The operation has become one of finding and eliminating hot spots, as the 130-strong team on the ground sets about tightening a 35km perimeter around the 2331ha fire area. Photo / Tim Cuff
The operation has become one of finding and eliminating hot spots, as the 130-strong team on the ground sets about tightening a 35km perimeter around the 2331ha fire area. Photo / Tim Cuff
The bush fire that's raged across Nelson's Pigeon Valley has been knocked down – yet crews still have some of the toughest work ahead of them.
Principal rural fire officer Ian Reade said the operation had now become one of finding and eliminating hot spots, as the 130-strong team on the ground began tightening a 35km perimeter around the 2331ha fire area.
And this phase came with big dangers and challenges of its own.
Yesterday, crews were working to create a "black out" zone – a cold containment line where no material was able to ignite – which would eventually be stretched to 30m around the perimeter.
The task to come was "huge", Reade said, and could take weeks to complete.
"The fire is no longer running through the tree canopies, or crowning as we call it, although there are still parts where you get the odd bit of vegetation flaring up on the ground."
The bigger problem was still what lay under the ground.
Because of the dryness that had helped drive the inferno – which had been costing an estimated $2m each day – the fire had been able to penetrate deep into the ground to burn tree roots or anything else that was flammable.
"So what we need to do is go out, find where they are and put these things out – because if that heat creeps back up to the surface, then ignites any vegetation on the ground, it can ruin your day."
Reade said the depth of these hot spots could range to several metres – as what was seen in the 2017 Port Hills fires – and it could take just one dry, blustery day with low humidity for them to climb upward.
"They'll just pop up out the ground and ignite whatever is around."
To pin-point the hot spots, crews were flying drones fitted with infrared and thermal imaging technology around the perimeter areas each night.
"They reveal where the spots are and then that information is downloaded on to maps that can either be produced in paper form or downloaded on to peoples' phones."
That was perhaps the easy part: crews then had to either dig up the hot wood entirely, or douse it using a deep-reaching instrument Reade likened to a mosquito's proboscis.
"Once we've extinguished all of those hot spots, we get that cold perimeter – and then we can announce that that part of the fire is controlled."
Crews are working to create a "black out" zone - a containment line where no material was able to ignite - which would eventually be stretched to 30m around the 35km-long perimeter. Photo / Tim Cuff
Not every one of them had to be taken care of; isolated hot spots that posed no risk could be left so crews could direct their resources elsewhere.
"The only difficulty comes if you come to a fire area that's unburned – sometimes you've got to actually burn that fuel to get rid of it, so you don't get a fire that ladders up from the ground to the tree tops, and then sends embers some distance," he said.
"This is the challenge we currently have in assessing some of those unburnt areas."
The operation still involved a large amount of machinery – including 28 fire appliances, five tractors, five bulldozers, eight excavators and feller bunchers used to tear down trees and create fire breaks.
Along with facing the threat of fire breaking out in their vicinity, crews were having to deal with the combination of heat from the ground and high temperatures. Photo / Video Grab.
"On top of that we've got 16 hazardous tree assessors who are going ahead of where our people are working, and on to peoples' properties," he said.
"Their job is important because a tree that might look completely fine, but which has lost its integrity after its roots have been burnt, can fall over even in a very slight wind.
"So we have to look for those fire-infected trees and flag and identify them.
"The other thing we have to look out for in situations like this is are ash pits: these are where you get a lot of dead vegetation covering the ground, and underneath it is a pit where the roots of a tree has been burnt out completely.
Fire crews construct a fire break near the perimeter. Photo / Video Grab.
"If you step into one of these pits, it's not a happy ending."
Along with facing the threat of fire breaking out in their vicinity, crews were having to deal with the combination of heat from the ground and high temperatures and stone and clay terrain featured 30-degree slopes.
"While there's not a huge amount of smoke about there, there is a lot of dust and soot, so our guys are having to wear filter masks to keep that stuff out of their air waves," he said.
"Temperatures have been very hot this week, so it's hard yards. We'll be on this operation until we get significant rain – about 75mm is what we really need."
Today, rainfall was expected to be no more than 2mm, with temperatures lingering in the mid-20s.
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Meanwhile, authorities have given owners of 40 properties in the fire-affected valleys approval to return to their homes from this morning.
Daytime access had also been granted, allowing residents of the valleys to access their homes for the first time since the fire broke out.
However, returning residents were being told to be prepared to leave their homes if the situation changed.
Nelson-Tasman Civil Defence Group Controller Roger Ball said there were now only 94 properties remaining evacuated: those were in Pigeon Valley, most of Redwood Valley and Teapot Valley.
Members of the 130-strong crew fighting the Nelson fires have an evening meeting. Photo / Tim Cuff
"We are delighted to be able to return people to another 40 homes across the affected valleys as part of our conditional re-entry programme.
"It is vitally important that all returning residents remain prepared to evacuate at short notice if required," he says.
"We also ask the public to stay away from all of the recently reopened valley roads for the weekend – re-entry is for residents only.
"However Wakefield is open for business and visitors are very welcome."
"While we are working at pace to get people back into their homes, residents from the remaining 94 properties should plan on being away from home until at least the end of this weekend, and possibly longer."
