 (22) 18 (4) 12 (4) 13 (4) 41 (12) 331 (100)
82
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
trated methanol peroxide was ignited in the iron tube of the distillation tower model, the detonation occurred. 5.2. Explosion in the alkyl aluminum manufacturing factory (1996) 5.2.1. Summary A violent explosion and fire occurred in an aluminum alkyl reactor resulting in the formation of aluminum alkyl ‘bombs’ which exploded continuously. The reactor was destroyed and the factory was burnt down. Thirteen employees were injured. 5.2.2. Process Sodium hydrogen aluminum (NAH) and sodium alkyl aluminum (SAH) were produced alternately using multipurpose reactors by the following reaction:
Fig. 4. Process flow diagram for the production of surfactants.
reacted with hydrogen peroxide and with the methanol peroxide produced, as follows: SO3 ⫹ CH3OH→CH3OSO3H CH3OSO3H ⫹ H2O2→CH3OOH ⫹ H2SO4 Fig. 5 shows the result of the simulation for the concentration of the permethanol during the operation of distillation process. The concentration of the methanol peroxide has been estimated to be ⱕ 30%. The high value for the energy of decomposition of the condensed methanol peroxide was estimated by ARC (Accelerating Rate Calorimeter) measurement. When the 60% concen-
Fig. 5.
Na ⫹ Al2 ⫹ 2H2→NaAlH4 (NAH, 9 MPa: H2, 130–135°C; solvent: tetrahydrofurane [THF]) Na ⫹ Al ⫹ 4CH3OCH2CH2OH→NaAl(CH3OCH2)4 ⫹ H2 (0.1 MPa: N2, 80–120°C, solvent: toluene) Na ⫹ Al ⫹ NaAl(CH3OCH2CH2O)4 ⫹ H2→2NaAl(CH3OCH2CH2O) 2H2 (SAH, 9 MPa: H2, 135–140°C, solvent: toluene) 5.2.3. Cause The accident occurred while manufacturing SAH. However, although there are some doubts about it, the direct cause of the explosion was suggested to have been triggered by the decomposition of SAH. Some NAH adhered on the wall of the reactor as a residue of the previous reaction, while THF used as solvent on the previous batch remained in the solvent. It was assumed that
Simulation of the condensation of per-methanol during the stop operation of distillation process.
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
the heat of reaction of the remaining NAH and THF accumulated causing a runaway reaction, thus inducing the decomposition of SAH. A large amount of SAH stored in gas cylinders close to the manufacturing area exploded as a result of induced heat radiated by the first explosion. 5.2.4. Lessons learned To operate the multipurpose reactor safely, it is necessary to clean off any residues and to evaluate the influence of impurities. To prevent a similar accident, neither raw materials nor products with high combustibility or reactivity should be stored near the manufacturing facilities. 5.3. Poisoning accident caused by H2S during maintenance work (1995)
83
(CH3O)2PSCl ⫹ NH3→(CH3O)2PSNH2 ⫹ HCl The reactant containing DPAT was stored after the first condensation, then acephate is obtained through a second condensation. 5.4.3. Cause Reactants had accumulated under high temperature for 11 h in the tank due to a flow pump failure. It was suggested that the low decomposition temperature of DPAT (99°C) induced the runaway reaction in about 6 h. 5.4.4. Lessons The hazard evaluation data (e.g. by ARC measurement) of the raw material and of the intermediate measured by the safety laboratory were not used as a safety measure on the site of the process itself. 5.5. Other recent major chemical accidents
5.3.1. Summary H2S gas leaked from a refinery’s sulfur collection device during the regular maintenance of the chemical process. Forty-seven employees were injured and three people died. 5.3.2. Cause H2S gas generated as a by-product in the sulfur collection device was usually collected in a sulfuric acid player. During regular maintenance work the valves of the H2S flow line need to be closed, but in this case another maintenance team opened the valve and H2S flowed into the maintenance area. 5.3.3. Lessons learned Prior arrangement between the maintenance operators and an understanding of all operations by the administrator are important in the maintenance work of a chemical process. Not only is there a need for an operations manual but also a rescue manual is necessary if the working area is to come in contact with harmful chemicals.
