A company at the centre of a Sydney hospital gas bungle which killed one baby and left another brain-damaged has been found not guilty.

Judge Wendy Strathdee on Thursday found that SafeWork NSW had not proven its case against BOC Limited over a series of accidents at Bankstown-Lidcombe Hospital in mid-2016.

Two newborn babies were given nitrous oxide – commonly referred to as laughing gas – instead of oxygen after works carried out by BOC and a sub-contractor resulted in a fatal mix-up.

Instead, she found that the company was deceived after subcontractor Christopher Turner and the hospital’s assistant engineer, Paul Brightwell, had both signed forms declaring they had carried out testing following the works, despite having not done so.

John Ghanem died in July 2016, a month after Amelia Khan was left with brain damage, epilepsy and blindness.

In the Downing Centre District Court on Thursday, Judge Strathdee said the prosecution had not proven beyond a reasonable doubt that BOC had failed to comply with its health and safety duty.

After completing the work overnight, Turner on the morning of July 16, 2015 signed a form indicating that he had carried out testing on the pipes in one of the hospital’s operating theatres and that it showed oxygen was flowing through them.

He also convinced Mr Brightwell that he did not have to witness the testing before he signed off on the paperwork.

“If the testing had been done by Mr Turner, and such testing had been witnessed by Mr Brightwell, the error would have been revealed,” Judge Strathdee said in her judgment.

“Whilst the testing process was in effect foolproof, it cannot be so when persons involved in the process engage in falsehoods.”

It had previously been revealed Mr Brightwell was a fitter and turner by trade, did not hold any professional engineering qualifications and did not have any experience in the administration of medical gases to patients.

Judge Strathdee rejected the prosecution’s argument Turner should have inquired as to Mr Brightwell’s qualifications.

Turner has pleaded guilty to failing to comply with a health and safety duty and appeared in a neighbouring court on Thursday as BOC was cleared over its involvement.

Judge Strathdee found BOC was not liable because Turner had lied to the company, Mr Brightwell and the hospital.

“The defendant cannot be held responsible for the behaviour of a disobedient worker, Mr Turner, for his conduct which I view as lying,” she said.

She was also highly critical of the hospital for appointing Mr Brightwell to a position for which he was not qualified.

This is despite SafeWork NSW last year dropping charges against the hospital because of its good health and safety record.

“I find it of great concern that the witnessing of testing of medical gasses that are piped into operating theatres in hospitals was allowed to be performed by someone with no medical or engineering training or qualification,” she said.

Turner will be sentenced next week and is facing a fine as well as having to pay SafeWork’s legal bills of about $150,000.

“The defendant has asked me to convey to the court his deepest sorrow and distress at his involvement in the work which led to the serious injury of baby Amelia Khan and the death of baby John Ghanem,” Turner’s barrister, Patricia Lowson, told his sentence hearing.