More than six years later the image still gives him nightmares, but Mr O'Brien also lives with the pride of knowing his efforts on the January afternoon saved the lives of three boys.

For his efforts Mr O'Brien, of Red Hill, was awarded a commendation for brave conduct.

"We were out just for the afternoon going to Berrima for afternoon tea and a stroll … it turned into a horror," he said.

When he stumbled across the accident scene on the sweeping bend of Berrima Road he didn't hesitate to run to the car lying upside down in the paddock.

Miraculously the driver had been thrown from the vehicle unharmed after it hit a tree, but Mr O'Brien soon noticed three boys were still trapped inside the overturned cabin.

"There was a lot of petrol leaking down the rear of the car and it did occur to me it could catch fire that's why I acted so quickly," he said.

"I just saw what needed to be done, made a quick assessment."

Mr O'Brien crawled into the car and made the decision to leave one boy who had serious neck injuries unmoved and focus his attention on another who was groaning with pain.

"On closer inspection I saw that he had his left arm completely torn out of his shoulder with blood gushing everywhere," he said.

Mr O'Brien dragged the injured boy from the car through a window and tied a tourniquet onto his arm while the boy's mother, who had been travelling in a car behind looked on.

He then went to the aid of a third boy and managed to move a large timber log from his legs and stay with him until emergency services arrived.

While Mr O'Brien believes his time as an army officer helped him compose himself and focus on the task at hand, the full gravity of the situation hit him afterwards.

"When it was all done and dusted I stood there with the local police superintendent ... we were chatting away and all of a sudden I just burst into tears," he said.

"You're trained to do it and you do it, but sometimes the memory is just hard to get rid of."

More than six years later, the bravery commendation came out of the blue for Mr O'Brien.

He is unsure who nominated him and has never had the opportunity to reunite with the people he saved.

It wasn't until last year when he was called to testify in a court case against the driver that police told him the boys all survived, but one is an amputee and the other a quadriplegic.

"I have a real feeling of pride that I actually saved at least one life possibly two, but when it was just raised again recently with the Governor-General's secretary I had recurring nightmares," he said.