Other major chemical accidents having recently occurred in Japan are shown in Table 3. Recently the waste treatment industry has been developing processing methods with a subsequent increase in wastes produced by the chemical factories. As a consequence, an increase in the number of chemical accidents occurring in the course of waste treatment processes can be observed in the last years, mainly because of wrong mixing processes involved.
6. Hazard evaluation Fig. 6 shows a summary of the hazard evaluation flow used by Mitsubishi Chemical (Iiduka, 1997). Some
5.4. Explosion in agricultural chemicals manufacturing process (1996) 5.4.1. Summary A storage tank of condensed agricultural chemicals intermediates in a newly developed process suddenly exploded. Some of the facilities were destroyed, and one employee was injured. 5.4.2. Process Intermediate (DPAT: dimethylacetyl-phoshoraminothioate) of agricultural chemical (acephate: dimethylacetyl-phoshoramidothioate) was produced from the following reactions:
Fig. 6.
Hazard Evaluation Flow in Mitsubishi Chemical Ltd.
84
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
Table 3 Recent major chemical accidents in Japan Date
Chemicals
Activity
Equipment
Accident description
97.5
Acrylonitrile, peroxide, toluene
Waste treatment, incineration
Storage tank
Explosion and fire occurred at the storage tank for waste oils. As acrylonitrile and other waste solvents containing peroxide were mixed in the same tank exothermic polymerization occurred and toluene strafed in the same tank evaporated suddenly and ignited to a large fire. Thus, it is important to estimate the chemical and physical characteristics of materials treated at waste processes.
97.5
Ethylene
Processing
Heater
Ethylene gas leaked from the pipeline of ethanol synthesis process, then explosion and fire occurred.
97.4
Ethylene
Processing
Reactor
Explosion occurred at the polyethylene manufacturing process using catalyst. Ethylene gas leaked from rupture disks and ignited.
96.11
TNT
Processing
Reactor
Explosion occurred at the refinery process. To recognize the completion of the repair, sodium carbonate solution was flowed and mixed with TNT in the purification reactor. Then impurities in TNT caused runaway reaction contacted with sodium carbonate. Six employees were injured. Lack of safety assessment and inadequate quenching system turned out to be the accident causes.
96.12
Dicyclo-pentadiene, diethyl aluminum–chlorite
Processing
Tank
Runaway reaction and explosion occurred. The splinter in the upper part of the tank dispersed 200 m or more. It was assumed that a rapid polymerization occurred because of excessive catalyst. Temperature and pressure of the explosion were 234°C and 5.4 MPa though the operating temperature was 55°C.
chemical companies use a similar evaluation scheme, but in general it has to be said that such systematic approaches are not yet standard in the chemical industry in Japan.
7. Conclusions As mentioned above, the consequences and causes of chemical accidents in Japan have been changing in the last years in accordance with the technical developments of the chemical processes involved. Since most of the fine chemicals plants in Japan are close to residential areas, there are strict regulations on preventing releases of dangerous chemical substances from these facilities. Therefore, in order to maintain a high level of safety of the chemical industry in Japan, the following steps have been taken by joint research groups:
1. development of simple methods and apparatus for hazard evaluations; 2. development of risk assessment systems in chemical industries; 3. development of a training system for the operators, such as operation simulators corresponding to the increase of automatic chemical processes; and 4. set-up and operation of accident databases and performance of systematic case study analyses.
References Iiduka, Y. (1997). Hazard evaluation of runaway polymerization. J. Japan Chem. Eng. Sci., 61, 837. Wakakura, M. (1997). Case study of recent chemical disaster. J. Japan Chem. Eng. Sci., 61, 854. Yoshida, T., Nakamura, M., & Hasegawa, K. (1996). Case study of the explosion of distillation process. J. Japan Soc. Safety Eng., 35, 370.
