A method for identifying instrument faults in nuclear power plants possibly leading to wrong situation assessment

In this paper, we propose a method for identifying instrument faults that could potentially affect an operators’ situation assessment capability in nuclear power plants (NPPs), an issue which has received a lot of attention recently. In the proposed method, patterns of selected plant parameter trends in selected plant states and NPP operators’ patterns of selected plant parameter trends in selected plant states are analyzed, and a comparison between the two kinds of patterns is performed to identify instrument faults which could potentially affect a NPP operators’ capability to correctly assess a plant's conditions. An example application is presented to demonstrate how the proposed method can be used to identify the possibilities of operators’ developing a wrong situation assessment because of instrument faults and to identify the corresponding safety concerns. We conclude that in order to get more accurate results, an analysis with a full-scope NPP simulator and interviews with NPP operators will be necessary.     

Development of the step complexity measure for emergency operating procedures using entropy concepts

For a nuclear power plant (NPP), symptom-based emergency operating procedures (EOPs) have been adopted to enhance the safety of NPPs through reduction of operators’ workload under emergency conditions. Symptom-based EOPs, however, could place a workload on operators because they have to not only identify related symptoms, but also understand the context of steps that should be carried out. Therefore, many qualitative checklists are suggested to ensure the appropriateness of steps included in EOPs. However, since these qualitative evaluations have some drawbacks, a quantitative measure that can roughly estimate the complexity of EOP steps is imperative to compensate for them.In this paper, a method to evaluate the complexity of an EOP step is developed based on entropy measures that have been used in software engineering. Based on these, step complexity (SC) measure that can evaluate SC from various viewpoints (such as the amount of information/operators’ actions included in each EOP step, and the logic structure of each EOP step) was developed.To verify the suitableness of the SC measure, estimated SC values are compared with subjective task load scores obtained from the NASA-TLX (task load index) method and step performance time obtained from a full scope simulator. From these comparisons, it was observed that estimated SC values generally agree with the NASA-TLX scores and step performance time data. Thus, it could be concluded that the developed SC measure would be considered for evaluating SC of an EOP step.     

The effect of two complexity factors on the performance of emergency tasks—An experimental verification

It is well known that the use of procedures is very important in securing the safety of process systems, since good procedures effectively guide human operators by providing ‘what should be done’ and ‘how to do it’, especially under stressful conditions. At the same time, it has been emphasized that the use of complicated procedures could drastically impair operators’ performance. This means that a systematic approach that can properly evaluate the complexity of procedures is indispensable for minimizing the side effects of complicated procedures. For this reason, Park et al. have developed a task complexity measure called TACOM that can be used to quantify the complexity of tasks stipulated in emergency operating procedures (EOPs) of nuclear power plants (NPPs). The TACOM measure consists of five sub-measures that can cover five important factors making the performance of emergency tasks complicated. However, a verification activity for two kinds of complexity factors—the level of abstraction hierarchy (AH) and engineering decision (ED)—seems to be insufficient. In this study, therefore, an experiment is conducted by using a low-fidelity simulator in order to clarify the appropriateness of these complexity factors. As a result, it seems that subjects’ performance data are affected by the level of AH as well as ED. Therefore it is anticipate that both the level of AH and ED will play an important role in evaluating the complexity of EOPs.     

The effect of safety climate on seafarers’ safety behaviors in container shipping

This study empirically examined safety climate and its effects on safety behaviors from seafarers’ perceptions in the container shipping context. Research hypotheses were formulated and tested using survey data collected from 608 seafarers working on 124 vessels belonging to 13 of the top 20 global container carriers. A structural equation model was used to examine the effect of safety climate dimensions, namely, safety policy, perceived supervisor safety behavior, and safety management, on safety behavior. The results revealed a positive association between safety climate and seafarers’ safety behavior. The contribution of the study findings to the development of safety climate theory and their managerial implications for vessel safety in shipping operations are discussed.     

Prospect theory based estimation of drivers’ risk attitudes in route choice behaviors

This paper applied prospect theory (PT) to describe drivers’ route choice behavior under Variable Message Sign (VMS), which presented visual traffic information to assist them to make route choice decisions. A quite rich empirical data from questionnaire and field spot was used to estimate parameters of PT. In order to make the parameters more realistic with drivers’ attitudes, they were classified into different types by significant factors influencing their behaviors. Based on the travel time distribution of alternative routes and route choice results from questionnaire, the parameterized value function of each category was figured out, which represented drivers’ risk attitudes and choice characteristics. The empirical verification showed that the estimates were acceptable and effective. The result showed drivers’ risk attitudes and route choice characteristics could be captured by PT under real-time information shown on VMS. For practical application, once drivers’ route choice characteristics and parameters were identified, their route choice behavior under different road conditions could be predicted accurately, which was the basis of traffic guidance measures formulation and implementation for targeted traffic management. Moreover, the heterogeneous risk attitudes among drivers should be considered when releasing traffic information and regulating traffic flow.     

