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This thesis looks into ways of developing a new approach for fault tree automation. Initially an extensive literature survey was undertaken to try and identify if any methods contained useful features that might warrant further development. The two methods that were chosen were the decision table method and the digraph method. The new hybrid method is based on the flexibility of the decision table method but incorporates a way of detecting, classifying and analysing control loops, similar to the use of operators in the digraph approach. As well as using operators to deal with control loops new operators are introduced that deal with current and no current in electrical circuits. These new operators have been developed to be able to handle components that are common to multiple circuits. The advantages of applying operators during fault tree construction is to reduce the number of repeated and inconsistent events that may occur in the tree, and to significantly reduced the size of the constructed fault tree. Thus producing a tree logic that can easily be followed by an analyst and is in an appropriate format for direct input to an fault tree analysis code. The new method has been automated and successfully applied to three railway safety systems obtained from London Underground Ltd. To test the ability of the Automatic Fault Tree Construction Code (AFTCC) the complexity of each of the three systems increased. The first system, the Train Stop system, did not contain any circuits; the second, the Train Detection system, contained simple circuits and lastly the Train Braking system, contained multiple nested circuits.

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Inherent safety is that which is intrinsic to a chemical plant. Chemical plants should be designed to be acceptably safe and it is better if this can be achieved through inherent safety, which can not be compromised, rather than engineered safety. The earlier that inherent safety is considered, the greater are the benefits. The choice of chemical route, that is the raw materials and the sequence of reactions that converts them to the desired products, is a key early design decision that influences the inherent safety of a plant. The inherent safety must be quantified in order to choose the optimum route from a number of alternatives. A trial inherent safety index has been developed for ranking alternative chemical routes by inherent safety. The physical properties of the chemicals involved, and the conditions in the reaction steps are parameters in the index calculation procedure. The index has been tested on a number of routes to methyl methacrylate (MMA). In order to verify and improve the index, a panel of experts was asked to rank the routes, and to make comments about the index and how it could be improved. This expert judgement exercise used three questionnaires and a group meeting to elicit the required information. Statistical methods were used to analyse the results from the questionnaires. The experts agreed closely among themselves on the rankings. The rankings from the trial index and the rankings from the experts matched closely. A new index was produced based on the comments of the experts and further research. The new index is more structured than the trial index, and separation and storage steps are included in addition to reaction steps. The inherent safety of the routes to MMA has been assessed with the new index. Developing a method for quantifying the inherent safety of chemical routes has proved to be a large and difficult task. Further research is needed to decide how the interactions between parameters affect the assessment of inherent safety. The ultimate goal is a computerised tool that could be used in the early stages of industrial process development.

The work described in this thesis is concerned with formal safety analysis methods and their application to the "design for safety" process of marine and other large Made-To- Order (MTO) products with particular reference to the incorporation of safety aspects into the design process from the initial stages. Large MTO products are complex assemblies of components for which building and testing of prototypes is not usually possible. This thesis proposes a "design for safety" methodology for large MTO products based upon the general spirit of the recommendations from recent government reports including the Cullen and Carver reports. Such a methodology, consisting of five phases, namely problem definition, risk identification, risk estimation, risk evaluation and design review, is used as the basis for the development of more scientific and objective safety analysis methods and techno-economic modelling techniques applicable to the control of major accidents of large MTO products. An analysis of the input requirements and the outcomes of the typical safety analysis methods is conducted to identify their possible inter-relationships within the "design for safety" 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 MTO products. Problems concerned with failure and repair data collection programmes are studied and some typical failure and repair data sources are described. In order to systematically and effectively identify and estimate risks of large MTO products, an inductive bottom-up Modified Boolean Representation Method (MBRM) is developed to directly make use of the information produced using Failure Mode, Effects and Criticality Analysis (FMECA) to identify and estimate all possible system failure events and respective causes. Such a method can be used to analyse any engineering system which is capable of being broken down into subsystems and components. The overall model and the algorithms are described and tested in association with appropriate computer software. A modified qualitative reasoning method is developed to describe the behaviour of a large complex system. Such a modelling method can be used for failure propagation analysis. The proposed qualitative modelling method is further combined with the MBRM to form a flexible mixed safety modelling methodology. In this methodology, the MBRM is used to process the information produced from the qualitative reasoning analysis at the component level to obtain a description of the total system behaviour. This methodology allows a bottom-up safety analysis approach to be taken even in those cases where it is difficult to obtain complete input-output relations for all the components of the system. Two general simulation models are developed to process the information produced using FMECA and the MBRM. Such simulation models can be used as a quantitative safety analysis tool to simulate system availability, component/subsystem failures, and the probability of occurrence of each identified system failure event. These two models are developed in an Object-Oriented Programming (OOP) environment. This thesis also presents a new safety analysis and synthesis methodology involving the use of fuzzy Set modelling and evidential reasoning, where fuzzy set modelling is used to describe each failure event and an evidential reasoning approach is then employed to synthesise the information produced to assess the safety of the whole system. This subjective reasoning methodology can be used as an alternative approach by safety analysts to carry out analysis particularly in those situations where mostly nonnumerical safety data is available or where there is a lack of information regarding distributions of variables for use in probabilistic risk studies. A techno-economic modelling methodology is also developed to determine where reasonably practicable design actions are required. The proposed methodology brings together risk and cost objectives into the decision making process for the improvement of design aspects and maintenance policies. Information produced using the safety analysis approaches developed in this thesis can be utilised to construct a technoeconomic model. Multiple Objective Decision Making (MODM) techniques are then employed to process the constructed model. The results produced can assist designers in developing good compromise designs that take into account risks, their possible consequences, maintenance cost, repair cost and design review cost. A hydraulic transmission system of an offshore pedestal crane is used to demonstrate the methodologies developed in this thesis. Finally, the results of the research project are generally summarised and the areas where further effort is seen to be required to improve the developed methodologies are outlined.

