Probabilistic risk analysis and risk-based priority scale for the tiles of the space shuttle

The thermal protection system of the space shuttle is one of its most critical subsystems because it protects the orbiter from heavy heat loads at reentry into the atmosphere. To optimize NASA's allocation of risk management resources, a probabilistic risk analysis model is developed for the black tiles, and a risk-criticality index is computed for each tile based on its contribution to the overall probability of loss of vehicle and crew (LOV/C). This assessment is based on the susceptibility of the tiles (i.e. their probabilities of debonding), and on the vulnerability of the orbiter to specific tile losses given the criticality of the subsystems under the aluminum skin in various locations. The two main initiating events are linked to the debonding of a tile, caused either by debris hits or by a weak bond because of poor tile installation. The PRA model relies on a partition of the orbiter's surface according to four parameters: the probability of debris hits, the probability of secondary tile loss once a first tile has debonded, the probability of burnthrough given a failure patch of specified size, and the probability of LOV given a hole in the orbiter's aluminum skin. The results show that the contribution of the tiles to the overall probability of LOV is about 10%. They also include a map of the orbiter's surface showing the relative risk-criticality of tiles at various locations. It was found that 85% of the risk can be attributed to 15% of the tiles, thus allowing the management to allocate more effort and resources to the maintenance of the most risk-critical tiles.     

A risk-based optimisation for pavement preventative maintenance with probabilistic LCCA: a Chinese case

Compared to major structural repair or even replacement, preventative preservation of in-service pavements has been more popular in engineering practices, but recently, pavement preventative maintenance (PPM) has become more complex in China as the competition for pavement preservation funds has grown and the need to justify decisions has increased. Therefore, the life cycle cost analysis (LCCA) has increasingly attracted attention from transportation agencies. However, most of previous studies were conducted deterministically or only focused on a single factor, while PPM is apparently affected by many potential sources of uncertainty. The risk-based analysis to investigate potential risks and combined effects of multiple factors is a necessary component of PPM. This paper aims at presenting a risk-based PPM with the probabilistic LCCA for a Chinese highway case. Major analysis variables of different range are examined to probe risks of different scenarios, investigate combined effects of multiple variables and identify an optimal preservation strategy.     

Probabilistic risk analysis for the NASA space shuttle: a brief history and current work

While NASA managers have always relied on risk analysis tools for the development and maintenance of space projects, quantitative and especially probabilistic techniques have been gaining acceptance in recent years. In some cases, the studies have been required, for example, to launch the Galileo spacecraft with plutonium fuel, but these successful applications have helped to demonstrate the benefits of these tools. This paper reviews the history of probabilistic risk analysis (PRA) by NASA for the space shuttle program and discusses the status of the on-going development of the Quantitative Risk Assessment System (QRAS) software that performs PRA. The goal is to have within NASA a tool that can be used when needed to update previous risk estimates and to assess the benefits of possible upgrades to the system.     

Columbia space shuttle: Failure analysis of a fuel valve

A crater was formed on a fuel valve of the Columbia by an unknown high-temperature heat source during re-entry and catastrophic failure of the space shuttle. Stereomicroscopy, light optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy were used to analyze the failure. Aluminum deposits were found on the surface of the valve as well as on the fracture surface, indicative of molten deposition during breakup of the Columbia. The area around the crater contained higher-than-usual levels of delta ferrite, probably because of reheating of the valve into the ferrite region during re-entry and then slow cooling as a result of the descent to earth.     

Life Cycle Assessment as a tool for environmental management

 This paper illustrates, using data from test cases, how Life Cycle Assessment (LCA) may be used to enhance environmental management, particularly when used in conjunction with Environmental Management Systems. There are a number of areas where LCA can be helpful: in the identification of significant environmental effects; in the quantification of those effects; in the assessment of year-to-year changes in environmental performance and in the assessment of the environmental benefits (or disadvantages) arising from changes (actual or planned) in operating conditions, equipment, procedures, raw materials or products. There are some issues which cannot (at present) be adequately assessed using LCA and these are also discussed. Received: 8 January 1999 / Accepted: 11 February 1999     

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.     

