A damning WorkSafe report has emerged about the Saint Kentigern School's production of Sweeney Todd which left two students with life-threatening injuries.

The report contains graphic details of other injuries during rehearsals, and recommended St Kents be prosecuted.

However, despite an in-depth investigation which was signed off by the chief inspector and supported by the families of the victims, WorkSafe ignored the report's recommendation to lay charges.

On the show's opening night in April 2016, two students were rushed to hospital after their necks were slit with a sharp shaving razor.

One boy had a cut almost 5cm deep. St John Ambulance staff noted that "trachea and some cartilage" were visible.

"Major veins and arteries are located in the region where contact with the straight razor is made. Damage to these veins, and especially the arteries, was life threatening," the WorkSafe report states.

"There was a potential for death."

It wasn't the first time students were injured by the razors, but despite numerous incidents there was no investigation into the razors' safety.

The razors had been wrapped in tape by a teacher, but this wasn't sufficient.

During one rehearsal, a student received a small cut. Another pupil suffered a friction burn a few days before the show.

The WorkSafe report states Saint Kentigern's Board of Trustees wasn't informed real razors were being used, and "missed the opportunity" to investigate the injuries.

"On balance, the prosecution is warranted," it concluded.

However, WorkSafe then announced the school could go through a restorative justice process instead.

"WorkSafe undertook a full enquiry into this and we accept their findings of serious failings in the systems and processes that were followed, up to and surrounding the accidents," the Saint Kentigern Trust Board said in a statement.

"The Saint Kentigern Trust Board takes full responsibility for the fact that the failures arose in the first place and that they should have been prevented.

"We accept Worksafe's findings. We apologise for what happened. These were very serious injuries and the Trust Board members personally feel deep regret and take full responsibility for the emotional and physical harm that was suffered as a result of them.

"Finally I'd note that Saint Kentigern has commenced a restorative justice process with the families concerned and we do not want to comment further while that process is underway."

Newshub.