The fire destroyed significant sections of the historic building in February, leaving businesses gutted and shutting down one of city's busiest areas.

The response to the fire was significant, requiring a large firefighting contingent and the deployment of the territory's only Bronto aerial firefighting platform, one of the most critical assets possessed by ACT Fire and Rescue.

The ACT opposition has criticised Emergency Services Agency Commissioner Dominic Lane, who personally attended the fire, for questioning an ACT Fire and Rescue superintendent about the placement of the Bronto as firefighters worked to bring the fire under control.

ACT law strictly limits the commissioner's operational role and, in many cases, his power to issue directions to service chiefs on how they should respond to emergencies like the Sydney Building fire.

Those laws, first introduced after the 2003 bushfires, are designed chiefly to reduce confusion and create a clear chain of command through the individual services.

The firefighters at the Sydney Building fire told Mr Lane that the Bronto was in the proper spot, and it was not moved.

Shadow Emergency Services Minister Brendan Smyth said Mr Lane was acting outside his powers by questioning firefighters about the Bronto.

"We should all be concerned, and I'm particularly concerned," Mr Smyth said.

"Whether you dress it up as 'the commissioner asking a question', there's a fundamental premise here of why is the commissioner on the fire ground at all, distracting an officer who was conducting the suppression of the fire in the Sydney Building.

"[The question] is for the debrief afterwards, it's not while operations are being conducted. This is entirely unsatisfactory."

An ESA spokesman said the commissioner's actions were appropriate, and that he did not interfere with ACT Fire and Rescue officers as they sought to control the fire.

He said the commissioner's role required him to provide "strategic direction and management of the emergency services" and "strong, cohesive, strategic and operational direction" to the services.

The commissioner, the spokesman said, was also required to brief government and be briefed himself by ACT Fire and Rescue, but the fire chief and deputy chief officer were interstate at the time.

"In the absence of the chief officer and the deputy chief officer ACT Fire & Rescue at the time of the emergency, the commissioner asked the ACT F&R superintendent for operations on progress of the fire suppression activities at the site.

"This was appropriate to ensure briefing of government about the fire."

Mr Smyth also criticised Emergency Services Minister Simon Corbell for what he claimed were differing answers on the issue given to the Legislative Assembly and to Fairfax Media.

Mr Smyth and fellow Liberal Nicole Lawder used question time last month to ask Mr Corbell about the commissioner's actions.

Mr Corbell twice denied that the commissioner had directed the fire officer, but made no mention of him questioning the Bronto placement until responses were provided to Fairfax Media.

"While initially denying that anything happened, we now know that something happened, it's just the detail is obscured," Mr Smyth said.

"I have to say that sets the alarm bells ringing in my mind," he said.

That claim was denied by Mr Corbell's office, who said his answers had been consistent.

Mr Smyth said the law clearly prevented the commissioner from interfering with the operation.

"The act says quite specifically that the commissioner cannot direct a service chief in the actual undertaking of an operation, let alone moving down the chain to a superintendent.

"It does raise the question for me of why was he on the fire ground, clearly taking an active role.

"The variation in the stories we've got over the last couple of weeks fills me with concern."