Failure analysis of a thermal tile on the space shuttle Columbia

Several high-temperature reusable surface insulation (HRSI) tiles from the space shuttle Columbia were analyzed for their response to the catastrophic events during re-entry. The analysis of the HRSI tile focused on the outer surface, which was composed of silica tile with a reaction-cured glass (RCG) coating, and the inner surface strain isolation pad, which is bonded to the tile using a room-temperature vulcanizing silicone adhesive. Light optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to evaluate the tile surfaces. The tiles were found to have a heavily damaged outer surface, with much of the top RCG coating eroded by impact from shuttle debris and/or plasma flow during the shuttle’s breakup and re-entry. The RCG experienced slumping and the silica exhibited melting and glassification due to temperatures exceeding the glass transition temperature and the anticipated tile operating temperatures. Deep cavities present in the material were found to contain metal particles that are not normally present and suggest impact with shuttle debris. Silicone adhesive degradation was also found. The slumping of the silica, the degraded adhesive, and the erosion of the tile contributed to a complex process during which the individual tile delaminated from the shuttle airframe.     

Quantifying human and organizational factors in accident management using decision trees: the HORAAM method

In the framework of the level 2 Probabilistic Safety Study (PSA 2) project, the Institute for Nuclear Safety and Protection (IPSN) has developed a method for taking into account Human and Organizational Reliability Aspects during accident management. Actions are taken during very degraded installation operations by teams of experts in the French framework of Crisis Organization (ONC). After describing the background of the framework of the Level 2 PSA, the French specific Crisis Organization and the characteristics of human actions in the Accident Progression Event Tree, this paper describes the method developed to introduce in PSA the Human and Organizational Reliability Analysis in Accident Management (HORAAM). This method is based on the Decision Tree method and has gone through a number of steps in its development. The first one was the observation of crisis center exercises, in order to identify the main influence factors (IFs) which affect human and organizational reliability. These IFs were used as headings in the Decision Tree method. Expert judgment was used in order to verify the IFs, to rank them, and to estimate the value of the aggregated factors to simplify the quantification of the tree. A tool based on Mathematica was developed to increase the flexibility and the efficiency of the study.     

On the quantification of the effects of organizational and management factors in chemical installations

The quantitative effects of organizational and management factors in chemical installations are assessed through a linking of the results of a safety management audit with the basic events of a quantified risk assessment (QRA). A safety management audit establishes the relative position of the organizational and management aspects of a particular chemical installation with respect to an ideal management scheme, and for a number of failure causes and failure prevention combinations. A quantitative risk analysis including detailed system analysis offers a plant-specific decomposition of the plant-damage-state frequencies into events like hardware failures, maintenance-related failures, operation-related failures and so on. The basic events incorporated in the QRA are then categorized into classes similar to those explored by the management audit and are quantitatively linked to the audit results. Knowledge of these quantitative links would allow for the reflection of the deficiencies or strengths that might exist in the safety management system on the quantitative risk indices. A case study of an ammonia storage facility that has been audited demonstrates that the sensitivity of the risk indices to the value of the quantitative links is extremely high and that hence great care should be exercised in assessing these links.     

The quality management system as a tool for improving stakeholder confidence.

The Corps of Engineers works with local restoration advisory boards (RAB) to exchange information and develop plans for restoration of closed military bases for civilian reuse. Meetings of the RAB to discuss progress in environmental assessment and restoration of former defense sites can be contentious due to the complex technical nature of the information to be shared and the personal stake that the members of the community have in ensuring that contentious areas are restored for safe use. A prime concern of community representatives is often the quality of the data used to make environmental decisions. Laboratory case narratives and data flags may suggest laboratory errors and low data quality to those without an understanding of the information's full meaning. RAB members include representatives from local, state, and tribal governments, the Department of Defense, the Environmental Protection Agency, and the local community. The Corps of Engineers representatives usually include project technical and management personnel, but these individuals may not have sufficient expertise in the project quality assurance components and laboratory data quality procedures to completely satisfy community concerns about data quality. Communication of this information to the RAB by a quality assurance professional could serve to resolve some of the questions members have about the quality of acquired data and proper use of analytical results, and increase community trust that appropriate decisions are made regarding restoration. Details of the effectiveness of including a quality assurance professional in RAB discussions of laboratory data quality and project quality management are provided in this paper.     

