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Electrostatic Risk Assessment for Chemical Plants: Fire and Explosion Prevention

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Electrostatic Risk Assessment for Chemical Plants: Fire and Explosion Prevention Sumitomo Chemical Co., Ltd. Electrostatic Risk Assessment for Production & Safety Fundamental Technology Center Chemical Plants: Kiyoshi OTA Fire and Explosion Prevention An electrostatic discharge is one of the most concerning ignition sources for combustible substances. In order to carry out appropriate safety measures to prevent from ignition, it is necessary to understand correct fundamental phenomena of charging and discharging and to master the technology by considerable training. And next step, application of a risk assessment technology of static electricity is desired. Sumitomo Chemical Co., Ltd. has developed one of these technologies. This paper introduces one practical case study from it. This paper is translated from R&D Report, “SUMITOMO KAGAKU”, vol. 2018. Introduction Safety was released anew by the International Elec- trotechnical Committee (IEC).3), 4) Thus an environ- According to the White Papers on Fire Service which ment has gradually been established in which cover the past ten years (2008 – 2017), electrostatic dis- advanced electrostatic safety technology is widely charge was deemed to be the most significant fire igni- adopted. Along with this trend, the attempt to assess tion source in facilities handling dangerous goods in electrostatic hazard as a risk has begun. If we are able seven separate years during this period, and was to assess electrostatic hazard as a risk, the following ranked as the second most common ignition source in advantages can be expected: By making a relative the other years. Other ignition sources include con- comparison of the risks, the validity and adequacy of tacting with high-temperature surfaces, overheating, safety measures can be confirmed, and safety meas- electric sparks, open flames, and sparks from weld- ures can be prioritized. However, although the risk ing/fusing. It can be believed that one of the reasons assessment technology for fire and explosions has why electrostatic discharge is ranked highest as an advanced in the field of leakage/ignition caused by ignition source is because the electrostatic charging equipment breakdown and/or malfunction, there is and discharging phenomena are difficult to under- still no systematic risk assessment technology that stand, resulting in poor safety measures. Considering focuses on electrostatic discharge as an ignition such circumstances, one can say that it is important to source. Therefore, Sumitomo Chemical developed a release and disseminate static electricity accident pre- proprietary electrostatic risk assessment technology, vention technologies. incorporated it into the revised guidelines for electro- The author of this paper introduced the electrostatic static safety for Sumitomo Chemical and its group hazards and safety measures in 2004 in SUMITOMO companies, and began its implementation in 2010. Sub- KAGAKU.1) Subsequently, in Japan the Electrostatic sequently, Ohsawa of JNIOSH has developed a method Safety Guidelines2) of the Japan Organization of Occupa- for electrostatic risk assessment (hereinafter referred tional Health and Safety (currently known as the Japan to as the Ohsawa method), the guidelines5) of which Organization of Occupational Health and Safety, Nation- were released in 2011. Sumitomo Chemical cooperated al Institute of Occupational Safety and Health, Japan in its test operation and dissemination activities. (hereafter referred to as JNIOSH)) was revised in 2007. This paper will introduce the overseas trends in elec- Also, in 2013 the Technical Guidelines for Electrostatic trostatic risk assessment technologies and also the SUMITOMO KAGAKU 2018 1 Electrostatic Risk Assessment for Chemical Plants: Fire and Explosion Prevention electrostatic risk assessment technology of Sumitomo published by the CCPS (Center for Chemical Process Chemical along with implementation examples. Fur- Safety) in 201710) also does not contain any systematic thermore, as a reference, several cases will also be ana- commentaries for their electrostatic risk, but it intro- lyzed using the Ohsawa method, and the results of duces implementation examples of risk base assess- such comparison will be introduced. Lastly, as the basic ment in some processes. knowledge required for understanding electrostatic The key to the development of electrostatic risk risk assessments introduced in this paper, electrostatic assessment technology is how to determine the likeli- countermeasures and electrostatic induction for con- hood of ignition caused by electrostatic discharge. In ductors, electrostatic countermeasures for insulators the field of leakage ignition by liquefied petroleum gas, and the discharge phenomenon