When a major chemical accident occurs, emergency response is an important measure to reduce accident losses. Some actions in an emergency response may be more important than others in reducing accident losses, so they need to be carried out as a matter of priority. The impact of the number of emergency personnel on the relationship between emergency response actions and time of emergency response process is analyzed in this paper in the circumstance that the number of responders is not enough to carry out emergency actions with priority at the same time, and a Petri-net based approach is proposed to model and analyze the actions. An emergency response action that needs to consider its priority is divided into two stages, one is to determine the personnel for executing the action, the other is the execution of the action. This division facilitates the handling of dynamic changes in the relationship between actions and differences in start time of the actions. The approach is illustrated by taking the emergency response of on-site emergency personnel of a chemical plant to a fire as an example. The efficiency of the emergency process is analyzed, and for the action of rescuing the wounded, which has the highest priority in the example, the time and the probability when considering the priority of emergency response actions are compared with those when not considering the priority.

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If a fire occurs in an area with multiple installations storing or handling flammable materials, it may escalate from one installation to another to form so-called domino effects. The propagation of fire-induced domino effects has temporal properties due to the heating effect of the thermal radiation of fires. Under the action of thermal radiation, the surrounding installations may be damaged, and the probability of damage can be estimated by Probit models. As a result, the propagation path exhibits characteristics of randomness. As new installations catch fire due to domino effects, the thermal radiation received by a target installation changes, so that the damage probability changes dynamically throughout the accident process. This study aims at further improve the previous study of the matrix modeling approach for fire-induced domino effects by considering the heating process of facilities under fire accidents. The analysis process incorporating the damage probability calculation algorithm is presented. The improved approach is illustrated by the study of two cases.

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Risk assessment can reveal the level of a safety situation which can be very important info for company safety management. Considering the multiple factors in risk assessment of a system and the vagueness nature of many factors, and using the benefits of the Petri-net in modeling and reasoning, a weighted fuzzy Petri-net (WFPN) based risk assessment approach which combines WFPN with the SPA-fuzzy method is proposed in this paper. The SPA-fuzzy method is utilized to establish the membership functions for fuzzy assessment, taking its advantage in comparing identity, contrary and discrepancy features of two different sets. In this study, the WFPN is redefined to model relationships between assessment factors, and the matrix-based fuzzy reasoning algorithm is provided to assess the factors in parallel. The application of the proposed risk assessment approach is illustrated by case studies: the risk assessment of a chemical storage tank area and the ignition accident assessment of hydrogen refueling stations.

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In order to identify and clarify the association between the factors leading to accidents in a petrochemical tank area, this study analyzes investigation reports of 212 petrochemical tank farm accidents and combines this with the “association rule” mining and science related to complex networks. The main risk factors are determined and a risk factor data set is constructed; 75 association rules are extracted from the factor data set based on the Apriori algorithm. Then the obtained association rules are used to construct an accident factors network of the petrochemical storage tank area, and the topology characteristics of the network are further analyzed to reveal the importance of factors. Factors with large node degree, betweenness, and clustering coefficients are obtained, such as “violation of operating regulations”, “high concentration of flammable gas in the air”, “lack of experience and professional skills”, etc. These factors play an important role in the formation and development of accidents. The results also show that the accident cause network of the petrochemical storage tank area has a small average shortest path length and a large cluster coefficient, indicating a relatively close connection between the accident factors. The contributions of this study is not only extracting the hidden relationships among contributory factors to tank farm accidents using association analysis, but also revealing which factors are more important for the tank farm safety through the complex network.@en

Fire is one of the main accident scenarios occurring in chemical and process plants, and it can lead to domino effects due to thermal radiation. Emergency response is necessary to prevent fire escalation, in addition to safety barriers. In major industrial fire accidents, backup is usually required in emergency response, due to the lack of emergency response capacity of a single emergency response department. A method addressing the optimal allocation of emergency response forces, specifically considering the front-line departments, is developed in the present study. The emergency response of the front-line departments can reduce the thermal radiation received by the equipment adjacent to the primary fire and thus prolong the time to failure of the equipment, such that the backups have more time to get to the fire scene. The allocation analysis of emergency response teams is carried out considering the dynamic ttf of an adjacent equipment item resulting from the change in time of the thermal radiation received. A timed colored hybrid Petri-net (TCHPN) approach is proposed to model the emergency response process. The probability of preventing fire escalation is obtained from the TCHPN model and the optimal allocation of firefighting forces is determined. A case study illustrates the proposed approach, two scenarios are compared and results show that if a request for backup can be issued immediately according to the fire state, fewer emergency forces can be deployed on the front line department, such as the reduction from 6 emergency response teams to 3 teams to maintain the success probability of 0.91. The influence of other factors such as the position of fire departments and the layout of tanks on the allocation of emergency forces is also discussed.@en

