Ignition of iron blocks in a pure oxygen atmosphere is studied using the following model. A heated iron block is exposed suddenly to 100% oxygen atmosphere. Oxidation occurs at the iron block surface, and an iron oxide layer is formed on the surface. Beneath the oxide layer, a melted iron layer exists. Ignition occurs when the melted iron layer flows. Critical conditions for ignition were calculated. When the initial oxide layer thickness was constant, the maximum surface temperature increased as the initial temperature increased. Ignition occurred when the maximum surface temperature exceeded a critical value of about 1540 K. Ignition occurred also at lower initial temperature, as the initial oxide layer thickness decreased. The conditions were compared with experimental data for ignition of iron cylinders. It was found that the model proposed in this study can accurately describe iron block ignition.
Smoky gases in an atrium can pass through leakage paths in an atrium facade to affect adjacent accommodation and its escape routes. It is possible for the designers of smoke control systems to take advantage of thermal buoyancy due to the fire to prevent such infiltration, by using a technique known as depressurisation. This is Part 1 of a two-part paper in which equations are derived for the design of smoke control systems using either natural or powered depressurisation. The influence of wind pressures on the building is included in design formulae. It is shown how depressurisation and 'throughflow' smoke ventilation can be combined in a hybrid system, either to keep the atrium smoke layer at a specified height, or below a specified temperature. The limits beyond which depressurisation cannot be used are explored.
This is Part 2 of a two-part paper in which it is shown how the depressurisation design equations derived in Part 1 are sensitive to the atrium layer temperature, and hence to heat losses from the layer. A method of calculating the heat balance in glazed atria (in the event of fire) is outlined. Practical design strategies which take layer cooling into account are discussed. Finally, a general design procedure for smoke control in atrium buildings is given.