Failure analysis of a titanium strut tank support in the space shuttle Columbia

A titanium midtank strut support from the Columbia space shuttle was submitted for failure analysis. Stereomicroscopy, light optical microscopy, and scanning electron microscopy with energy-dispersive spectroscopy were used to investigate the failed part. Evidence of melting was found on the fracture surface. Additionally, the high temperature associated with the melting was combined with cooling from the β-phase field, as indicated by the formation of a martensitic microstructure in the surrounding material. Craters were found on the surface of the part due to impact of foreign particles containing iron, nickel, and chromium. Failure of the titanium strut support was due to the severe high temperatures encountered as a result of the shuttle breakup and re-entry into the earth’s atmosphere.     

Plasma chemistry as a tool for green chemistry, environmental analysis and waste management

The applications of plasma chemistry to environmental problems and to green chemistry are emerging fields that offer unique opportunities for advancement. There has been substantial progress in the application of plasmas to analytical diagnostics and to waste reduction and waste management. This review discusses the chemistry and physics necessary to a basic understanding of plasmas, something that has been missing from recent technical reviews. The current status of plasmas in environmental chemistry is summarized and emerging areas of application for plasmas are delineated. Plasmas are defined and discussed in terms of their properties that make them useful for environmental chemistry. Information is drawn from diverse fields to illustrate the potential applications of plasmas in analysis, materials modifications and hazardous waste treatments.     

Cold chain database development and application as a tool for the cold chain management and food quality evaluation

Cold chain management can optimize freshness and safety to the consumer end. Within FRISBEE European project (http://frisbee-project.eu) a web-based platform was developed for temperature conditions data collection throughout the chilled and frozen food supply chain. Data including all cold chain stages (industry, distributors, retailers and consumers), were collected. This extensive database comprising more than 14,000 time-Temperature (t–T) profiles can serve as a valuable Cold Chain Management tool. The user can define a sequence of cold chain stages for selected food products. The Cold Chain Predictor (CCP) software based on the Cold Chain Database (CCD) allows calculation of product shelf-life status at different cold chain stages based on existing or user defined kinetic data. Conducted field tests expanded the Cold Chain Database and validated the software. The developed tools offer the potential to run simulation scenarios based on real cold chain data and contribute to effective cold chain improvement and management.     

IAEA activities on extending PSAPACK as a tool for use in NPP safety management

The paper reviews the current efforts of the International Atomic Energy Agency (IAEA) towards developing a PC based PSA software (PSAPACK) as a tool for operational safety management of nuclear power plants. Safety decisions which can be supported by PSA and the types of results needed are presented.

The basic elements contained in the package for the options of recalculating or remodelling a PSA are presented. Two potentially important problems associated with the reevaluation of core melt frequency using a predetermined file of cut sets, namely: the generation of ‘super sets’ and the use of truncated cut sets are discussed.

Finally, IAEA's future activities in this area are mentioned.     

The simplex simulation as a tool to reveal publication strategies and citation factors

Scientometrics - Scientists’ evaluations are commonly made by h-index calculated from citation levels of published papers. Although single index way is simple, synthetic, rapid and popular,...     

Human and organizational biases affecting the management of safety

Management of safety is always based on underlying models or theories of organization, human behavior and system safety. The aim of the article is to review and describe a set of potential biases in these models and theories. We will outline human and organizational biases that have an effect on the management of safety in four thematic areas: beliefs about human behavior, beliefs about organizations, beliefs about information and safety models. At worst, biases in these areas can lead to an approach where people are treated as isolated and independent actors who make (bad) decisions in a social vacuum and who pose a threat to safety. Such an approach aims at building barriers and constraints to human behavior and neglects the measures aiming at providing prerequisites and organizational conditions for people to work effectively. This reductionist view of safety management can also lead to too drastic a strong separation of so-called human factors from technical issues, undermining the holistic view of system safety. Human behavior needs to be understood in the context of people attempting (together) to make sense of themselves and their environment, and act based on perpetually incomplete information while relying on social conventions, affordances provided by the environment and the available cognitive heuristics. In addition, a move toward a positive view of the human contribution to safety is needed. Systemic safety management requires an increased understanding of various normal organizational phenomena - in this paper discussed from the point of view of biases - coupled with a systemic safety culture that encourages and endorses a holistic view of the workings and challenges of the socio-technical system in question.