Principles of engineering safety: Risk and uncertainty reduction

This article provides a systematised account of safety engineering practices that clarifies their relation to the goal of safety engineering, namely to increase safety. We list 24 principles referred to in the literature of safety engineering, dividing them into four major categories: Inherently safe design, Safety reserves, Safe fail and Procedural safeguards. It emerges from this systematisation that important aspects of these methods can be better understood with the help of the distinction between risk and uncertainty.     

Risk significance and safety significance

Existing measures of the risk significance of elements of risk models (such as the Fussell–Vesely, or ‘F–V’, importance of basic events) are based on the properties of cut sets containing the element. A measure of safety significance (prevention worth, or ) is proposed, based on the properties of path sets containing the element. A high value of F–V means that cut sets containing the element contribute significantly to top event frequency; a high value of means that path sets containing the element contribute significantly to top event prevention. The properties of as a measure of basic event significance are illustrated first with a simple block diagram example, and then with an example based on nuclear power plant risk models. can also be understood as a property of a set of success scenarios, and as such, can be applied more broadly than just as a measure of element significance.     

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.     

Risk estimation studies in the context of a machine control function

Nowadays the safety requirements of a machine are increasingly associated with programmable electronic control systems. Risk estimation is an essential part of risk analysis in a machine development process, because the categorisation and allocation of safety requirements is based on this. It is important to know how the risk estimation is performed, since wrong safety integrity level (SIL) or performance level (PL) selection may lead to multiple costs of the safety-related part of the control system. On the other hand, wrong PL or SIL selection can weaken the safety of the system. In this article, a risk estimation process of a safety-related control function is presented. Different groups carried out three case studies including risk estimation for the same safety-related control function of a machine. The results of the risk estimations of the groups differ from each other. The possible reasons for the variations are discussed.     

Fatigue Failure of a Ground-Engaging Tool

A cast steel tooth used in an earth-moving application was analyzed to determine the cause of failure. The tooth reportedly failed prematurely during service was analyzed for chemical composition, hardness, and microstructure, in addition to extensive scanning electron microscopy of the fracture surface. The presence of a casting defect caused the initiation of a fatigue process due to a loose fit between the tooth and its adapter.     

出口机电产品风险识别及动态RAC风险评估

风险分析已逐步在出口机电产品检验监管中应用,但风险识别和发生可能性评估主要依据个人经验。文中根据历史数据和出口机电产品的特点,识别了出口机电产品的主要风险,采用了对风险发生可能性进行动态评估的动态RAC法进行风险评价。与常用的方法相比,动态RAC法更加客观、更易操作,且对外部环境变化更敏感。     

Evaluation of allowed outage time considering a set of plant configurations

Allowed outage time (AOT) is the maximum time for which certain safety equipment can be put out of the operation without the plant is put in a safer operating state. A method for risk informed evaluation of AOTs is developed, which enables consideration of a set of plant configurations in the evaluation. The method bases on risk measures obtained from probabilistic safety assessment, e.g. conditional change of core damage frequency considering selected plant configurations. The results of selected examples show that better methods and more data included into the models may reduce the conservatism in the evaluations and may contribute to increased flexibility about decisions on AOT.     

谈氧气及相关气体项目工程职业安全卫生评价

简述了职业安全卫生评价的基本概念、分类、目的和意义。自氧气被列入“危险化学品”后 ,对氧气及相关气体项目工程进行安全评价尤为重要 ,列举了氧气及相关气体项目安全预评价和安全综合评价需提供的资料。对安全评价中存在的一些问题发表了看法     

A new computational method of a moment-independent uncertainty importance measure

For a risk assessment model, the uncertainty in input parameters is propagated through the model and leads to the uncertainty in the model output. The study of how the uncertainty in the output of a model can be apportioned to the uncertainty in the model inputs is the job of sensitivity analysis. Saltelli [Sensitivity analysis for importance assessment. Risk Analysis 2002;22(3):579-90] pointed out that a good sensitivity indicator should be global, quantitative and model free. Borgonovo [A new uncertainty importance measure. Reliability Engineering and System Safety 2007;92(6):771-84] further extended these three requirements by adding the fourth feature, moment-independence, and proposed a new sensitivity measure, δ_i. It evaluates the influence of the input uncertainty on the entire output distribution without reference to any specific moment of the model output. In this paper, a new computational method of δ_i is proposed. It is conceptually simple and easier to implement. The feasibility of this new method is proved by applying it to two examples.     

