Quantitative Safety Research Articles

Simulation Program for Hazard Training and Safety Evaluation of Chemical Processes

Mathematical modeling and simulation are valuable tools for the quantitative safety investigation of chemical processes and for training the plant personel to deal with hazardous situations. However, the wide dissemination of such methods is limited by comparatively high development costs. A simulator that would match the requirements encountered in everyday practice has to incorporate broad knowledge of the application field. Special programing and mathematical expertise is necessary to develop such a program. The development of realistic simulators demands the efforts of a team of specialists and is very time-consuming. The simulation system described in this paper incorporates all the required knowledge that makes the simulation technique available to a broad spectrum users. The program also provides an easy-to-use man/machine interface for engineers and chemists, enabling them to carry out complex simulations afetr a short period of learning.

Application of micro Markov models for quantitative safety assessment to determine safety integrity levels as defined by the IEC 61508 standard for functional safety

Abstract This paper presents a method that will drastically reduce the calculation effort required to obtain quantitative safety and reliability assessments to determine safety integrity levels for applications in the process industry. The method described combines all benefits of Markov modeling with the practical benefits of reliability block diagrams.

New quantitative safety standards: different techniques, different results?

Abstract Safety Instrumented Systems (SIS) are used in the process industry to perform safety functions. Many factors can influence the safety of a SIS like system layout, diagnostics, testing and repair. In standards like the German DIN no quantitative analysis is demanded (DIN V 19250 Grundlegende Sicherheitsbetrachtungen fur MSR-Schutzeinrichtungen, Berlin, 1994; DIN/VDE 0801 Grundsatze fur Rechner in Systemen mit Sicherheitsaufgaben, Berlin, 1990). The analysis according to these standards is based on expert opinion and qualitative analysis techniques. New standards like the IEC 61508 (IEC 61508 Functional safety of electrical/electronic/programmable electronic safety-related systems, IEC, Geneve, 1997) and the ISA-S84.01 (ISA-S84.01.1996 Application of Safety Instrumented Systems for the Process Industries, Instrument Society of America, Research Triangle Park, 1996) require quantitative risk analysis but do not prescribe how to perform the analysis. Earlier publications of the authors (Rouvroye et al., Uncertainty in safety, new techniques for the assessment and optimisation of safety in process industry, D W. Pyatt (ed), SERA-Vol. 4, Safety engineering and risk analysis, ASME, New York 1995; Rouvroye et al., A comparison study of qualitative and quantitative analysis techniques for the assessment of safety in industry, P.C. Cacciabue, I.A. Papazoglou (eds), Proceedings PSAM III conference, Crete, Greece, June 1996) have shown that different analysis techniques cover different aspects of system behaviour. This paper shows by means of a case study, that different (quantitative) analysis techniques may lead to different results. The consequence is that the application of the standards to practical systems will not always lead to unambiguous results. The authors therefore propose a technique to overcome this major disadvantage.

Optimal Simulation-Based Operations Planning with Quantitative Safety Constraints

A new two-layer optimization scheme is presented for operating procedure synthesis in the presence of quantitative safety path contraints. Layer 1 optimizes the overall operations time by varying the operator time constant - the time that an operator is applied to the system. Layer 2 performs the path-constrained optimization by minimizing the sum-of-squared errors between the current system state vector and a prespecified goal state vector by applying the system operators. New system states are calculated using dynamic simulation of the equations describing the system. A detailed example involving mixture control of potentially flammable chemicals is described, illustrating all aspects of the proposed methodology.

Strukturelle Sicherheit qauantifizieren

Safety of Structural Components - The Damage Tolerance Design. The ICE-train accident in Eschede raises questions concerning the safety of structural components in advanced transportation and energy systems. The following contribution tries to answer the question whether the in Germany and in Europe prevailing structural safety concept, the Safe Life concept, fulfills the stringent requirement of present days technological systems. By the nature of the Safe Life concept, it can not furnish a measure of quantitative safety. The Damage Tolerance Design concept is presented, as it is used in the U.S.A. since over 20 years. The ability of flawed structural part to withstand failure for a definable time is termed damage tolerance. The effort of designers to manipulate this definable time in respect to engineering objectives is a damage tolerant design.

