Ben Ale

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.

Modeling accidents for prioritizing prevention

The Workgroup Occupational Risk Model (WORM) project in the Netherlands is developing a comprehensive set of scenarios to cover the full range of occupational accidents. The objective is to support companies in their risk analysis and prioritization of prevention. This paper describes how the modeling has developed through projects in the chemical industry, to this one in general industry and how this is planned to develop further in the future to model risk prevention in air transport. The core modeling technique is based on the bowtie, with addition of more explicit modeling of the barriers needed for risk control, the tasks needed to ensure provision, use, monitoring and maintenance of the barriers, and the management resources and tasks required to ensure that these barrier life cycle tasks are carried out effectively. The modeling is moving from a static notion of barriers which can fail, to seeing risk control dynamically as (fallible) means for staying within a safe envelope. The paper shows how concepts develop slowly over a series of projects as a core team works continuously together. It concludes with some results of the WORM project and some indications of how the modeling is raising fundamental questions about the conceptualization of system safety, which need future resolution.

A logical model for quantification of occupational risk

Abstract Functional block diagrams (FBDs) and their equivalent event trees are introduced as logical models in the quantification of occupational risks. Although a FBD is similar to an influence diagram or a belief network it provides a framework for introduction in a compact form of the logic of the model through the partition of the paths of the equivalent event tree. This is achieved by consideration of an overall event which has as outcomes the outmost consequences defining the risk under analysis. This event is decomposed into simpler events the outcome space of which is partitioned into subsets corresponding to the outcomes of the initial joint event. The simpler events can be further decomposed into simpler events creating a hierarchy where the events in a given level (parents) are decomposed to a number of simpler events (children) in the next level of the hierarchy. The partitioning of the outcome space is transferred from level to level through logical relationships corresponding to the logic of the model. Occupational risk is modeled trough a general FBD where the undesirable health consequence is decomposed to “dose” and “dose/response”; “dose” is decomposed to “center event” and “mitigation”; “center event” is decomposed to “initiating event” and “prevention”. This generic FBD can be transformed to activity—specific FBDs which together with their equivalent event trees are used to delineate the various accident sequences that might lead to injury or death consequences. The methodology and the associated algorithms have been computerized in a program with a graphical user interface (GUI) which allows the user to input the functional relationships between parent and children events, corresponding probabilities for events of the lowest level and obtain at the end the quantified corresponding simplified event tree. The methodology is demonstrated with an application to the risk of falling from a mobile ladder. This type of accidents has been analyzed as part of the Workgroup Occupational Risk Model (WORM) project in the Netherlands aiming at the development and quantification of models for a full range of potential risks from accidents in the workspace.

Accidents in the construction industry in the Netherlands: An analysis of accident reports using Storybuilder

Abstract As part of an ongoing effort by the Ministry of Social Affairs and Employment of the Netherlands, a research project is being undertaken to construct a causal model for occupational risk. This model should provide quantitative insight into the causes and consequences of occupational accidents. One of the components of the model is a tool to systematically classify and analyse reports of past accidents. This tool ‘Storybuilder’ was described in earlier papers. In this paper, Storybuilder is used to analyse the causes of accidents reported in the database of the Dutch Labour Inspectorate involving people working in the construction industry. Conclusions are drawn on measures to reduce the accident probability. Some of these conclusions are contrary to common beliefs in the industry.

Technical modeling in integrated risk assessment of chemical installations

Abstract This paper presents the technical model of an Integrated Quantitative Risk Assessment method, taking into account management as well as technical design and producing risk level measures. The basic steps of the technical model consist in developing a Master Logic Diagram (MLD) delineating the major immediate causes of Loss of Containment and associated quantitative models for assessing their frequency. Appropriate management models quantify the parameters of the technical model on the basis of the safety management system of the installation. The methodology is exemplified through its application on the risk assessment of a LPG scrubbing tower of an oil refinery. A detailed technical model simulating the response of the system to various initiating events is developed, along with a detailed model simulating the influence of the plant-specific management and organizational practices. The overall effect is quantified through the frequency of release of LPG as a result of a Loss of Containment in scrubbing towers of the refinery.

Living with risk: a management question

Abstract Public authorities started to be really involved in risk management of hazardous materials some 30 years ago. Recent developments have led to fresh attention for this matter and many further developments are underway. The history of risk management and safety regulation is one of strongly variable interest, forgotten lessons and rude awakenings. The impetus exerted by accidents is short lived. Safety cases become documents to satisfy regulation rather than instruments to reduce risk. Deregulation, privatisation, and outsourcing pose new challenges to safety and risk management. Some of the unfortunate side effects have already become apparent. This invariably leads to the next disaster, which will have a striking resemblance to the previous one when abstracted from the immediate technological context. Lessons can be learned if we really want. The question remains: ‘Do we?’.

Risk maps and communication

The use of maps to convey information on the environmental burden and accident risks is increasing. This development is associated with the redefinition of environmental problems in terms of spatial planning. The increased use of maps solves a number of communication problems but also introduces others. The examples given here form the basis for recommendations for future developments.

Managing safety barriers and controls at the workplace

There have been major developments in the analysis, modelling and management of major hazards in the last two decades. European projects such as PRIMA [1], I-Risk [2] and ARAMIS [3] have developed integrated models linking the technical and procedural factors in loss of containment incidents to the management systems needed to implement and guarantee risk control. Whilst there are many issues still to be resolved in making these links quantitatively and in assessing the quality of the management systems and culture, this work has provided systematic and transparent models of the scenarios which have to be controlled. In contrast, workplace safety has far fewer systematic models and approaches. It operates far more on accumulated good practice and generic approaches, which lack precision, consistent coverage and the ability to form the basis for decisions on priority for improvement.

Analysis of the crash of TK 1951 using CATS

On February 25, 2009, flight TK 1951, a Boeing 737-800 operated by Turkish Airlines, crashed approximately 1.5 km before the intended runway at Amsterdam Schiphol Airport. On board were 135 people—128 passengers and 7 crew. Of these 9 were killed and 86 were injured. The aircraft was destroyed. The official inquiry into the cause of the accident is being conducted by the Dutch Safety Board (Onderzoeksraad Voor Veiligheid, OvV). Prior to the accident the Netherlands Ministry of Transport, Public Works and Water Management had already embarked on a project to model the accident genesis of air transport accidents with the aim of quantifying the risks of air traffic and supporting the development of further measures and methods to reduce these risks. In this paper information regarding the accident is confronted with an analysis using the Causal model for Air Transport Safety (CATS). This enables drawing of some more theoretical conclusions about the accident and about the validity of CATS.

Language issues, an underestimated danger in major hazard control?

Language issues are problems with communication via speech, signs, gestures or their written equivalents. They may result from poor reading and writing skills, a mix of foreign languages and other circumstances. Language issues are not picked up as a safety risk on the shop floor by current safety management systems. These safety risks need to be identified, acknowledged, quantified and prioritized in order to allow risk reducing measures to be taken. This study investigates the nature of language issues related danger in literature, by experiment and by a survey among the Seveso II companies in the Netherlands. Based on human error frequencies, and on the contents of accident investigation reports, the risks associated with language issues were ranked. Accident investigation method causal factor categories were found not to be sufficiently representative for the type and magnitude of these risks. Readability of safety related documents used by the companies was investigated and found to be poor in many cases. Interviews among regulators and a survey among Seveso II companies were used to identify the gap between the language issue related dangers found in literature and current best practices. This study demonstrates by means of triangulation with different investigative methods that language issue related risks are indeed underestimated. A recommended coarse of action in order to arrive at appropriate measures is presented.