Lessons in Process Safety Management ... - Wiley Online Library

Lessons in Process Safety Management Learned from a Pesticide Plant Explosion in Taiwan Horng-Jang Liaw Department of Safety, Health, and Environmental Engineering, National Kaohsiung First University of Science and Technology, 1 University Road, Yanchao District, Kaohsiung, Taiwan; [email protected] (for correspondence) Published online 17 July 2017 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/prs.11913

A massive explosion in Taichung, Taiwan, in 2016, which was attributed to the thermal decomposition of o,odimethyl phosphoramidothioate, resulted in one fatality and one injury. This accidental explosion stemmed from certain elements being absent from process safety management (PSM), including process safety information, the management of change, process hazard analysis, mechanical integrity, operating procedures, training, and the pre-startup safety review. Problems encountered during the promotion of PSM were also identified, such as the hazards associated with highly hazardous chemicals at normal temperatures and pressure as outlined in the safety data sheet and the fact that these may be different from those under the conditions C 2017 American Institute of Chemical Engineers of the process. V Process Saf Prog 37: 104–109, 2018

Keywords: process safety management; phosphoramidothioate; thermal explosion

o,o-dimethyl

Inspection Act [6]. A business entity shall not allow employees to work in certain specified workplaces without the approval of the labor inspectorate or having passed inspection(s) [6]. The management of most plants with hazardous workplaces wanted to pass the inspection(s); however, they did not wish to implement PSM. In 2010, three severe fire and accidental explosions promoted the Formosa Plastics Group to implement PSM. Now, the Formosa Plastics Group is the best company in terms of practicing PSM in Taiwan. In 2014, Process Safety Assessment Regular Implementation Rules [7] were enacted according to Article 15 of Occupational Safety and Health Act [8] by the Taiwanese government. The rules require that entities in the petrochemical industry that are engaged in petroleum cracking and workplaces that are involved in the manufacturing, storage, or use of hazardous chemicals in excess of 30-fold of the threshold quantities need to implement the 14 elements of PSM.

INTRODUCTION

THE EVENT

On February 1, 2016, a fire and explosions occurred at the Syntai pesticide plant in a suburban of Taichung, Taiwan; this resulted in one fatality and one injury [1,2]. Another gas explosion in Kaohsiung, Taiwan, had recently killed 32 and injured 321; this latter explosion has been previously analyzed based on Process Safety Management (PSM) principles [3]. Not only the deficiencies associated with a lack of PSM in relation to such an accident but also the practical problems that are encountered when developing PSM systems, such as the application of the wrong technological concepts, are identified in that study. Thus, specifically, we analyze the Syntai accidental explosion according to PSM principles in order to identify the management deficiencies and problems encountered during the development and promotion of PSM. After the Bhopal catastrophe in India, the Occupational Safety and Health Administration (OSHA) of the USA promulgated 29 CFR 1910.119, Process Safety Management of Highly Hazardous Chemicals [4] in 1992, in order to prevent/minimize the consequences of a leakage of hazardous material. Specifically, processes involving one or more specific chemicals at or above a particular threshold level required the implementation of PSM. In 1994, the Taiwanese government enacted the Hazardous Workplace Review and Inspection Rules [5], which are the PSM rules of Taiwan, according to Article 26 of the Labor

At Syntai, crystalline impurities were found in a chemical, o,o-dimethyl phosphoramidothioate (DMPAT), which is a raw material used in the manufacturing of the agricultural chemical acephate. In late January 2016, production management decided to filter the DMPAT to remove the impurities; 40 drums of DMPAT needed to be filtered. Filtering impurities of DMPAT had never been done. Since no filtering equipment was available, the DMPAT was pumped into a batch reactor (3R-202) to await filtering (Figure 1). The filtering process was to be conducted at room temperature. If difficulties arose in the filtering operation, the DMPAT would be heated to 408C to reduce its viscosity. The heat source of the temperature control system was hot water at 808C, which was heated by steam from a boiler. The impurities were to be removed by filtration through a filter cloth by gravity. On February 1, 2016, five tons of DMPAT was pumped to the reactor; transfer started at 03:00 and was completed at 03:50. The pumping process was carried out at room temperature. After the pumping operation had been completed, the DMPAT was to remain at room temperature awaiting filtration by the day shift staff. However, one operator has indicated that the temperature of the reactor had reached 358C at sometime between 3:00 and 4:00 a.m., although the room temperature at the time was only 15.68C. The reactor exploded at 5:35 a.m. The resulting fire spread to drums containing various organic solvents, such as toluene, xylene, ethylene glycol, and methyl isobutyl ketone, which were in the vicinity of the workshop building. This resulted in a major

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Figure 3. The explosion scene (II). The reactor completely disintegrated and disappeared. [Color figure can be viewed at wileyonlinelibrary.com] Figure 1. The diagram of the reactor, 3R-202.

