Justin Parr has been working frantically all morning helping to build a defence for Nerriga. He’s managed only a handful of hours of decent sleep since his 22-hour overnight firefight on Thursday, but he’s not feeling fatigued. While the volunteer firefighter has known since he was a boy it was his duty to protect his community, this is the first time the threat has ever got so close.Parr and his small brigade have just received much-needed support. Earlier that morning, a strike team with eight Rural Fire Service (RFS) trucks from towns closer to Canberra arrived, joining the three based in Nerriga.The morning’s strong nor’wester is not the concern – it’s just blowing the Currowan fire deeper into the national park. What everyone’s worried about is the forecast southerly change, expected to hit mid-afternoon.Crews are working off fire trails deep in the forest, using heavy machinery to push and scrape wide lines of bare earth. These lines are about 10km south of the village; the Currowan fire is approximately another 8km south again. The hope is that once the southerly hits and pushes the fire towards town, these lines will be enough to stall or at least slow it.When 48-year-old Nick Hornbuckle, captain of the Queanbeyan RFS, turned up for his shift earlier that morning and was handed the job of leading the strike team bound for Nerriga, it was a responsibility he gladly accepted. Hornbuckle has been a volunteer firefighter for 20 years. He’s a former army officer who now manages operations for a large technology firm in Canberra – he thrives on risk analysis and exercising leadership, so leading a team on a catastrophic fire day seems a good opportunity to use these skills.By around 2pm, the line he’s walking between completing the defensive lines for Nerriga and exposing his crews to unacceptable risk is becoming razor thin. Right now, his crews are working on the flank of the Currowan fire; it’s moving away from them. But once the southerly hits and the fire changes direction, they’ll be directly in its path. Fire scientists call this space the ‘dead man zone’ – because this is what can happen to firefighters if they don’t get out of the way in time when the wind changes.Hornbuckle has driven up to a vantage point. He’s getting constant updates on the progress of the southerly change as it makes its way up the south coast, and he has his eyes locked on the smoke plumes of the Currowan fire, looking for signs of change.‘Fire everywhere’When he sees an enormous billowing cloud forming over one of the smoke columns, then another, he realises instantly the line has been crossed. While this is the first time he’s ever directly witnessed such a thing, he knows what he is looking at is the formation of pyrocumulonimbus clouds – also known as fire thunderstorms. He gets on the radio and orders everyone out of the forests, now.The Currowan fire front as seen from the Princes Highway, south of Nowra, on 4 January 2020 Photograph: Jessica Hromas/The GuardianStill watching, he sees a mushroom-shaped cloud growing exponentially, higher and higher into the still-blue sky, when suddenly the smoke column that’s holding it up like a stalk collapses – as though it’s been cut with a knife – and the world around him goes black.A pyrocumulonimbus is created when hot air from an intense fire burning over a large area rises up in a smoke column, drawing in cooler air, before punching through the stratosphere upwards of 15km above the ground. It’s here that the cool air and latent heat combine to create a thunderstorm inside the smoke plume, producing lightning, turbulent winds and vertical blasts of air that hit the ground. Under such intense conditions, fires can spread rapidly in any direction, embers fall instead of rain, and spot fires start dozens of kilometres away. Fire tornados have even been known to form.These firestorms used to be a rare phenomenon. Between 1978 and 2001, just two were recorded over southeastern Australia. Over the following decade, there was a steady but significant increase, with close to 60. But in the month of March 2019 there was a sudden upswing, with 15 detected in the Victorian High Country – 12 of them in just four days.Now, in this final week of December 2019, scientists on the other side of the world – at the United States Naval Research Laboratory in Washington, DC – are watching what’s happening in Australia with astonishment. Over this week and the next, they will count more than 20. “By our measures, this is the most extreme pyrocumulonimbus storm outbreak in Australia,” one of their meteorologists observes.A pyrocumulonimbus storm cloud forms over fire-affected areas near the NSW and Victoria border on 10 January 2020. Photograph: Australian Department Of Defence Handout/EPADavid Hanzl, a fire captain on board one of the fire trucks in the strike team, has also seen the pyrocumulonimbus forming, and so is already scrambling his crew to make a quick getaway when Hornbuckle’s evacuation order comes over the radio. They drive hard for 15 minutes until they’re well out of the forest, pulling into a cul-de-sac that runs off the main road into Nerriga only once they’re confident they’ve outrun the fire. The sky outside is still blue, and they’ve met up with a water tanker, so everyone piles out to start refilling the truck.Hornbuckle and his truck come