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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.

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.

Thesis (M. S.)--Texas A&M University, 2004. / "Major Subject: Safety Engineering" Title from author supplied metadata (automated record created on Apr. 14, 2006.) Vita. Abstract. Includes bibliographical references.

Thesis (M. S.)--Texas A&M University, 2005. / "Major Subject: Safety Engineering" Title from author supplied metadata (automated record created on Apr. 27, 2007.) Vita. Abstract. Includes bibliographical references.

A study was made of the hazard presented by, and the risks associated with, the road and rail transport of conventional explosives. Its purpose was firstly to review the transport environments associated with the hazardous goods and in particular conventional accident and carriage of explosives. Secondly, to identify and assess those stimuli present in transport and accident environments which are liable to cause accidental initiation of explosives. Thirdly, to identify explosion consequence models suitable for the assessment of injury and damage suffered by roadside and rail-side populations as a result of explosion. Finally, to apply and develop a risk assessment methodology capable of identifying, quantifying, evaluating and monitoring individual and societal risks. The study formulates a basic methodology for the assessment of transient hazards and more specifically, a methodology suitable for quantitative risk assessment of the road and rail transport of conventional commercial and military explosives.

Explosion suppression system design has relied historically on the validity of Hartmann apparatus explosibility test data, and on interpolation from available suppression system test data. This research has identified improved methods of explosion hazard assessment and suppression system efficacy assessment, from a study of explosion propagation, suppressant action, and discharge of suppressors. The controversy over the validity of Hartmann dust explosibility data was resolved. It was found that the ignition methodology was responsible for the uncertainly of Hartmann data. A 43dm[3] spherical explosion test apparatus was developed which provided more useful explosibility data. The influence of turbulence on explosion hazards was recognised and an empirical measure of turbulence level was defined. Systematic trials with suppressed and unsuppressed explosions were undertaken in a 1m[3] apparatus. The results of these trials provided the foundation for the development of a mathematical model of explosion suppression. A 6.2m[3] explosion test facility was set up in alignment with the requirements of a proposed International Standard. Explosion and explosion suppression trials in this apparatus substantiated the model. Certain artefacts were identified in 6.2m[3] quiescent gas explosions. An interactive computer program based on the model for explosion suppression was tested and proved. The work has culminated in the establishment of a large scale explosion test facility in the UK. The effectiveness of three suppressants, Halon 1011, water, and mono-ammonium phosphate powder, against both gas and dust explosions was established experimentally . The influence of suppression system detection pressure and explosion suppressor discharge characteristics on the resultant suppression system effectiveness was determined experimentally. A computer model of explosion suppression has emerged which provides an improved level of confidence in adjudging the performance of explosion suppression measures. Areas for further work include larger scale explosion and explosion suppression trials and a study of artefacts identified with large volume quiescent gas explosions.

Fire development in a vented enclosure can proceed in an explosive and disastrous manner called flashover. This thesis examines when, why and how flashover occurs and gives the answers in terms of a few determining dimensionless parameters. The mechanism of flashover considered in this thesis is an enhancement of the burning rate because of thermal radiation from a layer of hot smoke, produced in the course of the fire, to the fire bed. A model, which is proposed for the problem, describes the development fro~ the moment of ignition incorporating the traditional two-zone approach. During early fIre development the density and temperature of the lower zone are reasonably assumed to be close to their initial value. Flashover itself is assumed to occur early in the fIre development, within the fuel controlled combustion regime. The model is analysed using the techniques of classical thermal explosion theory. Explicit criteria are found analytically and graphically to determine if the fIre will achieve flashover or not. The temperature-time characteristics of the fIre development are obtained explicitly for the fIrst time. It is shown that the thermal inertia of the compartment walls can have a significant effect upon the development. The effect of geometrically scaling the compartment is considered. Nondimensional analysis makes such study effective and leads to a square root relationship for the temperature/time characteristics of the fire development. The correlation between the model, four prevIOUS models and small scale experiments is examined. Under reasonable assumptions all models are shown to be described by the same mathematical problem. This means that the criterion for flashover and the development characteristics can be used for any of the modified models observed. Results are illustrated for an experimental fire box used in many experiments.

The use of small scale facilities in experimental fire research studies is well estabhshed. This thesis concerns the use of small scale facilities to examine principally the influence of thermal inertia of the lining material on ventilated enclosure fire The radiation error of the thermocouple reading was studied using radiation network models. Previous theoretical studies were implemented to provide improved models appropriate to the more complex arrangements considered here. Modeling was used to assess the radiation error of different sizes of thermocouple in the hot layer measuring position for post and pre flashover fires, and the models were compared with experiment. The current range of thermal inertia values for building products is much wider than those used in the regression by which the classical theory of pre-flashover temperature was derived (McCaffery et al. 1981). The range considered here is greater then has previously been considered by systematic experimental testing whilst maintaining all other independent key variables constant. Using of reasonable assumptions, the mass loss rates of non-flashover and flashover conditions were predicted by numerical calculation integrated with a zone model. Successful prediction was also made for published tests where sufficient information was available, and good agreement was found irrespective of flashover, scale or geometry. Two important and necessary assumptions used in the zone model, concerning specifically radiation heat transfer in the flashover condition are: that an average temperature of hot gas and flashover flame may be represented by a single thermocouple measurement; and that the massive increase in production of flanu-nable vapours from the fuel surface during flashover leads to a "cool core" partial scattering or blocking of the incident radiant heat from the flashover flame and hot gas. A computer programme was developed to implement and test recent flashover theory (Graharn et al. 1995). A logarithinic relationship has here been suggested between the thermal inertia parameter ', 8' and thermal inertia value of lining material. That relationship matches the current experimental results and other published data. The occurrence of flashover and the value of hot gas peak or steady temperature can be predicted using the computer programme, based on the published theory.

Complex computer models, built on basic physical principles, have the potential to aid in the understanding and prediction of wildland fire behavior. However, there remain significant uncertainties and assumptions in the way such models describe the fire, the vegetation, and the interaction of the two. To understand a model’s capabilities, limitations, and the improvements which are still necessary, comparison of model predictions to experimental measurement is critical. Unfortunately, collecting such measurements is particularly difficult at the large scale over which real wildland fires occur and, as a result, this happens infrequently. To address this, an opportunity was seized to collect a detailed set of measurements of fire behavior in a real forest environment. These measurements are thoroughly analyzed for the description they provide of the fire behavior. They are then used as a benchmark to test the capabilities of a particular complex model to describe such a fire and to highlight the limitations and uncertainties. As a result of this evaluation, a set of recommendations for future research, both in experiments and modeling, are offered, in order provide a coherent strategy for the future which will significantly advance these models.