A logical model for quantification of occupational risk

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

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.     

An analysis of safety control effectiveness

The cost of injuries and “accidents” to an organisation is very important in establishing how much it should spend on safety control. Despite the usefulness of information about the cost of a company's accidents, it is not customary accounting practice to make these data available. Of the two kinds of costs incurred by a company through occupational injuries and accidents, direct costs and indirect costs; the direct costs are much easier to estimate. However, the uninsured costs are usually more critical and should be estimated by each company. The authors investigate a general model to estimate the above costs and hence to establish efficient safety control. One construction company has been a pilot for this study. By analysing actual company data for three years, it is found that the efficient safety control cost should be 1.2–1.3% of total contract costs.     

ARAMIS project: a comprehensive methodology for the identification of reference accident scenarios in process industries

In the frame of the Accidental Risk Assessment Methodology for Industries (ARAMIS) project, this paper aims at presenting the work carried out in the part of the project devoted to the definition of accident scenarios. This topic is a key-point in risk assessment and serves as basis for the whole risk quantification.

The first result of the work is the building of a methodology for the identification of major accident hazards (MIMAH), which is carried out with the development of generic fault and event trees based on a typology of equipment and substances. The term “major accidents” must be understood as the worst accidents likely to occur on the equipment, assuming that no safety systems are installed.

A second methodology, called methodology for the identification of reference accident scenarios (MIRAS) takes into account the influence of safety systems on both the frequencies and possible consequences of accidents. This methodology leads to identify more realistic accident scenarios. The reference accident scenarios are chosen with the help of a tool called “risk matrix”, crossing the frequency and the consequences of accidents.

This paper presents both methodologies and an application on an ethylene oxide storage.     

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 proposed occupational health and safety risk estimation tool for manufacturing systems

There are numerous hazards to be found in almost any workplace. Annually, millions of workers die, are injured or become ill as a result of these occupational hazards. Industrial machines are often involved in these occupational accidents. Because of the demands of regulatory compliance, and the potentially high cost in terms of human suffering and lost production, businesses should place particular emphasis on safety measures. Risk is defined as a combination of the probability of harm and the severity of its consequences. Generally, risk estimation involves examining the hazards associated with a situation or with the use of a machine. A large number of techniques have been proposed for risk estimation, and recent studies have revealed that some of them have serious flaws. The main objective of this paper is to develop a proposed risk assessment tool based on the findings of an earlier study. Our research results constitute a first step towards the integration of occupational health and safety (OHS) concerns into facility planning models which traditionally do not consider OHS. The proposed risk estimation tool is developed based on the characteristics, strengths and weaknesses of 31 existing risk estimation tools, and is then applied to 20 scenarios representing different hazardous situations. To evaluate the performance of the proposed tool, the results were compared with those of other risk estimation tools and confirmed its proposed ability to estimate risk relative to other risk estimation tools.     

A preliminary evaluation of the impact of local accident information on the public perception of road safety

The World Health Organisation (WHO) estimate that road traffic accidents represent the third leading cause of “death and disease” worldwide. A number of countries have, therefore, launched safety campaigns that have reduced their fatalities. In almost every case, however, this reduction has not been matched by a fall in the total frequency of road traffic accidents. Low-severity incidents remain a significant problem. “Attribution error” provides one plausible explanation for this phenomenon. Most drivers believe that they are less likely to be involved in an accident than other motorists. Existing road safety campaigns do little to address this problem; they focus on national and regional statistics that often seem remote from the local experiences of road users. This paper, therefore, describes the design and development of a system to provide the general public with access to information on the location and circumstances of road accidents in a Scottish city. The closing sections describe the initial results from a psychometric study that is intended to determine whether the information provided by such an application will have any impact on individual risk perception.     

