A final safety report has been released investigating the Hunter Valley bus crash on Richardson road on February 8, which put the lives of 79 Irrawang high students at risk.

The investigation found that the rear wheels of the Hunter Valley bus dislodged after the nuts came loose.

The wheels had been removed and replaced 42 days prior to the accident and due to human error had not undergone final re-tensioning. It was also revealed that this was the second similar incident for the ComfortDelGro Cabcharge company which owns Hunter Valley buses. In May 2009 a bus lost a rear wheel while approaching an intersection in Bonnyrigg and as a result the company was advised to introduce a trial of plastic indicator tags on wheel nuts.

According to the report these tags were not fitted to the bus involved in the accident on Richardson road.

Hunter Valley buses general manager Rodney Landers said the company supported the findings of the report and would have every recommendation implemented by next week.

"Before we relied on the supervisor, now a tag is left on the bus handbrake to remind the driver and mechanic of the re-tensioning," he said.

The report also recommended the Roads and Traffic Authority should consider installing barriers along Richardson Road to prevent the risk of vehicles ending up in the dam. An RTA spokesman said at this stage it was too early to make a decision.