He instinctively swung his left arm out to protect his youngest daughter, 16-year-old Lily, while avoiding the crash, Barnett said.
Emerging from his car he could hear a woman screaming, children crying and a stuck car horn blasting.
Shattered glass was everywhere, the cars were steaming and air bags had been deployed.
The air was thick with a smell he likened to that of gunpowder.
"It was just as you would imagine it to be - ghastly. I'll never forget it."
Looking towards the car he could see the outline of two carseats and yelled back to his own children, trailing behind him, to stay back.
He was afraid what they might find, Barnett said.
A woman trapped by her seatbelt in the silver car was screaming "get a knife, get a knife", so he retrieved one from a campervan, ignoring a cut to his fingers received while trying to pull the woman free.
"She kept saying 'I'm so sorry, I'm so sorry' ... she kept hugging her kids. They were two girls aged about seven and three. One was crying 'I want to go home'."
The gunpowder smell had him rattled, Barnett said.
"It went through my mind 'imagine if this thing bursts into flames'."
Next to the silver car, those in the Hyundai - what appeared to be an extended family of eight - looked "completely bewildered".
A police spokesman said all of those involved escaped injury, and investigations were continuing. But Barnett said the woman in the silver car went to hospital.
The woman recognised him, as did the driver of the car, the longtime DJ said.
"The ambulance driver said to her 'is that your husband?' and she said 'no, that's Simon Barnett'."
He was embarrassed by the attention, as many people helped in the aftermath of the crash, including the "amazing" emergency services.
A police officer later called him to say the woman had been discharged from hospital the same day suffering only from bruising, Barnett said.
"They were all just so lucky."