Stochastic software safety/reliability measurement and its application

Safety and reliability have become important software quality characteristics in the development of safetydcritical software systems. However, there are so far no quantitative methods for assessing a safetydcritical software system in terms of the safety/reliability characteristics. The metrics of software safety is defined as the probability that conditions that can lead to hazards do not occur. In this paper, we propose two stochastic models for software safety/reliability assessment: the dataddomain dependent safety assessment model and the availabilitydrelated safety assessment model. These models focus on describing the timed or executionddependent behavior of the software faults which can lead to unsafe states when they cause software failures. The application of one of these models to optimal software release problems is also discussed. Finally, numerical examples are illustrated for quantitative software safety assessment and optimal software release policies.

A Review of Safety Analysis Methods Applied to the Design Process

SUMMARY Design for safety is a process of identifying hazards, estimating them and finally evaluating them in terms of two basic parameters, namely the occurrence probability of each hazard and the magnitude of possible consequences. These two parameters can be assessed using either a top-down or a bottom-up approach on either a qualitative or a quantitative basis, depending on the nature of the particular engineering system and the safety assessment techniques in hand. This paper describes the concepts of qualitative and quantitative safety analysis, and bottom-up and top-down safety modelling approaches. The typical safety analysis techniques are studied with respect to the proposed design for safety framework. An analysis of the input requirements and the outcomes of the safety analysis methods is carried out to identify their possible interrelationships within the safety analysis process in order to make full use of the advantages of each method. The selection of these safety analysis methods is discussed in the context of large engineering products. Problems concerned with failure and repair data collection programmes are also studied and some typical failure and repair data sources are described.

Disposition, metabolism, and toxicity of methyl tertiary butyl ether, an oxygenate for reformulated gasoline.

Studies of the toxicology of methyl tertiary butyl ether (MTBE) were reviewed as a possible information base for evaluating the health effects of evaporative emissions from reformulated gasoline (RFG). The major metabolites of the oxidative demethylation of MTBE in vivo were methanol and tertiary butyl alcohol (TBA), whereas formaldehyde and TBA were the principal products of hepatic microsomal oxidation by cytochrome P-450. Pharmacokinetic studies in rats treated with intragastric MTBE in corn oil gave an initial disposition T1/2 for MTBE of 0.32 h. The decline in the serum drug versus time curve for MTBE in rats was accompanied by a progressive increase in serum methanol concentrations to levels more than 50-200 times those of the parent compound. Repeated exposure of MTBE vapor by inhalation in rats resulted in dose-dependent increases in MTBE in the blood, brain, and adipose tissue compartments. Blood concentrations of TBA were also dose dependent and provided an estimate of the total amount of MTBE distributed to peripheral drug metabolizing compartments. Perirenal fat/blood MTBE concentration ratios ranged from 9.7 to 11.6 after 15 wk of intermittent exposure. During an oxyfuels program in Fairbanks, AK, blood levels of occupationally exposed workers were 0.2-31.5 microgram/L MTBE and 1.6 to 72.2 microgram/L TBA with a mean TBA:MTBE blood concentration ratio of 4.2. In patients who received MTBE by percutaneous, transhepatic puncture for the dissolution of cholesterol gallstones, concentrations of MTBE in fat tissue reached 60 and 300 microgram/g at a treatment time when mean blood MTBE was less than 20 microgram/ml. The results of laboratory and clinical studies indicate that metabolites of MTBE may contribute to the nephropathy, neoplasms, and other pathological changes associated with repeated exposure to MTBE in experimental animals. It is concluded that such studies can provide a well-defined database for quantitative safety comparisons and health risk-benefit analyses of MTBE and other oxygenates in RFG.

A Unified Approach for Calculating Core Melt Frequency Caused by Internal and External Initiating Events

A unified approach for calculating the core melt frequency of a specific reactor caused by both internal and external accident initiators is demonstrated. Two classes of internal initiators are examined: transients, of which turbine trip is the chosen example, and loss‐of‐coolant events of various sizes. The concepts of hazard and fragility analysis first proposed for seismic risk analysis are linked to the frequencies of internal initiating events, and to the plant response as a function of the event intensity. Uncertainties are propagated using discrete probability distribution (DPD) arithmetic. Advantages of this approach include mathematical and conceptual consistency, and an improved uncertainty analysis, which are important considerations if risk studies are to be utilized in decision‐making based on quantitative safety goals.

