Four Queensland coal miners have been diagnosed with pneumoconiosis or "black lung" — a potentially fatal disease thought to have been eradicated in Australia more than 60 years ago.

Unions fear the cases could be just the tip of the iceberg, with hundreds, possibly thousands of workers potentially at risk.

Key points: Four Queensland coal miners diagnosed with pneumoconiosis (black lung)

Four Queensland coal miners diagnosed with pneumoconiosis (black lung) Mines Department admitted technology used to detect disease not available in Queensland

Mines Department admitted technology used to detect disease not available in Queensland Mines Minister says thousands of lung X-rays remain unassessed

Mines Minister says thousands of lung X-rays remain unassessed CFMEU accuses Mines Department of cover-up

"This is one this of the most serious issues facing workers in the coal industry," Queensland Construction, Forestry, Mining and Energy Union (CFMEU) president Stephen Smyth told 7.30.

"The health and safety of the workers is paramount and this is a time bomb ticking away."

X-rays and lung tests have been used since 1947 as an early warning system to detect early signs of black lung and dust levels in mines have been constantly monitored.

However, the mining boom and new longwall mining techniques have exposed more miners to more dust.

At the same time, the monitoring system appears to have failed.

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Recently, the Queensland Mines Department admitted that qualified 'B readers' of X-rays — the industry standard developed by the International Labour Organisation to identify black lung — "were in very short supply in Australia".

The union was told there were none in Queensland.

"Workers have relied on this, that professional people would say 'OK, get your X-rays done every five years as a minimum, get them reviewed, you're fine, off to work you go'," Mr Smyth said.

"Well, guess what? For at least 15 years that we know of, people haven't had that.

"People have been relying on a system that is broke."

Thousands of miners' X-rays have not been reviewed

Queensland Mines Minister Anthony Lynham has promised urgent action, commissioning a study through Monash University.

The Minister conceded to 7.30 that there were thousands of miners' X-rays stored by the Mines Department that had not been reviewed.

What is black lung? Pneumoconiosis is a potentially fatal disease caused by long exposure to coal dust, more commonly known as "black lung" because those with the disease have lungs that look black instead of a healthy pink. Black lung most often stems from working in the coal industry or in the manufacturing of graphite or man-made carbon products and has no known cure. The risk of getting black lung depends on how much time has been spent around coal dust. There are two types of black lung: simple and complicated. There are relatively few symptoms associated with simple black lung, also known as coal worker's pneumoconiosis (CWP), and the prognosis is usually good. But CWP can progress into the more complicated progressive massive fibrosis (PMF), the symptoms of which may include a long-term cough and shortness of breath. There is no cure for black lung, but doctors may be able to treat complications caused by the disease. In 2013, coal worker's pneumoconiosis killed 25,000 people, according to UK medical journal The Lancet. Source: University of Kentucky, US National Library of Medicine and The Lancet

"There are hundreds of thousands, but we obviously can't do a review of those, but will be looking very closely at doing a cohort with Professor Sims at Monash University," Dr Lynham told 7.30.

"I'm here to look after the health and safety of our coal workers here in Queensland.

"I'll be doing everything possible to make sure that these X-rays are appropriately read.

"If it means that we have to have an expert team of readers sent in to look at coal workers' pneumoconiosis, then that's what will happen."

But according to one Mines Department document, as long ago as 1983, one person did look.

Then recently retired director of industrial medicine, Mannie Rathus, reviewed 7,907 X-rays and identified 75 with signs of black lung out of 499 abnormal X-rays.

His report has never been made public.

"It does feel like a cover-up," CFMEU industry safety and health representative Stephen Woods told 7.30.

"That was 30 years ago.

"Most of those people are probably pretty crook, if they've got this debilitating disease — 75 and 490 others.

"It could blow the top off this industry."

Union angry mines not complying with regulated dust levels

The Queensland mining industry itself acknowledges there is a problem.

"I think we probably all became somewhat complacent when there wasn't a case that emerged for many decades," Queensland Resource Council chief executive Michael Roche said.

"It's a bit of a wake-up call."

What makes the mining union even angrier is that no current underground mine in the state has been in compliance with the regulated level of dust.

"There's not one mine that's in compliance," Mr Smyth said.

"All mines have exceeded the legal limit of dust."

Dr Lynham has threatened closure of the worst performing mines.

"Those mines will soon be compliant, rest assured of that," he told 7.30.