will be explained. where more advanced quantitative risk assessment is Those who want to systematically understand the elec- conducted, abundant statistical data (e.g., the numbers trostatic charge/discharge phenomena and counter- of near miss, equipment breakdown/malfunctions and measure technology in more detail can refer to accidents) have been systematically collected over a Reference2)– 4) at the end of this paper. long period of time for the purpose of developing a risk assessment technology. In this field, certain malfunc- Overseas Trends in Electrostatic Risk tions, failures and likelihood of ignition–which are Assessment specifically applicable to the above assessment–have been determined in the form of numerical values. How- Technical guidelines pertaining to electrostatic safe- ever, there is no known large-volume accumulation of ty were released in the United Kingdom in 1980 and statistical data over a long period of time with focus on 1983, and those guidelines were amended in 1991. electrostatic discharge as an ignition source. There- They were later passed onto the CENELEC (Euro- fore, it can be assumed that this fact may have caused pean Committee for Electrotechnical Standardization), the delay in developing a quantitative risk assessment which in turn released technical guidelines in 2003. technology that focuses on electrostatic discharge. Subsequently, European countries have adopted guide- 3), 4) lines similar to those released by the IEC in 2013. Electrostatic Risk Assessment of Sumitomo However, not all of these guidelines describe specific Chemical electrostatic risk assessment technologies that focus on the ignition likelihood of electrostatic discharge. Fig. 1 shows the implementation flow (Step 1) of Moreover, some books and papers on electrostatic electrostatic risk assessment. In Step 1 the necessity of risks and safety-measure technologies written by Euro- implementation of the electrostatic risk assessment is pean researchers do not mention them at all. determined in consideration of the likelihood of igni- Although the VDI (the Association of German Engi- tion and the level of its impact. First, the characteristics neers) published the guidelines6)– 8) introducing of the target substances are categorized, and then the implementation examples of the dust explosion risk probability of the target substance causing combustion assessment on the VDI2263 series, using the matrix or explosion is assessed under each category. method in consideration of the ignition likelihood and “*1” in Fig. 1 is the process to determine whether level of damage, they also describe ignition sources the saturated vapor pressure of the flammable liquid other than electrostatic discharge, which can be has reached the concentration level that can cause an assumed to occur in the target facility. Although they explosion. Sumitomo Chemical has set four safety fac- are very useful for those facilities, these guidelines do tors, ranging from 5°C to 30°C, taking into account the not comprehensively compile electrostatic risk assess- error11) between the generally-known flash point and ment technologies. the true flash point. Regarding “*2,” if no data on the The NFPA (National Fire Protection Association) in flash point of the flammable liquid slurry cake itself is the United States has issued technical guidelines for available, it will be determined by referring to the flash electrostatic safety measures.9) However, as with the point of the flammable liquid alone. Regarding “*3,” European guidelines, none of them comprehensively the Oxygen Concentration Control Criteria12) stipulated compiles electrostatic risk assessment technologies. A by the NFPA can be used as an evaluation criterion. book regarding the hazard analysis on dust explosions “*4” is to determine the likelihood that a combustible SUMITOMO KAGAKU 2018 2 Electrostatic Risk Assessment for Chemical Plants: Fire and Explosion Prevention Substances Mist Gas/Vapor Liquid Slurry cake Powder Is it Yes non-flammable ? Is its No concentration Yes 25% LEL or less or is its 1 handling area Does its * Yes Zone 2 ? temperature satisfy Does its 2 flammable safety * Yes Yes No margin ? temperature satisfy Is its dust cloud flammable safety non-explosive ? No margin ? No No Is it 1 kg Yes Yes Is its dust cloud or less ? non-explosive ? No No 4 Does it *4 Does it * Yes consist of only large Yes *3 consist of only large Is it applied Yes particle (0.5 mm or larger particle (0.5 mm or larger diameter) ? inerting ? diameter) ? No No No Further Further assessment is required. assessment Go to step 2. is not required. Fig. 1 Flow diagram for electrostatic risk assessment (Step 1) dust-air mixture will form. Generally, when there are advice regarding the safety measures. Thus the great- only particles with the size of 0.5 mm or larger, it can est feature of Sumitomo Chemical’s
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