Steady temperatures in a wall penetrated by a hole and exposed to fire on one side

A hole in a wall weakens the wall's ability to withstand fire. Key parameters that control the safety of the system are identified through a calculation of the temperatures. To obtain the most severe case, a steady state is assumed. The mass flow rate ṁ g through the hole and the thickness l of the wall are the most important parameters. These may be grouped with the gas viscosity μ g to form the dimensionless quantity ṁ g /lμ g . When the value of this quantity is near 1, the back face of the wall and the emerging gases are cool. They are dangerously hot when ṁ g /lμ g is near 100.