Trends in chemical hazards in Japan Masahide Wakakura b
a,*
, Yoshiaki Iiduka
b
a Kanagawa Industrial and Technology Research Institute, 705-1 Shimoimaidumi, Ebina, Japan Mitsubishi Chemical Corporation Yokohama Research Center, 1000 Kamoshida-cho, Aoba-ku, Yokohama, Japan
Abstract In the past, the chemical industry in Japan has been the cause of a number of major industrial accidents. Subsequent to each accident, specific lessons have been learned. These lessons learned have been implemented in terms of safety education of the employees and/or safety measures of the equipment and facilities resulting in a rapid decrease of corresponding accident frequencies. In this paper, we summarized both recent and past major accidents caused by chemical substances in fixed installations in Japan. Case studies show that runaway reactions are among the main causes of major accident occurrences in the chemical process industry in Japan. A recent fatal poisoning accident caused by H2S gas generated during maintenance work again highlights the necessity of adequate safety management in a chemical factory. Therefore, even if hazard evaluation of chemical substances and chemical processes is necessary to prevent runaway reactions, human error is also an important factor contributing to reaction hazards [Wakakura, M. (1997) Human factor in chemical accidents, J. Safety Eng. High Press. Gas. Safety Inst. Japan, 34, 846]. 1998 Published by Elsevier Science Ltd. All rights reserved. Keywords: Chemical hazards; Japan; Safety
1. Introduction Although the number of major chemical accidents has been decreasing in the last years in Japan, industrial development in the chemical process industry has caused new problems related to safety. These problems are due to the use of various reactive chemicals such as crude materials, an increase of automatic processes or the use of multipurpose reactors, etc. All these different problems cause difficulty in ensuring the safety of chemical processes and their products by simply imposing new laws and regulations. Reflecting on this situation, the Japanese Chemical Engineering Society (JCES) started actions to ensure the protection of the health and safety of employees and the public as well as of the environment. The proper implementation of these actions guarantees such protection during production, transportation, use or disposal of the chemical products. Of course, each chemical company needs to develop such safety measures according to the type and extent of their specific processes. The
* Corresponding author
development of such an industrial safety system is, however, quite a basic task, dealing with lessons learned from previous accidents, a task which has to be supported by the fact that data concerning major chemical accidents have been collected and analyzed in the past. The trends of such accidents together with some recent case studies are described in this paper.
2. Tendency of major industrial accidents in Japan in the last 50 years Fig. 1 shows the frequency of injuries in industry in Japan (per 106 h). Before the 1960s this rate had a considerably high value when compared with Europe and the United States. However, this value has decreased rapidly since, and recently Japan has been classified as the country with the lowest industrial accident rate in the world. The Ministry of Labor has defined “major accidents” as follows: an accident resulting in fatalities, or an accident where three or more persons are injured.
0950–4230/99/$ - see front matter 1998 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 4 2 3 0 ( 9 8 ) 0 0 0 4 1 - 2
80
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
45 40
Frequency Rate (10-6)
35 30 25 20 15 10 5 0 52 955 958 961 964 967 970 973 976 979 982 985 988 991 994 1 1 1 1 1 1 1 1 1 1 1 1 1 1
19
Year
Fig. 1. Frequency rate of injuries in industry in Japan (per 106 h).
In 1996 about 40 000 employees died or suffered injuries while working in the manufacturing industry. The classification of the number of injuries in relation to the type of processes involved is shown in Fig. 2 (status 1996). A similar classification concerning fire and explosion accidents is shown in Fig. 3 (status 1996). Accidents caused by fire or explosions are the dominant types of accidents in the chemical process industry in comparison to any other type of industry.
3. Past major chemical accidents in Japan During the start up period of the chemical industry in Japan after World War II, fatal accidents occurred frequently in old type chemical plants, such as ammonia synthesis plants or in extraction processes involving the
Fig. 3. Classification of fire and explosion accidents according to type of processes involved (status 1996).
refinery of fat, as can be seen from the accident data given in Table 1. During the mid 1970s the chemical industry developed rapidly, and during the same period of time an increase in the number of fire, explosion and environmental pollution accidents due to releases in the petrochemical industry was observed. Since then the number of major chemical accidents has decreased, and any accident occurring recently is mainly due to the technical development of chemical processes or to the use of reactive or unstable chemicals. Moreover, the tolerance of the public with regard to accidental releases of chemical substances is decreasing more and more, which puts additional weight on the necessity to achieve high levels of safety in the chemical industry (Wakakura, 1997).
