Measurements of flaming combustion of pure and fire-retarded cellulose

Abstract The burning of charring materials is studied using samples prepared from pure cellulose and from cellulose which has been fire-retarded by the addition of sodium hydroxide and sodium carbonate. Vertically oriented, hemispherical-nosed cylinders are burned at atmospheric pressure in mixtures of oxygen and nitrogen. The techniques developed for the preparation of homogeneous samples are described. The char layer thickness after a fixed burning time has been measured and is found to be a slowly varying function of retardant concentration. Measuremetns of the burning rates for pure and retarded cellulose show an increase with ambient oxygen concentration, and a decrease with time at fixed oxygen concentration. Extinction of the flame begins at the stagnation point and then moves downstream. Measurements of the surface temperatures show an increase with time which is attributed to the growth of the char layer. Results are presented giving the effects of retardant concentration on both burning rate and surface temperature. The amount of retardant needed to cause extinction is found to increase sharply as the ambient oxygen concentraion is increased.