Risk analysis of fracture and failure

 This paper is inspired by the work of Professors Heinz Wilsdorf and Doris Kuhlmann-Wilsdorf on fundamental aspects of ductile fracture mechanism. Risk – a measure of the probability and severity of adverse effects – is introduced and related to the consequences associated with elastic (reversible) deformation, plastic (irreversible) deformation, and catastrophic deformation (total failure). Cost-benefit-risk trade-off analysis is discussed. Received: 25 February 1998 / Accepted: 10 March 1998     

Fracture surface topography analysis (FRASTA)—Development, accomplishments, and future applications

In the late 1970s, Dr. George Irwin suggested to his colleagues at the University of Maryland that valuable information about a fracture event was recorded in fracture surface topography. Under his urging, Takao Kobayashi, an associate professor at the time, began quantifying and interpreting topographical features. Over the subsequent 30 years the procedures for quantifying and interpreting fracture surface topography grew continuously into an established technology that allows a fracture event to be reconstructed in microscopic detail. FRASTA (fracture surface topography analysis) has now been applied to achieve solutions to a wide variety of failure problems. This paper chronicles the historical development of FRASTA, recounts several notable achievements, and presents the plan for further development and future applications.     

Assessment of snowmelt triggered landslide hazard and risk in Japan

This study is pertaining to an evaluation of landslide occurrence on natural terrain due to snowmelt in Japan, using a probabilistic model based on multiple logistic regression analysis. The evaluation concerns several physical parameters such as hydraulic parameters, geographical parameters and geological parameters which are considered to be influential in the occurrence of landslides. A Snow Water Equivalent model (SWE) is utilized to estimate snowmelt and associated infiltration in light, heavy and normal snow years. Using the constructed spatial data-sets, we apply a multiple logistic regression model to produce landslide susceptibility maps showing the spatial–temporal distribution of landslide hazard probabilities throughout Japan using 1 km × 1 km resolution grid cells. The results have revealed that, over 95% landslide hazard probability exists in the mountain ranges on the western side of Japan (the Japan Sea side). In particular, this study is dealing with the Aizu region of Fukushima prefecture in order to verifying the landslide hazard probability. Verification proved that, the areas identified as high risk areas (having over 90% landslide hazard probability in numerical modeling) show 87% agreement with observed landslides in the Aizu region. Also we evaluated the relationship between landslides and snow melting process giving special concern to change of temperature in the spring.     

Comparison of global sensitivity analysis techniques and importance measures in PSA

This paper discusses application and results of global sensitivity analysis techniques to probabilistic safety assessment (PSA) models, and their comparison to importance measures. This comparison allows one to understand whether PSA elements that are important to the risk, as revealed by importance measures, are also important contributors to the model uncertainty, as revealed by global sensitivity analysis. We show that, due to epistemic dependence, uncertainty and global sensitivity analysis of PSA models must be performed at the parameter level. A difficulty arises, since standard codes produce the calculations at the basic event level. We discuss both the indirect comparison through importance measures computed for basic events, and the direct comparison performed using the differential importance measure and the Fussell–Vesely importance at the parameter level. Results are discussed for the large LLOCA sequence of the advanced test reactor PSA.     

Assessment of notched structural components using Failure Assessment Diagrams and the Theory of Critical Distances

This paper illustrates the need to develop specific methodologies for the assessment of notched structural components. These are usually analysed under the assumption that notches behave as cracks, providing results that may be overconservative. The proposal consists, on the one hand, in the application of the Theory of Critical Distances for the estimation of the apparent fracture toughness, and for the conversion of the notched situation into an equivalent cracked situation in which the material develops a higher fracture resistance (the apparent fracture toughness). On the other hand, once the apparent fracture toughness has been defined, the assessment is performed using the Failure Assessment Diagram methodology, and assuming that the notch effect on the plastic collapse load is negligible. The methodology has been applied to notched fracture specimens made of PMMA and Al7075-T651, providing satisfactory results and a noticeable reduction in the overconservatism derived from analyses in which the notch effect is not considered.     