In this thesis it is suggested that the cost-effectiveness of road safety expenditure on low cost engineering remedial works could be improved because the currently adopted methods for assessing expenditure priorities do not necessarily identify thosa sites at which the greatest potential for accident reduction exists. An alternative method for the generation of more cost-effective programmes of works is proposed and justified. This method adopts the rationale of identifying those sites at which accidents are occurring in higher numbers than would otherwise be expected for such sites with equivalent traffic volumes and locations. The justification for the method involves detailed statistical analyses of over 10,000 accidents occurring in Lothian Region for the years 1979-1982 which demonstrate that there are significant relationships between accidents and traffic volumes and location details (eg junction type, form of junction control, adjacent roadside development and carriageway type). On this basis, models for accident occurrence have been determined. The analyses show that the temporal distribution conforms with a Poisson process and that the spatial distribution is negative binomial. It is shown - for both links and junctions - that whilst there are significant differences between the models for different accident types, they do not, in aggregate, produce significantly better models for all accidents than simple all accident models. In addition, the importance of regression-to-mean has been established as an effect which should be accounted for not just at the monitoring stage of completed schemes but as an integral part of the initial site selection process. Finally, it is demonstrated that the proposed method, which is called Potential Accident Reduction (PAR), may provide an improvernent of cost-effectiveness of road safety expenditure of up to 25% over the currently adopted methods.

An Intelligent Pedestrian Device (IPD) is a new concept in pedestrian safety. It is defined as a microprocessor based information device which detects the approach of oncoming vehicles and informs the pedestrian whether or not it is safe to cross. IPDs could be portable or fixed to a roadside station. They could help reduce pedestrian accidents, which cost £2681 million in the UK in 1994. This study aims to assess whether the concept is socially acceptable and what the design criteria might be. A study of social acceptance involved group interviews of 5-10 participants with 84 pedestrians in five categories: adults aged 18-60, elderly aged 65+, visually restricted, parents of children aged 5-9 and children aged 10-14. The results suggest that vulnerable pedestrians are more positive about the device than the more able-bodied. Theories that may help explain this are discussed and it is concluded that, with education and marketing, the IPD could gain a degree of social acceptance. Observation of more than 900 pedestrian crossing movements at four different sites showed a range of behaviours, and that people often take risks in order to reduce delay. IPDs will require pedestrians to change some of their behaviours, especially those that are risky. Legal acceptance will demand high levels of costly product research and development, and a portable device will not be technologically feasible until well into the next century. However, the wider social benefits of IPDs may be worth the costs. An outline of design criteria for basic and sophisticated portable IPDs is given, and alternative functions are suggested. It is recommended that further work concentrate on developing software and hardware for fixed modes of IPD. It is concluded that, ultimately, acceptance will probably depend on whether Government decides that the IPD has a place in the road environment of the future.

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