On the fire dynamics of vehicles and electrical equipment: Dissertation

The fire behaviour of passenger cars, electronic cabinets, and electrical ignition sources has been studied by experimental, modelling and statistical methods. The research presented in this thesis gives new quantitative information on variables essential for estimating fire safety of these subjects and structures relating to them. Full-scale fire experiments on ordinary medium-size passenger cars, equipped as in practise with oil, four tyres, spare tyre and 30 litres of petrol in the fuel tank are presented. Rate of heat release by means of oxygen consumption calorimetry, mass loss and rate of mass loss, heat flux, carbon monoxide and carbon dioxide production rate, smoke production rate, gas temperatures above the car and temperatures inside the car were determined as a function of time. The experimental rate of heat release curves are parametrised by superposition of one Boltzmann curve and three symmetrical Gaussian curves. The car fire is modelled by two fire plumes, one emerging from the centre of the windscreen of the car, the other from the centre of the rear window. Gas temperatures are calculated using rate of heat release for the model plumes and Alpert's equations for maximum ceiling jet temperature, and compared to experimental temperatures from the car fire experiments. The calculated and measured temperatures were found to be in good accordance. The results can be used in design calculations for car park buildings and other structures related to passenger cars. Electrical ignitions of fires in nuclear power plants are studied by analysing statistical information from incident reports, by modelling the most frequent physical ignition mechanisms, and by experiments on some scenarios. Statistical data indicated cables have a significant role in electrical ignitions. Modelling some relevant cable fire scenarios give quantitative information on the conditions and physical processes of possible cable fire situations. Full and reduced scale experiments have been carried out on electronic cabinets with differing ventilation conditions, contents and structure, igniting the cabinet with a small propane burner beneath a cable or wiring bundle. Measurements on rate of heat release, mass loss, carbon monoxide, carbon dioxide and smoke (carbon) production rate, gas and surface temperatures were performed. The potential rate of heat release bound in carbon (smoke) and carbon monoxide production due to incomplete combustion was determined from measured production rates and reaction equations, and found to be considerable. Ignition power and energy sufficient for sustained burning leading to flashover in the cabinet were determined. The fire growth rate after ignition was concluded to be slow. The effect of the cabinet fire on an adjacent cabinet and a cabinet 1 m apart was studied, and times to ignition of cables in the adjacent cabinet were estimated. A model for estimating the maximum rate of heat release in an electronic cabinet is proposed, and checked against experimental data. It is found to describe the main features of a burning cabinet after flashover when the fire becomes ventilation-controlled. The model seems to be quite insensitive to parameters of the burning cabinet and a formula is proposed which depends on cabinet dimensions only. Furthermore, an analytic formula is suggested to estimate the minimum rate of heat release needed for flashover in an electronic cabinet. The formula is consistent with available experimental data, although the amount of data is still small. The results of the cabinet study can be used in safety assessment studies of fires originating in an electronic cabinet, e.g. estimating fire size, or as energy release input data in fire development calculations on control rooms in process plants and other sites containing electronic cabinets.