Canberra researchers say they have confirmed the first case of a fire tornado from analysis of evidence collected during the January 2003 Canberra fires.
The researchers say the findings point to a possible shortcoming in the building codes in Australia's fire prone environments.
Building standards specify higher levels of structural engineering for cyclonic winds, but specifically exclude tornadoes.
Lead researcher, report co-author and Special Risks Analyst at the ACT Emergency Services Agency (ESA) Rick McRae said the finding, just published in the journal Natural Hazards, was based on extensive research into weather observations and radar data at the time of the fires combined with video footage and photographs taken by members of the public.
"The various data were combined and analysed to provide information on the occurrence and behaviour of the phenomenon known as pyro-tornadogenesis," Mr McRae said.
"Pyro-tornadogenesis is the technical term used to refer to the ability of a large fire to produce a genuine tornado.
"Researchers had speculated about the ability of a fire to produce a tornado, but this is the first documentation of the creation of a true tornado by the convection column of a large fire," he said.
"The tornado formed in the plume of the McIntyres Hut Fire mid-afternoon on January 18, 2003, and initially crossed the Brindabella Ranges adjacent to Mt Coree. It then moved through Uriarra and Pierces Creek Pine Plantations and grazed the edge of the suburb of Chapman. The fire tornado faded as it entered Kambah, south of Mt Taylor."
The two year project also involved Dr Jason Sharples from the University of NSW, Canberra, who is also a volunteer firefighter, Stephen Wilkes from the ACT Territory and Municipal Services directorate and Alan Walker from the ESA.
"Our analysis indicated that the tornado had a rating of at least a 2, on the Enhanced Fujita scale of tornado severity.
"It had major effects on the behaviour of the fire on the urban edge and had enough force to remove roofs from houses and to blow cars off the road," Mr McRae said.
"It moved at over 30 km/h across the ground and had a basal diameter of nearly half a kilometre when it reached Chapman. It was a major tornado, but was barely noticed given the setting," he said.
The research team also showed how a fire tornado is fundamentally different from a fire whirl, which is commonly associated with fires.
"Tornadoes are associated with thunderstorms and as such they are anchored to a thundercloud above, and are able to sporadically lift off the ground. Fire whirls, on the other hand, are anchored to the ground and do not require the presence of a thunderstorm," Dr Sharples said.
The study provides more insight into the behaviour of thunderstorms that form over large fires, which is currently the subject of an international research effort.
The ESA will raise potential impacts of a fire tornado with the Standards Australia Wind Loadings Committee and the Australian Buildings Code Board."