'I could smell the hair on my face cooking': At the scene of the blow-up

There was a massive roar before millions of embers filled the air. A block of thick bush, about 300 metres long and 50 metres deep, blew up at once. Flames over 100 metres tall licked the night sky.

The Sydney Morning Herald's chief photographer Nick Moir had been at the Green Wattle Creek fire, just south-west of Sydney, since 5.30pm on Thursday as it burned at emergency level and threatened homes. Three firefighters were flown to hospital from that fireground earlier in the day, suffering minor burns. Then at about 9pm, a swathe of bush instantly went up in flames.

"Firefighters at the scene agreed they had never seen anything like it," Moir said.

"It was simply an explosion of all of the bush being converted to raw energy. It was a massive roar. The sense immediately was just of intense heat. Myself, another Herald photographer Dean Sewell and the Fire and Rescue NSW members just ran as fast as we could.

Firefighters are overwhelmed by flames and embers at the bushfire in Orangeville.Credit: Nick Moir

"The air was filled with heat and embers. Not just thousands but millions of them, stinging our faces in areas that weren't exposed. The radiant heat pushed everyone back, but spot fires and the embers swept through us as the winds increased to about 80 kilometres per hour.

"Immediately we retreated, counted our numbers, and established where our friends and other firefighters were as visibility dropped to metres."

Visibility on the fireground disappears in stages: thousands of embers light up the sky before the smoke sweeps through and it feels like being engulfed by a dense fog.

"I could smell the hair on my face cooking, being singed," Moir said. "One NSW member jumped in the truck and got it out of harm’s way while the buildings they had been tasked to protect were incinerated."

A fire truck escapes the scene after being overwhelmed by flames at the bushfire in Orangeville.Credit: Nick Moir

This was when Moir captured photographs of a lone Fire and Rescue NSW truck escaping the blaze as it roars metres high in the background, and of firefighters surrounded by millions of embers.

Such an event is called a "blow-up" in fire terminology: a sudden increase in fire intensity or a rate of spread strong enough that it disrupts any plans that were in place to control it.

Moir was waiting with Fire and Rescue NSW at the northern edge to the east of the Green Wattle Creek fire when it happened. Westerly winds had dropped off and the fire had settled down from earlier in the afternoon when a moderate southerly wind swept through and a number of spot fires took hold. Moir said the bush was thick with fuel and had been "essentially cooking" at a lower intensity for an hour before it erupted about 9pm.

Sheds were engulfed by flames, but houses were spared.Credit: Nick Moir

Property lost in the blow-up included a few sheds that had been converted into a barbecue and recreation room. "I don't think any homes were lost there, it was pretty amazing," Moir said.

Several fire trucks, property owners and friends worked for about an hour after the blow-up to put out hundreds of spot fires and grass fires that threatened houses. Hours earlier, at nearby Silverdale Road in Orangeville, Moir came upon resident Geoff Gardener who was watching as the fire approached.

Geoff Gardener watches the fire approach his home at Silverdale Road in Orangeville.Credit: Nick Moir

"They were definitely considering evacuating," Moir said. "But after talking to Fire and Rescue NSW they felt they had a defendable home. Several trucks defended his property into the evening, after the blow-up. Grass fires were attacking his property, but the firefighters were not struggling. The fire itself didn’t have the wind to drive strongly through the grass. It was really relying on the heavy fuel loads in the valleys to move."

Moir says 25 years of bushfire experience has left him able to judge which houses are "relatively safe and defendable". "While it's extremely tense and the moment itself is incredible, I knew no matter what happened, as long as I kept calm and remembered where my safety zone was and my escape routes were, I would be OK."