Event Sequence Diagram Research Articles

Further development of a Causal model for Air Transport Safety (CATS): Building the mathematical heart

The development of the Netherlands international airport Schiphol has been the subject of fierce political debate for several decades. One of the considerations has been the safety of the population living around the airport, the density of which has been and still is growing. In the debate about the acceptability of the risks associated with the air traffic above, The Netherlands extensive use has been made of statistical models relating the movement of airplanes to the risks on the ground. Although these models are adequate for the debate and for physical planning around the airport, the need has arisen to gain a more thorough understanding of the accident genesis in air traffic, with the ultimate aim of improving the safety situation in air traffic in general and around Schiphol in particular. To this aim, a research effort has started to develop causal models for air traffic risks in the expectation that these will ultimately give the insight needed. The concept was described in an earlier paper. In this paper, the backbone of the model and the way event sequence diagrams, fault-trees and Bayesian belief nets are linked to form a homogeneous mathematical model suitable as a tool to analyse causal chains and quantify risks is described.

Incorporating organizational factors into Probabilistic Risk Assessment (PRA) of complex socio-technical systems: A hybrid technique formalization

This paper is a result of a research with the primary purpose of extending Probabilistic Risk Assessment (PRA) modeling frameworks to include the effects of organizational factors as the deeper, more fundamental causes of accidents and incidents. There have been significant improvements in the sophistication of quantitative methods of safety and risk assessment, but the progress on techniques most suitable for organizational safety risk frameworks has been limited. The focus of this paper is on the choice of “representational schemes” and “techniques.” A methodology for selecting appropriate candidate techniques and their integration in the form of a “hybrid” approach is proposed. Then an example is given through an integration of System Dynamics (SD), Bayesian Belief Network (BBN), Event Sequence Diagram (ESD), and Fault Tree (FT) in order to demonstrate the feasibility and value of hybrid techniques. The proposed hybrid approach integrates deterministic and probabilistic modeling perspectives, and provides a flexible risk management tool for complex socio-technical systems. An application of the hybrid technique is provided in the aviation safety domain, focusing on airline maintenance systems. The example demonstrates how the hybrid method can be used to analyze the dynamic effects of organizational factors on system risk.

QRAS—the quantitative risk assessment system

This paper presents an overview of QRAS, the Quantitative Risk Assessment System. QRAS is a PC-based software tool for conducting Probabilistic Risk Assessments (PRAs), which was developed to address risk analysis needs held by NASA. QRAS is, however, applicable in a wide range of industries. The philosophy behind the development of QRAS is to bridge communication and skill gaps between managers, engineers, and risk analysts by using representations of the risk model and analysis results that are easy to comprehend by each of those groups. For that purpose, event sequence diagrams (ESD) are being used as a replacement for event trees (ET) to model scenarios, and the quantification of events is possible through a set of quantification models familiar to engineers. An automated common cause failure (CCF) modeling tool further aids the risk modeling. QRAS applies BDD-based algorithms for the accurate and efficient computation of risk results. The paper presents QRAS' modeling and analysis capabilities. The performance of the underlying BDD algorithm is assessed and compared to that of another PRA software tool, using a case study extracted from the International Space Station PRA.

The British Airways human factors reporting programme

Abstract This paper describes three safety programmes that provide BA flight operations with feedback on operational quality. Two of these are flight data recording and air safety reporting. These earlier programmes are described primarily to set in context the development of the most recent of the three, the human factors reporting programme (HFR). This is a confidential programme that records and analyses data using a distinctly different process from most reporting programmes. It requests not only information about ‘What’ happened in an event but ‘Why’ the event occurred and ‘How’ the crew dealt with the problem. Analysis uses ‘factors’ describing crew actions and the influences on crew actions. Actions and influences can describe safety positive as well as negative events and the analysis produces causal event sequence diagrams of each reported event. The paper describes these processes and offers some illustrative examples taken from the database.

Identification of missing scenarios in ESDs using probabilistic dynamics

Abstract The event sequence diagram (ESD) framework can be used to qualitatively represent dynamic scenarios. The solution of ESDs can be performed in an analytical manner. Since the construction of ESDs has some inherent analyst dependence, there is scope for omitting scenarios due to certain simplifying assumptions. This is one of the prime drawbacks of the ESD framework. This paper presents an approach for identifying missing scenarios by combining ESDs with probabilistic dynamics. The approach also helps in reducing the variance of a Monte Carlo simulation procedures.

The mathematical formulation for the event sequence diagram framework

Abstract The Event Sequence Diagram (ESD) framework allows modeling of dynamic situations of interest to PRA analysts. A qualitative presentation of the framework was given in an earlier article. The mathematical formulation for the components of the ESD framework is described in this article. The formulation was derived from the basic probabilistic dynamics equations. For tackling certain dynamic non-Markovian situations, the probabilistic dynamics framework was extended. The mathematical treatment of dependencies among fault trees in a multi layered ESD framework is also presented.

The Event Sequence Diagram framework for dynamic Probabilistic Risk Assessment

Dynamic methodologies have become fairly established in academia. Their superiority over classical methods like Event Tree/Fault Tree techniques has been demonstrated. Despite this, dynamic methodologies have not enjoyed the support of the industry. One of the primary reasons for the lack of acceptance in the industry is that there is no easy way to qualitatively represent dynamic scenarios. This paper proposes to extend current Event Sequence Diagrams (ESDs) to allow modeling of dynamic situations. Under the proposed ESD representation, ESDs can be used in combination with dynamic methodology computational algorithms which will solve the underlying probabilistic dynamics equations. Once engineers are able to translate their knowledge of the system dynamics and accident evolution into simple ESDs, usage of dynamic methodologies will become more popular.

Operational decision alternatives in failure situations of standby safety systems— development of probabilistic approach and PC program TeReLCO

Abstract The TeReLCO software package provides advanced tools for the risk based evaluation of alternative test and repair arrangements and limiting conditions for operation in standby safety systems. The methodological key features include event sequence modeling by use of an Event Sequence Diagram incorporating imbedded state submodels. This enhances the modeling of operational dependences over phased missions, recovery paths and other types of time dependences. Several risk variables related to the operational alternatives and problem resolution are quantified: risk frequency, cumulative risk over predicted or given scenario, expected risk over given scenario or plant lifetime. These are graphically displayed to enhance comparisons and sensitivity considerations.

Design-safety enhancement through the use of hazard and risk analysis

The application of qualitative and quantitative hazards/risk analysis methods is discussed. Two examples of both qualitative and quantitative methods are discussed. The relative advantages of each, as well as relative manpower requirements for their application, are examined. The two qualitative analysis examples are: (1) hazards and operability (HAZOP) analysis, based on the conceptual design analysis of an offshore gas-processing platform, and (2) a qualitative fault-tree analysis based on a design review of a land-based oil-processing facility. The two quantitative analysis examples are: (1) the use of event sequence diagrams for the risk analysis of a batch chemical-operation plant, and (2) an event-tree analysis relative to the consequences of the loss of electric power for the same batch plant. In these examples, design operations and maintenance-safety enhancements that have been implemented are identified. >