Nijs Jan Duijm

Safety-barrier diagrams as a safety management tool

Abstract Safety-barrier diagrams and “bow-tie” diagrams have become popular methods in risk analysis and safety management. This paper describes the syntax and principles for constructing consistent and valid safety-barrier diagrams. The latters relation to other methods such as fault trees and Bayesian Networks is discussed. Important advantages of safety-barrier diagrams as compared to other graphical risk-analysis methods are, firstly, the relative simplicity that supports communication with non-expert stakeholders and, secondly, the focus on deliberately inserted safety systems that supports the management and maintenance of these systems. Safety-barrier diagrams provide a useful framework for an electronic data structure that integrates information from risk analysis with operational safety management.

Risk terminology—a platform for common understanding and better communication

The sciences analyzing and describing risks are relatively new and developing, and the associated terminologies are developing as well. This has led to ambiguity in the use of terms, both between different risk sciences and between the different parties involved in risk debates. Only recently, major vocabularies have been compiled by authoritative agencies. Some of these vocabularies are examined and explained based on a division into fundamental and action oriented risk terms. Fundamental terms are associated with description and characterization of the chemical, biological and physical processes leading from risk source(s) to possible consequences/effects. The approach to these terms is based on a cause-effect skeleton. The action oriented terms cover administrative, scientific, sociological, etc. processes associated with the work of identifying, characterizing, regulating and communicating risks in the society, and their internal connection and iterative character have been illustrated. Focus is laid on engineering and toxicological risks, but to some extent, the thoughts presented may be extrapolated to other areas. Differences in applied terminology probably cannot be eliminated, but they can be identified and clarified for better understanding. With the present paper, the authors hope to contribute to reducing the probability of derailing risk discussions from the risk issue itself.

Supporting decision makers in land use planning around chemical sites. Case study: expansion of an oil refinery.

An approach for supporting decisions on land use around chemical sites - along with a software decision support system (DSS) - based on multi-criteria decision analysis (MCDA; and particularly on the establishment of the set of efficient solutions and letting the final selection depend on local procedures and value tradeoffs) is being illustrated through a case study where five alternative expansions of a refinery are considered along with the existing situation. Alternative land use plans are based on combinations of alternative uses of specific land cells coupled with alternative expansion options. Criteria for evaluating alternative land use plans are the potential loss of life (PLL), the noise levels and the economic benefit resulting for each specific land use plan.

Evaluating and Managing Safety Barriers in Major Hazard Plants

The European ARAMIS project (Hourtolou and Salvi, 2003) is developing an integrated approach to the modelling and management of major hazard risks for major hazard plants. Central to the model being used is the concept of safety functions and barriers.

Airborne releases from fires involving chemical waste : a multidisciplinary case study

A multidisciplinary study of fires in chemical waste at a Danish chemical company has been carried out in order to estimate the concentrations of combustion products in the surroundings. The first part of the study addressed the characterisation of the waste and the assessment of fire cases which formed the basis for the experimental work and determination of fire effluents. The combustion experiments were carried out using a tubular furnace, following DIN 53436. Secondly, the source term concentrations were estimated, and calculations of plume rise and dispersion of combustion products in the surroundings were performed. Finally, an uncertainty assessment has been carried out for each part of the study. For some of the issues the uncertainties are described qualitatively and for others the uncertainties are expressed quantitatively.

Safety-barrier diagrams

Safety-barrier diagrams and the related so-called ‘bow-tie’ diagrams have become popular methods in risk analysis. This paper describes the syntax and principles for constructing consistent and valid safety-barrier diagrams. The relation of safety-barrier diagrams to other methods such as fault trees and Bayesian networks is discussed. A simple method for quantification of safety-barrier diagrams is proposed. It is concluded that safety-barrier diagrams provide a useful framework for an electronic data structure that integrates information from risk analysis with operational safety management.

