Combustion propagation through solid materials I—downward propagation of smouldering along a thin vertical sheet of paper

Abstract As the first step in the general study of the propagation of combustion in the open air through solid materials which contain no oxidant in themselves, the downward propagation of smouldering along vertical strips of cardboard was studied. The velocity v of combustion propagation perpendicular to the fire front was observed in a large chamber of temperature T a with strips of breadth b and thickness d. The results were summarized and an experimental formula for v in terms of b, d and T a was obtained. In the theoretical part, it was assumed that: (1) the heat produced by the combustion of a solid body per unit time is proportional to the rate of the air supplied by natural convection which, again, is assumed to be proportional to (T−T a ) where T is the temperature of the solid body; (2) this heat is inversely proportional to (T i −T a ) where T i is the temperature at which the solid material ignites instantaneously, and (3) there is a stagnant boundary layer of combustion gases covering the surface of the solid and both the fresh air supply and heat dissipation from the solid into the air take place at the surface of this layer. The formula for v derived mathematically with these assumptions showed a perfect coincidence with the experimental formula.