Direct Arc Furnace earthing

Sir, In DAF through slag door furnace man do blocking with metal tools 2 or 3 at a time.I saw electric sparks when it touchs the metal body of furnace.They say they dont get shock as the furnace is earthed.In case they wear shoes also,but is it a probabilty that the 20000Amp furnace with 3 electrode delta connected more enough to give shock. Or The ground concept is that solid,or the closed circuit dont give shock or is it voltage that give shock not current.i doubt Shoe insulation got insulation coordination. Please give the facts/secrets.