A vehicle losing its rear wheel and dragging its undercarriage along the road sparked ae fire which swept through 3000 hectares of Tongariro National Park in November.
By Robin Martin of RNZ
A fire investigation report released under the Official Information Act describes witnesses seeing a vehicle with no left rear-wheel being pushed on State Highway 47 by three people.
About 50m away a fire was quickly growing which a member of the public called in just after 3pm, November 8 last year.
"The fire size was noted at around the size of two cars and quickly grew to as big as a house, with flames up to 2.5m tall, then very rapidly, by three-to-five minutes, it was the size of a large farm implement shed," specialist wildfire fire investigator Grant Detheridge-Davies said in his report.
"After the 111 call was terminated, it was estimated the fire to be almost a football field in size."
The vehicle in question was discovered parked in a layby on the opposite side of the road, hidden from sight, about 400m from the specific fire origin area.
"When found the vehicle did have four wheels fitted however the left-hand rear wheel was not fitted correctly and there was significant damage to the underside of the vehicle."
Large tracts of Tongariro National Park blackened with ash from a huge wildfire over the weekend. (Source: Supplied)
Detheridge-Davies said inspection of the road showed marks consistent with an item being dragged across the surface from about 60m before the specific fire origin area and then on for approximately 320m.
"The use of a magnet and metal detector confirmed the presence of metal filings and steel pieces in and around these drag marks, most showing they had been subjected to high temperature."
Based on physical evidence gathered at the scene, witness statements and photographs, Detheridge-Davies concluded the probable cause of the blaze was the "wheel, contacting the road surface creating hot metal sparks setting roadside vegetation on fire".
The specific ignition area of the fire was narrowed down to the edge of a drain on the side of SH47 where "dry tussock vegetation and rubbish had built up".
Detheridge-Davies said once the grass was ignited the fire spread quickly to other dry fuels.
"On the day of the fire, scrub fuels had an extreme fire rating. This along with a 15km/h wind recorded at National Park enabled the fire to increase in intensity and rate of spread, becoming a high intensity and fast-moving fire.
"A witness described the fire as the size of a car, but quickly spread to the size of two rugby fields by the time the brigade arrived."
Detheridge-Davies concluded the fire was accidental.
Second fire sparked by caravan breaking axle
It comes just a month after a massive blaze scorched 3000 hectares in the area. (Source: 1News)
Remarkably, documents show a second fire was sparked in the same area in similar circumstances just 30 days later.
A second fire investigation report released under the Official Information Act describes how a caravan breaking an axle sparked a 300ha fire on December 8.
Also penned by Detheridge-Davies it said FENZ received a 111 call to several vegetation fires on Volcanic Loop Highway SH47 at 1.10pm.
"An overflying helicopter reported the fire as over an 1/2-hectare in size and growing. Due to fire conditions a 3rd alarm [was raised] and a request for three helicopters was transmitted."
Motorists travelling north on SH47, between State Highway 48 and Mangapopo reported seeing a camper van towing a trailer travelling South towards Waimarino, "the towed trailer was emitting large number of sparks onto the side road from what appeared to be a major mechanical fault".
Emergency services were alerted to the fire, near the site of a blaze in November, just after 1.10pm on Monday. (Source: Supplied)
A motorist who saw smoke and came across a number of fires on the roadside called 111.
The first arriving Fire and Emergency appliance and passing police officers confirmed at least four fires started on the roadside over about 850m.
Once tussock on the side of the road was ignited the fires grew quickly and merged.
Detheridge-Davies concluded the fire was sparked accidentally.
"The probable cause of the fire was a trailer being towed by a camper van having a flat tyre then breaking an axle, resulting in the underside of the trailer contacting the road surface creating hot metal sparks setting roadside vegetation on fire."
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