Abstract:Permissible CO concentration limits for three types of transverse ventilation tunnels were predicted by calculating under certain Carboxyhemoglobin(COHb) saturation level on the basis of CO concentration profile in tunnels and difference form of Coburn Forster Kane equation(CFK equation). A fitting equation for predicting permissible CO concentration limits is presented for each kind of transverse ventilation tunnels. Furthermore, a fitting equation for air supply type semi transverse ventilation tunnel for emergency ventilation is presented as well. The results show that the permissible CO concentration limits for transverse and air supply type semi transverse ventilation tunnels should be the same which is approximate 1/3 of the values for air exhaust type semi transverse ventilation tunnel.