A fire accident is one the most dangerous accidents that may lead to knock-on effects, especially in the plants dealing with large quantities of hazardous substances. Different from other accidents, e.g., explosions, fires can last certain period of time and the thermal radiations emitted by them have a synergistic effect. At the same time, the heat-up of target installations under the effect of thermal radiation is also a process that takes a certain amount of time. These characteristics make fire induced domino effects a dynamic process. During an emergency response due to a fire accident, emergency personnel may arrive at the fire scene at different times, so they may face different accident situations. In this work, an adaptive timed Petri-net (ATPN) based approach is proposed to model the propagation of fires and perform a dynamic analysis of potential domino effects. The definition of ATPN as well as the enabling and execution rules is provided. Through simulations, not only the probabilities of fires in different installations, but also the probabilities of the fire extension propagated over time can be obtained. An example of a tank farm fire illustrates the approach. Our developed approach for carrying out a dynamic analysis of domino effects is helpful for emergency preparation.@en

Emergency response is an important way to reduce losses after a major industrial accident occurs and mitigation measures should be arranged and analyzed in preparedness. The cooperation in emergency response actions which make up an emergency response process has a significant impact on the efficiency and success rate (or reliability) of emergency response, and improper arrangement of actions may reduce emergency response efficiency. As emergency response is characterized by rapid response, this work studies the success of emergency response based on time analysis. In this paper, cooperation modes of emergency response actions and their time characteristics are analyzed. A timed colored Petri-net (TCPN) based approach is proposed to model the cooperation of the actions and perform time analysis. The proposed approach is illustrated by an example of fire brigades’ response to a tank fire. Simulations are performed and the probabilities of preventing fire escalation under different cooperation modes are analyzed. TCPN based modeling and analysis of emergency response actions are helpful for planning the necessary actions in the preparation of an emergency situation.@en

This chapter introduces a methodology based on Petri net to assess domino effects, emphasizing on probability analysis of higher level domino effects. Based on the definition of basic Petri net and modeling approach, two probabilistic analysis approaches for domino effects are discussed. The first is combining probability with Petri net to form the probabilistic Petri net (PPN), so that probabilities of accidents at any level of a domino effect can be determined through the probability reasoning of PPN. The second is based on the simulation of Petri nets. Each simulation represents a propagation process of a domino effect. In this way, the interaction that may exist in the probability analysis of accidents in a domino effect can be avoided. These two approaches are illustrated by vapor cloud explosion accidents occurring in storage tank area.@en

Accidents resulting in industrial fires in chemical and process installations and in industrial parks where relevant quantities of hazardous substances are stored or processed may cause domino effects. Probit models developed and used in a multitude of studies can provide the probability of equipment failure, but they do not consider the effect of multiple radiation sources, and thus fail to capture the effects of severe scenarios as those where multiple fires start at different times in different units. In the present study, a critical thermal dose for equipment failure is defined. A direct procedure for the calculation of ttf based on the critical thermal dose is then introduced, which is able to account for the time at which the different secondary fires start or are extinguished. This allows considering the effects of the primary and of several secondary fire scenarios in causing a domino effect, updating the time to failure on the basis of the dynamic evolution of multiple fire scenarios. The proposed approach is demonstrated through case-studies addressing fire-induced domino effects in an oil storage tank farm.

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Identifying critical installations in an area containing many chemical installations is important for the safety management of the chemical area. In this study, the area impact degree of chemical installations is defined, which is determined by analyzing the probability of accidents at other installations in the area when an accident occurs at a given installation, and the losses caused by each installation in the event of corresponding accident. Critical installations for area safety can be easily identified by comparing the area impact degree of different installations in the area. An illustrative example demonstrates the proposed approach. Analysis of the area impact degree of 6 tanks in a storage area and identification of more important installations for the safety of the entire area illustrate the applicability of this approach. Furthermore, our novel area importance analyzing approach is also compared with the graph approach.

