Dave and Janine Brownlee are still waiting for answers about why their son was crushed to death at work.

Jack Brownlee was trapped for three hours after the trench he was working in collapsed beneath him at a Ballarat construction site in March.

The 21-year-old died in hospital the next day. His workmate Charlie Howkins died at the scene.

Ms Brownlee told The Law Report that directors of companies should be held to account for the deaths of their employees.

"If you kill someone in your car your licence is automatically taken from you. You're automatically disqualified," she said.

"And yet in a company, you kill workers on the job but you can still have a licence, and the next day your company still goes on.

"That needs to be changed."

Victoria Police and Worksafe Victoria are investigating the circumstances surrounding the Ballarat incident, and no-one has been charged over it.

Mr Brownlee has publicly backed a union campaign to introduce industrial manslaughter as a crime in Victoria — a move he said would encourage employers to take care of their workers.

"If it makes people safe at work, it is all good," he said.

"I don't believe it's about jailing people, I believe it's about making workplaces safer."

Lana Cormie's husband Charlie Howkins and Dave Brownlee's son Jack were killed in the trench collapse ( ABC News )

Queensland and the ACT are currently the only jurisdictions in Australia where industrial manslaughter is a crime, with penalties of up to 20 years' imprisonment.

By contrast, under current workplace laws in most states and territories, people conducting businesses (or officers of those businesses) can be jailed for up to five years and fined $600,000 for recklessly exposing their employees to the risk of death, serious injury or illness.

This is known as a "category one" offence.

Labor in Victoria and NSW has promised to introduce industrial manslaughter laws if it wins in state elections — though it is still unclear how those laws will be framed — and unions are pushing other state and territory governments to follow that lead.

Industrial manslaughter laws are among the proposals before a current Senate inquiry into the laws around industrial deaths in Australia.

Fines, jail would make those with power 'take it seriously'

The inquiry is looking at how well the national workplace health and safety model laws are working in different states and territories, including the effectiveness of laws that penalise employers over workplace deaths and injuries.

Law firm Maurice Blackburn has told the inquiry that Queensland's model for industrial manslaughter should be replicated across Australia.

Sorry, this audio has expired How does the law prevent deaths at work?

In Queensland, any person conducting a business — or senior officer responsible for conduct — that negligently causes a workplace death can be prosecuted for industrial manslaughter.

"It's a fairly significant hurdle to get over," Maurice Blackburn lawyer Michelle James said.

"This is conduct that should be avoided, that if a person tried hard enough and thought about it enough, they would've been able to have avoided the death.

"In that situation [a charge of industrial manslaughter is] entirely appropriate."

Ms James, who specialises in workplace law, said the crime should also be extended to include those with "genuine power" to change the culture of health and safety in the workplace, and reckless behaviour that could have led to a workplace death but did not.

"There's nothing like the threat of either a personal fine or the loss of freedom to heighten the minds of those who have the responsibility and power to control workplace health and safety to really take it seriously," she said.

How many deaths at work?

Safe Work Australia estimates that the rate of deaths at work has halved over the past decade to 1.5 fatalities per 100,000 workers in 2016.

The group's director of evidence Kris Garred said the number of criminal prosecutions and fines issued against employers had also fallen in that time, though these numbers fluctuated from year to year.

"We are seeing that the number of fatalities and also the number of injuries within workplaces are trending downwards," he said.

"That may be an indicator of what's driving the fall in prosecutions, but it's just too hard to say based on the national high-level data that we have."

A worker lays a hard hat in memory of an Australian who died at work in 2016. ( ABC News: Casey Briggs )

Business groups have told the Senate inquiry the decline in workplace deaths and injuries is proof the current laws are working.

Mark Goodsell, the head of workplace health and safety at the Australian Industry Group, questioned the need for harsher penalties against employers.

Apart from the "category one" offence under current laws, Mr Goodsell said the crime of manslaughter had also been known to apply to some workplace deaths.

He doubted industrial manslaughter laws would deter bad employers from unsafe work practices, or encourage them or their staff to create safer work environments.

"There's an assumption that if you have industrial manslaughter that the only reaction will be [from] a group of bad employers out there, who will suddenly wake up the next morning and go 'Oh well I won't be bad any more, I will now take safety seriously'," he said.

"It may be that happens in some cases.

"It's more likely ... that good companies just revisit their systems and confirm that they're working well."

Mr Goodsell said employers were concerned about how such a crime would be prosecuted and investigated in practice.

"It's also very important that it's not prosecuted with any suggestion of there being a bias, or that unions can't unfairly influence a government to prosecute an employer that they may be having an industrial dispute with," he said.

He said any crime of industrial manslaughter should not excuse others who had also contributed to the problems that led to a workplace death.

"It is a bit of a loaded term because ... it's usually used to describe a set of laws that can only apply to senior managers," he said.