Effectiveness of cable barriers,guardrails, and concrete barrier walls in reducing the risk of injury

Roadway departure crashes tend to be severe, especially when the roadside exposes the occupants of errant vehicles to excessive injury hazards. As a cost-effective method when the clear zone width is insufficient, road barriers are often installed to prevent errant vehicles from colliding with dangerous obstacles or traversing steep slopes. This paper focuses on the safety performance of road barriers in Indiana in reducing the risk of injury. The objective of the study presented here is to compare the risk of injury among different hazardous events faced by an occupant in a single-vehicle crash. The studied hazardous events include rolling over, striking three types of barriers (guardrails, concrete barrier walls, and cable barriers) with different barrier offsets to the edge of the travelled way, and striking various roadside objects.     

Towards a better reliability of risk assessment: Development of a qualitative & quantitative risk evaluation model (QREM) for different trades of construction works in Hong Kong

Since the safety professionals are the key decision makers dealing with project safety and risk assessment in the construction industry, their perceptions of safety risk would directly affect the reliability of risk assessment. The safety professionals generally tend to heavily rely on their own past experiences to make subjective decisions on risk assessment without systematic decision making. Indeed, understanding of the underlying principles of risk assessment is significant. In this study, the qualitative analysis on the safety professionals’ beliefs of risk assessment and their perceptions towards risk assessment, including their recognitions of possible accident causes, the degree of differentiations on their perceptions of risk levels of different trades of works, recognitions of the occurrence of different types of accidents, and their inter-relationships with safety performance in terms of accident rates will be explored in the Stage 1.     

The Risk Line: a special telephone line to provide means of reporting potential dangers and to increase public participation

Injuries constitute a significant public health problem. There is a risk of injury in any environment in which persons are present. The purpose of this paper is to describe the development and experiences from the Risk Line. The Risk Line is a special telephone number to provide means of reporting potential risks for injuries and dangerous products and to increase public participation in injury reporting. Various strategies have been used to make the Risk Line well known in the population. Weekly reports on the risk of playground, traffic, recreational, and residential injuries and dangerous products have been distributed to those who are responsible for eliminating these hazards. The major risk environments reported were traffic, recreational, residential environments, and playgrounds. Seventy-seven percent of the reported hazards had been eliminated. A majority of the public (72%) who had phoned the Risk Line stated that they had become more observant and aware of risks for injuries. In conjunction with injury statistics and safety inspections, information from the Risk Line can contribute to give an improved overall picture of where priorities are needed in safety promotion and injury prevention work.     

Inspection and monitoring planning for RC structures based on minimization of expected damage detection delay

The deterioration mechanism of reinforced concrete (RC) structures under corrosion is highly dependent on environment and material properties. Uncertainties in structural damage occurrence and propagation due to corrosion should be considered in a rational way using a probabilistic approach. In this study, such an approach is proposed to establish a life-cycle optimum inspection plan under uncertainty. This plan leads to cost-effective maintenance interventions, considering uncertainties associated with damage occurrence/propagation and inspection methods. Uncertainties associated with prediction of damage occurrence time are considered by using the Monte Carlo simulation. A damage detectability function is used to assess the quality of inspection method according to damage intensity. The inspection planning is formulated as an optimization problem with the objective of minimizing the expected damage detection delay. This formulation is further used for optimum monitoring planning. Effects of number of inspections and/or monitoring actions, quality of inspection, monitoring duration, and uncertainties associated with damage occurrence/propagation are investigated. The proposed approach is applied to an existing highway bridge. This approach can be used to develop cost-effective management strategies by considering effects of damage detection delay on life-cycle cost and performance of deteriorating structures.     

近地轨道航天器微流星及空间碎片风险度分析研究

以单防护屏防护结构为例,根据描述其防护性能的撞击极限方程,微流量及空间碎片环境数学模型,建立了航天器结构的有限元分析模型,进行了航天器在微流星及空间碎片环境下风险度的初步分析,其结论可供工程实践参考。