The purpose of this study is to identify firm safety practices, safety technologies, and firm characteristics that are related to motor carrier accident rates. The theory of the firm suggests that firms maximize profit by investing in safety practices and safety technologies until marginal cost is equal to the marginal benefit. The data set used in the empirical analysis is unique, in that it will allow for testing of the relationship between firm safety performance and safety practices, new safety technologies, and firm marketing strategies. By testing the impact of the safety performance marketing strategy on carrier accident rates, it can be shown that firm managers have control over the safety performance of their firm through management decisions. The results indicate that firms with a safety performance marketing strategy have significantly lower accident rates. All tested technologies, and most safety practices, are found to be negatively related to carrier accident rates. These results support the idea that through investment policies, safety practices, and choice of marketing strategy managers have a direct impact on their carrier accident rate. Interestingly, the firm characteristics of unionization and use of owner-operators are found to reduce carrier accident rates the most. This suggests that motor carrier managers should consider their firm's characteristics in their management of carrier safety. / Graduation date: 2003

Blood safety is an issue of public health concern. Sensitive screening assays for excluding infectious donations have been widely adopted to reduce the risk of transfusion-transmitted infections, especially for hepatitis B virus (HBV), hepatitis C virus (HCV) and (human immunodeficiency virus) HIV infections. Even with sensitive screening assays, residual risk of undetectable infectious donations remains because donations may be made in the “window period” when the infection is present but difficult to detect with serological tests. Currently, serological screening tests are mainly used in China, rather than the more expensive and sensitive DNA based tests. From a public health perspective, choice of the screening test depends on overall cost-effectiveness, including assessment of the residual risk. To facilitate a full cost-effectiveness analysis, this review identifies the best residual risk estimating model in a Chinese setting. The search was conducted using databases including PubMed and ISI Web of Knowledge filtered by publication date, English language and accessibility of full text. Both exclusion and inclusion criteria were used for articles identification. Five papers on residual model estimation were retrieved. The blood donor profile in China was used to understand how these models differ and how these differences would affect their use and interpretation. This study identified the Michael P. Busch model as the optimal residual risk estimating model for Chinese blood banks’ to facilitate the cost-effectiveness assessment of a screening strategy in terms of achieving a balance of blood safety and cost. / published_or_final_version / Public Health / Master / Master of Public Health

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In radiological protection, models are used to assess radiation risk by means of extrapolation from high dose and dose rate to low dose and dose rate. In this thesis five main biophysical models of radiation action have been evaluated, appraised and inter-compared. The five models are lethal and potentially lethal (LPL) by Curtis, pairwise lesion interaction (PLI) by Harder, cellular track structure (CTS) by Katz, hit size effectiveness (HSE) by Bond and Varma and track core (TC) by Watt. Each model has been developed based on certain underlying mechanisms or phenomena, to permit interpretation and prediction on the induction of a specified biological endpoint such as cell reproductive death, chromosome aberrations and mutations. Biological systems of interest are, for example, mammalian cells containing deoxyribonucleic acid (DNA). Evidence is mounting that double strand breaks in the DNA are the critical lesions for various biological end points. To proceed with this work the TC model has been chosen. Cancer induction by ionising radiation is the stochastic effect of prime concern in radiological protection. Cancer induction cannot be avoided entirely but its frequency of occurrence may be reduced to acceptable level by lowering the amount of radiation received. The methods of assessment developed by ICRP, in terms of the cancer risk coefficients, are presented in this thesis. In the conventional (legal) system of dosimetry, radiation is quantified by the amount of energy absorbed per unit mass of tissue. Quality factors, superseded by radiation weighting factors, are needed to account for the quality dependence on radiation type. As an alternative, a new dosimetry system is proposed here which is based on the mean free path for primary ionisation along particle tracks and the integral fluence generated by the radiation field, whether directly or indirectly ionising radiation. From the study of cellular data, the mean free path for primary ionisation along particle tracks (lambda) emerges as a parameter which best unifies biological damage data. Radiation effect is found to depend, not on the energy transferred but to depend mainly on the frequency and spatial correlation of interactions. Maximum effect occurs when lambda is equal to lambda0 (2 nanometre, nm). The term 'Absolute Biological Effectiveness' (ABE) is introduced as a parameter which indicates the probability to induce a specified effect, per unit incident fluence. In this endeavour, only direct effects are considered in deriving ABE values for various radiations. However other factors such as indirect effects, inter-track action, repair processes and radiation rate, can be incorporated later if required, in the derivation of ABE. ABE values for photons up to 60Co i.e 1253 keV and neutrons up to 105 keV, have been calculated and presented in this thesis. An attempt has been made to re-express the cancer risk coefficients, derived by ICRP, in the new dosimetry system, in terms of the ABE (Absolute Biological Effectiveness). The hypothesis put forward in this thesis is that the induction of a specified biological-end-point in a biological system due to ionising radiations, is determined not by the amount of energy absorbed per unit mass (dose), but rather by the number of events (ionizations) spatially correlated, along the primary radiation track. Based on this hypothesis, a new unified dosimetry system, independent of radiation type, is proposed. Suggestions are made for possible measuring instruments which have the equivalent response characteristics, namely maximum efficiency of detection for the mean free path Success in devising such types of instrument would ensure the practicability of the new dosimetry system, in operational radiological protection.

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published_or_final_version / Transport Policy and Planning / Master / Master of Arts

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2017 / This study examines the application of the investigation process in industry to reduce electrical arc flash incidents. Literature indicates that three streams (policies, completed investigations and investigators) influence the application of the investigation process; however, these are traditionally analysed independently without examining the dynamic influences between them. This study combines and analyses those dynamic interactions, and testing at a steel plant demonstrates that this approach allows industry to identify site specific deficiencies. The investigation process requirements, identified in literature, were used to qualitatively and quantitatively analyse the three streams. The results were interpreted using triangulation. Deficiencies around disseminating reports and using experienced investigators were identified. These plant specific deficiencies are an improvement from generic findings in literature. This study contributed to knowledge in the field of incident investigations by proposing a holistic approach that is operationally ready, and identifies deficiencies specific to the industry in which it is used. / MT 2018