around the corner. Hornbuckle has also briefly managed to get ahead of the fire, but he can see the darkness closing in behind him and knows they’ve only got seconds left before it catches them again. When he sees Hanzl and his crew standing on the road outside their truck, he tells his driver to lean on the horn to warn them.Before they can respond, Hanzl feels it: “Fire everywhere, ferocious heat, smoke, embers blowing into faces, down necks, into ears.” He and his crew dive back into their truck, hauling the water-tanker driver in with them.Stay still, let the truck protect you, let the equipment protect youDavid Hanzl, RFS captainBeing overrun by fire, called a flashover or burnover, is potentially deadly, even inside a fire truck. The men and women inside both trucks in the cul-de-sac are now using everything they have to survive: everyone dons their full personal protective equipment, including goggles and masks; external water sprays are turned on; crew members hold shields up against the windows to deflect the intense radiant heat.Hornbuckle radios all the other trucks in his team, telling everyone to hold their position. “Stay still, let the truck protect you, let the equipment protect you,” he says. While it may feel counterintuitive to stop fleeing, he knows the greatest risk now is a vehicle accident caused by trying to outrun the firestorm.But he has no way of knowing if everyone has heard him or how they have reacted to his instruction. Some of the crew leaders are veterans, but others are “fairly green”. From inside the truck he can hear the wind howling and the tink, tink, tink of embers against the vehicle, like hail on a tin roof. Outside, everything is red. There is no smoke, just intense burning, as though they’re “sitting in hell”.Flames from the Currowan fire impacting properties along the Sussex Inlet road on 31 December 2019. Photograph: Mike Bowers/The GuardianYet the worst thing is not knowing the fate of the rest of his team. “I just had to trust their crew leaders had put them in a position that was survivable when it came through,” he says. “It just happened so quickly.”The fire front passes after about 10 minutes, and Hornbuckle opens the door and steps out into a world transformed. All the foliage is gone, replaced by black sticks on bare, smouldering earth. “It was strange,” he says. “And the wind, it was strong and really cold, like ice.”‘It’s coming straight for town’For those in the village, memories are foggy about the exact moment it turned from a hot, blue day of interminable waiting to one of sheer terror.Pamela Parr remembers leaving her caravan to walk over to the pub to buy a lemonade when she noticed cars pulling up outside the community hall, the designated evacuation centre. She thought, I’d better go and see what’s happening. The next thing, smoke starts rolling in, thicker and thicker. Then she’s inside the hall; more and more people are coming in; she can barely breathe.Inside the pub, someone rings the landline. “It’s happening. It’s coming straight for town and you don’t have long.” The mobile phone network is down, so owner Sarah Martin takes a walkie-talkie and gives one to her husband, Phil. A friend who’s arrived to help defend the pub gives her an old RFS jacket to wrap around six month old baby Oliver as she walks the few hundred metres down to the hall.It’s dark inside the old weatherboard building – the town’s power has just gone out – and the room is hot and dense with smoke. There are about 40 people inside, many of them elderly, all struggling to breathe. Through the windows, Sarah can see the sky is turning red and clouds of grey ash are billowing through the air.The door flings open, and Pamela’s partner, Terry, comes charging in. “It’s gone,” he says to her. “It’s all gone.” Pamela can hear herself screaming hysterically and feels a woman’s arms wrap around her. Sarah crouches by her side, saying, “Breathe, just breathe.” All Pamela is thinking is, I don’t want to breathe, I want my home.By the time they finish fiddling around with the baby capsule it’s too late and the road is no longer safe to travelEveryone in the hall, most of all Sarah, is worried about Oliver, the only child in Nerriga. One of the older women, a former nurse, tells Sarah she’s worried about the effect the smoke could have on his lungs. Sarah radios Phil, her husband, who’s still at the pub. When her father left with their elder son on Thursday, Phil asked her to go with him and take both the children, but she was the one who said no. Now, quietly weeping, she keeps telling him she’s sorry, that she didn’t know it would be this bad.There’s one road out of town still open and a couple is about to attempt an escape. Sarah agrees to give them Oliver, but by the time they finish fiddling around with the baby capsule it’s too late and the road is no longer safe to travel.From the hall, Sarah can see that the fire shed over the road is still empty – none of the brigade’s three trucks that left earlier that morning has returned. She steps outside and walks through the thick smoke and blasting ash-filled wind to the shed, where a single volunteer is manning the radio.“Is anyone coming?” asks Sarah.