The first day of the long-awaited state inquiry into the March 2018 Reedy Swamp bushfire has focused on the evidence of police arson experts.
Under the guidance of Deputy State Coroner Elaine Truscott, the coronial inquiry heard dead trees, infested with termites, likely fell on powerlines, igniting the fire which burned through more than 1000 hectares of forest, causing $63.5million worth of damage, and destroying 56 homes and 35 outbuildings in and around Tathra.
The inquiry, requested by then NSW Rural Fire Service Commissioner Shane Fitzsimmons, began on Monday, and will run until August 21.
It will investigate the origin and cause of the fire, as well as the management of energy infrastructure, the management of fuel loads before the fire and the response of emergency services.
Detective Sergeant El Khansa told the inquiry he believes a tree fell on powerlines at Reedy Swamp in heavy wind, causing a conductor to fall to the ground, "igniting dry fuel" in the six seconds it took before state-owned Essential Energy infrastructure was turned off.
He said video and photographic evidence from eye-witnesses shows the fire grew quickly over a period of just nine minutes.
The investigation of later property damage spanned eight months and included 12 officers, he said.
Detective Sergeant El Khansa said the original estimate of 65 destroyed buildings by the RFS was inaccurate as it was calculated without speaking with the home owners.
When asked by counsel assisting Adam Casselden SC why Essential Energy had widened the easement in question in May 2018, he said he did not know.
Detective Senior Sergeant Craig Harris, who has investigated up to 30 bushfires, also gave evidence to the inquiry on Monday.
Mr Casselden said while experts disagree on the exact details of what caused the fire, they do agree the fire started somewhere between four trees and powerlines in an easement at Reedy Swamp around midday on March 18, 2018.
"The fact that no-one lost their life in the fire is remarkable," he said during his opening address.
All investigations found no sign of human activity near the start of the fire, and lightning strikes were also ruled out.
Mr Casselden said arborist Marcus Lodge will likely tell the inquiry termites had likely damaged decaying dead trees in the area, causing them to fall in high winds.
Electrical engineer Trevor Blackburn will likely give evidence a tree fell on powerlines, creating embers, while bushfire risk management consultant Paul de Mar will likely say a different tree snapped a line which ignited vegetation on the ground.
Mr Casselden said a statement from an Essential Energy electrical engineer is yet to be received by the inquiry.
He said none of the trees in question had been identified as possible risks, despite being dead for some years, and questioned whether Essential Energy contractors were qualified to locate defects along easements.
The trees were last assessed for defects in December 2016, and a remote survey of vegetation encroachment was conducted in December 2017 but results weren't received until nine days after the fire.
Drone footage of devastated areas were shown, as was eye-witness video of smoke coming from the Reedy Swamp area.
One firefighter described Tathra as being "under siege from embers from the sky", the inquiry heard.
Mr Casselden said the embers were large and "unpredictable" in nature, and said with six other fires burning in the region, firefighters to a reactive approach, with "every available brigade deployed".
He said while the community had been warned of the possible fire danger, modelling of the fire by authorities was not fast enough to warn residents of the danger.
The inquiry heard information from locals was likely more useful than that from authorities, who made a "determined effort" to protect the community.