Australian Workers Union Victorian state secretary Ronnie Hayden said the mining technique caused the floor of the mine to cave in.

"They should not have been doing that task in that mine," he said.

An "air leg" is a large, manually operated drill that uses compressed air to pulverise the rock face it is drilling into.

Federation University geology lecturer Haydn Swan said the drill bit could be up to 1.8 metres long.

"The drill is sat on a telescopic jack that's usually connected to the roof and the floor, so the weight of it isn't carried by the person, but it's still movable," Mr Swan said.

"They're horrendously noisy and messy and dusty so it's a pretty tough gig working an air leg."

Mr Swan said air legs were much smaller and more mobile than other current mining equipment, which was why they were still used for gold mining.

"The alternative to air legging is using a jumbo rig... which is a much bigger piece of equipment. It needs a space three by three metres, whereas an air leg you can mine something a metre wide," he said.

"An air leg is favoured in conditions where you've got narrow veins of minerals, but you don't want to take all the stuff around it.

"That's particularly the case with the gold deposits we have through Victoria, which are often veins only 30 or 40 centimetres wide."

Mr Swan said using an air leg was more dangerous than other techniques because it put the miner closer to the rock face being drilled.

"If you're close to a working face, that's the most dangerous spot, because as they move past that area they support the ground with bolts and cables and glue and mesh and spray concrete on it to make sure it's as stable as possible," he said.

"That first four to seven metres that's unsupported is the most dangerous, there's literally a void underneath it."

But Western Australian mining contractor John Johnston said air legging wasn't inherently dangerous.

"In the 1970s and 1980s there were basically no regulations and air leg mining was a common method of mining when ground support was barely used, so there were a lot of fatalities and that stigma still exists," Mr Johnston said.

"Mine management procedures have more to do with the safety of what you're doing than the technique you're using."

Mr Johnston said he'd been air leg mining for 24 years and couldn't recall a fatality in WA since 2002.

"I can think of at least six mining fatalities in that time that have nothing to do with air legging," he said.

The length of the drill bit means an air leg miner can advance about two metres with each cut. Mr Johnston said he didn't know the Victorian rules, but the worker would have to put in ground support after every cut according to WA safety protocols.

"In WA no one should be going past unsupported ground," he said

Mr Johnston said it was incorrect for the union to blame air leg mining for the accident.

"I don't know the mine and don't know the mine conditions, but to point the finger at air leg mining is wrong," he said

"I'm saying that as a mine owner and a mine contractor, the buck stops with me."