OPERA—a human performance database under simulated emergencies of nuclear power plants

In complex systems such as the nuclear and chemical industry, the importance of human performance related problems is well recognized. Thus a lot of effort has been spent on this area, and one of the main streams for unraveling human performance related problems is the execution of HRA. Unfortunately a lack of prerequisite information has been pointed out as the most critical problem in conducting HRA. From this necessity, OPERA database that can provide operators’ performance data obtained under simulated emergencies has been developed. In this study, typical operators’ performance data that are available from OPERA database are briefly explained. After that, in order to ensure the appropriateness of OPERA database, operators’ performance data from OPERA database are compared with those of other studies and real events. As a result, it is believed that operators’ performance data of OPERA database are fairly comparable to those of other studies and real events. Therefore it is meaningful to expect that OPERA database can be used as a serviceable data source for scrutinizing human performance related problems including HRA.     

Parametric instability of functionally graded beams with an open edge crack under axial pulsating excitation

This paper studies the parametric instability of functionally graded beams with an open edge crack subjected to an axial pulsating excitation which is a combination of a static compressive force and a harmonic excitation force. It is assumed that the materials properties follow an exponential variation through the thickness direction. Theoretical formulations are based on Timoshenko beam theory and linear rotational spring model. The governing equations of motion are derived by using Hamilton’s principle and transformed into a set of Mathieu equations through Galerkin’s procedure. The natural frequencies with different end supports are obtained. The boundary points on the unstable regions are determined by using Bolotin’s method. Numerical results are presented to highlight the influences of crack location, crack depth, material property gradient, beam slenderness ratio, compressive load, and boundary conditions on both the free vibration and parametric instability behaviors of the cracked functionally graded beams.     

Elastic bending analysis of bilayered beams containing a gradient layer by an alternative two-variable method

Aifantis’s strain gradient elasticity theories and Zhang’s two-variable method are used to study elastic bending problems of bilayered micro-cantilever beams, containing a gradient layer, subjected to a transverse concentrated load. The differential element method is used to obtain differential governing equations. The variational method is employed to overcome the difficulty in deriving nonlocal natural boundary conditions, which could not be automatically fulfilled in gradient theories, not like that in classical theories. Then the differential governing equations subjected to the related boundary conditions are solved analytically to obtain the deformation field, which could be degenerated to that in classical elasticity theories. The gradient parameters of epoxy polymeric resin and copper single crystals in the present model are provided by fitting Lam’s and Demir’s experiments. The influences of length and layer thickness on normalized deflection and effective rigidity are discussed in a representative case of a Cu/epoxy polymeric resin beam. Results show that size effect makes the effective rigidity vary more prominently with shorter beam length or larger layer thickness. For given materials, although size effect exists, classical elasticity theories are still valid in some particular combination of three geometric parameters: beam length, upper and lower layer thicknesses.     

Normal mode solutions of linear dynamic field theories using Green's extended identity

Normal mode solutions of certain classes of linear, spatially time-invariant, self-adjoint and nonself-adjoint differential operators, with inhomogéneous boundary conditions in a finite region of arbitrary shape, are obtained by the use of Green's extended identity [1] in conjunction with the eigenvalue problems associated with the differential operators. Thus, continuum field theories belonging to these classes of operators, which encompass arbitrary (a) material and geometrical parameters, (b) spatial and time-dependent boundary conditions, (c) initial conditions can be solved by this technique. This is illustrated by the determination of the transient response of an axisymmetric, finite, thick transversely isotropic elastic hollow cylinder under inhomogeneous boundary conditions of all types (both pure and mixed). It is also shown that the displacement (separation-of-variables, integral transforms) and acceleration (Mindlin-Goodman, Williams) methods currently used for solutions of dynamic problems can both be derived from Green's extended identity.     

A computational model for evaluating the effects of attention, memory, and mental models on situation assessment of nuclear power plant operators

Operators in nuclear power plants have to acquire information from human system interfaces (HSIs) and the environment in order to create, update, and confirm their understanding of a plant state, as failures of situation assessment may cause wrong decisions for process control and finally errors of commission in nuclear power plants. A few computational models that can be used to predict and quantify the situation awareness of operators have been suggested. However, these models do not sufficiently consider human characteristics for nuclear power plant operators.In this paper, we propose a computational model for situation assessment of nuclear power plant operators using a Bayesian network. This model incorporates human factors significantly affecting operators’ situation assessment, such as attention, working memory decay, and mental model.As this proposed model provides quantitative results of situation assessment and diagnostic performance, we expect that this model can be used in the design and evaluation of human system interfaces as well as the prediction of situation awareness errors in the human reliability analysis.     

