South Australia's beleaguered workplace safety watchdog SafeWork SA has apologised over yet another failed prosecution, admitting it has failed two women crushed by a steel construction gate in Adelaide's CBD.

Key points: SafeWork SA says it will not prosecute site manager regarding incident in 2016

SafeWork SA says it will not prosecute site manager regarding incident in 2016 Two women were significantly injured when a gate fell on top them on North Terrace

Two women were significantly injured when a gate fell on top them on North Terrace Safety watchdog has apologised and said it failed to secure evidence

The women were walking past the North Terrace construction site for the University of Adelaide's new medical and nursing school in October 2016, when the gate came out of its restraints and fell on top of them, causing significant injuries.

SafeWork SA launched an immediate investigation into the incident.

But today — as the statute of limitations on prosecutions lapsed exactly two years after the incident — the regulator revealed it would not be prosecuting the site's manager Lendlease.

SafeWork SA executive director Martyn Campbell acknowledged the regulator had failed to secure evidence which could have resulted in charges being laid.

"This incident was done in a time that wasn't great in the history of SafeWork and we should have done better," he told reporters.

"We should have done better in our initial response in securing evidence. That didn't happen. It won't happen again."

Mr Campbell said he had contacted the women injured in the accident to apologise.

"I extend my sympathy to those people that they won't have their day in court. But that said, they understand the decision and the reason for that," he said.

"I understand this is a very disappointing outcome for them; I am equally disappointed."

Failed prosecutions attract ICAC scrutiny

The case is the latest in a series of bungled prosecutions which have piqued the interest of the Independent Commissioner Against Corruption, Bruce Lander.

Commissioner Lander launched a secret investigation into the regulator this year. ( ABC News: Nick Harmsen )

Commissioner Lander launched a secret investigation into the regulator in May after SafeWork SA dropped charges over a fatal Royal Show ride accident that claimed the life of eight-year-old Adelene Leong.

He also announced a public evaluation of the regulator's practices after receiving a series of complaints and reports.

The commissioner is yet to publicly deliver his findings.

But in August, counsel assisting the commissioner, Holly Stanley, told a public hearing the regulator had a "cultural dysfunction" which had eroded employee morale, suffered from "change fatigue" and was "immature in recognising the risks of corruption, misconduct and maladministration".

SafeWork SA's executive director Martyn Campbell, who was appointed to lead the organisation last year, said significant change was already underway — including a new investigation team, new processes and new training.

"We've done a huge amount of work over the past year to raise standards, give our people guidance and make sure that people expect the best from us and we deliver that," he said.