Insufficient admissable evidence has led safety regulators not prosecuting construction group LendLease over an incident in Adelaide that injured two pedestrians.
The women were seriously injured in 2016 when a steel construction gate fell on them as they walked along a footpath on North Terrace.
The gate rolled out of its two restraint frame posts while being manually moved, falling flat onto the footpath.
SafeWork SA executive director Martyn Campbell said on Thursday the victims had been told of the reasons why the prosecution would not proceed.
"I understand this is a very disappointing outcome for them. I am equally disappointed," Mr Campbell said in a statement on Thursday.
The decision follows concerns raised with WorkSafe SA's operations, including a recent investigation by the Independent Commissioner Against Corruption.
In final submissions to that investigation, counsel assisting Holly Stanley said parts of the organisation were plagued by "cultural dysfunctional" which had eroded employee engagement and morale.
But Mr Campbell said SafeWork SA had undergone rigorous and widespread reform since he joined 12 months ago, including the recruitment of a new investigation team.
"I am confident that as we continue to improve our processes you will see a very different SafeWork SA in future investigations, leading to even greater protections for South Australian workers," he said.