This matter is related to the Western Australian Supreme Court, Court of Appeal decision in Tobiassen v Reilly.
Reilly v Devcon Australia Ltd  WASCA 84
Devcon Pty Ltd + Glenpoint Nominees Pty Ltd
(Shared directors and shareholders)
(Tobiassen – Manager of Devcon and a registered builder)
(Fuller – Site Manager)
Kefo Steel Erection + Fabrication
(The deceased) Mr Kelsh
= Mr Kelsh
Side panel Roof rafters Side panel
Both the prosecutions of Devcon and Tobiassen arose out of the same incident described in the diagram.
Reilly was the prosecutor for the Western Australian Worksafe body. In the Magistrates’ Court both Glenpoint and Devcon were acquitted. The magistrate found that neither was an employer or deemed employer of the deceased
Worksafe appealed to the Supreme Court. Murray J heard the matter and upheld the magistrate’s finding.
Worksafe appealed to the Court of Appeal. Worksafe argued that Murray J had been incorrect to find that Devcon had no control over the identified hazard which occurred and led to the death of Mr Kelsh. It was common ground between the parties that the relevant hazard was the “lateral restraint of the steel roof beams”.
It is to be noted that there was no evidence that Devcon had any legal right to control or give directions in relation to the hazard identified, 
The Court found that there was no general obligation on a “head contractor” to supervise the work of an independent contractor having a particular expertise which the head contractor itself lacks, , .
After making these findings in relation to ground one, essentially the Court of Appeal dismissed the prosecutions appeal. However the Court went on to consider the notion of what constitutes practicability. It made a finding that what is practicable rests on the relevant state of knowledge in the industry. It said that the relevant state of knowledge is an objective state of knowledge rather than a subjective state of knowledge, -.
In the case of Tobiassen v Reilly Worksafe Western Australia prosecuted Mr Tobiassen separately to Devcon. At the time of the incident involving Mr Kelsh, Mr Tobiassen was the manager of Devcon as well as being a registered builder.
In the Magistrates’ Court proceeding Mr Tobiassen was acquitted of all charges but Worksafe appealed to the Supreme Court and the magistrate’s decision was overturned. Mr Tobiassen appealed to the Court of Appeal. The Court of Appeal upheld his appeal and dismissed the charges against him. This case was brought after the decision in Devcon above. The court relied heavily on the decision in Devcon.
The essential finding is at paragraph  where the court, in keeping with Devcon, found that the erection of the concrete panels and the fixing of the rafters was a task that was outside the expertise of the appellant, being Mr Tobiassen. As a result it fell outside the control of Mr Tobiassen.