THE SPEED OF A FIRE FRONT AND ITS DEPENDENCE ON WIND-SPEED

The results of a number of laboratory tests of wind-driven fires indic ate the existence of a characteristic wind speed, U'. The form of the fire spread (V) as a function of mid-flame wind speed (U) differs abov e and below this characteristic speed. The scatter in field data is so great that it is difficult to confirm this result for field data. How ever, expressions of the form: V/V(o) -1 = a(U/U')0.5 U/U' < 1 and V/V (o) -1 = a(U/U')3 U/U' > 1 with U' = 2.5 m s-1 perform in a similar ma nner to existing models. For many fuel types a = 15. A difficulty with existing fire spread models is the measurement and definition of V(o) , the no-wind rate of spread. It can hardly ever be measured in the fi eld and has to be inferred from analytical formulae, or by extrapolati ng measured data. The value of a depends on the method used estimate V (o).