BushFIRE Arson Bulletin No.20 looked at some of the factors that influence cause determination in bushfire investigations. The NSW Rural Fire Service (RFS) has provided the bushfire arson project with an extract from its investigations database for analysis. This extract covers 466 fires occurring from 2001/2002 to 2003/2004.
Figure 1 shows the causes of fires investigated by the RFS Investigations Unit. The majority of investigated fires (n=298; 64%) were determined to be the result of deliberate ignitions. This is a higher rate than is usually seen in bushfire data, and is a result of the particular subset of bushfires that the RFS Investigations Unit is tasked with examining. While somewhat skewed in comparison with bushfires overall, this finding indicates the prominence of deliberate ignition amongst significant bushfires.
Natural ignitions due to lightning strikes and, in one case, spontaneous combustion caused 51 ignitions (11%). A similar number of fires resulted from accidental ignitions, including fires caused by powerlines, machinery or equipment and campfires or barbecues. Private burning activities, usually for hazard reduction or disposal, led to 36 fires (8%). Given that the fires in this dataset were the subject of a dedicated investigation effort, the proportion of unknown fires (n=13; 3%) is much lower than often seen in bushfire data sets.
Figure 1 : Cause of investigated bushfires in New South Wales 2001/02 to 2003/04 [see attached PDF]