Realising he might not have long before an explosion, Brandon managed to open the door of the cabin and pull the driver out. He put him across his shoulders and got him as far away from the truck as he could.

Thirty or 40 seconds later, the truck burst into flames. Police say Brandon's efforts, without thought for his own safety, almost certainly saved the driver's life.

"I would describe the passerby as heroic and he will be nominated for a bravery award," said Senior Sergeant John Mason.

Brandon recalled the incident on Saturday afternoon, saying that it didn't hit him until later that he could have been killed trying to help a stranger.

"Afterwards while I was on the phone with emergency services it was going through my mind a lot, it could have been over," the West Footscray man said.

"I was in a lot of shock, knowing that if we were there any later it could have been worse, but I didn't really think about it at the time."

His girlfriend, Felicity Wu, watched the whole incident unfold as she called triple zero. For a moment, when she heard the huge boom, she wasn't sure if Brandon had got himself clear.

"My heart sunk a bit and I thought, 'Are they far enough away from the truck to be safe?'," the 23-year-old said.

Now that it's had some time to sink in, Felicity said she was proud of her boyfriend and had been calling him a hero all day.

"I was like, 'Oh look, I'm on the phone with the hero'. All the boys are like, 'Look it's the legend'. He might cop a bit of that," she laughed.

"I can't believe how selfless he is. He didn't even realise that he had saved someone."

Brandon said he would do it all again if the opportunity arose. When asked how it felt to be called a hero he said, with a bashful smile: "I guess it's a good feeling."

The driver, a 44-year-old Noble Park man, was taken to The Alfred hospital with non-life threatening injuries, including shoulder and neck injuries. 

Police are investigating the crash, focusing on whether speed or fatigue were factors.