And people outside the coal mining industry, such as those working on Brisbane's tunnel projects or in agriculture, could also be at risk.

Robert Cohen, director of Occupational Lung Disease from Northwestern University in the US, agreed many Queenslanders could have gone to their grave as a result of black lung, without being diagnosed.

"If physicians in the communities believe that this disease was eradicated, and somebody dies of a respiratory death, they wouldn't likely certify that or think about black lung as a part of that," he said.

Dr Cohen spoke at Queensland's Coal Workers' Pneumoconiosis Select Committee on Wednesday.

The committee is investigating the re-emergence of black lung in Queensland, which sent shockwaves through the 30,000 coalminers working in the state.

It has become apparent the disease never went away, but was instead "rediscovered", with 20 cases confirmed since 2015.

"If you don't look for something you may not actually find it," Dr Cohen said.

When asked if there could be hundreds or thousands of cases yet to be diagnosed, Dr Cohen said: "Correct."

Dr Cohen's team in the US tested 2300 X-rays provided by the Queensland government, which mostly included still-working coal miners, and about 30 tested positive for coal workers' pneumoconiosis.

But despite the dangers, the first two Queenslanders properly trained as "B readers", to be able to find black lung on an X-ray, have only become qualified in recent weeks.

The Department of Natural Resources and Mines was offered training in late 2015 for radiologists in "B reading" - or classifying radiographs for pneumoconiosis - via the US National Institute for Occupational Safety and Health (NIOSH), but did not take it up, the committee was told.???

Dr Cohen said quality issues, with X-rays being taken incorrectly in Queensland, were plaguing their work.

His team reviewed about 3000 X-rays from Australia in total but about one in five were too difficult to read.

"Not to have one single case [being diagnosed for years], it sort of begs the imagination. That's something that really should ring alarm bells," Dr Cohen said, pointing out black lung had not vanished in the US.

"To see nothing, is something I think that public health officials should take note of and then you would wonder if there's something wrong with the surveillance rather than congratulating yourself that you've eliminated the disease."

Dr Cohen said the prevalence of black lung in the industry was between 2-12 per cent in the US.

To make matters worse, the committee heard chest X-rays and films were kept by the department in broom cupboards and shipping containers, with members visiting the now empty containers at Redbank on Tuesday.

"I think it would be true to say that this committee was quite shocked and disgusted and were dismayed at the treatment of people's personal records including those X-rays," committee chair Jo-Ann Miller said.

"No one in the department from what we've been able to gather here actually read the medical reports.

"We've actually a committee been gobsmacked by this evidence."

Ms Miller said Brisbane's tunnels, such as Legacy Way and Clem7 involved drilling rock, and questioned whether those workers should receive testing for silicosis, a lung disease caused by inhaling silica dust.

"I doubt that that they are or have been," Ms Miller said.

Dr Cohen responded: "I hope you don't mean to tell me that they're not being tested for silicosis."

"Silica is probably more dangerous than coal mine dust. Quarriers, tunnellers, metal miners, anyone who is disturbing the Earth's crust and drilling through rock is at risk for quartz and silica exposure," he said.

In the US, workers who are exposed to more than 25 micrograms of silica for more than three months of the year must undergo spirometry, chest X-ray with B reading and medical surveillance.

"I recommend that," Dr Cohen said.

A Brisbane City Council spokeswoman said council appointed contractors for major projects such as Legacy Way and Clem7.

"These contractors are responsible for meeting requirements of Workplace Health and Safety regulations for their employees," she said.

Safe Work Australia's Guide for tunnelling work stipulates ventilation systems, risk assessment for silica, using protective equipment and using water sprays among methods to reduce risks of dust.

Health monitoring for workers exposed to silica includes medical history checks, a questionnaire, respiratory function tests and chest X-rays.