ExSys-LOPA for the chemical process industry Adam S. Markowski a, * , M. Sam Mannan b,1 a Process Safety and Ecological Division, Faculty of Process and Environmental Engineering, Technical University of Lodz, 90-133 Lodz, ul. Wolczanska 213, Poland b Mary Kay O’Connor Process Safety Center, Artie McFerrin Department of Chemical Engineering, Texas A&M University System, 3122 TAMU, College Station, TX 77843-3122, USA article info Article history: Received 16 February 2010 Received in revised form 10 May 2010 Accepted 18 May 2010 Keywords: Process industries Risk assessment Expert system LOPA HF alkylation Seveso II Directive abstract The chemical process industries are characterized by the use, processing, and storage of large amounts of dangerous chemical substances and/or energy. Among different missions of chemical plants there are two very important ones, which: 1. provide a safe work environment, 2. fully protect the environment. These important missions can be achieved only by design of adequate safeguards for identified process hazards. Layer of Protection Analysis (LOPA) can successfully answer this question. This technique is a simplified process of quantitative risk assessment, using the order of magnitude categories for initiating cause frequency, consequence severity, and the likelihood of failure of independent protection layers to analyze and assess the risk of particular accident scenarios. LOPA requires application of qualitative hazard evaluation methods to identify accident scenarios, including initiating causes and appropriate safeguards. This can be well fulfilled, e.g., by HAZOP Studies or What-If Analysis. However, those tech- niques require extensive experience, efforts by teams of experts as well as significant time commitments, especially for complex chemical process units. In order to simplify that process, this paper presents another strategy that is a combination of an expert system for accident scenario identification with subsequent application of LOPA. The concept is called ExSys-LOPA, which employs, prepared in advance, values from engineering databases for identification of loss events specific to the selected target process and subsequently a accident scenario barrier model developed as an input for LOPA. Such consistent rules for the identification of accident scenarios to be analyzed can facilitate and expedite the analysis and thereby incorporate many more scenarios and analyze those for adequacy of the safeguards. An asso- ciated computer program is under development. The proposed technique supports and extends the Layer of Protection Analysis application, especially for safety assurance assessment of risk-based determination for the process industries. A case study concerning HF alkylation plant illustrates the proposed method. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Among different missions of chemical plants there are two very important ones, which: 1. provide a safe work environment, 2. fully protect the environment. These important missions can be ach- ieved only by design of adequate safeguards for the existing, identified process hazards. These conditions could be fulfilled by two main approaches: e Experience-based decision of operators and, e Risk-based decisions of operators. Experience-based decisions frequently may be sufficient to ensure safe work conditions, especially for industry with years of experience in their operation. However, the process industries with its complex hazards and uncertainty involved, especially in human activities, can lead to abnormal process conditions that may initiate accident scenarios often developing to major accidents. These were the reasons to introduce regulatory requirements that are based on risk assessment, e.g., Seveso Directive (COMAH, 1996). There are two approaches to process safety risk assessment, which are as follows: 1. a traditional quantitative risk analysis (QRA), where risk measures such as risk contours, F&N curves, and averages of fatality rates are used to present safety assurance, and 2. a semi quantitative risk analysis, like LOPA, where the level of risk is expressed by means of the risk numerical range (CCPS, 2001). The general use of QRA in commercial settings has been somewhat limited, partially due to: the confusion as to how to use these measures to make decisions and the highly complex analysis required to develop the scenario leading to a particular accident. * Corresponding author. Tel./fax: þ48 426313745. E-mail addresses: markowski@wipos.p.lodz.pl (A.S. Markowski), mannan@tamu. edu (M. Sam Mannan). 1 Tel.: þ1 979 862 3985; fax þ1 979 458 1493. Contents lists available at ScienceDirect Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp 0950-4230/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jlp.2010.05.011 Journal of Loss Prevention in the Process Industries 23 (2010) 688e696