Thesis (MTech (Chemical Engineering))--Peninsula Technikon, Cape Town, 2004 / Current Risk Assessment procedures for the estimation of the acute health impacts resulting from the accidental release of toxic chemicals into the atmosphere involve the definition or construction of a representative accidental release scenario and the use of one or other air quality or dispersion model to estimate ambient air concentrations and exposure durations in the vicinity of the source. Legislation such as the South African Occupational Health and Safety Act, 1993, Major Hazard Installation Regulations, United States Risk Management Plan Rule and the European Union Seveso n, to prevent and or minimize impacts of such events require owners of installations to perform a Risk Assessment if they handle hazardous substances above specified threshold quantities. Mathematical modeling has been widely used to assist with the Exposure Assessment to perform off-site worst-case release analysis. Governmental departments, agencies and local authorities increasingly (but not exclusively) rely on air pollution models for making decisions related to air quality, traffic management, urban planning, and public health. As a result, the model users' community is becoming larger and more diverse. Most of the air quality modeling work has so far been based on the "deterministic" approach of using only set input parameters and specific applications. The selected model provides estimates of averaged concentrations using specific meteorological and emission data sets.

On August 31, 1992, Quality Printing Circuits, a circuit board manufacturing plant in Phoenix, Arizona, burned to the ground. The fire lasted approximately eight hours, creating a thick, black smoke that blew into the surrounding community. Emergency evacuation was erratic and since no air samples were taken during the fire, community exposure levels were unknown. Immediately afterwards, residents reported health problems but government studies on the community were unable to link reported health problems and the fire. Eight months after the fire, a local advocacy group performed a health study on the community. The 690 people surveyed reported symptoms such as asthma, blurred vision, vomiting, hair loss, rashes, and extremity numbness. The survey was never analyzed and the case was closed. Community members continued to report health problems and five years after the fire, the US Environmental Protection Agency reopened the case. They performed two sampling studies but results found that chemical levels were below allowable exposure levels. This thesis contains three chapters that investigate the political, health, and scientific issues related to the QPC fire. The scientific chapter uses the EPA's ISCST3 dispersion model and a mixed-box model, to approximate community exposure concentrations and compare them to allowable human exposure levels. Results of the ISCST3 model show that four (hydrogen chloride, polycyclic aromatic hydrocarbons, Acrolein, and naphthalene) of the twenty chemicals modeled were above government allowable concentrations. Inhalation exposure to these chemicals causes similar symptoms as those reported by residents. The health-focused chapter characterized health symptoms reported in the 1993 health survey. Results found that symptoms experienced by residents were similar to those documented in other studies of exposure to chemical smoke. The study also found that residents living closest to QPC reported a greater number of symptoms than residents living further away. The political chapter analyzed the debate as to whether QPC officials and government agencies took the steps needed to protect the exposed community during and after the QPC fire. What became evident was that a significant conflict existed between the interests of residents involved in the QPC fire and the government agencies responsible for protecting them. / Graduation date: 2004