Figure 4. Timeline of the accident. Figure 2. The explosion scene (I). The wall of the workshop building is deformed and bulging. [Color figure can be viewed at wileyonlinelibrary.com]

fire and a series of explosions. The blast wave threw one worker several meters and, unfortunately, he died from his wounds [9]. Another worker suffered burns to 20% of his body [1,2]. The explosion also deformed the walls of the workshop building (Figure 2). Except for the manhole cover and a stirrer, the main body of the reactor destroyed completely and was found to have disappeared after the accident (Figure 3). The fire burned the control room to the ground and damaged a number of storage devices that contained operational data. Thus, it was found eventually that the damage caused by the incident had destroyed all of the operational data associated with the accident and therefore none was able to be recovered for investigation. CAUSE ANALYSIS

The events and conditions of this accident are summarized in the timeline depicted in Figure 4. Based on the timeline, a causal factor chart has been constructed and is presented in Figure 5. The evidence indicates that the causal factors included Management of Change (MOC), Pre-startup Safety Review (PSSR), and Process Hazard Analysis (PHA) Process Safety Progress (Vol.37, No.1)

being not performed, as well as a lack of understanding of the reactivity hazards associated with DMPAT. In addition, an operational error and/or the failure of the temperature control loop are also possible causal factors. In addition, this accident was also analyzed using a fault tree analysis and the result are presented in Figure 6. The explosion resulted from a lack of mitigation safeguards with respect to the decomposition of DMPAT. The decomposition of the DMPAT could be attributed to the failure of the heating system of the reactor. Two possible causes may have resulted in the failure of the heating system. There was an operational error and/or a failure of the temperature control loop. The possible operational error could be associated with a lack of operating procedures or a lack of training. The lack of mitigation safeguards is attributable to the reactor not being designed to treat DMPAT originally, and this is associated with MOC. In parallel with the above, this hazard would have been able to be identified if PHA or PSSR had been conducted. In Summary, the results of causal factor chart and fault tree analysis indicate that the root causes of the accident are related to several elements of PSM, these being Process Safety Information (PSI), MOC, PHA, Mechanical Integrity (MI), operating procedures, training, and PSSR. The details of these elements are discussed below.

Published on behalf of the AIChE

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Figure 5. Causal factor chart of the accident.

Figure 6. Fault tree analysis of this accident.

LESSONS LEARNED

Process Safety Information The main root cause of the accidental explosion was a lack of understanding of the reactivity hazards associated with DMPAT. The Safety Data Sheet (SDS) describes DMPAT as stable under normal conditions [10–12]. However, the thermal gravimetric analysis indicates that mass loss begins at 93.58C (Figure 7), and that mass loss is greater than 20% 106

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when DMPAT is heated to 808C for 5 h (Figure 8). In this case, the chemical stability description of DMPAT on the SDS is misleading and this resulted in workers being careless about temperature control. The process conditions are almost always far from the temperatures and pressures specified by the SDS data and the chemical hazards provided by the SDS may be not appropriate for the process conditions being used. The information associated with the hazards of highly hazardous chemicals that are being used in the process is typically provided by the SDS. This hazard information is one of the three pieces of information required in a PSI by the United States (US) OSHA. Since the information provided on the SDS meets the Hazardous Workplace Review and Inspection Rules of Taiwan, it is the only required information that needs to be used to identify hazards associated with highly hazardous chemicals used in Taiwanese workplaces. The SDS provides broad and general information on the hazards of chemicals; however, it does not provide detailed data on all chemical hazards. The detailed information necessary for the management of chemical processes differs for each process and therefore has to be associated with the characteristics of each process. In the accident that is the topic of this report, the thermal hazard data for DMPAT is critical. However, the SDS does not provide such data. Not only can such thermal hazard data be applied to prevent process temperature out-of-control conditions during an operation, but it can also be used in incident investigations after an accident. Relying only on the SDS is inadequate as it does not provide enough workplace chemical hazard information. The employer should identify and develop the fully detailed safety information needed for their processes based on the characteristics of the given processes. For highly hazardous chemicals that have not been used in a given process, we suggest assessing their critical safety data, the chemical hazards under the process conditions and the properties used in determining the safe operational limits of the system, before the chemicals are introduced into process. Management of Change The duty manager indicated that the reactor was to be used as a buffer tank for filtering the DMPAT because no DOI 10.1002/prs


Figure 7. Thermogravimetric data for DMPAT.

