Predicting the radiant heat flux from burning logs in a forest following a fire

The radiant heat flux resulting from burning logs on the forest floor determines how soon after the passage of a bushfire people can survive on the burnt-out ground. A method to predict this flux was developed from the bum-out time of logs expressed as a function of initial log diameter and a given size-class distribution of logs and branches. This gives an estimate of the fraction of total power emitted per unit area, and an estimate of the radiant heat flux. In jarrah (Eucalyptus marginata) forest, 7 years after the last prescribed bum and carrying 36.5 t ha-1 of log and branch material, it takes 15 min before the radiant heat flux drops below the threshold for near-instantaneous pain and 31 min before it drops below the threshold value for long-term survival. Examples of minimum times to thresholds for other forest type groups are given, along with field observations that support the estimates.