Introduction to Process Risk Management (PRM) – Dow Chemical’s Hierarchical Risk Analysis Method

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1. Process Risk Management Standard (PAMS) Dow Chemical applies the theory of process risk management to corporate safety management, formulating its own corporate standards and promoting the Dow Chemical Process Risk Management Standard widely within its companies. Production line managers within enterprises achieve the goal of continuously reducing risks by using and implementing risk management techniques ； Apply systematic risk management to assess and control hazardous substances, processes, and activities that may cause harm to people or damage to property and the environment. 1) Purpose of implementing process risk management standards The purpose is to carry out process risk management for sudden hazards caused by fires, explosions, or chemical leaks, to establish risk assessment requirements throughout the entire lifecycle of factory facilities, and to identify, analyze, and prioritize risks. 　　2) Scope of application of process risk management standards This standard applies to investment projects, existing facilities and their modifications, mergers and joint ventures controlled by Dow, as well as sudden process hazards in market development or semi-commercial facilities. 　　2. Main contents of the process risk management standards The main tools for process risk management standards are 5: Reactive chemicals – Process Hazard Analysis (RC-PHA), Fire and Explosion Index (F&EI), Chemical Exposure Index (CEI), Structured Hazard and Operability Study (HAZOP), and Layer of Protection Analysis (LOPA). 　　1) Reactive Chemicals—Process Hazard Analysis (RC-PHA) Review The Reactive Chemicals—Process Hazard Analysis (RC-PHA) is a 1 to 2-day review activity carried out by a multidisciplinary team, covering aspects such as process chemistry, the completeness of the risk management plan, assumptions for worst-case scenarios and the establishment of key safeguards, historical accidents, process changes, training and education programs, questionnaires, and the implementation of recommendations from previous reviews. Dow Chemical requires that all plants with capital investment of over $50,000 be inspected every 3 to 5 years, and it mandates that all new production managers conduct an RC-PHA inspection 90 days after taking office. In addition, Dow Chemical is also actively promoting the establishment of global standards for chemical reactivity. 　　2) Dow Chemical Fire and Explosion Index (F&EI). The Dow Chemical Fire and Explosion Index method is a technique for analyzing the fire and explosion risks associated with chemical processing processes and production facilities. It was developed based on accidents that have occurred in companies other than Dow Chemical over the years, and is primarily used during the design phase and in periodic preliminary reviews, focusing on areas where the risks are highest. This method uses a calculation table to classify the risk of other related process steps based on the calculation results. Its main advantages are: it helps to take into account equipment layout issues during the design process, encourages inherently safer design, and leads to more thorough reviews. 　　3) Dow Chemicals Exposure Index (CEI) The CEI is a simple method for predicting vapor diffusion, designed primarily to address potential serious injuries in industrial accidents. It is based on the Emergency Response Planning Guide (ERPG) concentrations, and is applicable to pipeline ruptures, container and tank ruptures resulting in spills, as well as other standard accident scenarios identified through HAZOP and empirical analysis. According to industrial health and safety standards, based on the concentration of chemicals, three different concentration levels are defined. Level 1 (minimum), Level 2 (medium), Level 3 (maximum). 　　4) Structured scenario analysis Structured scenario analysis is a systematic method for analyzing the hazards associated with a device by examining the process step by step (line by line). Various methods can be used, such as HAZOP, fault hypothesis analysis, checklists, etc., to conduct structured scenario analysis, among which HAZOP is the most commonly used. In accordance with the requirements of risk management standards for high-risk (process) operations, CEI and F&EI are used for high-risk target areas. This method performs well in identifying causal pairs. Local design criteria for most process changes. Dow Chemical uses third-party software (PHA-Pro provided by Dyadem) for structured scenario analysis. 　　5) Layer of Protection Analysis (LOPA) Layer of Protection Analysis (LOPA) is a semi-quantitative analysis method that serves as a bridge between qualitative analysis and fully quantitative analysis methods. Protection layer analysis is a risk analysis technique that evolved from event tree analysis. Starting from the initial event, it determines whether safety protection measures are effective (successful or failed) throughout the progression of an accident, checks whether the analysis meets the required safety level, and proposes corresponding safety measures to reduce risks to an acceptable level. Compared to other analysis methods, protective layer analysis has the following advantages: it requires less time than quantitative risk assessment (QRA) ； It can be confirmed that a protective layer effective against various triggering events is present ； Resources for risk reduction can be allocated effectively. Deficiencies can be compensated for by the safety instrument system. Due to the aforementioned advantages of LOPA, Dow Chemical has been actively promoting and using layer of protection analysis in its subsidiaries in recent years, while structured hazard analysis (HAZOP, fault hypothesis analysis, checklists) is used less frequently. Dow Chemical’s technical personnel also combine layer of protection analysis with fault tree analysis in order to obtain more accurate results. 　　3. Overview of Dow Chemical’s Process Risk Management (PRM) Due to the differences in risk analysis methods, varying amounts of time and resources are required, as well as different levels of expertise and management skills. It is neither possible nor necessary to apply complex risk analysis methods to all facilities and all substances. To make more effective use of skill resources, Dow Chemical’s process risk management primarily employs a hierarchical risk analysis approach, with the entire process divided into four levels. 　　1) The first layer involves conducting process hazard analyses for all facilities, using methods such as the Fire and Explosion Index (F&EI), Chemical Exposure Index (CEI), LOPA target values, and the Reactive Chemicals – Process Hazard Analysis (RC/PHA) questionnaire. 　　2) The second layer involves conducting additional risk assessments for specific unit operations of the facilities, using methods such as causal pair analysis, LOPA (Dow Chemical conducts HAZOP analyses on all new processes), explosion shock (building overpressure) assessment, and structured hazard analysis (HAZOP). 3) The third layer involves an enhanced risk assessment of the target process, primarily focusing on the identification through quantitative risk assessment (QRA). 　　4) The fourth layer involves selecting a few devices for qualitative and quantitative risk assessment. Selection is made based on the combinations analyzed from the results and the frequency of accidents; quantitative risk assessment focuses on high-risk activities. 　　The sequence of the analysis process is from simple methods to more complex analyses, from lower levels of management to higher levels of management, and from all substances to a select few. Adopt a progressive approach, applying more complex risk analysis tools in high-risk analyses.