Fire Safety Science Digital Archive

Hot zones form as an effect of the boiling range of oils, for especially heavier oils. Scattered vapor bubbles are produced throughout most parts of a hot zone. The generation, ascent and growth of these bubbles cause continual and vigorous convection. The temperature, density and chemical composition of oil in a hot zone are uniform throughout the entire hot zone, both vertically and horizontally. In a tank which is less than 800 mm in diameter, formation of a hot zone depends largely on both material and diameter of the tank. Hot zone formation in a 900 mm or larger diameter tank depends only on retention of the prescribed quantity of residual fractions of distillation at the surface temperature of the burning oil as determined by a distillation curve. Rate of conversion to a hot zone has a close relationship to the complicated oscillations accompanying the transfer of heat and mass through the interface.