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Risk assessment is important for plant safety, and fuzzy set theory is useful for such assessment because many risk factors have fuzzy characteristics. In this study, veto factors for risk assessment are taken into account. Weighted fuzzy Petri nets (WFPN) with inhibitor arcs are proposed to model relationships between risk factors and establish the risk assessment structure considering veto factors. Definitions of WFPNs as well as the enabling rule and execution rule are provided. The modeling approach for the assessment combining normal factors with veto items is discussed. The proposed fuzzy risk assessment approach is illustrated by an example of the assessment of production installations and process technology of plants that deal with hazardous chemicals. Veto factors and non-veto factors are presented and the assessment structure based on WFPNs is established. Using the factor data of a plant, an assessment value is obtained through the operation of WFPNs and the verification of the approach is discussed.

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Emergency response was usually not taken into account in the analysis of safety barriers to prevent fire-induced domino effects. When emergency response is considered, in addition to failure events, successful events may also have an impact on fire escalation, and there may be a dependency between pre- and post-events. To model such events and carry out probability analysis, a probabilistic Petri-net (PPN) approach is proposed. The definition of a PPN with the complementary arc and its execution mechanism are provided, and a probability reasoning algorithm reflecting the parallel processing of PPNs is developed. On this basis, a PPN model discussed in two parts for failure analysis of fire escalation prevention is established. The application of the methodology is demonstrated by fire prevention in a chemical storage tank farm, focusing on the influence of fire detection on follow-up actions. In addition to that the fire is not been found, the time at which the fire is found will also have an impact on the success of preventing the fire escalation. The influences of not considering/considering fire detection time are analyzed by the fault tree method and the PPN method, respectively, and there is a difference of about 11% between the results.

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Emergency response is an important measure to reduce the loss of any major fire and prevent its escalation. There may be many fire trucks participating in the fire-fighting at the same time, and the scheduling of them will affect the fire-fighting efficiency and thus, capacity. This work focuses on the cycle process of fighting fire and refilling water of fire trucks, and analyzes and compares the scheduling strategies of the fire trucks. The simulation tool eM-plant is utilized to model the fire-fighting process. In view of the emergency response in relation to a chemical fire accident and to prevent its escalation, strategies in the analysis consider the allocation of fire trucks according to the distance of hydrants, the distribution of fire trucks according to the number of fire hydrants, etc. The results of this paper show that an even distribution of fire trucks leads to a good performance, but can be further adjusted to find a more optimal strategy. This study provides guidance for fire truck scheduling in case of emergency response.

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Historical data analysis shows that escalation accidents, so-called domino effects, have an important role in disastrous accidents in the chemical and process industries. In this study, an agent-based modeling and simulation approach is proposed to study the propagation of domino effects in the chemical and process industries. Different from the analytical or Monte Carlo simulation approaches, which normally study the domino effect at probabilistic network levels, the agent-based modeling technique explains the domino effects from a bottom-up perspective. In this approach, the installations involved in a domino effect are modeled as agents whereas the interactions among the installations (e.g., by means of heat radiation) are modeled via the basic rules of the agents. Application of the developed model to several case studies demonstrates the ability of the model not only in modeling higher-level domino effects and synergistic effects but also in accounting for temporal dependencies. The model can readily be applied to large-scale complicated cases.

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If flammable gas is mixed with air, and the mixture is ignited, it is possible to form a vapor cloud explosion (VCE) which may be very destructive, and easy to trigger a domino effect of accidents because of its large extent of impact. A VCE accident may induce secondary VCE accidents, then tertiary VCE accidents, and so on. This is called the cascading effect of VCE accidents, which requires an understanding of probabilities and propagation patterns to prevent and mitigate the potential damages. In this work, a methodology based on Petri-net is proposed to model the cascading effect of VCE accidents and perform probability analysis, taking the mutual influence between the accidents into account. The deficiency in probability analysis of VCE accidents is discussed. According to the limits of states and their changes which reflect characteristics of VCE propagation, a Petri-net approach is provided for modeling and analysis of VCE cascading effect, and the modeling approach and analysis process of VCE cascading effect are presented. The application and efficacy of the methodology are demonstrated via an example of VCE accidents occurring in a gasoline tank storage area. The results show that the developed methodology can effectively reveal the propagation patterns of VCEs cascading and calculate the respective probabilities of VCE accidents.

