The authors have sampled dust samples in the modelling shop of the enterprise, that produced asbestos cement products, performed the dispersal analysis of chrysotile asbestos dust and cement dust, built areas of integral curves particle mass distribution by diameters for aspiration systems, general exhaust ventilation and sanitary protection zone. For description of dispersal composition of dust were used two-link splines in log-probabilistic coordinate system. Carried out a mathematical evaluation of these functions as random. The method of "dissection" is used for their description.