Modelling of Safety Barriers Including Human and Organisational Factors to Improve Process Safety

It is believed that traditional safety management needs to be improved on the aspect of preparedness for coping with expected and unexpected deviations, avoiding an overly optimistic reliance on safety systems. Remembering recent major accidents, such as the Deep Water Horizon, the Texas City explosion, and the Mont Blanc Tunnel Fire, such an approach may have helped to maintain the integrity of the designed provisions against major deviations resulting in these disasters. In order to make this paradigm operational, safety management and in particular risk assessment tools need to be refined. A valuable approach is the inclusion of human and organisational factors into the simulation of the reliability of the technical system using event trees and fault trees and the concept of safety barriers. This has been demonstrated e.g. in the former European research project ARAMIS (Accidental Risk Assessment Methodology for IndustrieS, see Salvi et al 2006). ARAMIS employs the bow-tie approach to modelling hazardous scenarios, and it suggests the outcome of auditing safety management to be connected to a semi-quantitative assessment of the quality of safety barriers. ARAMIS discriminates a number of different management issues such as competence management, dealing with conflicts, management of maintenance and inspection, and management of procedures. Shortcomings in these management processes effectuate increased probabilities of failure-on-demand (PFD) of the safety barriers, depending on the type of safety barrier (passive, automated, or involving human action). Such models are valuable for many purposes, but are difficult to apply to more complex situations, as the influences are to be set individually for each barrier. The approach described in this paper is trying to improve the state-of-the–art, and it is based on the understanding that certain human and organisational factors may be seen as a kind of common cause failures that influence the performance of several barriers. Therefore, the model links the performance of a barrier with the necessary set of specific activities to maintain and/or to control that barrier. These specific activities are executed within one of the aforementioned management processes, and the efficiency of the activity will depend on the quality of this management process.

Demonstration of risk profiling for promoting safety in SMEs

Purpose – The purpose of this paper is to identify and assess the risks and potential risks that may lead to accidents. It aims to look at how to improve risk assessment within SMEs for the benefit of all staff.Design/methodology/approach – The research included results from a Dutch project which identifies accident risks and safety barriers that are presented in a huge database and risk calculator. The method was first to develop a simple way of accessing this enormous amount of data, second, to develop a tool to observe risks and safety barriers in SMEs and to investigate the usefulness of the developed tools in real life, third, to collect data on risks and safety barriers in SMEs for two occupations by following 20 people for three days each and to create a risk profile for each occupations.Findings – The result is a simple way to go through all types of risks for accidents – a tool for risk observations for external safety experts, and useful for SMEs and for risk profiles for two occupations. Finall...

Process Risk Assessment using Dynamic Simulation of Scenarios

Process plants may be very complex and may combine various processes in close proximity. Hence, the response to accidents may easily grow complex. Traditionally, after gathering and getting acquainted with the plants technical information, risk is analysed in prescribed steps starting with hazard identification, description of accident scenarios and using the conventional approach to develop static event trees for events following a loss of containment. Modelling the impacts and consequences needs models to describe the release, dispersion and effect of the hazardous material, as well as models for predicting the egress time of people, response times of detectors and other safety equipment. A common assumption is the independence of these models and their sequential treatment, but often the consequences and effects are mutually dependent. The prediction of the consequences and effects are deterministic assignments applying simplified engineering models with averaged/expected values as input to account for the characteristics of the system, e.g. describing the physical and environmental phenomena and workers responses. The size of the release and dispersion depends on technical and environmental parameters. Ignition sources may be permanent or temporarily present at various locations near the release. The response times of detectors may be dependent on the velocity of cloud spread. The available save egression time depends on these parameters. Such dynamics are easily modelled using Discrete Event Simulation (DES) of the scenarios, which is a Monte Carlo type method. The paper describes the application of DES to conduct the analysis part of a risk assessment that enables better time resolution in the modelling of the specific scenarios, simulate the interactions between concurrent chains of events under the hazardous scenarios, and produce probabilistic risk measures. The outcome provides possibilities to structure the results in a comprehensive way. Scenarios with severe consequences can be ‘played back’ to learn from them and can be animated, which apart from the learning effect provides a new way of validation.