The GDE bridge collapse in 2010 occurred during a concrete pour.

The GDE bridge collapse in 2010 occurred during a concrete pour. Photo: Lannon Harley

Fears of budget blowouts and long delays are pressuring construction companies to ignore dangers during concrete pours, the ACT's work safety watchdog says.

Work Safety Commissioner Mark McCabe has described concrete pours as a major ''pressure point'' in ACT construction and one of the most dangerous activities in the industry.

Mr McCabe is investigating malpractice in the industry as part of a government inquiry, which was ordered after four deaths on ACT construction sites in less than a year.

The inquiry will be completed later this month, but Mr McCabe said it had already become clear that pressures to lower costs were forcing workers to ignore safety problems in a range of works, including concrete pours.

A pour was stopped midway at an Empire Building Group worksite on Flemington Road in Harrison on Friday after serious safety breaches surrounding site access were discovered.

Truck loads of concrete were turned away from the site, which was likely to cost the company dearly.

There was a dangerous incident during a pour at the Nishi building in New Acton this year. In 2010 the Gungahlin Drive extension bridge collapsed, and in 2008 a slab collapsed on Marcus Clarke Street.

Mr McCabe said there were two factors that made concrete pours particularly dangerous.

Lengthy waiting lists for concreting contractors, created by the surging growth in the ACT's construction sector, made companies reluctant to delay a pour for safety.

Postponing a concrete pour can hold up all other work on a site, putting a huge financial burden on the project, Mr McCabe said.

''Once they're booked in, they've got a bit of momentum about them … companies can, on occasion, be reluctant to hold them because they'll lose their place in the queue,'' he said.

''If someone identifies a problem, there is some disincentive to doing something about it, and that's a bit of a problem.''

He said his inquiry into construction safety had revealed ''enormous'' pressures on ACT companies to meet deadlines.

''That deadline becomes the goal on most projects, and the damages can run into tens of thousands of dollars per day [of delay],'' he said.

''Now, if you lose three weeks on your concrete pour, that's a real problem.''

The Flemington Road site was shut down on Friday, and the company was expected to work frantically to fix the safety issues.

WorkSafe ACT investigators are expected to return to the site today.

Mr McCabe said shutting down sites may present other problems.

The pressure for construction projects to meet deadline was so intense that companies would work lengthy hours to catch up, putting workers at risk.