Safety climate and safety behavior in the passenger ferry context

This research empirically evaluates safety climate and safety behavior in the passenger ferry context. Using survey data collected from 155 respondents working for passenger ferry companies in Taiwan, hierarchical regression analysis was used to examine the effects of safety climate on self-reported safety behaviors. Confirmatory factor analysis identified five main dimensions of safety climate as measured on a passenger ferry safety climate scale: safety policy, safety motivation, emergency preparedness, safety training, and safety communication. Further, safety training and emergency preparedness were found to positively affect self-reported safety behaviors with respect to safety compliance and safety participation. The study also revealed positive associations among respondents’ age, ferry capacity, and safety compliance. Implications of the study findings for increasing safety in ferry operations and their contribution to the development of safety management are discussed.     

Behavior-based safety on construction sites: A case study

This work presents the results of a case study and describes an important area within the field of construction safety management, namely behavior-based safety (BBS). This paper adopts and develops a management approach for safety improvements in construction site environments. A rigorous behavioral safety system and its intervention program was implemented and deployed on target construction sites. After taking a few weeks of safety behavior measurements, the project management team implemented the designed intervention and measurements were taken. Goal-setting sessions were arranged on-site with workers’ participation to set realistic and attainable targets of performance. Safety performance measurements continued and the levels of performance and the targets were presented on feedback charts. Supervisors were asked to give workers recognition and praise when they acted safely or improved critical behaviors. Observers were requested to have discussions with workers, visit the site, distribute training materials to workers, and provide feedback to crews and display charts. They were required to talk to operatives in the presence of line managers. It was necessary to develop awareness and understanding of what was being measured. In the process, operatives learned how to act safely when conducting site tasks using the designed checklists. Current weekly scores were discussed in the weekly safety meetings and other operational site meetings with emphasis on how to achieve set targets. The reliability of the safety performance measures taken by the company's observers was monitored. A clear increase in safety performance level was achieved across all categories: personal protective equipment; housekeeping; access to heights; plant and equipment, and scaffolding. The research reveals that scores of safety performance at one project improved from 86% (at the end of 3rd week) to 92.9% during the 9th week. The results of intervention demonstrated large decreases in unsafe behaviors and significant increases in safe behaviors. The results of this case study showed that an approach based on goal setting, feedback, and an effective measure of safety behavior if properly applied by committed management, can improve safety performance significantly in construction site environments. The results proved that the BBS management technique can be applied to any country's culture, showing that it would be a good approach for improving the safety of front-line workers and that it has industry wide application for ongoing construction projects.     

Overly cautious and dangerous: An empirical evidence of the older driver stereotypes

Negative comments regarding the competency of older drivers are frequently heard in the general population. While negative stereotypes of older drivers seem to be present, their existence has yet to be empirically validated. We thus investigated the stereotypes pertaining to older drivers in two experiments. In both experiments young adults viewed 12 simulated clips of three categories of driving behaviors (i.e., younger adults’ unsafe behaviors, older drivers’ unsafe behaviors and appropriate-safe driving behaviors) without knowing the driver's age. They were asked to rate how representative the behaviors were of a typical younger, middle-aged, or older driver. Experiment 1 showed that older drivers’ unsafe behaviors were rated as significantly more representative of the typical older driver, while young adults’ unsafe behaviors were perceived as significantly more representative of the typical younger driver. In Experiment 2, younger participants viewed the same clips but were only asked to indicate whether the observed behavior was representative or not of the typical older driver. The main findings were replicated. When asked to describe the main features of the typical older drivers, participants qualified them as being overly cautious, uncomfortable behind the wheel, and unsafe and dangerous. The potential implications on driving performance of older drivers and on driving cessation and are discussed.     

Economic worry and the presence of safety hazards on farms

In recent years the agricultural sector has experienced historical levels of economic challenges. Yet, the effects of these economic conditions on the physical safety of farm work environments remain poorly understood. We studied these possible etiological relationships in a cross-sectional analysis. A baseline survey of 2390 Saskatchewan farm operations was conducted in 2007. A single respondent from each farm provided information about the farm operation, its residents, perceptions of worry surrounding farm economic conditions, and the presence of six types of physical hazards. Binomial regression analyses were used to study the focal relationships between economics and safety while simultaneously adjusting for confounders at the farm level. Farms with high perceived levels of economic worry experienced elevations in risk for: the absence of well maintained buildings (RR 1.52; 95% CI: 1.27–1.87), the absence of safety shields on combines (RR 1.41; 95% CI: 1.05–1.89), and the absence of safety shields on augers (RR 1.15; 95% CI: 1.02–1.30). No apparent differences were observed by level of economic worry for the presence of ROPS on tractors, ladder safety cages on grain bins, and barriers around water hazards. We observed that financial conditions on farms appear to contribute to the decisions that farm operators make about safety. These are not innocuous choices as they in turn affect the health and safety of the entire population that works and lives in these occupational environments. Farm operators need to be supported in decisions to invest the physical safety of their farms. They also require evidence that investments in safety are indeed economically sensible and healthy management decisions.     

