Factors affecting human reliability in the chemical process industry

This research was concerned with identifying factors which may influence human reliability within chemical process plants - these factors are referred to as Performance Shaping Factors (PSFs). Following a period of familiarization within the industry, a number of case studies were undertaken covering a range of basic influencing factors. Plant records and site `lost time incident reports' were also used as supporting evidence for identifying and classifying PSFs. In parallel to the investigative research, the available literature appertaining to human reliability assessment and PSFs was considered in relation to the chemical process plan environment. As a direct result of this work, a PSF classification structure has been produced with an accompanying detailed listing. Phase two of the research considered the identification of important individual PSFs for specific situations. Based on the experience and data gained during phase one, it emerged that certain generic features of a task influenced PSF relevance. This led to the establishment of a finite set of generic task groups and response types. Similarly, certain PSFs influence some human errors more than others. The result was a set of error type key words, plus the identification and classification of error causes with their underlying error mechanisms. By linking all these aspects together, a comprehensive methodology has been forwarded as the basis of a computerized aid for system designers. To recapitulate, the major results of this research have been: One, the development of a comprehensive PSF listing specifically for the chemical process industries with a classification structure that facilitates future updates; and two, a model of identifying relevant SPFs and their order of priority. Future requirements are the evaluation of the PSF listing and the identification method. The latter must be considered both in terms of `useability' and its success as a design enhancer, in terms of an observable reduction in important human errors.

Fabrication of high quality optical coherence tomography (OCT) calibration artefacts using femtosecond inscription

Optical coherence tomography (OCT) is a non-invasive three-dimensional imaging system that is capable of producing high resolution in-vivo images. OCT is approved for use in clinical trials in Japan, USA and Europe. For OCT to be used effectively in a clinical diagnosis, a method of standardisation is required to assess the performance across different systems. This standardisation can be implemented using highly accurate and reproducible artefacts for calibration at both installation and throughout the lifetime of a system. Femtosecond lasers can write highly reproducible and highly localised micro-structured calibration artefacts within a transparent media. We report on the fabrication of high quality OCT calibration artefacts in fused silica using a femtosecond laser. The calibration artefacts were written in fused silica due to its high purity and ability to withstand high energy femtosecond pulses. An Amplitude Systemes s-Pulse Yb:YAG femtosecond laser with an operating wavelength of 1026 nm was used to inscribe three dimensional patterns within the highly optically transmissive substrate. Four unique artefacts have been designed to measure a wide variety of parameters, including the points spread function (PSF), modulation transfer function (MTF), sensitivity, distortion and resolution - key parameters which define the performance of the OCT. The calibration artefacts have been characterised using an optical microscope and tested on a swept source OCT. The results demonstrate that the femtosecond laser inscribed artefacts have the potential of quantitatively and qualitatively validating the performance of any OCT system.

Advances in characterisation, calibration and data processing speed of optical coherence tomography systems

This thesis describes advances in the characterisation, calibration and data processing of optical coherence tomography (OCT) systems. Femtosecond (fs) laser inscription was used for producing OCT-phantoms. Transparent materials are generally inert to infra-red radiations, but with fs lasers material modification occurs via non-linear processes when the highly focused light source interacts with the materials. This modification is confined to the focal volume and is highly reproducible. In order to select the best inscription parameters, combination of different inscription parameters were tested, using three fs laser systems, with different operating properties, on a variety of materials. This facilitated the understanding of the key characteristics of the produced structures with the aim of producing viable OCT-phantoms. Finally, OCT-phantoms were successfully designed and fabricated in fused silica. The use of these phantoms to characterise many properties (resolution, distortion, sensitivity decay, scan linearity) of an OCT system was demonstrated. Quantitative methods were developed to support the characterisation of an OCT system collecting images from phantoms and also to improve the quality of the OCT images. Characterisation methods include the measurement of the spatially variant resolution (point spread function (PSF) and modulation transfer function (MTF)), sensitivity and distortion. Processing of OCT data is a computer intensive process. Standard central processing unit (CPU) based processing might take several minutes to a few hours to process acquired data, thus data processing is a significant bottleneck. An alternative choice is to use expensive hardware-based processing such as field programmable gate arrays (FPGAs). However, recently graphics processing unit (GPU) based data processing methods have been developed to minimize this data processing and rendering time. These processing techniques include standard-processing methods which includes a set of algorithms to process the raw data (interference) obtained by the detector and generate A-scans. The work presented here describes accelerated data processing and post processing techniques for OCT systems. The GPU based processing developed, during the PhD, was later implemented into a custom built Fourier domain optical coherence tomography (FD-OCT) system. This system currently processes and renders data in real time. Processing throughput of this system is currently limited by the camera capture rate. OCTphantoms have been heavily used for the qualitative characterization and adjustment/ fine tuning of the operating conditions of OCT system. Currently, investigations are under way to characterize OCT systems using our phantoms. The work presented in this thesis demonstrate several novel techniques of fabricating OCT-phantoms and accelerating OCT data processing using GPUs. In the process of developing phantoms and quantitative methods, a thorough understanding and practical knowledge of OCT and fs laser processing systems was developed. This understanding leads to several novel pieces of research that are not only relevant to OCT but have broader importance. For example, extensive understanding of the properties of fs inscribed structures will be useful in other photonic application such as making of phase mask, wave guides and microfluidic channels. Acceleration of data processing with GPUs is also useful in other fields.

A prototype bone screw design for osteoporotic bone

Poster. Introduction: One in five menand one half of women over the age of 50 will experience a bone fracture, whichis frequently accompanied by poor bone health. This combination of poor bonehealth and fracture is a two edge sword, because not only does poor bone healthmake fractures more likely, it also reduces the efficacy of standard fracturetreatments. Currently available surgical fixation devices that were originallydeveloped for healthy bone, such as pins, plates and bone screws, are often noteffective for patients with osteoporosis, resulting in unsatisfactory outcomesor longer and more painful recovery times. One major issue is the design ofbone screws, which can loosen or pull-out from osteoporotic bone. Osteopenicscrews with larger outer thread diameters have been developed to try andaddress this problem. The larger diameter screws have been shown to be 60–70 %stronger in lab tests of individual screws but the larger diameter screwscannot be used with the standard spacing in fixation plates without the risk ofcausing fractures between the screws. In addition, many fractures occur nearjoints where there is not room to increase the spacing between screws.Therefore, new bone screws are needed for treatment of fractures in osteoporoticbone. Materials and Methods: Afterdeveloping a novel bone screw design, we fabricated screws using rapidprototyping methods. Screws were inserted into 10 pcf density sawbones polyurethanefoam as a model for osteoporotic bone. Pull-out tests were conducted using theprototype bone screw design and the standard screw design for comparison inaccordance with ASTM 543-13. Results and Discussion: Ourprototype screws have the same outer diameter as standard bone screws, but haveoptimised threads. For pull-out tests in 10 psf density sawbones poly-urethanefoam, the prototype screw design was 60 % stronger than the standard bone screwdesign (p<0.01). Conclusion: Our novel bonescrew design provides significant improvement in standard tests with syntheticbone material. Additional tests are needed to determine if the bone screwswould be suitable for human trials.