An approach to maintenance optimization where safety issues are important

The starting point for this paper is a traditional approach to maintenance optimization where an object function is used for optimizing maintenance intervals. The object function reflects maintenance cost, cost of loss of production/services, as well as safety costs, and is based on a classical cost–benefit analysis approach where a value of prevented fatality (VPF) is used to weight the importance of safety. However, the rationale for such an approach could be questioned. What is the meaning of such a VPF figure, and is it sufficient to reflect the importance of safety by calculating the expected fatality loss VPF and potential loss of lives (PLL) as being done in the cost–benefit analyses? Should the VPF be the same number for all type of accidents, or should it be increased in case of multiple fatality accidents to reflect gross accident aversion?In this paper, these issues are discussed. We conclude that we have to see beyond the expected values in situations with high safety impacts. A framework is presented which opens up for a broader decision basis, covering considerations on the potential for gross accidents, the type of uncertainties and lack of knowledge of important risk influencing factors. Decisions with a high safety impact are moved from the maintenance department to the “Safety Board” for a broader discussion. In this way, we avoid that the object function is used in a mechanical way to optimize the maintenance and important safety-related decisions are made implicit and outside the normal arena for safety decisions, e.g. outside the traditional “Safety Board”.A case study from the Norwegian railways is used to illustrate the discussions.     

EUROCONTROL—Systemic Occurrence Analysis Methodology (SOAM)—A “Reason”-based organisational methodology for analysing incidents and accidents

The Safety Occurrence Analysis Methodology (SOAM) developed for EUROCONTROL is an accident investigation methodology based on the Reason Model of organisational accidents. The purpose of a SOAM is to broaden the focus of an investigation from human involvement issues, also known as “active failures of operational personnel” under Reason's original model, to include analysis of the latent conditions deeper within the organisation that set the context for the event. Such an approach is consistent with the tenets of Just Culture in which people are encouraged to provide full and open information about how incidents occurred, and are not penalised for errors.A truly systemic approach is not simply a means of transferring responsibility for a safety occurrence from front-line employees to senior managers. A consistent philosophy must be applied, where the investigation process seeks to correct deficiencies wherever they may be found, without attempting to apportion blame or liability.     

Modeling and performance analyses of evaporators in frozen-food supermarket display cabinets at low temperatures

This paper presents modeling and experimental analyses of evaporators in “in situ” frozen-food display cabinets at low temperatures in the supermarket industry. Extensive experiments were conducted to measure store and display cabinet relative humidities and temperatures, and pressures, temperatures and mass flow rates of the refrigerant. The mathematical model adopts various empirical correlations of heat transfer coefficients and frost properties in a fin-tube heat exchanger in order to investigate the influence of indoor conditions on the performance of the display cabinets. The model is validated with the experimental data of “in situ” cabinets. The model would be a good guide tool to the design engineers to evaluate the performance of supermarket display cabinet heat exchangers under various store conditions.     

Safety analysis in design—Evaluation of a case study

Safety analysis was applied in the design of a section at a paper mill. The case study involved analysis of layout, transport system, machines, and a number of different activities. The purpose of the analysis was to find measures to decrease occupational accidents. Three years after the installation was finished the occurrence of accidents was investigated. There was a 56% decrease in the number of accidents; the number of working days lost due to accidents was diminished by 75% as compared to 4 years preceding. The results of the safety analysis were also evaluated with respect to the accidents which had occurred. The methods for safety analysis seem to have been efficient in identifying hazards. The general conclusion of the study is that safety analysis can be an effective tool to decrease occupational accident risks.     

Conceptualizing and communicating organizational risk dynamics in the thoroughness–efficiency space

