I'm modelling a number of diesel machines driving a tunnel ventilated by a forcing fan and ductwork. I get the error message "Fresh Air Deficit" x 5 when I try to run the model. The error persists even if I reduce the utilisation factor for the machines to 10%. The error isnt being caused by excessive DPM levels, or by excessive temperature. I assume its because the total flow available in the road is less than the total engine power x 0.06m3/s? How does the software assign this error? Is there a reason that the first 2 vehicles in the flow dont have the error but the last 5 do?