Quantitative safety goals for risk management of industrial facilities

This paper discusses the issues, constraints and conflicts involved in risk management for industrial facilities and proposes a global and explicit approach to numerical safety goals. The use of such quantitative targets is part of a more general strategy of risk management. The factors involved are technical, organizational, ethical, social, legal and economic. In order to set priorities among safety measures, the first step is a probabilistic risk analysis, which should not be limited to technical parameters but should also include organizational factors. A review of precedents and “floating numbers” commonly used as safety targets is presented. A general structure of safety goals is then proposed with illustrative numbers. The case of existing facilities and the treatment of uncertainties are discussed briefly.

A pregnancy register of patients receiving carbamazepine in the UK

AbstractFrom 1978 to 1990, CIBA‐GEIGY Pharmaceuticals (UK) were notified of the pregnancy outcome of 154 women who were being treated with Tegretol® (carbamazepine) during their pregnancy. The first contact of these reports occurred either before the end of the pregnancy (prospective reports) or after the result of the pregnancy was known (retrospective reports). Prospective reports were followed up in order to ascertain details of each pregnancy and the health status at birth of the offspring. The same information for the retrospective reports was collected after the pregnancy outcome occurred. Three possible outcomes of pregnancy were identified: (1) Patients whose pregnancies resulted in normal healthy babies, (2) patients whose pregnancies ended in premature spontaneous abortion and (3) patients whose pregnancies resulted in babies with congenital malformations. A total of 88 patient's reports were prospective. Of these, 75 pregnancies resulted in normal babies, 9 in spontaneous abortions and 4 in abnormal babies (5%). A total of 65 patient's reports were retrospective. Of these, 23 pregnancies resulted in normal babies, 8 in spontaneous abortions and 34 in abnormal babies (60%). This major reporting bias in the retrospective group discourages its use in the quantitative safety assessment of medicines given to pregnant women.

Quantitative safety assessment of the ventilation recirculation system in an undersea mine

AbstractThis paper describes a quantitative safety study carried out on a system which monitors the environmental conditions in an undersea mine. Of particular importance are the concentrations of methane and carbon monoxide present in the mine. Although the presence of these gases is of concern in all mines it is of particular concern in this undersea mine since up to 37 per cent of the return air of the ventilation system is recirculated. When high methane or carbon monoxide levels are detected recirculation is halted.Fault trees were constructed to represent two system failure modes for each of the trip conditions; failure to trip on demand and spurious trip. These logic diagrams were then analysed to produce the minimal cut sets and the probabilities for the system failure events. From this prediction of system performance the degree of improvement attainable by changing the system design, component repair times or test frequencies was investigated.

Safety objectives in nuclear power technology

While most potentially hazardous industrial undertakings have safety objectives of some kind, the nuclear power industry is relatively unique in the extent to which it has attempted to refine and quantify its particular ones. This paper discusses the reasons for this and reviews the range and variety of nuclear safety objectives by reference to studies carried out within the European Community and the International Atomic Energy Agency. It refers to recent developments in the UK which illustrate the advantages and disadvantages of attempting to use quantitative safety objectives in the public arena and concludes with some thoughts about the likely future development of nuclear safety objectives.

Relationship Between Integrated Sucking Pressures and First Bottle‐Feeding Scores in Premature Infants

Reasons for delays in initiating premature infant bottle-feeding and the complications associated with various methods of providing nutrition to premature infants are discussed. A quantitative, correlational study was undertaken to assess premature infants' readiness to bottle-feed. Thirty premature infants, weighing 1,230 to 2,020 g were studied to determine the relationship between integrated sucking pressures and bottle-feeding scores. Sucking pressures were measured with research nipples and an electronic suckometer. Feeding ability was measured using a complex research scale and a simpler clinical scale. Feeding scales correlated significantly (r = 0.79, p less than 0.001) while sucking pressures and feeding scores did not correlate significantly. Study limitations may have been responsible for the lack of a significant correlation between sucking pressures and feeding scores. Further research is needed to establish simple, quantitative safety parameters for beginning oral feedings for premature infants.

Probabilistic Reliability Analysis, Quantitative Safety Goals, and Nuclear Licensing in the United Kingdom

Although unpublicized, the use of quantitative safety goals and probabilistic reliability analysis for licensing nuclear reactors has become a reality in the United Kingdom. This conclusion results from an examination of the process leading to the licensing of the Sizewell B PWR in England. The licensing process for this reactor has substantial implications for nuclear safety standards in Britain, and is examined in the context of the growing trend towards quantitative safety goals in the United States.