4. Accident database
Fig. 2. Classification of injuries according to type of processes involved (status 1996).
The Industrial Fire Report (http://www.fdma.go.jp: Fire and Management Agency) and the Hazard and Accident Database of Hazardous Materials (http://www.aist.go.jp/RIODB: The Ministry of Trade and Industry) are the two official information documents concerning major industrial accidents in Japan which are provided on the WWW. Unfortunately, the information given is too limited in order to use it for case studies and/or to obtain any information for the purposes of loss prevention. On the other hand, the Accident and Disaster Information Database (ADID) provided by the Accident and Disaster Information Center (ADIC) gives effective information about natural and industrial disasters by means of a PC network. Recently, access to ADIC has also been made avail-
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
81
Table 1 Major chemical accidents in Japan after World War II Year
Accident description
1949 1952 1954
Explosion and fire in a fat extraction factory 5 Explosion in ammonium sulfate separation process 7 Explosion and fire caused by hexane which spouted in an oil and fat 21 extraction factory Explosion of hexane in a soybean oil extraction factory 11 Explosion of liquid air at gas separation device in ammonia synthesis process 11 An explosion and fire of hexane in oil and fat extraction factory 11 Runaway reaction in the polymerization of propylene oxide 18 Decomposition and explosion in high pressure polyethylene plant 38 A fire with combustible vapor in tire reproduction factory 11 Runaway reaction of acrylic polymerization reaction 0 Runaway reaction in reactor to produce medicine caused explosion 2 Reaction was runaway and reactor exploded during isomerization 6 Runaway reaction trigged by restart of agitation after power failure 6 Explosion in the manufacturing process of benzoyl peroxide 9
1956 1958 1960 1964 1964 1969 1973 1978 1978 1982 1990
No. of deaths
able on the WWW (http://www.rise.waseda.ac.jp/adic/ index—e.html). For the future, exchange of information included in databases in the area of industrial safety can be expected by means of cooperation with other countries or international institutions, such as the European Commission’s Major Accident Reporting System (MARS) (see another paper in this special issue: C. Kirchsteiger, The functioning and status of the EC’s major accident reporting system on industrial accidents). By analyzing data from ADID the trend of accidents in the chemical industry in Japan can be summarized as shown in Table 2. Total accident numbers do not seem to have changed significantly in the last 30 years, but reaction hazards are gradually increasing.
No. of injuries 2 11 162 7 40 10 171 0 7 101 10 9 184 17
distillation tower was destroyed due to the explosion, and splinters were dispersed within a range of 900 m. All panes within a radius of 50 m of the distillation tower were destroyed. Two employees died due to injuries caused by direct impact of splinters, and 13 people were injured (Yoshida et al., 1996). 5.1.2. Process Fig. 4 shows the process flow. After sulphonation in the detergent manufacturing plant, 2.5% hydrogen peroxide and 25% methanol were added for bleaching. The mixture of water and methanol was then distilled and the methanol was recovered. 5.1.3. Cause It has been suggested that the detonation was caused by the presence of a small amount of permethanol [CH3O–OH] in the used methanol. The permethanol then condensed during the drive stop process of the distillation resulting in the explosion. The reaction mechanism resulting in the production of permethanol is shown in the following chemical reaction. Sulfuric anhydride remaining in the bleaching liquid reacted with methanol, resulting in the formation of methylsulfate produced as a by-product. Then, the methylsulfate
5. Case studies
5.1. Explosion in the methanol distillation tower (1991) 5.1.1. Summary The explosion accident occurred during a distillation process used to recover methanol. The upper part of the Table 2 Trend in the consequences of accidents in the chemical industry in Japan Consequence
1968–1977(%)
1978–1987(%)
1988–1997(%)
Pollution, poisoning Fire, explosion (liquid) Fire, explosion (gas) Explosion (unstable material) Dust explosion Self ignition Runaway reaction Total
134 (30) 132 (25) 97 (22) 16 (4) 15 (3) 19 (4) 37 (8) 450 (100)
82 (26) 84 (26) 81 (25) 13 (5) 15 (5) 12 (4) 29 (9) 312 (100)
97 (29) 79 (24) 71 (22) 18 (4) 12 (4) 13 (4) 41 (12) 331 (100)
82
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
trated methanol peroxide was ignited in the iron tube of the distillation tower model, the detonation occurred. 5.2. Explosion in the alkyl aluminum manufacturing factory (1996) 5.2.1. Summary A violent explosion and fire occurred in an aluminum alkyl reactor resulting in the formation of aluminum alkyl ‘bombs’ which exploded continuously. The reactor was destroyed and the factory was burnt down. Thirteen employees were injured. 5.2.2. Process Sodium hydrogen aluminum (NAH) and sodium alkyl aluminum (SAH) were produced alternately using multipurpose reactors by the following reaction:
Fig. 4. Process flow diagram for the production of surfactants.