“Yes, they’ll come,” the woman replies with confidence.The sun struggles through the clouds as high winds push smoke and ash from the Currowan fire towards Nowra. Photograph: Tracey Nearmy/ReutersThe trucks retreatNick Hornbuckle and the strike team are nearly back to the village when he gets a radio message that there’s an elderly lady trapped in her house south of town. Taking one other truck with him, he turns back, heading down a dirt road through the forest to find her. It’s still daylight, but as they drive the sky suddenly darkens and huge trees start heaving onto the road. It’s not fire toppling the trees, though it’s getting close – he can see its glow now through the forests. It’s wind and the energy of the approaching front. For the first time that day, Hornbuckle feels fear.The sight of trees falling ahead “was the trigger point for me”, says Hornbuckle. “I realised that something much bigger than what we can deal with is going on here. I couldn’t put six people’s lives in danger for that one person. It was a hard call. But I told everyone to withdraw back to Nerriga.”When the first fire truck pulls into Nerriga around 5pm, its flashing lights are the only illumination in town – the village has been plunged into darkness. There’s no electricity or running water, no phone signal and the generator keeping power to the still-empty fire shed is nearly out of fuel. Those huddled in the undefended community hall are starting to panic.All of a sudden it was all on us.Phil Martin, publicanThe captain on the truck calls a quick meeting in the hall. He fears people are in danger of asphyxiating if they stay in this building; they need an alternative. Sarah offers up the pub as a refuge – they’ve got a generator, which means they can at least have light, running water and ventilation from ceiling fans. The wooden structure – built in 1862 – is hardly ideal to shelter a community from a climate change–fuelled catastrophic fire, but it’s the best they can do. When Sarah radios Phil to tell him that they are the new evacuation centre and everyone is on their way, he’s willing but feels daunted by the responsibility. “That was the lowest point because all of a sudden it was all on us. We are now looking after people, not just a building,” he says.As the pub fills, Phil wets towels and places them under doors to try to stop the smoke getting in; two older women take Oliver into a bedroom, giving him ice to suck, trying to soothe him, while Sarah starts distributing food and water.Then she looks out the window and sees a miraculous sight: fire truck after fire truck is rolling into the village.As 40 people cowered defenceless in the Nerriga Hotel and the Currowan fire bore down on the town, the local Rural Fire Service trucks arrived. Photograph: Brett Hemmings/Getty Images‘Everyone inside, it’s coming’When Nick Hornbuckle and his strike team pull in to Nerriga, he estimates they’ve got 20 minutes, maybe 30, before the fire hits. He sets up six trucks directly in front of the pub – their only job is to defend the building.He’s thankful to see another strike team from out of the area has just arrived, and that all the heavy machinery at work in the forests earlier in the day has made it back to town. He can now put in place an offensive strategy. He knows there’s no way to stop the fire, but “I didn’t want to pub to be hit at full force. So the idea was to split it.” He sets the machinery to work bulldozing lines in the paddocks in front of the pub – a physical barrier that will slow the fire and encourage it to run either side of the building. He puts the strike team in position to chase down any spot fires and help shepherd the fire around the pub.Mate, we have to go. We’re going to perish.Leon Hagel, localLeon Hagel, who just hours earlier was having a quiet coffee at the pub with Sarah, can see the plumes approaching his house and thinks they look “pretty nasty”. He’s fought plenty of fires in his navy days and always planned to stay and defend his home – a beautiful place made of pressed earth and rock, with big yellow-box beams – but at the sight of these plumes he changes his mind. He puts his two dogs in his ute, takes one last photo of the house and drives towards the pub.On his way, he spots his mate Pedro outside his house and stops to lend a hand. Before long, it’s pitch black and roaring. “You could hear gas bottles exploding through the bush as it was hitting different properties,” he says. “Pedro didn’t want to go. I said, ‘Mate, we have to go. We’re going to perish.’ I got in my car, and by the time I got to the pub it was raining fire. It was the scariest thing I had ever been in.”Currowan by Brownyn Adcock Photograph: Black Inc BooksInside the pub someone is yelling, “Everyone inside, it’s coming”.The crew of the six fire trucks are standing outside, hoses drenching the pub. Hornbuckle sees a glow, “and then, bang, there was flame”. The front has arrived.Inside, almost everyone is silent. They can hear gas bottles outside exploding like bombs, and know that each one represents someone’s home. Sarah notices the landline just keeps ringing and ringing. Pamela can hear the incessant yap of a dog. She’s thinking about her son Justin – his is the only fire truck still not back. Leon Hagel sticks his head out of the front door of the pub for a peek just in time to see his house explode.No one’s sure how long it takes – maybe 20 minutes, maybe more. But eventually the noise quietens. The fire has passed. And they’re alive.