Safety engineers should be reasonably assigned to construction sites in order to prevent accidents specially for large-scaled projects. More engineering-oriented safety engineers should be assigned to those large-scaled projects because accident causes are found to be due to more technical aspects rather than general safety problems. more experienced engineers should be assigned to larger scaled projects for covering more technical aspects. This one is analyzed by the existing accident results. This study is to find out some formulae to calculate how many safety engineers should be assigned to construction sites, by amounts, by project kinds, by project scales, by engineer grades. So that construction contractor can assign them to their site economically.