Differential quadrature analysis of functionally graded circular and annular sector plates on elastic foundation

The main purpose of this study is to investigate buckling and free vibration behaviors of radially functionally graded circular and annular sector thin plates subjected to uniform in-plane compressive loads and resting on the Pasternak elastic foundation. In-plane compressive loads may be applied to either radial, circumferential, or all edges of circular/annular sector plates. Based on the classical plate theory (CPT), critical buckling loads and fundamental frequencies of the circular/annular sector plates under simply-supported and clamped boundary conditions are obtained by using differential quadrature method (DQM). The inhomogeneity of the plate is characterized by taking exponential variation of Young’s modulus and mass density of the material along the radial direction whereas Poisson’s ratio is considered to be constant. Convergence study is carried out to demonstrate the stability of the present method. To confirm the excellent accuracy of the present approach, a few comparisons are made for limited cases between the present results and those available in literature. Critical buckling load and fundamental frequency parameters of the circular/annular sector thin plates are computed for different boundary conditions, various values of the material inhomogeneity constants, sector angles, and inner to outer radius ratios.     

Gender stereotype conformity and age as determinants of preschoolers’ injury-risk behaviors

Unintentional injuries continue to be a serious public-health problem for children and are higher for boys than for girls, from infancy through adulthood. Literature on differential socialization concerning risky behaviors and gender stereotypes suggests that sex differences in unintentional injuries could be explained by children's differential feedback to social pressure, leading to behaviors which conform to masculine and feminine stereotypes. We made the prediction that boys’ and girls’ conformity with masculine stereotypes influences injury-risk behaviors among preschoolers. Masculinity score, femininity score, and injury-risk behaviors of 170 3-6-year old children (89 boys and 81 girls) were measured indirectly on two scales filled out by their parents. Results show that boys’ and girls’ injury-risk behaviors are predicted by masculine stereotype conformity and that girls’ masculine behaviors decline with increasing age. These results underline the impact of gender-roles - and of the differential socialization associated with those roles - on sex differences in children's risky behaviors as early as the preschool period.     

施工作业人员不安全行为干预策略仿真研究

为有效控制施工作业人员不安全行为,采用系统动力学方法,构建施工作业人员不安全行为影响因素干预模型,借助Vensim软件模拟不安全行为的动态演化过程,通过算例数据进行仿真干预实验。研究分析结果表明：安全管理水平和作业人员个体的安全行为水平对其不安全行为产生具有明显的抑制作用;采取一定的组合干预策略后,作业人员的不安全行为水平明显下降,而基于“前摄性+反应性”思想的全面组合干预策略对不安全行为控制的正向促进作用更加显著。     

Relationships between psychological safety climate facets and safety behavior in the rail industry: A dominance analysis

The goals of this study were twofold: (1) to confirm a relationship between employee perceptions of psychological safety climate and safety behavior for a sample of workers in the rail industry and (2) to explore the relative strengths of relationships between specific facets of safety climate and safety behavior. Non-management rail maintenance workers employed by a large North American railroad completed a survey (n = 421) regarding workplace safety perceptions and behaviors. Three facets of safety climate (management safety, coworker safety, and work-safety tension) were assessed as relating to individual workers’ reported safety behavior. All three facets were significantly associated with safety behavior. Dominance analysis was used to assess the relative importance of each facet as related to the outcome, and work-safety tension evidenced the strongest relationship with safety behavior.     

Studying the role of vision in cycling: Critique on restricting research to fixation behaviour

In a recent study published in Accident Analysis & Prevention, Vansteenkiste et al. (2013) – as one of the first in this field – investigated the visual control of bicycle steering. They undertook the interesting task of testing cyclists’ eye fixation behaviour against Donges’ two-level model of steering, i.e. the guidance level to anticipate alternations in the course of the road and the stabilization level for lane keeping. Although the laboratory experiment itself is well conducted, we believe that its results cannot be used to test the two-level model of steering as developed for driving. The test track was only 15 m long, was completely straight and was known in advance. Accordingly, it did not provide adequate conditions for testing the guidance level. Furthermore, as the experimental lanes were much narrower than real-world cycling lanes, the stabilization level differed considerably from that in the real world. The study by Vansteenkiste et al. (2013) may provide valuable insight into the role of vision in ‘precision steering’, but, as we discuss in the paper, more elaborate research paradigms are needed to achieve more comprehensive knowledge of the role of vision in real-world cycling and cycling safety.