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A series of full-scale experiments were conducted in a mock-up commercial cooking area to study extinguishing mechanisms and effectiveness of water mist against cooking oil fires. The impact of water mist characteristics, such as spray angle, droplet size, flow rate, discharge pressure and type of nozzle, on the effectiveness of water mist against cooking oil fires was investigated. A series of oil splash experiments were also conducted to determine if the oil was splashed by water mist. In addition, the change in oil composition during heating and fire suppression was determined using Fourier Transform Infrared (FTIR) technique. The study showed that cooking oil fires were very difficult to extinguish, because they burned at high temperature and re-ignited easily due to changes in oil composition during heating and fire suppression. The water mist systems developed in the present work effectively extinguished cooking oil fires and prevented them from re-ignition. The spray angle, discharge pressure, and water flow rate were important factors to determine the effectiveness of water mist in extinguishing cooking oil fires.

Tris(methyltio)silane and tris(isopropylthio)silane effectively reduce a variety of organic substrates via free radical mechanisms. These silanes can also be used as hydrosilytating agents for alkenes having electron-donating substituents. The bond dissociation energy of the Si-H bonds have been measured by photoacoustic calorimetry and found to be around 83kcal mol -1 . The absolute rate constants for the reaction of the tert-butoxyl radical with (RS) 3 SiH have been measured by a laser flash photolysis technique and the optical absorption spectra of the corresponding radicals have been obtained

The heat of formation of benzophenone oxide, Ph2CO2, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph2CN2 + O2 Ph2CO2 + N2 was found to be −48.0 ±0.8 kcal mol−1 and ΔHf(Ph2CN2) was determined by measuring the reaction enthalpy for Ph2CN2 + EtOH Ph2CHOEt + N2 (−53.6 ±1.0 kcal mol−1). Taking ΔHf(PhCHOEt) = −10.6 kcal mol−1 led to ΔHf(Ph2CN2) = 99.2 ± 1.5 kcal mol−1 and hence to ΔHf(Ph2CO2) = 51.1 ± 2.0 kcal mol−1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph2CO2 2Ph2CO + O2 is exothermic by −76.0 ±4.0 kcal mol−1.

Heats of the reaction H{sub 2}O + 2RH {yields} 2H{sub 2}O + 2R{sup {sm bullet} were measured in water for a variety of organic substrates by using photoacoustic calorimetry. The values obtained were substantially lower than those calculated from gas-phase data and the difference was due entirely to the change in solvation energy associated with the conversion of 1 equiv of hydrogen peroxide to 2 of water. The solvation energies of R{sm bullet}} and RH were the same and their contributions to the measured heats of reaction therefore canceled. The results suggest that solution data, measured in extremely polar solvents, can be converted to their gas-phase equivalents (and vice versa) by considering only the heats of solvation of very small, polar molecules that participate in a given reaction. Moderately large organic molecules and their corresponding radicals are solvated to the same extent - even in water.

The role of substituent effects in free radical and carbene chemistry was investigated using a variety of techniques including e.s.r. spectroscopy, measurement of appearance energies, electrochemistry and kinetics. The thermodynamic data obtained in some of these experiments were used to probe the magnitude of substituent effects and their impact on group additivity methods. Electrochemical experiments showed that the removal of an electron from a substituent had a profound effect on the strengths of the neighbouring C-H bonds. Finally, examples drawn from carbene chemistry showed that sterically crowded substituents could be used to induce major electronic changes in these molecules.

Heats of the reaction H{sub 2}O + 2RH {yields} 2H{sub 2}O + 2R{sup {sm bullet} were measured in water for a variety of organic substrates by using photoacoustic calorimetry. The values obtained were substantially lower than those calculated from gas-phase data and the difference was due entirely to the change in solvation energy associated with the conversion of 1 equiv of hydrogen peroxide to 2 of water. The solvation energies of R{sm bullet}} and RH were the same and their contributions to the measured heats of reaction therefore canceled. The results suggest that solution data, measured in extremely polar solvents, can be converted to their gas-phase equivalents (and vice versa) by considering only the heats of solvation of very small, polar molecules that participate in a given reaction. Moderately large organic molecules and their corresponding radicals are solvated to the same extent - even in water.

The heat of formation of benzophenone oxide, Ph2CO2, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph2CN2 + O2 Ph2CO2 + N2 was found to be −48.0 ±0.8 kcal mol−1 and ΔHf(Ph2CN2) was determined by measuring the reaction enthalpy for Ph2CN2 + EtOH Ph2CHOEt + N2 (−53.6 ±1.0 kcal mol−1). Taking ΔHf(PhCHOEt) = −10.6 kcal mol−1 led to ΔHf(Ph2CN2) = 99.2 ± 1.5 kcal mol−1 and hence to ΔHf(Ph2CO2) = 51.1 ± 2.0 kcal mol−1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph2CO2 2Ph2CO + O2 is exothermic by −76.0 ±4.0 kcal mol−1.

A novel combination of the established techniques of laser flash photolysis and optoacoustic calorimetry was used as a means for quantitative investigation of relaxation mechanisms in two-laser, two-photon excited species. Flash photolysis was used to determine the absorbance of the initially formed intermediate at the wavelength and exact time of the second laser pulse. The amplitudes of the optoacoustic signals due to heat emission from the excited intermediate following the second pulse were plotted as a function of the fraction of absorbed photons or of the laser energy. The slope of such a plot for the excited diphenylmethyl radical in cyclohexane was compared to that of a two-laser, two photon reference system (1-(chloromethyl)naphthalene in cyclohexane) where the excited intermediate (1-naphthylmethyl radical) releases all its absorbed energy rapidly by nonradiative means. From such measurements, the quantum yield of fluorescence of the excited diphenylmethyl radical in cyclohexane was calculated to be 0.31. Other possible applications of the technique are discussed.