Lisa Turner, 33 and her four-year-old son Jack, and Peta Cox, 67, died after being hit by the BP petrol tanker at Staghorn Flat in August 2014.

Family members, including Lisa and Jack’s husband and father Damien Wallace, have attended a two-day committal at the Wodonga Magistrates Court.

They will learn next month if Heavy Mechanics stands trial after being charged by WorkSafe.

The company had serviced the truck and trailer days before the fatal crash on the Wodonga-Yackandandah Road.

Magistrate Ian Watkins told Thursday’s hearing it was a “particularly complex matter” which would require lengthy consideration.

Defence lawyer Daniel Gurvich told Thursday’s hearing the Wodonga business rejected claims it had done anything wrong.

BP had requested work on the truck and trailer, which Mr Gurvich said had limited the work Heavy Mechanics could undertake on the failed tow eye coupling.

He argued the petrol company specified the work it wanted, and effectively told the mechanics “don’t go beyond it”.

Mr Gurvich said any further obligations under occupational health and safety laws were the responsibility of BP, not the Wodonga mechanics.

But prosecutor Andrew Palmer said there was more Heavy Mechanics workers could have done. 

WorkSafe argues the failed component should have been disassembled for inspection, and the nut on the coupling tightened to a specific torque. 

“In this case, it's potentially catastrophic … there's a triple fatality,” Mr Palmer said. 

The tow eye had significantly deteriorated, he told the court, and a greater inspection was required. 

"We say they weren't careful enough,” he said. 

“There were steps they could have taken, but didn't take, to reduce risks. 

“But they deny that.”

Multiple mechanics told the court it was industry practice not to disassemble the component during servicing, unless issues had been detected in other tests. 

Heavy Haulage owner Keith Haire said no problems had been identified during the tests, which meant the component wasn't pulled apart. 

The matter will return on October 10.