PURPOSE: To prevent the heat generation in the blade of cutting tool and the oxidation and heat generation of cut material in the cutting work by blowing inert gas to the blade of cutting machine and cut work.

CONSTITUTION: When iron and non-ferrous metals are recovered from crushing scrap iron and scrap non-ferrous metals with cutters of high speed or high revolution speed at shredders, dust and gases of plastics, paint gases, oil, volatile matters, impure gases, etc., are generated, therefore, there is danger of causing dust explosion ignited by heated cutters and cut materials. To avoid such danger, inert gas atmosphere is formed by blowing inert gas to the cutter of a cutting machine and cut materials, resulting in the condition wherein, especially oxidation, heat generation and ignition are prevented quickly.