Rural Whanganui fire probably spontaneous combustion

A fire in sawdust and organic material on a Longacre Rd farm tied up firefighters for five hours. Photo / Gavin Pryce

The mixture of composting material and strong wind was the probable cause of a deep-seated fire on a rural Whanganui farm.

Firefighters were called to the farm in Longacre Rd at 1.23pm on October 25. Two Whanganui crews went, with the Whanganui rural fire force and the Koitiata fire crew, acting principal rural fire officer Gavin Pryce said.

They found a large pile of mixed sawdust, branches and other organic material on fire, with flames 1m high in places. It was fanned by a strong westerly wind and a lot of smoke was going up into the power pylons overhead.

Really dense smoke can conduct electricity and cause arcing. A Transpower representative was called in case the power had to be isolated - but the smoke diminished in time.

The fire was up to a metre deep in places, and a contractor with a digger was called in.

"He worked alongside us to open up and turn over the sawdust and organic materials so that we could get our hoses and a good amount of water in through all of that."

Getting enough water was a problem until firefighters managed to pump from a farm pond 300m down a hill.

About 16 people fought the fire for its most intense two hours, Pryce said.

"It was quite physically demanding for the crews, working in the wind, and some of it on a steep slope."

The last crew left about 7pm.

The fire was probably caused by spontaneous combustion. Decomposing material within the heap got to ignition point, with extra oxygen supplied by the wind.

A fire in a commercial composting operation at Balgownie in Whanganui a few years ago had the same cause, and took about six weeks to finally put out.

Such fires need to be attacked early, Pryce said.

"It can be long and tedious work and you have got to be quite thorough."