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In industrial chemistry, many flammable materials are handled and/or stored in various facilities. It is possible that major fires occur at these facilities possibly leading to domino effects due to the failure of neighboring facilities caused by thermal radiation. It will take a certain time that thermal radiation causes nearby facilities to fail and that a domino effect occurs. The time needed for escalation to take place allows emergency actions as a response to the primary fire to prevent the propagation of the fire. In the present study, a Timed Colored Hybrid Petri-net (TCHPN) based methodology is introduced to evaluate different emergency response actions based on their efficiency in preventing or delaying the propagation of domino effects. A TCHPN model of emergency response to flammable liquid tank fire is established, and a time based analysis of emergency response actions for preventing domino effects is performed. Based on the simulation analysis, the probability of domino effects is calculated and response actions are compared.

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Knock-on effects or so-called domino effects in the process industries may cause much greater losses than merely a primary event. Probability analysis of accidents resulting from domino effects is important for risk assessment. However, for the accident occurrence of a unit there may be mutual influences between the units in the area influenced by the accidents due to a domino effect, and this makes the calculation of probabilities of the accidents rather difficult. A matrix-based approach is proposed to model the influences between units influenced by a fire-induced domino effects, and the analysis approach for accident propagation as well as a simulation-based algorithm for probability calculation of accidents is provided. The synergistic effect of thermal radiation is taken into account during the accident propagation. The proposed approach is flexible to model and analyze domino effects in various conditions of primary fires by only changing the value of the initial matrix indicating the fire states. Two examples illustrate analyzing the fire propagation among tanks storing flammable liquids. The results show that this approach is simple but effective for offering an insight in the accident propagation process and for knowing the probabilities of equipment getting on fire.

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The propagation of accidents among process units may cause amplification of accident magnitude, resulting in a domino effect chain. Several catastrophic accidents occurred in the process and chemical industry presented these features. Hence, research efforts have been given to the analysis of the domino effects in order to enhance prevention and mitigation strategies. In this work, challenges of analysing domino effects in the chemical industries are discussed, highlighting that quantitative analytic approaches suffer from the complexity on assessing domino effects, especially when dealing with simultaneous accidents propagating among multiple units. Therefore, a bottom-up modelling approach, namely, the agent based modelling and simulation (ABM&S) approach, is introduced for analysing domino effects. Moreover, a prototype model for assessing domino effects in the chemical industries by using agent based modelling and simulation (DAMS) is given and further extensions of the prototype model is also discussed, highlighting the potential benefits.@en

As large amounts of hazardous chemicals are handled in the petrochemical industries, the plants in these industries are attractive for terrorists because they can cause great losses and have important social impact. Security risk assessment is important to determine the risk level of a plant in order to take targeted measures to reduce the security risk. Based on Security Risk Factor Table (SRFT) which covers the essential elements for the security risk assessment, a weighted fuzzy Petri-net (WFPN) based security risk assessment approach is proposed in this paper. This approach can easily model different relationships between the risk factors as well as their importance, and use the analysis method of Petri-nets to perform the risk assessment. Two WFPN models of security risk assessment are established according to different relationships between the factors, and a matrix operation based security risk inference method is developed. An illustrative example is used to demonstrate the approach. The results show that correctly determining and modeling the relationships among the risk factors is important to assess the security risk.

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During an emergency response after an accident, emergency actions often require certain emergency resources. The adequate use, or the lack thereof, of emergency resources will affect the efficiency and even the success of emergency response activities or processes. Different emergency actions form certain relationships on using emergency resources. The cooperation modes of emergency actions on using resources are analyzed in this paper, and Petri-net models for these cooperation modes are provided. On this basis, an approach to detect emergency action conflicts resulting from resource-use is proposed. For conflicts caused by limited resources sharing, the queuing system which is modeled by a Petri-net and integrated into the model of emergency actions, is adopted to avoid conflicts. An example of an emergency response activity related with a fire accident is used to demonstrate the modeling method. The conflicts are analyzed and a queuing system is used to avoid simultaneously employing the same resource.

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