3. Two canonical situations

3.1 Two-layer description

Up to now, we have only considered cases where the quantities were assumed to be homogeneous in the fire room, with a purely thermodynamic vision. In reality, as soon as a fire develops, the hot smoke tends to rise and settle in a homogeneous layer under the ceiling, above a layer of fresh air kept at the bottom as long as the fire is sufficiently ventilated. After considerations common to all two-layer flows, two canonical situations are successively considered: the case of an imposed extraction flow corresponding to mechanical smoke extraction, then the case of natural smoke extraction. These situations are canonical in the sense that between them they contain all the ingredients to be taken into account in all real cases.

To begin...