In autogenous welding, cutting and allied processes, so-called dry safety devices are used to protect the outlet terminals of gas distribution lines. To prevent flame transmission, these units are fitted with sintered metal flame arrester elements. At the Federal Institute for Materials Research and Testing (BAM), extensive investigations have been carried out with an experimental flame arrester to determine the limits of safety against flame transmission for sintered metal flame arrester elements in the case of flashback in fuel gas/oxygen mixtures. On the basis of the results of these investigations, it is possible to estimate the pore sizes up to which a sintered metal element can prevent any flame transmission with a given fuel gas.