A heavy steel rod narrowly missed a worker at a Cross River Rail construction site in Brisbane on the same day a man fell 12 metres from another site run by the same contractor, the union claims. 

Cross River Rail Delivery Authority confirmed a rod had fallen through the windscreen of a forklift in a tunnel at Roma Street in the city's CBD on Tuesday. 

They said no one was injured in the incident and it is being investigated by the authority. 

CPB has been accused by the construction union of repeated safety failings since a 54-year-old fell from scaffolding at the Boggo Rd site. 

He remains in hospital in a critical condition. 

In a post on Facebook the Construction Forestry Mining and Energy Union (CFMEU) said the rod missed the Roma Street worker "by inches". 

"The catastrophic incident at the Boggo Rd site on the Cross River Rail project is far from an isolated event," the post read.

"On the SAME DAY (Tuesday 25.7) that a 12 metre fall at Boggo Rd left a worker fighting for his life in hospital, a heavy piece of steel rod fell from height at the Roma Street tunnel site and through the windscreen of a telelifter (forklift) missing the operator by a matter of inches."

CFMEU claims CPB did not notify health and safety representatives or union officials, but the Cross River Rail Authority said they were immediately notified, and an improvement notice was issued. 

In response to "broader claims" about site safety, a spokesperson for the authority said "we reiterate that safety remains Cross River Rail's top priority and we expect the on-site contractor to uphold the highest possible safety standards".

They said the "majority" of the 331 Workplace Health and Safety notices issued over the project's lifetime happened in the early days of construction. 

"It is not unreasonable for a project of this size and scale to receive this kind of attention from the safety regulator," they said. 

'We should not accept harm'

On Wednesday, Transport Minister Mark Bailey said the number of injuries on Cross River Rail had been lower than the industry average. 

But David Cliff, a professor at University of Queensland specialising in workplace safety, said critical injury or fatality should never be an accepted risk. 

"Minor injuries are perhaps a different question because it could come down to minor slips," he said.

"But something like a fatality — that's why we do the management of risk.

"There are people whose job is to make sure those systems are in place and being properly implemented.

"We should not accept harm to people; if you accept that then the battle is lost." 

Mr Bailey also said scaffolding at the Boggo Road site had been given the "tick of approval" earlier this month.

However, Professor Cliff said it is more complex than that. 

"A tick of approval means an external assessor has had a look at it to the best of their abilities," he said.

"That tick of approval would've been on the construction of the scaffolding, but then you've to feed into that the task the worker was doing on the scaffolding at the time of incident."