Pigeon Valley fire cause confirmed as sparks from disc plough

Tuesday, 13 August 2019

The cause of the New Zealand's third largest wildfire at Nelson's Pigeon Valley has been confirmed as sparks from a disc plough.

Fire and Emergency Principal Rural Fire Officer for Nelson-Tasman Ian Reade said on Tuesday that an investigation found the fire was accidentally sparked by an agricultural contractor using a disc plough on a rocky paddock.

The report found that sparks from from metal on stone or metal on metal contact  ignited dry grass in the paddock at Pigeon Valley, 30 kilometres south-west of Nelson city, on February 5 this year.

It quickly spread onto a steep hillside of young pines. The Pigeon Valley fire burned out of control for days, covering more than 2300 hectares of forest, property and pastures. A three-bedroom house and a shed were destroyed in the blaze.

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'This fire proves that, in extreme weather conditions, a seemingly every-day rural activity can end up causing widespread damage,' Reade said.

The report by wildfire investigator Jamie Cowan said an inspection of the paddock where the fire started showed 18 significant stone strikes, some with 'a significant amount of steel smeared onto the rocks'.

'I was surprised it had been disced, it was so rocky,' Cowan said in his report. 

There were also marks on at least one of the metal scrapers on the plough, used to keep discs free of debris, indicating it had come into contact with a disc during its operation.

The report said the contractor who had been discing the paddock noticed smoke from an area he had ploughed about two minutes before. He tried to put the fire out with the discs and an extinguisher, but it was too hot.

He had no cellphone reception in the paddock but as he was walking out a passer-by said he had already called 111.

'I am confident this fire was caused by the operation of the discs in very stony ground on a very hot day,' Cowan concluded.

He said discing should be considered low risk for potential ignitions in most circumstances, but in extreme fire conditions it should be subject to 'trigger points' to identify when the risk is high and the operations should stop.

Cowan also carried out investigations for Fire and Emergency NZ into Nelson fires that broke out during the Pigeon Valley blaze - at Rabbit Island on February 6 and at Iwa Rd in Nelson city on February 8. He found that both had been deliberately lit.

At Iwa Rd where the fire came close to 10 hillside homes, Cowan looked at the possibility that a cigarette flicked from a passing vehicle could have sparked the blaze.

But that was ruled out because of the moderately high relative humidity on the day and the moderate fine fuel risk on the hillside. 

The origin of the blaze was on a steep slope at the side of lower Iwa Rd, at a height where a person could have reached over the roadside fence and ignited dry grass with a lighter or other open flame.

The fire covered nine-hectares but fortunately helicopters and fixed-wing planes that were working on the Pigeon Valley blaze were diverted to get it under control quickly.

At Rabbit Island there were two separate fires, and Cowan again concluded a person or persons used a lighter or other open flame to ignite the dry vegetation.

Reade said the extreme conditions in Nelson and Tasman this summer were not unique.

Parts of Marlborough, Canterbury, Otago, Bay of Plenty and Northland all had similar fire risk profiles.

Reade said it was likely these conditions would become increasingly common during summer in many parts of New Zealand, particularly on the eastern seaboard.

'There are many simple things people can do to prevent fires starting, from not using machinery which can emit sparks in hot, dry and windy conditions, to ensuring electric fences are not in a position or used where they could spark onto dry vegetation.

'Steps can also be taken to protect property from a fire, such as removing material near the home that could be ignited by flying embers, for example leaves in gutters, firewood heaps by the house or timber stored under the house.'