The explosion killed Alan Cummins (30), and Matt Hutchins (22) died later that afternoon from burns to about 80 per cent of his body.
Surviving victims David Richards and Glenn Smith continue burn treatment at Fiona Stanley Hospital.
The four workers were performing maintenance work near an electrical transformer when the explosion occurred.
EnergySafety previously issued an order relating to only Long & Crawford Manchester switchgear but has now extended the order to all HV oil-insulated combined-fuse switches.
Director Ken Bowron said while the investigation was not complete, it appeared there had been a short-circuit fault in the switch tank following the rupture and disintegration of the HV fuse within the unit.
�In light of the recent findings, I have formed the opinion that further precautions must be undertaken with this type of equipment,� he said.
�I have decided to extend the order to all equipment with similar design not just the Long & Crawford switch-fuse units.
�In addition to banning the opening of the lid, I have now also banned the commencement of any electrical work on this type of equipment, including operation of the switching or earthing mechanisms if a HV fuse has operated.�
Mr Bowron once again reiterated that it was unsafe to perform work on any item of electrical equipment, especially where there were live exposed HV electrical parts.