Wood dust is generated as a by-product of machining. This paper discusses the granulometric analysis of selected samples of wood-settled dust from spruce (Picea abies L.), fir (Abies alba Mill.), oak (Quercus petraea Liebl.), beech (Fagus sylvatica L.), and alder (Alnus glutinosa L.). It also includes a sample of a mixture from timber production grinders in order to select the percentages of the various fractions (32 μm, 63 μm, 80 μm, 125 μm, 250 μm, 500 μm, 1000 μm, 2000 μm) of wood dust samples. Wood dust samples were made using a hand orbital sander and sized on an automatic mesh vibratory sieve machine. Comparison of the resulting granulometric fractions’ contributions to wood sanding dust was confirmed by the particle size. This paper presents selected characteristics of the chosen wood dusts by the size of particle dust fractions on the base of continual thermal loading. Thermal properties of wood dust samples were characterized by thermal gravimetric analysis (TGA). The TGA results indicated different thermal degradation fractions of the wood dust samples during thermal loading. The wood dust consisted mainly of fractions of 80 µm, 32 µm, and < 32 µm. These fractions of all wood dusts species presented more than 70.00% of the sample (alder dust has more 80% of sample). Thermal characteristics were not confirmed by the particle size and different wood dust.