reacted with hydrogen peroxide and with the methanol peroxide produced, as follows: SO3 ⫹ CH3OH→CH3OSO3H CH3OSO3H ⫹ H2O2→CH3OOH ⫹ H2SO4 Fig. 5 shows the result of the simulation for the concentration of the permethanol during the operation of distillation process. The concentration of the methanol peroxide has been estimated to be ⱕ 30%. The high value for the energy of decomposition of the condensed methanol peroxide was estimated by ARC (Accelerating Rate Calorimeter) measurement. When the 60% concen-
Fig. 5.
Na ⫹ Al2 ⫹ 2H2→NaAlH4 (NAH, 9 MPa: H2, 130–135°C; solvent: tetrahydrofurane [THF]) Na ⫹ Al ⫹ 4CH3OCH2CH2OH→NaAl(CH3OCH2)4 ⫹ H2 (0.1 MPa: N2, 80–120°C, solvent: toluene) Na ⫹ Al ⫹ NaAl(CH3OCH2CH2O)4 ⫹ H2→2NaAl(CH3OCH2CH2O) 2H2 (SAH, 9 MPa: H2, 135–140°C, solvent: toluene) 5.2.3. Cause The accident occurred while manufacturing SAH. However, although there are some doubts about it, the direct cause of the explosion was suggested to have been triggered by the decomposition of SAH. Some NAH adhered on the wall of the reactor as a residue of the previous reaction, while THF used as solvent on the previous batch remained in the solvent. It was assumed that
Simulation of the condensation of per-methanol during the stop operation of distillation process.
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
the heat of reaction of the remaining NAH and THF accumulated causing a runaway reaction, thus inducing the decomposition of SAH. A large amount of SAH stored in gas cylinders close to the manufacturing area exploded as a result of induced heat radiated by the first explosion. 5.2.4. Lessons learned To operate the multipurpose reactor safely, it is necessary to clean off any residues and to evaluate the influence of impurities. To prevent a similar accident, neither raw materials nor products with high combustibility or reactivity should be stored near the manufacturing facilities. 5.3. Poisoning accident caused by H2S during maintenance work (1995)
83
(CH3O)2PSCl ⫹ NH3→(CH3O)2PSNH2 ⫹ HCl The reactant containing DPAT was stored after the first condensation, then acephate is obtained through a second condensation. 5.4.3. Cause Reactants had accumulated under high temperature for 11 h in the tank due to a flow pump failure. It was suggested that the low decomposition temperature of DPAT (99°C) induced the runaway reaction in about 6 h. 5.4.4. Lessons The hazard evaluation data (e.g. by ARC measurement) of the raw material and of the intermediate measured by the safety laboratory were not used as a safety measure on the site of the process itself. 5.5. Other recent major chemical accidents
5.3.1. Summary H2S gas leaked from a refinery’s sulfur collection device during the regular maintenance of the chemical process. Forty-seven employees were injured and three people died. 5.3.2. Cause H2S gas generated as a by-product in the sulfur collection device was usually collected in a sulfuric acid player. During regular maintenance work the valves of the H2S flow line need to be closed, but in this case another maintenance team opened the valve and H2S flowed into the maintenance area. 5.3.3. Lessons learned Prior arrangement between the maintenance operators and an understanding of all operations by the administrator are important in the maintenance work of a chemical process. Not only is there a need for an operations manual but also a rescue manual is necessary if the working area is to come in contact with harmful chemicals.
