The aim of this diploma thesis is to determine select fire-technical characteristics of Norway spruce dust. Wood dust samples were taken from the processing of spruce wood on woodworking machines, a four sided planer, a vertical saw, a circular saw, a longitudinal bottom milling machine, a radial cutter machine and a grinding machine. Different types of sawdust, shavings and wood dust created as waste in sawing, planing, grinding and milling. Using a sieve analysis, we separated the wood dust samples that are suitable for determining the lower explosive limit and specification of the hazardous thickness of the settled dust. We performed the sieve analysis on the analytical sieve machine RETSCH AS 200 using the methodology given by manufacture. Subsequently we calculated the bulk density of wood dust. To determine the lower explosive limit of wood dust of spruce wood, we used VK 100 explosion chamber. Experimentally, we have found that the lowest lower explosion limit has a particle size of less than 0.500 mm and bigger than 0.125 mm.We conducted the investigation to determine the hazardous settled dust layer in the wood processing. We determined the lowest thickness of the hazardous layer of wood dust for samples taken from a sawmill for particles smaller than 0.063 mm, 0.44 mm, this fraction is also the most dangerous for manufacturing process.Based on the research, we found that even with a thickness of 0.44 mm of the settled dust there is a risk of explosion in manufacturing process. As a precautionary measure, we recommend to place mobile suction device by each machine.