Organizations that design and/or operate complex systems have to make trade-offs between multiple, interacting, and sometimes conflicting goals at both the individual and organizational levels. Identifying, communicating, and resolving the conflict or tension between multiple organizational goals is challenging. Furthermore, maintaining an appropriate level of safety in such complex environments is difficult for a number of reasons discussed in this paper. The objective of this paper is to propose a set of related concepts that can help conceptualize organizational risk and help managers to understand the implications of various performance and resource pressures and make appropriate trade-offs between efficiency and thoroughness that maintain system safety. The concepts here introduced include (1) the thoroughness–efficiency space for classifying organizational behavior, and the various resource/performance and regulatory pressures that can displace organizations from one quadrant to another within this space, (2) the thoroughness–efficiency barrier and safety threshold, and (3) the efficiency penalty that organizations should accept, and not trade against organizational thoroughness, in order to maintain safety. Unfortunately, many accidents share a conceptual sameness in the way they occur. That sameness can be related to the dynamics conceptualized in this paper and the violation of the safety threshold. This sameness is the sad story of the Bhopal accident, the Piper Alpha accident, and score of others. Finally, we highlight the importance of a positive safety culture as an essential complement to regulatory pressure in maintaining safety. We illustrate the “slippery slope of thoroughness” along which organizational behavior slides under the influence of performance pressure, and suggest that a positive safety culture can be conceived of as “pulling this slippery slope” up and preventing the violation of the safety threshold.     

Longitudinal relationship between economic development and occupational accidents in China

The relativity between economic development and occupational accidents is a debated topic. Compared with the development courses of both economic development and occupational accidents in China during 1953–2008, this paper used statistic methods such as Granger causality test, cointegration test and impulse response function based on the vector autoregression model to investigate the relativity between economic development and occupational accidents in China from 1953 to 2008. Owing to fluctuation and growth scale characteristics of economic development, two dimensions including economic cycle and economic scale were divided. Results showed that there was no relationship between occupational accidents and economic scale during 1953–1978. Fatality rate per 10⁵ workers was a conductive variable to gross domestic product per capita during 1979–2008. And economic cycle was an indicator to occupational accidents during 1979–2008. Variation of economic speed had important influence on occupational accidents in short term. Thus it is necessary to adjust Chinese occupational safety policy according to tempo variation of economic growth.     

Study of the compatibility between criteria in a set of materials requirements: Application to a machine tool frame

This contribution to materials selection theory aims at developing methodological methods and tools to analyse a complex set of material requirements with the objective of forecast whether there are materials that can fulfil it, or alternatively, if multi-materials selection is more likely to provide a solution. This “pre-analysis” of requirements examines the two main reasons which may prevent a single material solution: nonuniformity of materials space filling, or intrinsic contradiction between properties.A variety of statistical tools is used, based on Multivariate Analysis Methods as Principal Component Analysis (PCA) and the estimation of density distribution in the materials space. These tools allow to evaluate the “statistical compatibility” between the requirements and the available materials, and provides an estimate of the likelihood to find a single material solution or not. The methodology is applied to the research of a material for a machine tool frame.     

A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength

Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term “design-centered” is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring “child” microstructure, obtained by “parent” microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.     

Tiring job and work related injury road crashes in the GAZEL cohort

The objective was to describe at-work and commuting crashes occurring in a cohort of French employees and to investigate occupational risk factors. The subjects were employees of the French national electricity and gas companies, Électricité de France and Gaz de France (EDF–GDF), who volunteered to join a research cohort (the GAZEL cohort which included 20,625 participants in 1989). Only crashes with injuries were considered. Crashes for the periods 1989–2001 were recorded together with the type of journey (commuting, work, private), the type of road-user, self-estimated responsibility, and injuries sustained by the subject. Annual incidences for gender/age groups and socio-occupational groups were computed for each of the two types of work related crashes. Occupational risk factor analyses were conducted using a Cox proportional hazards regression model with time-dependent covariates adjusting for the main confounders. A total of 146,285 person years at work were observed. Two indicators of self-reported work fatigue were associated with the occurrence of at-work crashes: “nervously tiring work” for males (RR = 1.6, 95% CI [1.1; 2.3]), sustained standing for females (RR = 3.0, 95% CI [1.0; 8.4]), adjusting for health status, location of residence, type of family, transport mode and mileage. As regards crashes while commuting, a self-reported uncomfortable position at work was a risk factor among women (RR = 1.9, 95% CI [1.1; 3.3]). On the other hand, these occupational factors were not linked to road crashes in private trips. Work related road crashes seem then to be a matter for a specific prevention. Preventing employees from becoming exhausted should be considered as the first way to initiate such a prevention.     