Other major chemical accidents having recently occurred in Japan are shown in Table 3. Recently the waste treatment industry has been developing processing methods with a subsequent increase in wastes produced by the chemical factories. As a consequence, an increase in the number of chemical accidents occurring in the course of waste treatment processes can be observed in the last years, mainly because of wrong mixing processes involved.
6. Hazard evaluation Fig. 6 shows a summary of the hazard evaluation flow used by Mitsubishi Chemical (Iiduka, 1997). Some
5.4. Explosion in agricultural chemicals manufacturing process (1996) 5.4.1. Summary A storage tank of condensed agricultural chemicals intermediates in a newly developed process suddenly exploded. Some of the facilities were destroyed, and one employee was injured. 5.4.2. Process Intermediate (DPAT: dimethylacetyl-phoshoraminothioate) of agricultural chemical (acephate: dimethylacetyl-phoshoramidothioate) was produced from the following reactions:
Fig. 6.
Hazard Evaluation Flow in Mitsubishi Chemical Ltd.
84
M. Wakakura, Y. Iiduka / Journal of Loss Prevention in the Process Industries 12 (1999) 79–84
Table 3 Recent major chemical accidents in Japan Date
Chemicals
Activity
Equipment
Accident description
97.5
Acrylonitrile, peroxide, toluene
Waste treatment, incineration
Storage tank
Explosion and fire occurred at the storage tank for waste oils. As acrylonitrile and other waste solvents containing peroxide were mixed in the same tank exothermic polymerization occurred and toluene strafed in the same tank evaporated suddenly and ignited to a large fire. Thus, it is important to estimate the chemical and physical characteristics of materials treated at waste processes.
97.5
Ethylene
Processing
Heater
Ethylene gas leaked from the pipeline of ethanol synthesis process, then explosion and fire occurred.
97.4
Ethylene
Processing
Reactor
Explosion occurred at the polyethylene manufacturing process using catalyst. Ethylene gas leaked from rupture disks and ignited.
96.11
TNT
Processing
Reactor
Explosion occurred at the refinery process. To recognize the completion of the repair, sodium carbonate solution was flowed and mixed with TNT in the purification reactor. Then impurities in TNT caused runaway reaction contacted with sodium carbonate. Six employees were injured. Lack of safety assessment and inadequate quenching system turned out to be the accident causes.
96.12
Dicyclo-pentadiene, diethyl aluminum–chlorite
Processing
Tank
Runaway reaction and explosion occurred. The splinter in the upper part of the tank dispersed 200 m or more. It was assumed that a rapid polymerization occurred because of excessive catalyst. Temperature and pressure of the explosion were 234°C and 5.4 MPa though the operating temperature was 55°C.
chemical companies use a similar evaluation scheme, but in general it has to be said that such systematic approaches are not yet standard in the chemical industry in Japan.
7. Conclusions As mentioned above, the consequences and causes of chemical accidents in Japan have been changing in the last years in accordance with the technical developments of the chemical processes involved. Since most of the fine chemicals plants in Japan are close to residential areas, there are strict regulations on preventing releases of dangerous chemical substances from these facilities. Therefore, in order to maintain a high level of safety of the chemical industry in Japan, the following steps have been taken by joint research groups:
1. development of simple methods and apparatus for hazard evaluations; 2. development of risk assessment systems in chemical industries; 3. development of a training system for the operators, such as operation simulators corresponding to the increase of automatic chemical processes; and 4. set-up and operation of accident databases and performance of systematic case study analyses.
References Iiduka, Y. (1997). Hazard evaluation of runaway polymerization. J. Japan Chem. Eng. Sci., 61, 837. Wakakura, M. (1997). Case study of recent chemical disaster. J. Japan Chem. Eng. Sci., 61, 854. Yoshida, T., Nakamura, M., & Hasegawa, K. (1996). Case study of the explosion of distillation process. J. Japan Soc. Safety Eng., 35, 370.