Safety goals for nuclear power plant regulation

A survey and comparison has been made of 10 widely disseminated safety goal proposals originating in Canada, the U.K. and the U.S. When the proposals are placed in a directly comparable numerical context, they are remarkably similar in the inferred levels of safety. The development of quantitative safety goals by the U.S. Nuclear Regulatory Commission is also reviewed. While progress has been made in structuring technically and politically defensible goals, because of the way the regulatory philosophy has evolved in the U.S. the implementation of such goals could well turn out to be more difficult than defining the goals themselves. The safety goals are useful in providing guidance to the designers, operators and regulators of nuclear power plants with regard to public safety concerns as well as plant reliability and engineering considerations.

On the usefulness of quantitative safety goals for state regulation of energy systems

The potential usefulness of quantitative safety goals for energy systems in the State of California is evaluated. Five energy-related risk issues, previously dealt with by state regulatory agencies, are examined for the role played by risk in decision-making and the possible role that quantitative safety goals might have played. Several other energy-related risk situations are identified and briefly discussed. It is concluded that quantitative safety goals do not appear to be needed for risk management of energy systems in California. However, there does appear to be a role for a central office of risk management in the State governmental structure. Such an office would provide a reference and evaluation service for other agencies. The potential usefulness of establishing threshold levels of risk for different kinds of action is also noted.

System Safety Approach to Robot Safety

The need and importance of considering robot safety issues are emphasized. Based on previous researches, major categories of robot accident causes are identified and listed. System safety is described as an appropriate approach to evaluating and designing robot safety systems. Then, qualitative and quantitative system safety techniques are introduced. Energy barrier analysis (a qualitative model) is selected and applied to a general human-robot system. Finally, as a result of this application, specific solutions and recommendations are discussed.

Quantitative safety goals through more adequate risk management and risk assessment

The paper offers an overview of the current regulatory background within the United States, emphasising nuclear regulation, related to the establishment of quantitative safety goals as a way to respond to the key issue of ‘How safe is safe enough?’ The approach described in the paper, based on use of probabilistic risk assessments techniques is centred around definition of quantitative safety regions. Regions are termed: design basis, safety margin, the design capability, and safety research. The design basis region is bounded by the frequency of 10 −4 per reactor year and consequences of no identifiable public injury. The frequency of 10 −4 per reactor year, is associated with the total projected lifetime of a commercial US nuclear power programme. Events which have a 50% chance of happening are included in the design basis region. In the safety margin region, which extends below the design basis region, protection is provided against events whose probability of not happening during the expected course of the US nuclear power programme is within the region of 50 to 90%. Setting the lower mean frequency to this region of 10 −5 per reactor year is equivalent to offering 90% assurance that an accident of given severity will not happen. A rare event with a mean frequency below 10 −5 can be predicted to occur. However, accidents predicted to have a probability of less than 10 −6 are 99% certain not to happen at all, and are thus not anticipated to affect public health and safety. Safety goals associated with individual risk to a maximum exposed member of the public, general societal risk, and public property risk are proposed in the paper. The derivation and rationale behind the above stated goals are briefly discussed.

Perspectives of accident research: Causes and prevention

Accident research deals with the causes and the prevention of industrial accidents. In the field of accident causes research in the German Democratic Republic are applied methods which allow to forecast hazards connected with equipment, operations and workplaces. The risk level is deduced from the accident analysis retrospectively. These well established methods are the basis for measures to reduce accidents. The development of science and technology, the social progress and the modified structure of accident causes demand the application of qualitative safety evaluation methods. These methods use the expert assessment of equipment quality and the quantitative safety evaluation according to the fault tree analysis. The investigation of the causes of errors in work performance leading to acccidents has been done predominantly by means of psychological methods until now. First results have been obtained from the systematic analysis of the reasons of error-free work of working teams. Every method may be applied in special cases. In the future preference will be given to the quantitative safety evaluation and the analysis of error-free work. The accident prevention research follows a strategy which gives priority to technological measures of accident prevention. Its future tasks and possibilities derive from the effective combination of the advantages of socialism and the scientific-technological revolution.