Here are some pithy comments from a very well-respected legal colleague on a position articulated by someone who should know better:
“It is entirely illogical (if not plainly idiotic) to suggest that on one hand a PCBU should be able to rely on the expertise of a contractor in relation to work which the PCBU itself has insufficient expertise to undertake (an entirely logical position) yet at the same time decide that the PCBU must instruct the contractor on how to do that work safely and then to supervise it to ensure that it does.
The PCBU must therefore instruct a contractor as to how the contractor should perform the work for which it has been contracted, not withstanding that it may well have no expertise in the work to be performed. Such logic can only make the work to be performed by the contractor, less safe.
By all means, ensure that the PCBU has proper pre-qualification procedures in relation to the work to be performed by its contractors, but to insist that it has a duty to instruct the contractor on how to carry out its work, even though it has no or less expertise in the contractor’s work than the contractor itself, is not only idiotic but must inevitably lead to unsafe work practices.”