Figure 8. Isothermal thermogravimetric data for DMPAT heated at 808C for 5 h.

filtration equipment was available. The use of the reactor as a buffer tank was to be temporary. Nevertheless, the impact of such a change should be evaluated regardless of whether it is a permanent or temporary change. Since such temporary changes were not included in the MOC procedures by the Syntai management, the MOC was not implemented for this transfer. Temporary changes need to be included in MOC procedures [4]. In addition, since the management assumed there was no significant hazard associated with the filtering process, a MOC evaluation was not performed. The purpose of MOC is to prevent the occurrence of hazards when changes are introduced. In this case, the hazard associated with the process of filtering in itself is not the key point; the assessment should have focused on the hazards associated Process Safety Progress (Vol.37, No.1)

with the use of an existing reactor as a buffer tank as part of the filtering process. It is possible that there are no significant hazards associated with the filtering process itself in this case. Nevertheless, the failure of a control valve may in the case have caused the temperature of the DMPAT to increase and become high enough to produce a thermal explosion. It was intended, if the filtering process was not able to be carried out smoothly, for the DMPAT to be heated to 408C by a temperature control system that used 808C hot water circulating through the jacket of the reactor. This hot water was heated by steam generated by a boiler. Any factor that causes an increase in the temperature of the hot water to greater than 808C would have resulted in an increase in the temperature of the DMPAT, therefore an increase in the possibility of


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a thermal explosion. In addition, a failure of the stirrer in the reactor could have produced a hot spot in the DMPAT and this might also have led to a thermal explosion. Process Hazard Analysis In Taiwan, workplaces such as Syntai that manufacture agricultural chemicals using specific raw materials are required to implement PSM. However, removing the impurities from DMPAT by filtration is not a regular process, but rather it is an unexpected process that is not considered to be one that required the implementation of PSM. Thus, PHA was not performed for this filtering process. In addition, MOC was not performed when there was a change of use of the reactor, namely the implementation of the reactor as a buffer tank during the filtering process. Again, because of this, the change of use was not evaluated. If such a change of use had been properly evaluated using a suitable methodology, such as a Hazard and Operability study, not only would the potential hazards of DMPAT in a batch reactor that is linked to a heating process have been identified, but the means of preventing and reducing such hazards could be have been determined. In such circumstances, perhaps, this tragedy would have been avoided. Mechanical Integrity The process equipment used for the storing and handling of hazardous materials needs to be designed, constructed, installed, and maintained properly in order to reduce the risk associated with process hazards [4]. The affected reactor in this case was being operated in a normal manner under atmospheric pressure; it was not designed to withstand high pressure and had no safety valve or rupture disc installed. DMPAT decomposes at an elevated temperature and this may result in a thermal explosion. In such circumstances, a mitigation safeguard device is necessary when a vessel contains DMPAT. Unfortunately, such a safeguard device was lacking in the reactor during the decomposition of the DMPAT. The temperature of the DMPAT increased to at least 358C after it was pumped into the reactor, which should have been at room temperature, namely 15.68C. The heating system of the reactor was set to the off position. Since all of the operational data were destroyed during the explosion and no identifiable wreckage of the reactor or auxiliary equipment could be found, determining the actual cause of the accident becomes a challenge. However, one possible cause is a failure of the temperature control valve. Finally, in terms of this accident, no records are available that support the fact that the control elements of the heating system were maintained properly by Syntai in order to ensure the continuous integrity of the system. Operating Procedures The plant manager indicated that using filtration to remove the impurities from the DMPAT had not been done previously. The filtering process was thought to be a simple process and that the workers were thought to be able to handle it effectively; as a result an operating procedure was not developed. This filtering process was the first implementation of such a process and therefore the required operation time of each step was unknown. In this case, an incorrect temperature control system set point while an operational error, namely the turning on of the heat source, might have caused the thermal explosion of DMPAT. Thus, an operating procedure for filtering the impurities of DMPAT using a temporary set of equipment, including the use of the reactor as a buffer tank, should have been developed. Such an operating procedure should be reviewed using the proper methodology, such as Job Safety Analysis 108

