Industrial accidents, which have taken, place recently at coal mining show that in spite of many operations ensuring safety, the menace of life and occurrence of losses caused by explosions is steel possible. In many works one can read that the dust (water-proof hydrophobized limestone dust) barriers very effective interrupt the flame propagation. Such limestone dust has been produced by coating regular dust with stearic acid during grinding in stone mills. In the consequence of modernization of quarries the quantity of possible producers of such dust could be reduce. For this reason new methods of manufacture of water-proof dust should be searched. In preliminary studies it is necessary to obtain the knowledge of the function and meaning of limestone dust in protection system against explosion at coal mine. Limestone dust must have hydrophobic properties. These are the consequence of quantity of stearic acid coated on dust particles and of used hydrophobisation method. Waterproof properties of dust should be kept for a long time. Hydrophobized limestone dust must be featured by certain floatage and must be cheap.