The deconstruction of safety arguments through adversarial counter-argument

The project Deconstructive Evaluation of Risk In Dependability Arguments and Safety Cases (DERIDASC) has recently experimented with techniques borrowed from literary theory as safety case analysis techniques [Armstrong. Danger: Derrida at work. Interdiscipl Sci Rev 2003;28(2):83–94. [9]; Armstrong J, Paynter S. Safe systems: construction, destruction, and deconstruction. In: Redmill F, Anderson T, editors. Proceedings of the 11th safety critical systems symposium, Bristol, UK. Berlin: Springer; 2003. p. 62–76. ISBN:1-85233-696-X. [10]]. This paper introduces our high-level framework for “deconstructing” safety arguments. Our approach is quite general and should be applicable to different types of safety argumentation framework. As one example, we outline how the approach would work in the context of the Goal Structure Notation (GSN).     

Identification and classification of dynamic event tree scenarios via possibilistic clustering: Application to a steam generator tube rupture event

This paper illustrates a method to identify and classify scenarios generated in a dynamic event tree (DET) analysis. Identification and classification are carried out by means of an evolutionary possibilistic fuzzy C-means clustering algorithm which takes into account not only the final system states but also the timing of the events and the process evolution. An application is considered with regards to the scenarios generated following a steam generator tube rupture in a nuclear power plant. The scenarios are generated by the accident dynamic simulator (ADS), coupled to a RELAP code that simulates the thermo-hydraulic behavior of the plant and to an operators’ crew model, which simulates their cognitive and procedures-guided responses.A set of 60 scenarios has been generated by the ADS DET tool. The classification approach has grouped the 60 scenarios into 4 classes of dominant scenarios, one of which was not anticipated a priori but was “discovered” by the classifier. The proposed approach may be considered as a first effort towards the application of identification and classification approaches to scenarios post-processing for real-scale dynamic safety assessments.     

The deviation concept in occupational accident control—I: Definition and classification

This paper, presented in two parts, assesses the potentialities and limitations of the deviation concept as applied to occupational accident control. A systems variable is classified as a deviation when its value falls outside a norm. In Part I, a systems model of accidents that incorporates the deviation concept is presented. Theories, models, terms, and taxonomies of the occupational accident research literature are analyzed in relation to this model in order to identify general elements. Theoretical and methodological problems concerning the definition of norms and taxonomies of deviations are discussed. In Part II measures of the significance of deviations with respect to the risk of accidents and criteria for the assessment of methods for the collection of data on deviations are operationalized. Empirical research on relations between deviations and accidents and on methods for data collection are reviewed on the basis of these measures and criteria. It is concluded that the deviation concept provides a valid basis for the design of information systems for the efficient control of accidents in production systems in operation. Considerations for the design of information systems for the collection, storing, processing, and feedback of information on deviations for accident prevention purposes are discussed.     

A re-parameterisation of the Power Model of the relationship between the speed of traffic and the number of accidents and accident victims

This paper presents a re-analysis of the Power Model of the relationship between the mean speed of traffic and road safety. Past evaluations of the model, most recently in 2009, have broadly speaking supported it. However, the most recent evaluation of the model indicated that the relationship between speed and road safety depends not only on the relative change in speed, as suggested by the Power Model, but also on initial speed. This implies that the exponent describing, for example, a 25% reduction in speed will not be the same when speed changes from 100 km/h to 75 km/h as it will when speed changes from 20 km/h to 15 km/h. This paper reports an analysis leading to a re-parameterisation of the Power Model in terms of continuously varying exponents which depend on initial speed. The re-parameterisation was accomplished by fitting exponential functions to data points in which changes in speed and accidents were sorted in groups of 10 km/h according to initial speed, starting with data points referring to the highest initial speeds. The exponential functions fitted the data extremely well and imply that the effect on accidents of a given relative change in speed is largest when initial speed is highest.