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(JSA), in order to ensure the safety of operation according to the newly developed operating procedure. When improving operating procedures of processes using JSA, the potential hazards should not be limited to the injury of people, but also include the taking into account of all process hazards. The potential hazards in the operation can be identified during the safety review, then useful recommendations and suggestions for overcoming them can be proposed at that time. Training Prior to being involved in the operation of a newly assigned process, each employee should be trained in the operating procedures and an overview of the process [4]. Since a PHA of the filtering process using the temporary equipment was not conducted, the potential hazards of such a process were not identified. As a result of the fact that an operating procedure was not developed and the filtering process was thought to be simple, and also any potential hazards were not identified, this resulted in the operators not being trained to carry out the correct operational procedures and they lacked an overview of the filtering process, which involved the use of the reactor as a buffer tank, including the hazards associated with this filtering process. Using the reactor as a buffer tank is a change; however, a MOC was not performed. Specifically, the workers, who were operating the filtering process, were not trained in or informed of this change or of the affected part of the process as is required by OSHA [4]. Pre-startup Safety Review For new facilities and modified facilities, when a modification is significant enough to change the PSI, management should perform a PSSR [4]. The reactor that was used as a buffer tank formed a temporary set of equipment for the filtering process. Since the piping and instrument diagram (P&ID), which is one of the PSI requirements, was different from the original one, a PSSR was necessary before the start of the filtering operation. However, Syntai operational management did not perform the PSSR. If the PSSR had been performed, the lack of MOC for the equipment change could have been identified, and an evaluation of the change would have been required. The possibility of a thermal explosion as a result of a high-temperature deviation could have been identified; at that point, the reliability of the temperature control would have been highlighted. Furthermore, the lack of operating procedures for the filtering would have also been identified, and the development of such operating procedures would have been required. When combined with the results of PHA, the operating procedures would have been required to be able to prevent the decomposition of DMPAT. Additionally, the workers performing the DMPAT filtering would have been required to be trained in the safe removal of impurities by filtering. Finally, the lack of strength of the buffer tank and the implementation of mitigation safeguards could have been identified by the safety review of the equipment by examining the design specifications of the buffer tank. If the PSSR had been performed, this tragedy might not have happened or its impact could have been significantly reduced. CONCLUSIONS

The purpose of implementing PSM is to prevent or minimize the consequences of a disastrous leakage of a hazardous chemical or chemicals [4]. These consequences include toxic, fire, and explosion hazards [4]; such hazards are considered to be major process hazards. However, it is not true that only the release of highly hazardous chemicals results in major process hazards. Explosions attributed to runaway DOI 10.1002/prs


reactions, such as the accident described above, and to oxidation reactions with improper fuel/air ratios are examples of major process hazards that are not associated with the leakage of highly hazardous chemicals. Since major process hazards are not limited to the release of highly hazardous chemicals, we suggest PSM should be performed on a process with the intention of identifying the potential major hazards associated with a process rather than just to determine if a process has the potential to release one or more highly hazardous chemicals.

LITERATURE CITED

1. China Daily, 1 killed in Taiwan chemical plant blast, Available at: http://www.chinadaily.com.cn/china/ 2016-02/01/content_23340580.htm/, Accessed on December 4, 2016. 2. New China, 1 killed in C. Taiwan chemical plant blast, Available at: http://news.xinhuanet.com/english/ 2016-02/01/c_135064656.htm/, Accessed on December 4, 2016. 3. H.J. Liaw, Lessons in process safety management learned in the Kaohsiung gas explosion accident in Taiwan, Process Saf Prog 35 (2016), 228–232.


4. OSHA (USA), Process Safety Management of Highly Hazardous Chemicals, 29 CFR 1910.119, Federal Regulations of USA, Occupational Safety and Health Administration, Washington, DC., 1992. 5. CLA (Taiwan), Hazardous Workplace Review and Inspection Rules, The Council of Labor Affairs, Taiwan, 1994. 6. CLA (Taiwan), Labor Inspection Act, The Council of Labor Affairs, Taiwan, 1993. 7. ML (Taiwan), Process Safety Assessment Regular Implementation Rules, The Ministry of Labor, Taiwan, 2014. 8. ML (Taiwan), Occupational Safety and Health Act, The Ministry of Labor, Taiwan, 2013. 9. Apple Daily, Available at: http://www.appledaily.com.tw/ realtimenews/article/new/20160201/787856/, Accessed on December 4, 2016. 10. IS Chemical Technology Innovative Service, Available at: http://www.ispharm.com/download/MSDS/I09-0510% 20MSDS_I09-0510.pdf, Accessed on December 4, 2016. 11. Hangzhou Jinghang Biotechnology Co., Ltd., Available at: http://www.hzjhbiotech.com/upload_img/1402042209. 10.pdf, Accessed on December 4, 2016. 12. Chem Service Inc., Available at: http://www.chemservice. com/media/product/msds/N-12701.pdf, Accessed on December 4, 2016.


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