The concentrations of bromochlorodifluoromethane (BCF) and of carbon tetrachloride needed to prevent the ignition by a particular type of flame of dispersed clouds of coal dust have been determined in a steel tube of 1.22 m diameter and 68.4 m length. The suppressants were premixed with the air in the tube, and tests were made in atmospheres at ambient temperature and at 70°C. Volume concentrations of about 1-1.5% were found to prevent ignition. Experiments were also carried out at 70°C to determine the amount of BCF, when injected into the tube in liquid form, to suppress established coal-dust explosions. Masses greater than 1.75 kg gave suppression. When the BCF was premixed with the air in the tube, both the pressure and spread of flame from the initial coal-dust explosion were reduced considerably, but when injected as a suppressant, the BCF prevented the extension of flame but had little effect on the development of pressure. The results for coal-dust concentrations ranging 1.3-3.2 times stoichiometric confirm the findings of Grumer and Bruszak [6] who, using a smaller-scale apparatus, noted that halons became relatively more effective on a weight-percentage basis as the concentration of coal dust was increased from 0.75 to 1.25 times stoichiometric.