Fire Safety Science Digital Archive

The smouldering of cork dust in an air draught has been investigated with dust fractions whose mean particle sizes ranged from O.OO65 cm to O.84 cm. Over this wide range the relation between the rate of smouldering of dust trains and the velocity of the applied air was shown to vary markedly; and it is probable that differences in the relations obtained previously with other dusts were due, at least in part, to the differences in the particle sizes of those dusts. With the finer cork fractions the appearance of the smouldering did not differ markedly from that of other dusts, but with the courser cork fractions the smouldering became more vigorous with copious evolution of smoke and intense glowing which led to the development of flaming under an air draught. Vigorous smouldering developed in the very coarse fractions, even in still air. The effect of airflow upon the smouldering rate was less marked when the airflow and the propagation of smouldering were in opposing directions, thus preventing the air from impinging directly upon the smouldering zone, and it therefore seems probable that the vigorous smouldering noted above resulted from the ease with which air could penetrate between the particles of coarse dusts. The minimum depth of dust layer for sustained smouldering in still air increased with particle size for the finer fractions, reached a peak value, and then decreased again with course fractions when the smouldering became more vigorous. There was no indication that cork dust might be too coarse to smoulder.