49 In relation to the first of the two incidents, the issue was said to turn on the failure of the respondents as the employer to fulfil their non-delegable duty to provide a safe system of work. In my opinion, however, there is room for argument that the respondents complied with that duty, but that the actions of Mr Hitch were carried out in circumstances where he failed to apply the system and took action on his own which put the appellant at risk. The negligence of Mr Hitch defeated the system. In particular, he exposed the appellant to a risk of harm when, knowing that the employees who operated the winch were not there, abandoned his own position and attempted to winch up the appellant independently of any authority of the Dive Supervisor and in breach of the system. As appears from Kondis at 673, the Full Court of the Supreme Court of Victoria had held by a majority (Young CJ and Murray J, Marks J dissenting) that the Authority was not responsible for a casual act of negligence by their independent contractor. In that case, during the manual extension of the jib of the crane, which was operated by the independent contractor of an employer, part of the crane fell on an employee. The contractor had deliberately dropped the part and was found to have failed to keep a proper lookout or to have warned of his intention to drop the part. The employee's foreman had not instructed him not to stand under the jib during the extension operation. It was held that the employer was in breach of his duty to provide a safe system of work. Mason, Brennan, Deane and Dawson JJ so held on the ground that the foreman had failed to direct the employee not to stand under the jib of the crane during the extension operation. Mason, Brennan and Deane JJ on the further ground and by Murphy J on the ground that the contractor's failure to adopt a safe system of work constituted a failure by the employer to satisfy a non-delegable duty to provide a safe system. In my view, however, the distinction between that case and this is, on the face of it, that there was a causal act of negligence in the course of the operation of an unsafe system in that the employer's foreman had not instructed the employee who was injured not to stand under the jib of the crane during the extension operation. This was the unsafe aspect of the system of work. In the present case it is open to the respondents to argue that Mr Hitch's negligence was in abandoning the system and endeavouring to raise the ROV on its own when he discovered that other members of his team were not present.